DRAFT 

Use of Biological 

Information to Better Define 

Designated Aquatic Life 

Uses in State and Tribal 

Water Quality Standards: 

Tiered Aquatic Life Uses 
DISCLAIMER 

The discussion in this draft document is intended solely to provide information on advancements in the 

field of bioassessments and on current State and Tribal practices using bioassessments to define their 

designated aquatic life uses. The statutory provisions and U.S. EPA regulations described in this 

document contain legally binding requirements. This document is not a regulation itself, nor does not it 

change or substitute for those provisions and regulations. Thus, it does not impose legally binding 

requirements on U.S. EPA, States, or the regulated community. This document does not confer legal 

rights or impose legal obligations upon any member of the public. 

While U.S. EPA has made every effort to ensure the accuracy of the discussion in this document, the 

obligations of the regulated community are determined by statutes, regulations, or other legally binding 

requirements. In the event of a conflict between the discussion in this document and any statute or 

regulation, this document would not be controlling. 

The general description provided here may not apply to a particular situation based upon the 

circumstances. Interested parties are free to raise questions and objections about the substance of this 

document and the appropriateness of the application of the information presented to a particular situation. 

U.S. EPA and other decision-makers retain the discretion to adopt approaches on a case-by-case basis that 

differ from those described in this document where appropriate. 

Mention of trade names or commercial products does not constitute endorsement or recommendation for 

their use. 

This is a living document and may be revised periodically. U.S. EPA welcomes public input on this 

document at any time. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – August 10, 2005 
Preface

Our Nation’s waters are a valuable ecological resource. Protecting them begins with State and authorized 

Tribal adoption of water quality standards. This draft document, the Use of Biological Information to 

Better Define Designated Aquatic Life Uses in State and Tribal Water Quality Standards: Tiered Aquatic 

Life Uses, provides up-to-date information on practical, defensible approaches to help States and Tribes 

more precisely define designated aquatic life uses in their water quality standards. Biologically-based 

tiered aquatic life uses, based on the scientific model presented in this document, can help States and 

Tribes develop aquatic life uses that more precisely describe the existing and potential uses of a 

waterbody and then use bioassessments to help measure attainment of the uses. 

Biologically-based tiered aquatic life uses coupled with numeric biological criteria provide a direct 

measure of the aquatic resource that is being protected. The condition of the biota reflects the cumulative 

response of the aquatic community to individual or multiple sources of stress – an environmental outcome 

measure. The technical approaches described in this document support U.S. EPA’s Environmental 

Indicators Initiative to move the Agency closer to a performance-based rather than process-based 

environmental protection system (http://www.epa.gov/indicators). Launched in November 2001, the 

Environmental Indicators Initiative responds to the President’s call to have agencies and departments 

manage for results by measuring environmental outcomes. 

This document is a compilation of the tools, practices, and experiences of State and Tribal scientists who 

have used biological information to more precisely define their aquatic life uses. The presented model 

brings biological condition and stressor information together to inform decisions on use designation. The 

document fulfills a commitment in the U.S. EPA Water Quality Standards Strategy to provide technical 

support, outreach, training, and workshops to assist States and Tribes with designated uses, including use 

attainability analyses and tiered aquatic life uses (EPA-823-R-03-010, Strategic Action #7, Milestone #2). 

U.S. EPA encourages States and Tribes to incorporate biological information into their decisions. U.S. 

EPA believes the use of bioassessments will help improve water quality protection. The information in 

this document can help States and Tribes use bioassessments to more precisely define their aquatic life 

uses and communicate this information to the public. U.S. EPA is making this document available so 

States and Tribes can pilot a bioassessment-based tiered approach to defining their designated aquatic life 

uses. If you choose to undertake a pilot, U.S. EPA would appreciate hearing about your experience. We 

are interested in feedback on the following questions: 

• Is this document helpful in addressing current issues in your program? 

• Does this document address the technical challenges in your Region, State, or Tribe? 

• How can this document be improved to help you develop tiered aquatic life uses in your


program?


• What additional information would be helpful to you? 

Should you have any questions or wish to provide feedback, please contact Susan K. Jackson via email at 

Jackson.Susank@epa.gov or at the following address: 

Tiered Aquatic Life Uses Document


Attn: Susan K. Jackson


Health and Ecological Criteria Division (4304T)


Office of Science and Technology


U.S. EPA, Office of Water


1200 Pennsylvania Avenue


Washington, DC 20460


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Executive Sum m ary

This document provides up-to-date information on how States and Tribes can use biological information to more 

precisely define designated aquatic life uses for their waters. Thirty years ago, under the Clean Water Act (CWA), 

States and Tribes were required to adopt in their water quality standards, where attainable, designated uses that 

included the protection and propagation of fish, shellfish, and wildlife. During the 1970s, the biological goals 

adopted into State or Tribal water quality standards as designated aquatic life uses may have been appropriately 

general (e.g., “aquatic life as naturally occurs”) given the limited data available and the state of the science. 

However, while such general use classifications meet the requirements of the Clean Water Act and the implementing 

federal regulations, they may constitute the beginning, rather than the end, of appropriate use designations. 

Improved precision may result in more efficient and effective evaluation of attainment of condition and utilization of 

restoration resources. Finally, improved precision in uses can enhance demonstrating progress towards management 

goals. In the years since the CWA was passed, considerable advancements have been made in the science of aquatic 

ecology and in biological monitoring and assessment methods. This document summarizes these advancements and 

provides a scientific model that States and Tribes can use to refine their designated uses in a manner that can 

improve their water quality assessment and management. 

This document was developed based on the technical expertise and practical experience of State and Tribal 

scientists. In 2000, the U.S. EPA convened a technical expert workgroup, including State and Tribal scientists, to 

identify scientifically sound and practical approaches to help States and Tribes provide more specificity in their 

designated aquatic life uses. The workgroup developed a scientific model, the Biological Condition Gradient (BCG), 

which describes biological response to increasing levels of stressors. The model describes how ten attributes of 

aquatic ecosystems change in response to increasing levels of stressors. The attributes include several aspects of 

community structure, organism condition, ecosystem function, and spatial and temporal attributes of stream size and 

connectivity. The gradient can be considered analogous to a field-based dose-response curve where dose (x-axis) = 

increasing levels of stressors and response (y-axis) = biological condition. The BCG differs from the standard doseresponse curve, in that the BCG does not represent the laboratory response of a single species to a specified dose of 

a known chemical, but rather the in situ response of the biota to the sum of stresses it is exposed to. The BCG is 

divided into six tiers of biological condition along the stressor-response curve, ranging from observable biological 

conditions found at no or low levels of stress to those found at high levels of stressors. The model provides a 

common framework for interpreting biological information regardless of methodology or geography. When 

calibrated to a regional or state scale, States and Tribes can use this model to more precisely evaluate the current and 

potential biological condition of their waters and use that information to inform their decisions on aquatic life 

designations. Additionally, States and Tribes can use this interpretative model to more clearly and consistently 

communicate these decisions to the public. 

Maine and Ohio have adopted biologically-based tiered aquatic life uses in their WQS and have over twenty years 

experience implementing this type of use designation approach. Both Maine and Ohio developed and adopted tiered 

aquatic life uses for similar reasons: 1) to incorporate ecologically relevant endpoints into decisions; 2) to inform 

water quality management decisions; 3) to quantify water quality improvements; and 4) to merge the design and 

practice of monitoring and assessment with the development and implementation of their water quality standards. 

Maine and Ohio scientists have identified a sequence of steps and milestones that U.S. EPA has compiled as a 

template that other States and Tribes may use to develop biologically-based tiered uses. Examples from Maine and 

Ohio are included in this document to illustrate how they used biological data to establish tiered uses and the 

programmatic gains from having done so. 

The U.S. EPA encourages States and Tribes to incorporate biological information into their decisions. The U.S. 

EPA believes that the use of biological information can help improve water quality protection. Currently, States and 

Tribes that use biological data as part of their assessment program apply some type of tiered aquatic life use to guide 

their interpretation of their biological data. States and Tribes have either explicitly adopted tiers directly into their 

water quality standards as designated uses, or used tiers in monitoring and assessment of their surface waters. This 

document provides examples of practical and scientifically sound approaches to using biological information to tier 

designated aquatic life uses. 

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FO REW O RD

W hy is U.S.EPA publishing this docum ent?

In the more than 30 years since the Clean Water Act (CWA) was passed, there has been considerable progress in the 

science of aquatic ecology and in the development of biological monitoring and assessment techniques. During the 

1970s, the biological goals adopted into State or Tribal water quality standards as designated aquatic life uses may 

have been appropriately general (e.g., “aquatic life as naturally occurs”) given the limited data available and the 

state of the science. However, while such general use classifications meet the requirements of the Clean Water Act 

and the implementing federal regulations, they may constitute the beginning, rather than the end, of appropriate use 

designations. Improved precision may result in more efficient and effective evaluation of attainment of condition 

and utilization of restoration resources. Finally, improved precision in uses can enhance demonstrating progress 

towards management goals. Tiered aquatic life uses, based on the biological condition gradient model presented in 

this document, can help States and Tribes to better define and develop more precise, scientifically defensible aquatic 

life uses that account for the natural differences between waterbodies and should result in more appropriate levels 

of protection for specific waterbodies. 

States and Tribes have created different use classification systems ranging from a straightforward replication of the 

general uses identified in the CWA (e.g., protection and propagation of fish, shellfish, and wildlife; recreation; 

agriculture; industrial and other purposes, including navigation) to more complex systems that express designated 

uses in more specific terms or establish classifications which identify different levels of protection. For example, 

some States designate general “aquatic life” uses, while others subcategorize waters based on the expected 

biological assemblage. Some have established tiers representing different levels of biological condition (e.g., 

excellent, good, fair). Although a variety of defensible approaches have evolved and become established in State 

and Tribal programs, current U.S. EPA regulations are not specific about the level of precision States or Tribes must 

achieve in designating uses. This document is designed to help inform States and Tribes how to better define and 

improve the precision of their designated uses. 

Over the past thirty years, both the state of aquatic science and the application of the science in State and Tribal 

water programs have advanced. Major areas of uncertainty in water management, such as distinguishing between 

natural variability and effects of stressors on aquatic systems as well as determining the appropriate level of 

protection for individual waterbodies, are being addressed. Many States and Tribes now use biological information 

to directly assess the biological condition of their aquatic resources (U.S. EPA 2002a). Three States have formally 

adopted biologically-based tiered aquatic life uses in their water quality standards. “Lessons learned” from two of 

these States indicate that implementation of tiered aquatic life uses supports more appropriate levels of protection 

for individual waters by promoting uses and criteria that are neither over- nor under-protective. U.S. EPA now 

recognizes that the States having implemented tiered aquatic life uses have significantly benefited from the 

approach. The use designation process needs to clearly articulate and differentiate intended levels of protection with 

enough specificity so that 1) decision makers can appropriately develop and implement their water quality standards 

on a site, reach, or watershed specific basis and 2) the public can understand, identify with, and influence the goals 

set for waters. 

In 2001, the National Research Council (NRC) published its report on Assessing the TMDL Approach to Water 

Quality Management (NRC 2001). In the report, the NRC recommended tiering designated uses as an essential step 

in setting water quality standards and improving decision-making. The NRC, finding that the Clean Water Act’s 

goals (i.e., “fishable,” “swimmable”) are too broad to serve as operational statements of designated use, 

recommended greater specificity in defining such uses. For example, rather than stating that a waterbody needs to 

be “fishable,” the designated use would ideally describe the expected fish assemblage or population (e.g., cold water 

fishery, warm water fishery, or salmon, trout, bass, etc.) as well as the other biological assemblages necessary to 

support that fish population. 

Additionally, the NRC recommended that biological criteria should be used in conjunction with physical and 

chemical criteria to determine whether a waterbody is meeting its designated use. The NRC described a “position of 

the criterion” framework, which reflects how representative a criterion is of a designated use according to its 

position along a conceptual causal pathway (Figure F-1). This alignment is comparable to that of performance 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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(indicators of point source quality) versus impact standards (indicators of resource condition) (Courtemanch et al. 

1989), or of stressor and exposure (effluent, chemical, and physical parameters) in contrast to response indicators 

(biological) (Yoder and Rankin 1998). In Figure F-1, stressor indicators correspond to box 1 and were termed 

effluent standards by the NRC. Pollutant-specific indicators that function as indicators of exposure and stress 

correspond to box 2. Biological indicators show responses to stress and exposure and correspond to box 3. Because 

designated uses are written in qualitative, narrative terminology, the challenge is to relate a criterion to the 

designated use. Establishing this relationship is easier as the criterion is positioned closer to the designated use, thus 

the NRC recommendation on the use of biological information to help determine more appropriate aquatic life uses 

and to couple the narrative use statements with quantitative methods. The “position of criterion” concept provides a 

useful construct for considering the relationship of water quality criteria (biological, chemical, and physical) to the 

designated uses they are intended to protect. 

1. Pollutant load from 

each source 

2. Ambient pollutant 

concentration in waterbody 

3. Human health and 

biological condition 

Appropriate designated use 

for the waterbody 

4. Land use, characteristics of the 

channel and riparian zone, flow 

regime, species harvest condition 

(pollution) 

FIGURE F-1. Types of water quality 

criteria and their position relative 

to designated uses (after NRC 

2001). 

To help States and Tribes more precisely define use descriptions, there is a need to incorporate current scientific 

understanding of aquatic ecology and the appropriate use of monitoring data. To this end, the U.S. EPA convened a 

technical expert workgroup to identify scientifically sound and practical approaches that would help States and 

Tribes provide more specificity in their designated aquatic life uses. The workgroup met four times between 2000 

and 2003. The workgroup, composed primarily of U.S. EPA, State, and Tribal scientists, also included research 

scientists from the U.S Geological Survey (USGS), the academic community, and the private sector. The 

workgroup was asked to base their recommendations on “lessons learned” from State and Tribal water programs in 

the development and the application of biologically-based aquatic life uses, bioassessments, and biocriteria. The 

workgroup developed a scientific model, the Biological Condition Gradient (BCG), which describes graduated tiers 

of biological response to increasing levels of stressors. This model was developed and tested through a series of 

data exercises using a diverse array of data sets. States and Tribes can use the BCG to more precisely define and set 

appropriate designated aquatic life uses for their waters. 

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During the final workgroup meeting in 2003, State and Tribal members discussed their current thinking on how 

using biological information to tier designated aquatic life uses could benefit their water quality management 

programs. The main reasons discussed included biologically-based tiered uses could help: 

• set ecologically-based aquatic life goals for waterbodies; 

• establish a consistent approach for identifying attainable, incremental restoration goals that are 

grounded in the concept of biological integrity; 

• provide a framework that better relates traditional water quality criteria (stressor and exposure 

variables) and biological criteria (response variables) in determining use attainment, thus strengthening 

stressor/response models implicit in designated uses and criteria in water quality standards; 

• better link monitoring and assessment with water quality standards; and 

• prioritize management actions that result in the more effective use of resources. 

When asked about the significant value-added outcomes of these benefits to their water programs, States and Tribes 

workgroup members anticipated being able to make more scientifically defensible listings of impaired waters as well 

as enhance identifying and protecting high quality waters. For several States, biologically-based tiered uses may 

help in the transition from reliance on current conditions in developing designated uses to being able to better 

consider the potential for improvement. Another important added value anticipated by all State and Tribal 

representatives was the ability to communicate more effectively with program managers, the public, and key 

stakeholders. Workgroup members expressed the opinion that biologically-based aquatic life uses could help 

maximize the return on their monitoring and assessment efforts by eliminating a major source of uncertainty in 

water quality management by 1) accounting for natural variability in aquatic systems and 2) helping to specify an 

appropriate level of protection for a waterbody that includes consideration of the system’s potential for 

improvement. 

Biologically-based aquatic life uses, as described in this document, are a natural evolution that reflects an improved 

understanding of surface waters resulting from more than 20 years of assessment data. The proposed approach will 

help better integrate the science of aquatic ecology into Water Quality Standards. This document represents the 

culmination of four years of workgroup deliberations, including four workgroup meetings and two workshops to 

“road test” the BCG model. Based on the collective experience of the workgroup members, the science and 

methods in the fields of biological assessments and criteria have progressed sufficiently over the past thirty-five 

years to support the use of biological information to tier designated aquatic life uses in State and Tribal water quality 

standards. 

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Acknow ledgm ents

U.S. EPA PROJECT LEAD 

Susan Jackson, U.S. EPA Office of Science and Technology 

WRITING & EDITING TEAM 

David Allan, University of Michigan; Margo Andrews, Tetra Tech, Inc.; Michael Barbour, Tetra Tech, Inc.; Jan 

Cibrowski, University of Windsor; Maggie Craig, Tetra Tech, Inc.; Susan Davies, Maine Department of 

Environmental Protection; Tom Gardner, U.S. EPA; Jeroen Gerritsen, Tetra Tech, Inc.; Charles Hawkins, Utah State 

University; Robert Hughes, Oregon State University; Susan Jackson, U.S. EPA; Lucinda Johnson, Natural 

Resources Research Institute, University of Minnesota – Duluth; Phil Larsen, U.S. EPA; JoAnna Lessard, Tetra 

Tech, Inc.; Abby Markowitz, Tetra Tech, Inc.; Dennis McIntyre, Great Lakes Environmental Center; Jerry Niemi, 

Natural Resources Research Institute, University of Minnesota – Duluth; Dave Pfeifer, U.S. EPA; Ed Rankin, 

Center for Applied Bioassessment and Biocriteria; Tom Wilton, Iowa Department of Natural Resources; Chris 

Yoder, Midwest Biodiversity Institute 

TIERED AQUATIC LIFE USES WORKGROUP 

U.S. EPA Chair: Susan Jackson, U.S. EPA Office of Science and Technology 

State Chair: Susan Davies, Maine Department of Environmental Protection 

STATE AND TRIBAL WORKGROUP MEMBERS 

Arizona Department of Environmental Quality – Patti Spindler 

California Department of Fish and Game – Jim Harrington 

Colorado Department of Public Health and Environment – Robert McConnell, Paul Welsh 

Florida Department of Environmental Protection – Leska Fore, Russ Frydenborg, Ellen McCarron, Nancy Ross 

Idaho Department of Environmental Quality – Mike Edmondson, Cyndi Grafe* 

Kansas Department of Health and Environment – Bob Angelo, Steve Haslouer, Brett Holman 

Kentucky Department for Environmental Protection – Greg Pond*, Tom VanArsdall 

Maine Department of Environmental Protection – David Courtemanch, Susan Davies 

Maryland Department of the Environment – Joseph Beaman, Richard Eskin, George Harmon 

Minnesota Pollution Control Agency – Greg Gross 

Mississippi Department of Environmental Quality – Leslie Barkley, Natalie Guedon 

Montana Department of Environmental Quality – Randy Apfelbeck, Rosie Sada 

Nevada Division of Environmental Protection – Karen Vargas 

North Carolina Department of Environment and Natural Resources – David Lenat, Trish MacPherson 

Ohio Environmental Protection Agency – Jeff DeShon, Dan Dudley 

Ohio River Valley Water Sanitation Commission – Erich Emery 

Oregon Department of Environmental Quality – Doug Drake, Rick Hafele 

Pyramid Lake Paiute Tribe – Dan Mosley 

Texas Commission on Environmental Quality – Charles Bayer 

Vermont Department of Environmental Conservation – Doug Burnham, Steve Fiske 

Virginia Department of Environmental Quality – Alexander Barron, Larry Willis 

Washington State Department of Ecology – Robert Plotnikoff 

Wisconsin Department of Natural Resources – Joe Ball, Ed Emmons, Robert Masnado, Greg Searle, Michael 

Talbot, Lizhu Wang** 

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U.S. EPA 

Office of Water: Chris Faulkner, Thomas Gardner, Susan Holdsworth, Susan Jackson, Kellie Kubena, Douglas 

Norton, Christine Ruff, Robert Shippen, Treda Smith, William Swietlik 

Regional Offices: 

Region 1: Peter Nolan 

Region 2: Jim Kurtenbach 

Region 3: Maggie Passmore 

Region 4: Ed Decker, Jim Harrison, Eve Zimmerman 

Region 5: Ed Hammer, David Pfeifer 

Region 6: Philip Crocker, Charlie Howell 

Region 7: Gary Welker 

Region 8: Tina Laidlaw, Jill Minter 

Region 9: Gary Wolinsky 

Region 10: Gretchen Hayslip 

Office of Environmental Information: Wayne Davis 

Office of Research and Development: Karen Blocksom, Susan Cormier, Phil Larsen, Frank McCormick, Susan 

Norton, Danielle Tillman, Lester Yuan 

USGS 

Evan Hornig*, Ken Lubinski 

SCIENTIFIC COMMUNITY 

David Allan, University of Michigan 

Michael Barbour, Tetra Tech, Inc. 

David Braun, The Nature Conservancy 

Jeroen Gerritsen, Tetra Tech, Inc. 

Richard Hauer, University of Montana 

Charles Hawkins, Utah State University 

Robert Hughes, Oregon State University 

James Karr, University of Washington 

Dennis McIntyre, Great Lakes Environmental Center 

Ed Rankin, Center for Applied Bioassessment and Biocriteria 

Jan Stevenson, Michigan State University 

Denice Wardrop, Pennsylvania State University 

Chris Yoder, Midwest Biodiversity Institute 

BCG STEERING COMMITTEE 

Michael Barbour, Susan Davies, Robert Hughes, Susan Jackson, Phil Larsen, Dennis McIntyre, Susan Norton, 

Maggie Passmore, Jan Stevenson, Chris Yoder, Lester Yuan 

STRESSOR GRADIENT STEERING COMMITTEE 

David Allan, Michael Barbour, Jan Cibirowski, Jim Harrison, Robert Hughes, Lucinda Johnson, JoAnna Lessard, 

Jerry Niemi, Doug Norton, Ed Rankin, Tom Wilton 

*Now with U.S. EPA 

**Now with Michigan Department of Natural Resources 

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Use of BiologicalInform ation to Better D efine D esignated

Aquatic Life Uses in State and TribalW ater Q uality

Standards:Tiered Aquatic Life Uses

TABLE O F CO NTENTS 

Preface.............................................................................................................................................. i


Executive Summary....................................................................................................................... iii


Foreword..........................................................................................................................................v


Acknowledgments.......................................................................................................................... ix


Table of Contents........................................................................................................................... xi


Tables, Figures, and Case Examples............................................................................................ xiii


INTRO D UCTIO N ....................................................................................................1


CHAPTER 1: What are Tiered Aquatic Life Uses? .......................................................................1


1.1 The CWA goals and objectives for aquatic life .................................................................................. 2


1.2 WQS statutory and regulatory background......................................................................................... 3


1.3 The role of designated aquatic life uses in Water Quality Standards.................................................. 4


1.4 State and Tribal experiences with tiered aquatic life uses................................................................... 5


1.5 The Biological Condition Gradient: A tool for better defining and developing more precise


aquatic life uses................................................................................................................................... 8


1.6 Conceptual basis for the Biological Condition Gradient................................................................... 10


1.7 Key points from Chapter 1................................................................................................................ 11


1.8 Organization of the document........................................................................................................... 12


TH E BIO LO G ICAL CO ND ITIO N G RAD IENT........................................................ 15


CHAPTER 2: What is the scientific basis of the Biological Condition Gradient? ......................16


2.1 What the BCG model looks like ........................................................................................................ 17


2.2 How the BCG was developed, tested, and evaluated......................................................................... 27


2.3 The relationship between the BCG and designated uses ................................................................... 30


2.4 Key points from Chapter 2................................................................................................................. 31


CHAPTER 3: How do you develop and calibrate a Biological Condition Gradient?..................39


3.1 Conceptual foundation of a regional BCG model.............................................................................. 40


3.2 Data needs: Assess and modify technical program............................................................................ 45


3.3 Calibrate a regional BCG model........................................................................................................ 46


3.4 Key points from Chapter 3................................................................................................................. 55


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CHAPTER 4: The x-axis: A Generalized Stressor Gradient................................................... 71


4.1 The scientific foundation for the stressor gradient............................................................................. 71


4.2 The conceptual model for a Generalized Stressor Gradient............................................................... 72


4.3 How the BCG model and management actions are linked ................................................................ 76


4.4 How a GSG can be developed and calibrated.................................................................................... 85


4.5 Key points from Chapter 4................................................................................................................. 89


INCO RPO RATING TIERED AQ UATIC LIFE USES INTO STATE AND

TRIBAL W Q S:CASE EXAM PLES ............................................................................ 91


CHAPTER 5: Key concepts and milestones in the development of Tiered Aquatic Life Uses...93


5.1 Key concepts for developing tiered aquatic life uses......................................................................... 93


5.2 Key milestones for developing tiered aquatic life uses...................................................................... 94


5.3 Using TALUs to support water quality management ........................................................................ 97


5.4 Key points from Chapter 5................................................................................................................. 98


CHAPTER 6: How have States and Tribes used TALUs in Water Quality Standards and


management? .................................................................................................................................99


References & Additional Resources ............................................................................................115


Glossary .......................................................................................................................................135


Acronyms.....................................................................................................................................141


Appendix A: Maine TALU Implementation Case History..........................................................143


Appendix B: Ohio TALU Implementation Case History ............................................................155


Appendix C: Technical Guidelines: Technical Elements of a Bioassessment Program


(Summary of Draft Document)...............................................................................181


Appendix D: The Role of Reference Condition in Biological Assessment and Criteria


(Introduction to Draft Document)...........................................................................185


Appendix E: Statistical Guidance for Developing Indicators for Rivers and Streams: A Guide


for Constructing Multimetric and Multivariate Predictive Bioassessment Models 

(Summary of Draft Document)...............................................................................187


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Tables,Figures,and Case Exam ples

Tables 

Table 1-1. Aquatic Life Subcategories in Texas WQS................................................................................. 6


Table 3-4. Definitions of six biological grades, developed by regional biologists of the Environment


Table 3-5. Maine water quality classification system for rivers and streams, with associated biological


Table 4-1. Example scenarios for humid-temperate (A) and arid (B) regions of the US under three levels


Table 4-2. Fundamental environmental processes typically altered by disturbances that ultimately


Table 4-3. Percent variance in biological response (R2

) explained by catchment and riparian land use, and


Table 6-2. Numeric targets for biological, habitat, and water quality parameters for the Stillwater River


Table 6-3. A matrix of stressor, exposure, and response indicators for the Ottawa River mainstem based


Table A-4. Examples of how numeric biocriteria results determine whether or not a waterbody attains


Table B-1. Biological criteria (fish) for determining aquatic life use designations and attainment of Clean


Table B-2. Biological criteria (macroinvertebrates) for determining aquatic life use designations and


Table B-3. Example of individual stream and/or segment use designations in the Ohio water quality


Table 1-2. The benefits and WQS regulation context for TALUs................................................................ 7


Table 2-1. Biological Condition Gradient matrix ....................................................................................... 18


Table 2-2. Evidence in support of the depicted changes in ecological attributes in the BCG .................... 21


Table 2-3. Biological Condition Gradient: Maine example scenario for a cold-water stream catchment .. 32


Table 3-1. Kansas stream biological integrity categories ........................................................................... 56


Table 3-2. Summary attribute matrix for New Jersey high gradient streams ............................................. 58


Table 3-3. Relative findings chart............................................................................................................... 60


Agency in England and Wales (Helmsley-Flint 2000) ............................................................................... 65


standards (Davies et al. 1995)..................................................................................................................... 66


Table 3-6. Proposed decision rules for New Jersey high gradient streams................................................. 68


of stressors .................................................................................................................................................. 74


generate stressors ........................................................................................................................................ 79


percent land use producing poor IBI scores (modified from Hughes et al. unpublished manuscript)........ 86


Table 5-1. Expertise and tasks for key TALU milestones .......................................................................... 96


Table 6-1. Statewide total phosphorus targets (mg/L) for Ohio rivers and streams ................................. 101


in western Ohio......................................................................................................................................... 102


on data collected in 1996 (after Ohio EPA 1998)..................................................................................... 109


Table A-1. Maine's narrative aquatic life and habitat standards for rivers and streams (M.R.S.A Title 38


Article 4-A § 464-465).............................................................................................................................. 146


Table A-2. Definitions of terms used in Maine’s water classification law............................................... 146


Table A-3. Maine tiered uses based on measurable ecological values ..................................................... 147


designated aquatic life uses in Maine ....................................................................................................... 152


Table A-5. Chronology of Maine’s biocriteria development.................................................................... 154


Water Act goals (November, 1980; after Ohio EPA 1981) ...................................................................... 160


attainment of Clean Water Act goals (November, 1980; after Ohio EPA 1981)...................................... 160


standards showing aquatic life, water supply, and recreational use designations..................................... 162


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Table B-4. Key features associated with tiered aquatic life uses in the Ohio WQS (OAC 3745-1-07) ... 166


Table B-5. Important timelines and milestones in the planning and execution of the rotating basin


approach conducted annually and since 1990 by Ohio EPA .................................................................... 170


Table B-6. Summary of recommendations for use designations in the Big Darby Creek watershed


based on a biological and water quality assessment completed in 2000................................................... 172


Table B-7. The tangible products that are symptomatic of aquatic ecosystem health and the measurable


biological, chemical, and physical indicators of healthy and degraded aquatic systems.......................... 178


Table B-8. Key events and milestones that occurred in the evolutionary development, adoption, and


implementation of biological assessments, numeric biocriteria, and tiered aquatic life uses in Ohio


between 1974 and the present ................................................................................................................... 179


Figures 

Figure F-1. Types of water quality criteria and their position relative to designated uses (after NRC


2001) ............................................................................................................................................................ vi


Figure 1-1. Conceptual model of the Biological Condition Gradient........................................................... 8


Figure 1-2. The causal sequence from stressors and their sources through the five major water resource


features to the biological responses, i.e., the biological endpoints ............................................................... 9


Figure 1-3. The five major factors that determine the biological condition of aquatic resources (modified 

from Karr et al. 1986) ................................................................................................................................. 10


Figure 1-4. Modification of the NRC “position of the criterion” concept (Fig. F-1) showing the causal


sequence from indicators of stress, exposure, and response in relation to point and nonpoint source


impacts, specific types of criteria, and designated uses that define the endpoints of interest to society


(after Karr and Yoder 2004)........................................................................................................................ 11


Figure 1-5. Roadmap to the document........................................................................................................ 12


Figure 2-1. Conceptual model of the Biological Condition Gradient......................................................... 25


Figure 2-2. Response of mayfly density to enrichment in Maine streams as indicated by a gradient of


increasing conductivity ............................................................................................................................... 26


Figure 3-2. Conceptual model of the response of fish and macroinvertebrate assemblages to a gradient of


impacts in warmwater rivers and streams throughout Ohio (modified from Ohio EPA 1987 and Yoder and


Figure 3-1. Technical components of the Biological Condition Gradient .................................................. 39


Rankin 1995b)............................................................................................................................................. 43


Figure 3-3. Ohio BCG tiers and copper concentration ............................................................................... 50


Figure 3-4. Hypothetical example of biotic index scores of sites assigned to BCG tiers, where the index


is able to discriminate tiers most of the time .............................................................................................. 52


Figure 3-5. Hypothetical example of biotic index scores of sites assigned to BCG tiers, where the index


is not able to discriminate tiers ................................................................................................................... 52


Figure 3-6. Decline in geographical distribution of black sandshell mussel in Kansas.............................. 57


Figure 3-7. Cumulative frequency distribution for Kansas streams with minimum three-year period-of­


record and five or more species historically ............................................................................................... 57


Figure 3-8. Vermont’s designated aquatic life uses as differentiated by biological threshold criteria. ...... 62


Figure 3-9. Series of four linear discriminant models................................................................................. 67


Figure 4-1. Conceptual model illustrating the linkages between pressure and biological condition.......... 72


Figure 4-2. Relationship between pressure, stressors, and biological response.......................................... 77


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xiv 
Figure 4-3. Perspective of scale for pressure-stressor-response variables (modified from Richards, C. and 

L.B. Johnson. 1998).................................................................................................................................... 84


Figure 4-4. The first principal component of the agricultural variables for the U.S. Great Lakes basin.... 87


Figure 4-5. Flow diagram detailing the steps used by GLEI researchers in quantifying their stressor


gradient (modified from Danz et al. 2005) ................................................................................................. 88


Figure 5-1. U.S. EPA Water Quality Based Approach to Pollution Control based on Chapter 7, Water


Quality Standards Handbook ...................................................................................................................... 91


Figure 5-2. TALU and biocriteria program development tasks: Timeline and key milestones

Figure 6-1. Dissolved oxygen concentrations (individual grab samples) vs. Index of Biotic Integrity (IBI)


.................. 97


values in the HELP and ECBP ecoregions of Ohio.................................................................................. 100


Figure 6-2. Box plots of minimum dissolved oxygen concentrations by IBI ranges for continuous


monitoring data at all locations monitored in 1998 and 1994................................................................... 100


Figure 6-3. 1986 photograph of Hurford Run near Canton, Ohio looking upstream at the reach that is


classified as a Limited Resource Water .................................................................................................... 103


Figure 6-4. Map of Hurford Run near Canton, Ohio showing Ohio EPA IBI (solid circles) and habitat


(QHEI, triangles) sampling stations.......................................................................................................... 103


Figure 6-5. Box and whisker plots of IBI (left) and QHEI (right) by stream segment in Hurford Run near


Canton, Ohio............................................................................................................................................. 104


Figure 6-6. Scatter plots showing values for two biological community variables, generic richness (left)


and generic diversity (right), from Sta. 129, the Penobscot River below Lincoln Pulp and Paper,


between 1974 and 1996 ............................................................................................................................ 105


Figure 6-7. Map of the Ottawa River with magnification of two reaches in the Lima, Ohio area (after


Ohio EPA 1998)........................................................................................................................................ 108


Figure 6-8. Results for two key fish assemblage measures (%DELT anomalies, upper left panel and IBI,


lower left panel) showing the thresholds for toxic responses in the Ottawa River study area between


1985 and 1996........................................................................................................................................... 110


Figure 6-9. Six leading causes of aquatic life impairment in Ohio up to the year 2000 (from Ohio EPA


2000) ......................................................................................................................................................... 111


Figure 6-10. Examples of habitat stressor gradients vs. IBI for Ohio wadeable streams in the ECBP and


HELP ecoregions ...................................................................................................................................... 112


Figure A-1. Differences in numbers and types of organisms that are associated with different levels of


disturbance can be evident even to the untrained eye............................................................................... 144


Figure A-2a. Subsidy-stress gradient: The ecological theory basis for Maine’s aquatic life use


descriptions (Odum et al. 1979)................................................................................................................ 144


Figure A-2b. Empirically observed subsidy-stress gradient in Maine streams, documented by changes


in benthic macroinvertebrate density. ....................................................................................................... 145


Figure A-3. Relation between Maine TALUs and other water quality standards and criteria.................. 147


Figure A-4. Maine TALUs in relation to the BCG tiers ........................................................................... 148


Figure A-5. Macroinvertebrate sampling stations in Maine ..................................................................... 150


Figure A-6. Maine five-year rotating basin sampling schedule................................................................ 151


Figure A-7. Increased designation of Class AA and Class A uses on major Maine rivers (as shown by


river miles) between 1970 and 2004, as a result of water quality improvements and public support for 

the Class AA/A goal in the Triennial Review Process ............................................................................. 153


Figure A-8. Percent of linear miles of all rivers and streams in each of Maine’s designated use classes


(year 2000)................................................................................................................................................ 154


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Figure B-1. Evolutionary development of TALU and allied tools, criteria and assessments from the


baseline of the 1974 WQS based on general uses and few specific water quality criteria to refined


TALUs and specific chemical, physical, and biological criteria implemented via an integrated


monitoring and assessment framework..................................................................................................... 157


Figure B-2. Numeric biological criteria adopted by Ohio EPA in 1990, showing stratification of


biocriteria by biological assemblage, index, site type, ecoregion for the warmwater habitat (WWH)


Figure B-3. The relationship of Ohio’s tiered designated uses and numerical biological criteria to the


Figure B-4. Five-year basin approach for determining annual watershed monitoring and assessment


Figure B-5. Strategic support provided over time by systematic monitoring and assessment; functions


Figure B-6. The number of individual stream and river segments in which aquatic life use designations


Figure B-7. The major steps of the Ohio EPA numeric biological criteria calibration and derivation


process leading to their application in biological and water quality assessments; this example is for the


Figure B-8. Box-and-whisker plots of Invertebrate Community Index (ICI) results in the mainstem of


Figure C-1. Conceptual illustration of confidence in detecting different stress levels as a function of


Figure C-2. Conceptual illustration of the capability of increasingly comprehensive bioassessments


and exceptional warmwater habitat (EWH) use designations................................................................... 163


Biological Condition Gradient.................................................................................................................. 166


activities and correspondence to support major water quality management programs............................. 170


related to the implementation of TALUs are italicized and underlined.................................................... 171


were revised during 1978-1992 and 1992-2001 ....................................................................................... 174


Index of Biotic Integrity (IBI) for wading sites ........................................................................................ 177


the Cuyahoga River between Akron and Cleveland between 1984 and 2000 .......................................... 180


assessment rigor........................................................................................................................................ 182


to detect and discriminate along the biological condition gradient........................................................... 183


Case Examples 

Case Example 3-1. Using Historical Information to Identify Reference Streams in Kansas...................... 56


Case Example 3-2. New Jersey Tier Description........................................................................................ 58


Case Example 3-3. Maine Biologists’ Assignment of Sites to Classes (Tiers)........................................... 60


Case Example 3-4. Vermont’s Use of Existing Biological Information for the BCG ................................ 62


Case Example 3-5. Developing Biological Condition Tiers in Great Britain............................................. 64


Case Example 3-6. Maine’s Use of Linear Discriminant Models to Assess Aquatic Life Use Tiers......... 66


Case Example 3-7. New Jersey Quantitative Rule Development............................................................... 68


Case Example 6-1. Refining Water Quality Criteria in Ohio ..................................................................... 99


Case Example 6-2. Development of More Precise Targets for Restoration in Ohio ................................ 101


Case Example 6-3. Determining Appropriate Levels of Protection in Ohio ............................................ 102


Case Example 6-4. Long-term Monitoring and Use Re-establishment in Maine ..................................... 105


Case Example 6-5. Development of Limits for NPDES Permits in Maine ............................................. 106


Case Example 6-6. NPDES Permitting and Use Attainability Analysis in Ohio...................................... 107


Case Example 6-7. Support for Dredge and Fill Permitting in Ohio........................................................ 111


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Introduction

This chapter provides the background and rationale for using biological information to tier designated 

aquatic life uses and better define them in State and Tribal water quality standards. Ideally, the use 

designation process clearly articulates and differentiates intended levels of protection with enough 

specificity so that 1) decision makers can appropriately develop and implement their water quality 

standards on a reach or watershed specific basis; and 2) the public can understand, identify with, and 

influence the goals set for waters. In 2000, the U.S. EPA convened a technical expert workgroup, 

including State and Tribal scientists, to identify existing scientifically sound and practical approaches 

using biological information to better define aquatic life uses. The workgroup produced a scientific 

model, the Biological Condition Gradient (BCG), for interpreting biological response to increasing levels 

of stressors. The workgroup’s findings are consistent with The National Research Council’s call for 

greater specificity in water quality standards that can result in improved decision-making (NRC 2001). 

The BCG is intended to help States and Tribes develop more precise aquatic life uses that should result in 

more appropriate levels of protection for their surface waters. 

CHAPTER 1. WHAT ARE TIERED AQUATIC LIFE USES? 

Designated aquatic life uses are State or Tribal descriptions of the biological goals for their waterbodies. 

Tiered aquatic life uses (TALUs) use biological information to more precisely define these goals relative 

to natural conditions. Bioassessments can then be used to measure attainment of the goals. U.S. EPA’s 

current thinking is that a system of tiered uses could: 

• accommodate observable differences in expected biological condition in waterbodies in different 

ecological regions; 

• provide an objective means of describing the biological potential for a specific waterbody; 

• recognize and accommodate observable differences in biological potential among waters with 

different types and levels of stressors; 

• reflect an understanding of the relationship between stressors and biological community response; 

• guide selection of environmental indicators for monitoring and assessment and make full use of 

available biological data; and 

• articulate a stressor-response model that maximizes the likelihood of success of water quality 

management actions based on water quality standards (assessment, 303(d) listings/TMDLS, 

NPDES permits). 

Tiered aquatic life uses are based on general observations about aquatic communities that have become 

central to aquatic ecology and consistent with 30 years of empirical observations. These are: 

• surface waters and the biological communities they support are predictably and consistently 

different in different parts of the country (classification along a natural gradient, ecological 

region concept); 

• within the same ecological regions, different types of waterbodies (e.g., headwaters, streams, 

rivers, wetlands) support predictably and consistently different biological communities 

(waterbody classification); 

• within a given class of waterbodies, observed biological condition in a specific waterbody is a 

function of the level of stress (natural and anthropogenic) that the waterbody has experienced (the 

biological condition gradient discussed in this document); 

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• similar stressors at similar intensities produce predictable and consistent biological responses in 

waters within a class, and those responses can be detected and quantified in terms of deviation 

from an expected condition (reference condition); and 

• waterbodies exposed to higher levels of stressors will have lower biological performance 

compared to the reference condition than those waters experiencing lower levels of stress (the 

biological condition and stressor gradients discussed in this document). 

The first three sections of this chapter provide the statutory and regulatory background of water quality 

standards, emphasizing the role of designated aquatic life uses. Section 1.4 explores how tiered 

biologically-based definitions can help set more appropriate and precise designated aquatic life uses in 

State and Tribal water quality standards. The next two sections discuss the primary products of the 

technical workgroup charged with identifying existing scientifically sound and practical approaches to 

help States and Tribes to better define and provide more precision in their designated aquatic life uses. 

Chapter 1 concludes with a summary of key points, organization of the document, and related technical 

support documents. 

1.1 The CWA goals and objectives for aquatic life 

One objective of the 1972 Clean Water Act (CWA) is to restore and maintain the chemical, physical, and 

biological integrity of the Nation’s waters (CWA sec 101a). In the scientific literature, an aquatic system 

with chemical, physical, and biological integrity has been described as being capable of “supporting and 

maintaining a balanced, integrated, adaptive community of organisms having a composition and diversity 

comparable to that of the natural habitats of the region” (Frey 1977). Over the intervening years, our 

understanding of how to define and measure the integrity of aquatic systems has advanced. The term 

integrity has been further refined in the literature to mean a balanced, integrated, adaptive system having a 

full range of ecosystem elements (genes, species, assemblages) and processes (mutation, demographics, 

biotic interactions, nutrient and energy dynamics, metapopulation dynamics) expected in areas with no or 

minimal human influence (Karr 2000). The aquatic biota residing in a waterbody are the result of 

complex and interrelated chemical, physical, and biological processes that act over time and on multiple 

scales (e.g., instream, riparian, landscape) (Karr et al. l986, Yoder l995). By directly measuring the 

condition of the aquatic biota, we are able to more accurately define the aquatic community that is the 

outcome of all these factors. 

To help achieve the integrity objective, the CWA also established an interim goal for the protection and 

propagation of fish, shellfish, and wildlife and recreation in and on the water. The protection and 

propagation interim goal for aquatic life has been interpreted by U.S. EPA to include the protection of the 

full complement of aquatic organisms residing in or migrating through a waterbody. As explained in U.S. 

EPA’s Questions and Answers on Antidegradation, the protection afforded by water quality standards 

includes the representative aquatic community (e.g., fish, benthic macroinvertebrates, and periphyton): 

“The fact that sport or commercial fish are not present does not mean that the water may not be 

supporting an aquatic life protection function. An existing aquatic community composed entirely 

of invertebrates and plants, such as may be found in a pristine tributary alpine stream, should be 

protected whether or not such a stream supports a fishery. Even though the shorthand expression 

‘fishable/swimmable’ is often used, the actual objective of the Act is to restore the chemical, 

physical and biological integrity of our Nation's waters (Section 101(a)). The term ‘aquatic life’ 

would more accurately reflect the protection of the aquatic community that was intended in 

Section 101(a)(2) of the Act.” (Appendix G, EPA-823-B-94-005) 

The representative community of aquatic organisms residing in, or migrating through, a waterbody will 

vary depending on the waterbody type. For example, fish, benthic macroinvertebrates, and, increasingly, 

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periphyton are aquatic assemblages typically measured by States and Tribes when assessing streams and 

rivers. In headwater streams and many wetlands, amphibians are an important component of the biotic 

community and fish may be absent. 

1.2 WQS statutory and regulatory background 

Section 101(a) of the CWA establishes broad national goals and objectives such as the chemical, physical, 

and biological integrity objective. Other sections of the CWA establish the programs and authorities for 

implementation of those goals and objectives. Section 303(c) sets up the basis of the current water quality 

standards program. Water quality standards (WQS) are parts of State (or, in certain instances, federal) 

law that define the water quality goals of a waterbody, or parts of a waterbody, by designating the use or 

uses of the waterbody and by setting criteria necessary to protect the uses. The standards also include an 

antidegradation policy consistent with 40 CFR Part 131.12. 

Although the CWA gives the U.S. EPA an important role in determining appropriate minimum levels of 

protection and providing national oversight, it also gives considerable flexibility and discretion to States 

and Tribes to design their own programs and establish levels of protection beyond the national 

minimums. Section 303 directs States and authorized Tribes to adopt water quality standards to protect 

public health or welfare, enhance the quality of water, and serve the purposes of the Clean Water Act. 

“Serve the purposes of the Act” (as defined in Sections 101(a), 101(a)(2), and 303(c) of the CWA) means 

that water quality standards should 1) include provisions for restoring and maintaining chemical, physical, 

and biological integrity of State and Tribal waters, 2) provide, wherever attainable, water quality for the 

protection and propagation of fish, shellfish, and wildlife and recreation in and on the water (i.e., 

“fishable/swimmable”), and 3) consider the use and value of State and Tribal waters for public water 

supplies, propagation of fish and wildlife, recreation, agricultural and industrial purposes, and navigation. 

Further requirements for water quality standards are at 40 CFR Part 131. 

State WQS provide the foundation for water quality-based pollution control programs. With the public 

participating in their adoption (see 40 CFR 131.20), such standards serve the dual purposes of 

establishing the water quality goals for a specific waterbody, and serving as the regulatory basis for the 

establishment of water quality-based treatment controls and strategies beyond the technology-based levels 

of treatment required by Sections 301(b) and 306 of the CWA. 

A waterbody’s designated use(s) are those uses specified in water quality standards, whether or not they 

are being attained (40 CFR 131.3(f)). The “use” of a waterbody is the most fundamental description of its 

role in the aquatic and human environments. All of the water quality protections established by the CWA 

follow from the waterbody’s designated use. As designated uses are critical in determining the water 

quality criteria that apply to a given waterbody, determining the appropriate designated use is of 

paramount importance in establishing criteria that are appropriately protective of that designated use. 

Section 131.10 of the regulation describes States’ and authorized Tribes’ responsibilities for designating 

and protecting uses. The regulation: 

• requires that States and Tribes specify the water uses to be achieved and protected, 

• requires protection of downstream uses, 

• allows for sub-category and seasonal uses, 

• sets out minimum attainability criteria, 

• lists six factors of, which at least one must be satisfied to justify removal of designated uses that 

are not existing uses, 

• prohibits removal of existing uses, 

• requires upgrading of uses that are presently being attained but not designated, and 

• establishes conditions and requirements for conducting use attainability analyses. 

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In addition, the regulations effectively establish a “rebuttable presumption” that the uses of protection and 

propagation of fish, shellfish, and wildlife and recreation in and on the water are attainable and should 

apply to a waterbody, unless it has been affirmatively demonstrated that such uses are not attainable. 

40 CFR 131.10(a) requires that States specify appropriate water uses to be achieved and protected. The 

classification of the waters of the State must take into consideration the use and value of water for public 

water supplies, protection and propagation of fish, shellfish, and wildlife, recreation in and on the water, 

and agricultural, industrial, and other purposes, including navigation. Changing designated uses for a 

specific waterbody requires a change in the water quality standards. Like all new and revised State and 

Tribal water quality standards, these changes are subject to U.S. EPA review and approval (see 40 CFR 

131.21). 

Where appropriate, a State may subcategorize or refine the aquatic life use designations for the receiving 

water. States may adopt subcategories of a use and set the appropriate criteria to reflect varying needs of 

such subcategories of uses, for instance, to differentiate between coldwater and warmwater fisheries (see 

40 CFR 131.10(c)). States may also adopt seasonal uses (40 CFR 131.10(f)). If seasonal uses are 

adopted, water quality criteria should reflect the seasonal uses; however, such criteria shall not preclude 

the attainment and maintenance of a more protective use in another season. 

Water quality criteria are elements of State WQS expressed as constituent concentrations, levels, or 

narrative statements representing a quality of water that supports a particular use. When criteria are met, 

water quality will generally protect the designated use (40 CFR 131.3). While some States have adopted 

a variety of criteria expressed as constituent concentration levels (or numeric criteria) for various 

pollutants for the protection of aquatic life, all States have adopted criteria expressed as narrative 

statements (or narrative criteria). Once adopted into standards, criteria can serve as the basis for 1) 

regulatory controls on point sources, 2) measuring attainment of standards and the effectiveness or 

programs, and 3) watershed planning. 

Section 304(a) criteria are developed by the U.S. EPA under authority of section 304(a) of the CWA 

based on the latest scientific information on the relationship that a constituent concentration, level, or 

measure has on a particular aquatic species and/or human health. This information is issued periodically 

to the States as guidance for use in developing criteria. In adopting criteria to protect their designated 

uses, States may establish criteria based on 1) section 304(a) guidance, 2) section 304(a) guidance 

modified to reflect site-specific conditions, or 3) other scientifically defensible methods. 

1.3 The role of designated aquatic life uses in Water Quality Standards 

It is in designating uses that States and Tribes establish the environmental goals for their water resources 

and then measure attainment of these goals. In designating uses, a State or Tribe weighs the 

environmental, social, and economic consequences of its decisions. The regulation allows the State or 

Tribe, with public participation, some flexibility in weighing these considerations and adjusting these 

goals over time. However, reaching a conclusion on the uses that appropriately reflect the current and 

potential future uses for a waterbody, determining the attainability of those goals, and appropriately 

evaluating the consequences of a designation can be a difficult and controversial task. 

A principal function of designated uses in water quality standards is to communicate the desired state of 

surface waters to water quality managers, the regulated community, and the interested public. An 

effective designated use system is one that translates readily into indicators (e.g., numeric water quality 

criteria, biological indexes) that respond in predictable ways to stress and can be evaluated using data 

collected from the waterbody. Experience with implementation of various State designated use systems 

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suggests that, regardless of the system selected, States that use biological data as part of their assessment 

program apply some type of refined, or tiered, aquatic life use approach to guide interpretation of their 

biological data. States have either made this explicit by adopting the tiers directly into their water quality 

standards as designated uses or implicit by using tiers in their monitoring and assessment protocols. 

Although the benefits of more specificity may apply to any of the designated uses described in CWA 

section 303, it may be most relevant for aquatic life uses. Aquatic communities can vary significantly 

from waterbody to waterbody. One major challenge in assigning designated uses for aquatic life to 

surface waters is separating the natural variability that is a function of stream type (e.g., naturally 

coldwater vs. warmwater stream) and location (ecoregion) from the variability that results from exposure 

to stressors. By accounting for natural variability in aquatic systems, biologically-based tiered aquatic life 

uses eliminate a major source of uncertainty and error in water quality management efforts. 

1.4 State and Tribal experiences with tiered aquatic life uses 

Over the years, States and Tribes have created many different use classification systems ranging from a 

straightforward replication of the uses specifically listed in section 303 of the CWA, to more complex 

systems that express designated uses in very specific terms or that establish subclassifications identifying 

different levels of protection. Some States designate general “aquatic life” uses while others list a variety 

of subcategories based on a range of aquatic community types, including descriptions of core aquatic 

species representative of each subcategory (e.g., coldwater and warmwater fisheries). Many States also 

have narrative biological criteria, which is often a general statement such as “aquatic life communities 

shall be maintained similar to aquatic life as naturally occurs.” Single thresholds for attainment of these 

general uses and narrative biological criteria are established with numeric biological criteria. For 

example, many State water quality agencies interpret narrative general use statements using an index 

(e.g., Index of Biotic Integrity (IBI)) (Karr et al. 1987, Karr 1990, Gibson et al. 1996, U.S. EPA 2002a). 

The index is standardized to regional reference conditions, and the biological criteria threshold is often 

established as a percentile of the distribution of reference site scores. The index is the basis for numeric 

biological criteria in many States and Tribes (U.S. EPA 2002a). 

The alternative to a single broad use is to divide the continuum of biological condition (the BCG) into 

several tiers for more precise management. As mentioned earlier, tiered aquatic life uses couple narrative 

descriptions of the use with criteria for measuring attainment of the use. Ideally, the narrative 

descriptions should incorporate biologically meaningful differences among tiers. The BCG provides an 

interpretative framework for defining reference conditions and articulating the biological condition that is 

being protected or restored in the water of interest. 

Several States and Tribes have adopted tiered aquatic life use statements in their water quality standards 

and some are developing the technical program and further tightening the linkage between their narrative 

use statements and numeric biological criteria (U.S. EPA 2002a). For example, Texas has had tiered 

aquatic life uses identified in their water quality standards for surface waters since 1984 (Table 1-1). 

Texas’ current WQS identify numeric dissolved oxygen criteria and include narrative aquatic life 

attributes. Numeric biological criteria have been developed for assessing both fish and benthic 

macroinvertebrate communities in wadeable streams. If site-specific conditions do not meet criteria for 

“High” use category as determined by receiving water assessment, a use attainability analysis will be 

conducted. Texas continues to evaluate the application of biological criteria for other aquatic systems, 

but at this point does not have a specific action plan to adopt numeric biological criteria for those systems. 

Other States cited elsewhere in this document, e.g., Maine, New Jersey, Ohio, and Vermont, have either 

developed or are considering developing tiered aquatic life uses. Though these approaches for tiering 

aquatic life uses may differ in detail and assessment methods, their uses share the same core elements: 

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• Biological information is the basis for the use designations. 

• Numeric biological indicators or biocriteria are developed for each use. 

• Development of tiers based on data from comprehensive, robust monitoring program. 

TABLE 1-1. Aquatic Life Subcategories in Texas WQS (Figure: 30 TAC §307.7(b)(3)(A)(i)). 

Aquatic Life 

Use 

Subcategory 

Dissolved Oxygen Criteria, mg/L Aquatic Life Attributes 

Freshwater 

mean/ 

minimum 

Freshwater 

in Spring 

mean/ 

minimum 

Saltwater 

mean/ 

minimum 

Habitat 

Characteristics 

Species 

Assemblage 

Sensitive 

species 

Diversity Species 

Richness 

Trophic 

Structure 

Exceptional 6.0/4.0 6.0/5.0 5.0/4.0 Outstanding 

natural 

variability 

Exceptional 

or unusual 

Abundant Exceptionally 

high 

Exceptionally 

high 

Balanced 

High 5.0/3.0 5.5/4.5 4.0/3.0 Highly 

diverse 

Usual association of 

regionally 

expected 

species 

Present High High Balanced 

to slightly 

imbalanced 

Intermediate 4.0/3.0 5.0/4.0 3.0/2.0 Moderately 

diverse 

Some 

expected 

species 

Very low 

in 

abundance 

Moderate Moderate Moderately 

imbalanced 

Limited 3.0/2.0 4.0/3.0 Uniform Most 

regionally 

expected 

species 

absent 

Absent Low Low Severely 

imbalanced 

- Dissolved oxygen means are applied as a minimum average over a 24-hour period. 

- Daily minima are not to extend beyond 8 hours per 24-hour day. Lower dissolved oxygen minima may apply on a site-specific basis, when natural daily 

fluctuations below the mean are greater than the difference between the mean and minima of the appropriate criteria. 

- Spring criteria to protect fish spawning periods are applied during that portion of the first half of the year when water temperatures are 63.0°F to 73.0°F. 

- Quantitative criteria to support aquatic life attributes are described in the standards implementation procedures. 

- Dissolved oxygen analyses and computer models to establish effluent limits for permitted discharges will normally be applied to mean criteria at steadystate, critical conditions. 

- Determination of standards attainment for dissolved oxygen criteria is specified in §307.9(d)(6) (relating to Determination of Standards Attainment). 

The insights and experiences from States and Tribes that have adopted tiered aquatic life uses and 

numeric biocriteria in their water quality standards, as well as from those currently developing biological 

assessment and criteria programs, reveal the values of tiered aquatic life uses implemented in State and 

Tribal WQS (Table 1-2). 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 1 – August 10, 2005 

6 
TABLE 1-2. The benefits and WQS regulation context for TALUs. 

Value-added Explanation Supporting WQS Regulation 

Set more appropriate designated 

ALUs 

Define ALUs in a more precise 

way that is neither underprotective of existing high-quality 

resources nor overprotective for 

waters that have been extensively 

and irretrievably altered 

40CFR131.10 

40CFR131.12 (Protect High 

Quality Waters) 

40CFR130.23 (Support 

attainment decisions and 

diagnose causes) 

Strengthen the linkage between 

designated ALUs and how 

attainment is assessed 

TALUs help to clarify and refine 

water quality goal statements so 

numeric biological, chemical and 

physical criteria can be adopted 

to protect the use 

40CFR131.10(c) 

40CFR131.12 (Protect High 

Quality Waters) 

40CFR130.23 (Support 

attainment decisions and 

diagnose causes) 

Enhance public understanding 

and participation in setting water 

quality goals 

TALUs provide a common frame 

of reference or generic yardstick 

to more clearly recognize 

common ground and differences 

in desired environmental goals of 

various stakeholders as 

designated uses are adopted 

40 CFR131.20 (a)(b) 

Building on these “lessons learned,” the U.S. EPA convened a technical workgroup in 2000 to identify 

existing scientifically sound and practical approaches that would help States and Tribes provide more 

precision, or specificity, in their designated aquatic life uses. The workgroup included biologists and 

aquatic ecologists from States, Tribes, U.S. EPA, USGS, the academic research community, and the 

private sector. The workgroup was asked to address the following questions: 

• What are effective technical approaches using biological information to provide more specificity 

in their designated aquatic life uses? 

• What are the “lessons learned” that can be capitalized on and shared with other States and Tribes? 

The workgroup was charged with developing a scientific framework using biological information to 

better define designated aquatic life uses, enabling more precise use descriptions. Their product is a 

narrative model describing graduated tiers of biological response to increasing levels of stressors, the 

Biological Condition Gradient (BCG). The model is founded on peer-reviewed work in the field of 

bioassessments over the past thirty years (Fausch et al. 1984, Karr et al. 1986, Cairns and Pratt 1993, 

Barbour et al. 1999) and on the experiences and empirical observations of States and Tribes that have 

developed tiered aquatic life uses and biological criteria for use in their water programs (Courtemanch et 

al. 1989, Courtemanch 1995, Yoder 1995, Yoder and Rankin 1995b). 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 1 – August 10, 2005 

7 
Extreme changes in structure; wholesale changes in

taxonomic composition; extreme alterations from

normal densities; organism condition is often poor;

3

2

5

4

6

Sensitive taxa markedly diminished;

conspicuously unbalanced distribution

of major groups from that expected;

organism

1

1.5	 The Biological Condition Gradient: A tool for better defining and developing more 

precise aquatic life uses 

The Biological Condition Gradient (BCG) is a scientific model for interpreting biological response to 

increasing effects of stressors on aquatic ecosystems (Figure 1-1). The model describes how ten 

attributes of aquatic ecosystems change in response to the increasing levels of stressors. The attributes 

include several aspects of community structure, organism condition, ecosystem function, and spatial and 

temporal attributes of stream size and connectivity. The gradient can be considered analogous to a fieldbased dose-response curve where dose (x-axis) = increasing levels of stressors and response (y-axis) = 

biological condition (see figure below). The BCG differs from the standard dose-response curve, in that 

the BCG does not represent the laboratory response of a single species to a specified dose of a known 

chemical, but rather the in-situ response of the biota to the sum of stresses it is exposed to. The BCG is 

divided into six tiers of biological condition along the stressor-response curve, ranging from observable 

biological conditions found at no or low levels (Tier 1) to those found at high levels of stressors (Tier 6). 

The BCG model was developed to provide a common framework for interpreting biological information 

regardless of methodology and geography. When calibrated to a regional or state scale, States and Tribes 

can use the model to more precisely evaluate the current and potential biological condition of their waters 

and use that information to better define their aquatic life uses. Additionally, States and Tribes can use 

this interpretative model to more clearly communicate the condition of their aquatic resources to the 

public. 

C

o

n

dition 

of the 

Biotic 

C

o

m

m

u

nity

L

OW [S

p

e

cific to 

E

c

oty

p

e] HIGH 

LOW Level of Stressors HIGH 

Natural structural, functional, and taxonomic integrity is preserved. 

Structure and function similar to natural community with some additional 

taxa & biomass; no or incidental anomalies; sensitive non-native taxa may be 

present; ecosystem level functions are fully maintained 

Evident changes in structure due to loss of some rare native 

taxa; shifts in relative abundance; ecosystem level functions fully 

maintained through redundant attributes of the system. 

Moderate changes in structure due to replacement of 

sensitive ubiquitous taxa by more tolerant taxa; overall 

balanced distribution of all expected taxa; ecosystem 

functions largely maintained. 

condition shows signs of physiological 

stress; ecosystem function shows reduced 

complexity and redundancy; increased build 

up or export of unused materials. 

anomalies may be frequent; 

ecosystem functions are 

extremely altered. 

1 

FIGURE 1-1. Conceptual model of the Biological Condition Gradient. 

The BCG model was developed based on common patterns of biological response to stressors observed 

empirically by aquatic biologists and ecologists from different geographic areas of the U.S. Once a draft 

model was constructed, it was tested at a workgroup meeting and then at two regional workshops. The 

model was tested by determining how consistently the scientists assigned samples of macroinvertebrates 

or fish to the different tiers of biological condition. Workgroup members identified similar sequences of 

biological response to increasing levels of stressors regardless of geographic area. These results support 

the use of the BCG as a nationally applicable model for interpreting the biological condition of aquatic 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 1 – August 10, 2005 

8 
systems. Chapter 2 discusses the development and makeup of the conceptual BCG and Chapter 3 

explores strategies for regionally modifying, or calibrating, the conceptual model. Chapter 4 describes 

how the x-axis of the BCG model, the stressor gradient, can be characterized and explains how the effects 

of stressors on biological condition play a role in constructing and using a BCG. Chapter 5 discusses the 

underlying principles and processes States have learned in using biological information to develop tiered 

aquatic life uses, and examples of how States have applied tiered uses in water quality management are 

presented in Chapter 6. 

Integral to the development of the BCG is characterizing the model’s x-axis, the stressor gradient (Figure 

1-1). Stressors are physical, chemical or biological factors that induce an adverse response from aquatic 

biota (U.S. EPA 2000b; EPA/822/B-00/025). For example, high concentrations of certain metals, 

nutrients, or sediment can adversely impact aquatic biota. Loss of aquatic habitat or presence of aquatic 

invasive species can also adversely impact, or stress, the aquatic biota expected for a specific waterbody. 

These stressors can cause aquatic ecosystems to change from natural conditions, exhibiting altered 

compositional, structural, and functional characteristics. The degree to which stressors affect the biota 

depends on the magnitude, frequency, and duration of the exposure of the biota to the stressors. 

Developing a BCG for a given system characterizes the general relationship between its stressors in total 

(the model’s x-axis) and its overall biological condition (the y-axis). Multiple stressors are usually 

present, and thus the stressor x-axis of the BCG seeks to represent their cumulative influence as a 

Generalized Stressor Gradient (GSG), much as the y-axis generalizes biological condition. 

Understanding the links between stressors and their sources and the response of the aquatic biota will help 

to more accurately determine the existing and potential condition of the aquatic biota (Figure 1-2). There 

are different approaches and emerging science to define and quantify the causal sequence between 

stressors and their sources and biological responses. Building on current State and Tribal approaches, a 

framework for characterizing stressors, the processes and mechanisms that generate them, and the 

resulting biological response is presented. This framework may not only help State and Tribal managers 

more precisely define designated uses, including potential future uses, but may support diagnosis of use 

impairment and help prioritize management decision making. 

FIGURE 1-2. The causal sequence from 

stressors and their sources through the 

five major water resource features to the 

biological responses, i.e., the biological 

endpoints. This model illustrates the 

multiple pathways that stressors and 

their sources can affect aquatic biota. 

Insert illustrates the relationship 

between stressor dose and the gradient 

of biological responses (after Karr and 

Yoder 2004; used by permission of J.D. 

Allan, originally presented at the 2002 

TALU Workgroup Meeting). Condition 

Stressors 

Habitat 

structure 

Biological 

responses 

Flow 

regime 

Energy 

source 

Biotic 

interactions 

Water quality 

and toxicity 

Stressor(s) 

Processes and 

mechanisms that Altered water Biological 

generate stressors resource features endpoint 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 1 – August 10, 2005 

9 
CONDITION OF THE

WATER RESOURCE

Principal Goal of the Clean Water Act

WATER RESOURCE

Principal Goal of the Clean Water Act

1.6 Conceptual basis for the Biological Condition Gradient 

The five factors that determine the integrity of a water resource, which were originally described by Karr 

and Dudley (1981; Figure 1-3), have been consistently used as the conceptual basis for biological 

assessment and tiered aquatic life uses. In the context of the TALU approach, consideration of the five 

factors in Figure 1-3 are components of the stressor axis of the BCG model, while the condition of the 

water resource is accounted for by the response of the biological community to the stressors, the 

Biological Condition Gradient (BCG). The health and well-being of the aquatic biota is an important 

barometer to measure progress towards achieving Clean Water Act goals. Biological integrity has been 

defined as the combined result of chemical, physical, and biological processes in the aquatic environment 

(Karr and Dudley 1981, Karr et al. 1986). Biological criteria help reconcile the mosaic of factors and 

interactions that exist, parts of which may be characterized and measured using chemical and physical 

indicators. 

Precipitation & 

Chemical 

Variables 

Hardness 

Turbidity 

pH 

D.O. 

Temperature 

Alkalinity Solubilities 

Adsorption 

Nutrients 

Organics 

Chemical

Variables

Hardness

Turbidity

pH

D.O.

Temperature

Alkalinity Solubilities

Adsorption

Nutrients

Organics

Flow 

Regime 

High/Low Extremes 

Runoff 

Velocity 

Diversions 

Ground 

Water 

Flow

Regime

Extremes

Runoff

Velocity

Ground

Water

Reproduction Biotic 

Factors 

Disease Parasitism 

Feeding 

Predation 

Competition 

Reproduction Biotic

Factors

Disease Parasitism

Feeding

Predation

Competition

Energy 

Source 

Nutrients 

Sunlight 

Organic Matter Inputs 1 and 2 

Production 

o o 

Seasonal 

Cycles 

Energy

Source

Nutrients

Sunlight

Organic Matter Inputs 1 and 2

Production

o o

Seasonal

Cycles

Habitat 

Structure 

Riparian Vegetation 

Siltation 

Current 

Substrate 

Sinuosity 

Instream Cover 

Gradient 

Channel 

Morphology 

Bank Stability 

Width/Depth 

H

ure

Riparian Vegetation

Siltation

Current

Substrate

Sinuosity

Instream Cover

Gradient

Channel

Morphology

Bank Stability

Width/Depth

Precipitation &

Chemical

Variables

Hardness

Turbidity

pH

D.O.

Temperature

Alkalinity Solubilit

Chemical

Variables

Hardness

Turbidity

pH

D.

abitat

Struct

“

ies

Adsorption

Nutrients

Organics

O.

Temperature

Alkalinity Solubilities

Adsorption

Nutrients

Organics

Flow

Regime

High/Low Extremes

Runoff

Velocity

Diversions

Ground

Water

Flow

Regime

Extremes

Runoff

Velocity

Ground

Water

Reproduction Biotic

Factors

Disease Parasitism

Feeding

Predation

Competition

Reproduction Biotic

Factors

Disease Parasitism

Feeding

Predation

Competition

Energy

Source

Nutrients

Sunlight

Organic Matter Inputs 1 and 2

Production

o o

Seasonal

Cycles

Energy

Source

Nutrients

Sunlight

Organic Matter Inputs 1 and 2

Production

o o

Seasonal

Cycles

Habitat

Structure

Riparian Vegetation

Siltation

Current

Substrate

Sinuosity

Instream Cover

Gradient

Channel

Morphology

Bank Stability

Width/Depth

Habitat

Structure

Riparian Vegetation

Siltation

Current

Substrate

Sinuosity

Instream Cover

Gradient

Channel

Morphology

Bank Stability

Width/Depth

BIOLOGICAL CONDITION OF 

THE WATER RESOURCE 

Canopy

(Modified from Karr et al. 1986). 

FIGURE 1-3. The five major factors that determine the biological condition of aquatic 

resources (modified from Karr et al. 1986). 

An important conceptual foundation of tiered aquatic life uses is the “position of the standard” that was 

described by the National Research Council Committee on Science in TMDLs (NRC 2001; Figure F-1). 

This concept describes the “position” of different types of criteria with respect to their position along a 

causal chain of indicators beginning with sources (stressor indicators), to changes in pollutant 

contributions or attributes of landscape and/or hydrology that emanate from those sources (exposure 

indicators), to instream exposures (pollutants, attributes of habitat), to indicators of biological condition 

(response indicators) that directly assess the designated use. Because designated uses are written in 

qualitative, narrative terminology, the challenge is to relate a criterion to the designated use. In general, 

establishing this relationship becomes easier as the criterion is positioned closer to the designated use, 

hence the NRC recommendation on the use of biological information to help determine more appropriate 

aquatic life uses and to couple the narrative use statements with quantitative methods. Thus biological 

criteria can fill a gap along this position spectrum and serve a useful role in the expression and 

implementation of water quality standards. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 1 – August 10, 2005 

10 
Karr and Yoder (2004) further elaborated upon this concept by adding the interactive relationships 

between pollution and pollutants from both point and nonpoint sources (Figure 1-4). It also relates 

different types of indicators in the causal sequence of events and exemplifies the appropriate roles of 

chemical, physical, and biological parameters as stressor, exposure, and response indicators (Yoder and 

Rankin 1998). In this scheme, attainment of a designated use is the desired result of the management of 

stressors (chemical, biological, physical) and is explained by how stressors influence and change the five 

factors that determine the integrity of an aquatic resource (Karr and Yoder 2004). In each of these 

process descriptions, the end outcome of water quality management is reflected in the status of a 

designated use. Attainment of the designated use confirms the effectiveness of the sequence of 

management actions; non-attainment is evidence of an incomplete process and a prompt to re-examine the 

management strategy. Each provides important feedback about the effectiveness of management 

strategies. Therefore, how designated uses are developed, assigned, and measured is key to the outcomes 

derived from water quality management. 

Designated use 

(water body specific) 

Pollutant loading 

for all sources 

(source specific) 

Pollution (specific 

human activities) 

Ambient pollutant 

levels in water body 

(chemical specific) 

Ecological health 

(cumulative effects on 

biological condition) 

Source 

Exposure 

(in -stream) 

Response 

Channel 

and flow 

alterations 

Landscape 

effects 

Riparian and 

i-n channel effects 

Endpoint 

Exposure 

(landscape) 

Human health 

(health outcomes 

including disease) 

FIGURE 1-4. Modification of the NRC 

“position of the criterion” concept 

(Figure F-1) showing the causal sequence 

from indicators of stress, exposure, and 

response in relation to point and 

nonpoint source impacts, specific types of 

criteria, and designated uses that define 

the endpoints of interest to society (after 

Karr and Yoder 2004). 

1.7 Key points from Chapter 1 

1.	 Section 101(a) of the CWA establishes broad national goals and objectives such as the chemical, 

physical, and biological integrity objective. To help achieve the integrity objective, the CWA 

also established, among other things, an interim goal for the protection and propagation of fish, 

shellfish, and wildlife. The protection and propagation interim goal has been interpreted by U.S. 

EPA to include the protection of the full complement of aquatic organisms residing or migrating 

through a waterbody. The health and well-being, or condition, of the aquatic biota is an 

important barometer to measure progress towards achieving Clean Water Act goals and 

objectives. 

2.	 State water quality standards provide the foundation for water quality-based pollution control 

programs. With the public participating in their adoption (see 40 CFR 131.20), such standards 

serve the dual purposes of establishing the water quality goals for a specific waterbody 

(designated uses) and serve as the regulatory basis for the establishment of water quality-based 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 1 – August 10, 2005 

11 
treatment controls and strategies beyond the technology-based levels of treatment required by 

Sections 301(b) and 306 of the CWA. 

3.	 A waterbody’s designated use(s) are those uses specified in water quality standards, whether or 

not they are being attained (40 CFR 131.3(f)). The “use” of a waterbody is the most fundamental 

articulation of its role in the aquatic and human environments. All of the water quality 

protections established by the CWA follow from the waterbody’s designated use. 

4.	 Tiered aquatic life uses are bioassessment-based statements of expected biological condition in 

specific waterbodies. Tiered uses allow more precise and measurable definitions of designated 

aquatic life uses. 

5.	 Several States and Tribes have adopted tiered aquatic life uses in their water quality standards. 

This document is based on the “lessons learned” from their experiences and the recommendations 

from a technical workgroup charged with integrating existing scientifically sound and practical 

approaches to 1) tier designated aquatic life uses using biological information, and 2) incorporate 

information on sources of stress as drivers of biological condition. 

1.8 Organization of the document 

This chapter provided the background and rationale for using biological information to designate aquatic 

life uses in tiers that more specifically differentiate the characteristics of the biological community 

currently present or desired in a waterbody. The following chapters are based on the recommendations of 

the TALU technical workgroup tasked with identifying existing scientifically sound and practical 

approaches that would help States and Tribes provide more precision, or specificity, in their designated 

aquatic life uses (Figure 1-5). Chapters 2 and 3 discuss the Biological Condition Gradient (BCG) – what 

it is, how the national conceptual model was developed and tested, and how to calibrate the conceptual 

model to a region. Chapter 4 describes how the x-axis of the BCG model, the stressor gradient, can be 

characterized and explains how the effects of stressors on biological condition play a role in constructing 

and using a BCG. Chapter 5 provides examples on how States have developed tiered aquatic life uses. 

The experiences of Maine and Ohio, two States that have completed this process, serve as comprehensive 

case histories that are found in Appendixes A and B. Chapter 6 details how Maine and Ohio have used 

tiered aquatic life uses in assessment and management as examples that might guide future 

implementation guidance. 

FIGURE 1-5. Roadmap to the


document.


Introduction 

1. What are Tiered Aquatic Life Uses 

(TALUs)? 

The Biological Condition 

Gradient (BCG) 

2. What is the scientific basis of the 

BCG? 

3. How do you develop and calibrate 

a BCG? 

4. The x-axis: A Generalized 

Stressor Gradient (GSG) 

Appendixes A – E 

• Maine TALU Implementation 

Case History (A) 

• Ohio TALU Implementation 

Case History (B) 

• Summary of draft documents 

Incorporating TALUs into State addressing technical elements 

of bioassessment programs (C), 

reference condition (D), and 5. Key concepts and milestones in the statistical guidance for 

developing indicators (E) 

References, 

Glossary & Acronyms 

development of TALUs 

6. How have states and tribes used 

TALUs in WQS and management? 

and Tribal WQS: Case Examples 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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12 
Related Technical Support Documents: 

Appendixes C, D & E contain summaries of three “companion” documents that are under development. 

Each contains detailed information relevant to developing tiered aquatic life uses, including components 

of State and Tribal bioassessment programs, statistical methods that use biological data, and best practices 

for developing reference conditions. Following is a brief description of each document. 

Technical Guidelines: Technical Elements of a Bioassessment Program – DRAFT 

This document is intended primarily for use by State and Tribal program managers and staff who are 

responsible for monitoring and assessment and water quality standards programs. The document 

describes the technical attributes of biological assessment programs, and can thus be used by States 

and Tribes to 1) determine where they are in the biological assessment and criteria development 

processes, and 2) develop, structure, and, if necessary, modify their programs and refine designated 

aquatic life uses. 

U.S. EPA project leads: Susan Jackson, Office of Water; Ed Hammer, Region 5; Tina Laidlaw, Region 8; 

and Gretchen Hayslip, Region 10 

The Role of Reference Condition in Biological Assessment and Criteria – DRAFT DOCUMENT ON 

DEVELOPMENT AND APPLICATION OF THE REFERENCE CONDITION CONCEPT 

This document will provide States, Tribes, and other practitioners with guidelines on using reference 

conditions in their water management programs, particularly for ecological assessments. The 

guidelines described are intended to facilitate greater implementation of best practices for reference 

condition, thereby improving the success of individual programs and leading to greater consistency 

among States and Tribes. 

U.S. EPA project leads: Evan Hornig, Office of Water; Phil Larsen, Office of Research and Development; 

and Wayne Davis, Office of Environmental Information 

Statistical Guidance for Developing Indicators for Rivers and Streams: A Guide for Constructing 

Multimetric and Multivariate Predictive Bioassessment Models – DRAFT 

This document will provide methods and outlines the steps required to complete multimetric and 

multivariate predictive assessment models, two methods for analyzing and assessing waterbody 

condition from assemblage and community-level biological information. 

U.S. EPA project lead: Florence Fulk, Office of Research and Development 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 1 – August 10, 2005 

13 
DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 1 – August 10, 2005 

14 
The Biological Condition Gradient

The Biological Condition Gradient (BCG) is a scientific model that allows consistent interpretation of 

biological condition although assessment approaches may differ. The BCG combines scientific 

knowledge with the practical experience and needs of resource managers and can assist environmental 

practitioners in the U.S. to better: 

° define aquatic resources The BCG is consistent with 

° establish direct relationships between biological condition ecological theory and is a means 

and stressors for standardizing interpretations 

° communicate clearly to the public both the existing and of the response of aquatic biota 

potential uses of a waterbody to stressors. The model should 

facilitate communication among 

Chapter 2 outlines the development and makeup of the BCG model. scientists, managers, and the 

The BCG describes changes in ten ecological attributes across a 

gradient of biological condition caused by increasing stressors (Table 

2-1). It is divided into six condition tiers, Tier 1 representing natural, 

or undisturbed, conditions through Tier 6 representing severely altered 

public on the current conditions 

and ecological potential for 

specific waterbodies. 

conditions. 

TALU Workgroup biologists from across the U.S. agreed that a similar sequence of biological alterations 

occur in streams in response to stressors, strengthening the feasibility of using the BCG as a common 

framework to guide management decisions that protect and restore aquatic systems in the U.S. (Davies 

and Jackson in press). The model is consistent with ecological theory and can be adapted or calibrated to 

reflect specific geographic regions. Scientific knowledge can be reviewed and consolidated and research 

needs can be expressed in a context relevant to management. Thus, the model also serves as a framework 

that 1) synthesizes what has been observed into testable hypotheses, and 2) identifies knowledge gaps in 

need of further research. 

Chapter 3 explores strategies for regionally modifying, or calibrating, the BCG including approaches for 

recalibrating existing indexes. Three States (Maine, Ohio, and Vermont) have incorporated a BCG into 

their water quality standards as well as numeric criteria. Several other States (e.g., New Jersey, Texas, and 

a consortium of New England states) have begun the process of evaluating the potential use of a BCG. 

Each of these States is following basically the same approach used by the national TALU Workgroup to 

develop the BCG model, reaching consensus among regional biological experts familiar with natural 

aquatic communities and their responses to stress. 

Chapter 4 describes the model’s x-axis, the stressor gradient that illustrates alteration in biological 

condition. The degree to which stressors affect the biota depends on the magnitude, frequency, and 

duration of the exposure of the biota to the stressors. Developing a BCG for a given system characterizes 

the general relationship between its stressors in total (the model’s x-axis) and its overall biological 

condition (the y-axis). Multiple stressors are usually present, and thus the stressor x-axis of the BCG 

seeks to represent their cumulative influence as a Generalized Stressor Gradient (GSG), much as the yaxis generalizes biological condition. Chapter 4 explains how stressors can be characterized and 

describes how the influence of stressors on biological condition plays a role in constructing and using a 

BCG. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 2 – August 10, 2005 

15 
CHAPTER 2. WHAT IS THE SCIENTIFIC BASIS OF THE BIOLOGICAL 

CONDITION GRADIENT? 

The Biological Condition Gradient (BCG) extends the empirical work of earlier researchers and 

practitioners to create a nationally consistent model that links management goals for resource condition 

with the quantitative measures used in biological assessments. The BCG was designed to describe 

ecological response to stressors in sufficient detail so that a site can be placed into a tier along the BCG 

continuum through use of the core data elements collected by most State or Tribal monitoring programs. 

The practice of using biological indicators to assess water quality is over a century old. The Saprobien 

System, a concept proposed by Lauterborn in 1901and further developed the following year by Kolkwitz 

and Marsson (Davis 1995), uses benthic macroinvertebrates and planktonic plants and animals as 

indicators of organic loading and low dissolved oxygen, and has been updated and is currently used in 

several European countries. Concurrently, the limnologists Thienemann and Naumann developed the 

concept of trophic state classification for lakes in the 1920s (Carlson 1992, Cairns and Pratt 1993). These 

early indexes described a response gradient (or response classes for lakes) to enrichment. The Saprobien 

System was explicitly developed to assess human pollution in rivers, but the trophic state concept was 

originally developed to describe natural conditions in lakes and only later became a concept to describe 

pollution-caused eutrophication (e.g., Vollenweider 1968). The 1950s marked the development of 

Beck’s biotic index in the U.S. and Pantle and Buck’s Saprobic Index in Europe, which were directly 

based on the Saprobien System (cited in Davis 1995). The Saprobic Index, which led to the development 

of the widely used Hilsenhoff Index (e.g., Hilsenhoff 1987) in the U.S., could be considered the 

predecessor of today’s biotic indexes (Davis 1995). 

The conceptual foundation of the BCG is based on many decades of biologists’ accumulated experience 

with biological assessment and monitoring. Biological information from monitoring programs has been 

frequently synthesized by constructing biotic indexes, such as the Index of Biotic Integrity (IBI) (Karr 

1981, Karr et al. 1986). The IBI integrated the concept of anchoring the measurement system in 

undisturbed reference conditions with the measurement of several indicators intended to reflect ecological 

components of composition, diversity, and ecosystem processes. It thus combined a conceptual model of 

ecosystem change in response to increasing levels of stressors with a practical measurement system for 

fish. The BCG is also grounded in the concepts in Cairns et al. (1993) describing “natural” conditions 

and the change in biological condition caused by stressors. To achieve maximum potential application 

nationwide, the BCG tiers were developed based on States’ various experiences designing and 

implementing tiered aquatic life use and management goals as well as the practical experience of aquatic 

scientists from different bio-geographic areas, each of whom had fifteen to thirty years of experience in 

the field. The BCG: 

1.	 Describes a complete scale of condition from natural (Tier 1) to severely altered (Tier 6); 

2.	 Synthesizes existing field observations and generally accepted interpretations of patterns of 

biological change within a common framework; and 

3.	 Helps determine the degree to which a system may have departed from natural condition, 

based on measurable, ecologically important attributes. 

At present, the description of biological attributes that make up the model applies best to permanent, hardbottom streams that are exposed to increases in temperature, nutrients, and fine sediments because this is 

the stream-type and stressor regime originally described by the model. The model has been further tested 

with States and Tribes in different parts of the country (e.g., arid west and great plains) to evaluate the 

national applicability of the model. Results have been successful with some necessary refinement of the 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 2 – August 10, 2005 

16 
model attributes to accommodate regional differences. For example, during a workshop in Texas where 

the BCG was being evaluated using Texas data, Attribute II (sensitive-rare taxa) was redefined as highly 

sensitive taxa because rarity of a taxon in the region was not deemed to be associated with sensitivity to 

stress. In arid streams, many rare, native taxa are highly tolerant to stressors such as low dissolved 

oxygen and high temperature. Thus, the BCG can be applicable to other aquatic ecosystems and stressors 

with appropriate modifications. The BCG should be viewed as an evolving model that must be 

responsive to changes in scientific understanding resulting from the analysis of empirical data. 

The value of a heuristic model such as the BCG is not only that it documents experimentally established 

knowledge, but also that it promotes a more rigorous testing of empirical observations by clearly stating 

them in a provisional model. Conceptual models formalize the state of knowledge and guide research. 

Empirically based generalizations have led to conceptual models that describe the behavior of biological 

systems under stress (Brinkhurst 1993; Margalef 1963, 1981; Odum, et al. 1979; Rapport et al. 1985; 

Schindler 1987; Fausch et al. 1990; Karr and Dudley 1981). For example, Brinkhurst observed that 

“Everyone knew [in 1929] that increases in numbers and species could be related to mild pollution, that 

moderate pollution could produce changes in taxa so that diversity remained similar but species 

composition shifted, and that eventually species richness declined abruptly and numbers of some tolerant 

forms increased dramatically.” Such ecosystem responses to stressor gradients have been portrayed as a 

progression of stages that occur in a generally consistent pattern (Odum et al. 1979, Odum 1985, Rapport 

et al. 1985, Cairns and Pratt 1993). Establishing and validating quantifiable thresholds along that 

progression with empirical data is a priority need for resource managers (Cairns l981). 

2.1 What the BCG model looks like 

The BCG model depicts ecological condition in terms of ten system attributes expressed at different 

spatial scales (Table 2-1). In biological assessments, most information is collected at the spatial scale of a 

site or reach and the temporal scale of a single sampling event. Many of the attributes that make up the 

BCG are based on these scales. Site scale attributes include aspects of taxonomic composition and 

community structure (Attributes I-VI) and organism and system performance (Attributes VII and VIII). 

At larger temporal and spatial scales, physical-biotic interactions (Attributes IX and X) were also 

included because of their importance in evaluating the longer term impacts, restoration potential and 

recoveries. 

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TABLE 2-1. Biological Condition Gradient matrix. 

Biological Condition Gradient Tiers 

Ecological 

Attributes 

1 

Natural or native 

condition 

Native structural, 

functional and 

taxonomic 

integrity is 

preserved; 

ecosystem 

function is 

preserved within 

the range of 

natural variability 

2 

Minimal changes 

in the structure of 

the biotic 

community and 

minimal changes 

in ecosystem 

function 

Virtually all native 

taxa are 

maintained with 

some changes in 

biomass and/or 

abundance; 

ecosystem 

functions are fully 

maintained within 

the range of 

natural variability 

3 

Evident changes 

in structure of the 

biotic community 

and minimal 

changes in 

ecosystem 

function 

Some changes in 

structure due to 

loss of some rare 

native taxa; shifts 

in relative 

abundance of 

taxa but 

Sensitiveubiquitous taxa 

are common and 

abundant; 

ecosystem 

functions are fully 

maintained 

through 

redundant 

attributes of the 

system 

4 

Moderate 

changes in 

structure of the 

biotic community 

and minimal 

changes in 

ecosystem 

function 

Moderate 

changes in 

structure due to 

replacement of 

some Sensitiveubiquitous taxa 

by more tolerant 

taxa, but 

reproducing 

populations of 

some Sensitive 

taxa are 

maintained; 

overall balanced 

distribution of all 

expected major 

groups; 

ecosystem 

functions largely 

maintained 

through 

redundant 

attributes 

5 

Major changes in 

structure of the 

biotic community 

and moderate 

changes in 

ecosystem 

function 

Sensitive taxa are 

markedly 

diminished; 

conspicuously 

unbalanced 

distribution of 

major groups 

from that 

expected; 

organism 

condition shows 

signs of 

physiological 

stress; system 

function shows 

reduced 

complexity and 

redundancy; 

increased buildup or export of 

unused materials 

6 

Severe changes 

in structure of the 

biotic community 

and major loss of 

ecosystem 

function 

Extreme changes 

in structure; 

wholesale 

changes in 

taxonomic 

composition; 

extreme 

alterations from 

normal densities 

and distributions; 

organism 

condition is often 

poor; ecosystem 

functions are 

severely altered 

I 

Historically 

documented, 

sensitive, 

long-lived or 

regionally 

endemic 

taxa 

As predicted for 

natural 

occurrence 

except for global 

extinctions 

As predicted for 

natural 

occurrence 

except for global 

extinctions 

Some may be 

absent due to 

global extinction 

or local 

extirpation 

Some may be 

absent due to 

global, regional or 

local extirpation 

Usually absent Absent 

II 

Sensitiverare taxa 

As predicted for 

natural 

occurrence, with 

at most minor 

changes from 

natural densities 

Virtually all are 

maintained with 

some changes in 

densities 

Some loss, with 

replacement by 

functionally 

equivalent 

Sensitiveubiquitous taxa 

May be markedly 

diminished 

Absent Absent 

III 

Sensitiveubiquitous 

taxa 

As predicted for 

natural 

occurrence, with 

at most minor 

changes from 

natural densities 

Present and may 

be increasingly 

abundant 

Common and 

abundant; relative 

abundance 

greater than 

Sensitive-rare, 

taxa 

Present with 

reproducing 

populations 

maintained; some 

replacement by 

functionally 

equivalent taxa of 

intermediate 

tolerance. 

Frequently absent 

or markedly 

diminished 

Absent 

IV 

Taxa of 

intermediate 

tolerance 

As predicted for 

natural 

occurrence, with 

at most minor 

changes from 

natural densities 

As naturally 

present with slight 

increases in 

abundance 

Often evident 

increases in 

abundance 

Common and 

often abundant; 

relative 

abundance may 

be greater than 

Sensitiveubiquitous taxa 

Often exhibit 

excessive 

dominance 

May occur in 

extremely high 

OR extremely low 

densities; 

richness of all 

taxa is low 

V 

Tolerant 

taxa 

As naturally 

occur, with at 

most minor 

changes from 

natural densities 

As naturally 

present with slight 

increases in 

abundance 

May be increases 

in abundance of 

functionally 

diverse tolerant 

taxa 

May be common 

but do not exhibit 

significant 

dominance 

Often occur in 

high densities 

and may be 

dominant 

Usually comprise 

the majority of the 

assemblage; 

often extreme 

departures from 

normal densities 

(high or low) 

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TABLE 2-1. Biological Condition Gradient matrix. 

Biological Condition Gradient Tiers 

1 

Natural or native 

condition 

2 

Minimal changes 

in the structure of 

the biotic 

community and 

minimal changes 

in ecosystem 

function 

3 

Evident changes 

in structure of the 

biotic community 

and minimal 

changes in 

ecosystem 

function 

4 

Moderate 

changes in 

structure of the 

biotic community 

and minimal 

changes in 

ecosystem 

function 

5 

Major changes in 

structure of the 

biotic community 

and moderate 

changes in 

ecosystem 

function 

6 

Severe changes 

in structure of the 

biotic community 

and major loss of 

ecosystem 

function 

VI 

Non-native 

or 

intentionally 

introduced 

taxa 

Non-native taxa, if 

present, do not 

displace native 

taxa or alter 

native structural 

or functional 

integrity 

Non-native taxa 

may be present, 

but occurrence 

has a nondetrimental effect 

on native taxa 

Sensitive or 

intentionally 

introduced nonnative taxa may 

dominate some 

assemblages 

(e.g. fish or 

macrophytes) 

Some 

replacement of 

sensitive nonnative taxa with 

functionally 

diverse 

assemblage of 

non-native taxa of 

intermediate 

tolerance 

Some 

assemblages 

(e.g., fish or 

macrophytes) are 

dominated by 

tolerant nonnative taxa 

Often dominant; 

may be the only 

representative of 

some 

assemblages 

(e.g., plants, fish, 

bivalves) 

VII 

Organism 

Condition 

(especially 

of long-lived 

organisms) 

Any anomalies 

are consistent 

with naturally 

occurring 

incidence and 

characteristics 

Any anomalies 

are consistent 

with naturally 

occurring 

incidence and 

characteristics 

Anomalies are 

infrequent 

Incidence of 

anomalies may 

be slightly higher 

than expected 

Biomass may be 

reduced; 

anomalies 

increasingly 

common 

Long-lived taxa 

may be absent; 

Biomass reduced; 

anomalies 

common and 

serious; minimal 

reproduction 

except for 

extremely tolerant 

groups 

VIII 

Ecosystem 

Functions 

All are maintained 

within the natural 

range of 

variability 

All are maintained 

within the natural 

range of 

variability 

Virtually all are 

maintained 

through 

functionally 

redundant system 

attributes; 

minimal increase 

in export except 

at high storm 

flows 

Virtually all are 

maintained 

through 

functionally 

redundant system 

attributes though 

there is evidence 

of loss of 

efficiency (e.g., 

increased export 

or decreased 

import) 

There is apparent 

loss of some 

ecosystem 

functions 

manifested as 

increased export 

or decreased 

import of some 

resources, and 

changes in 

energy exchange 

rates (e.g., P/R; 

decomposition) 

Most functions 

show extensive 

and persistent 

disruption 

IX 

Spatial and 

temporal 

extent of 

detrimental 

effects 

N/A 

A natural 

disturbance 

regime is 

maintained 

Limited to small 

pockets and short 

duration 

Limited to the 

reach scale 

and/or limited to 

within a season 

Mild detrimental 

effects may be 

detectable 

beyond the reach 

scale and may 

include more than 

one season 

Detrimental 

effects extend far 

beyond the reach 

scale leaving only 

a few islands of 

adequate 

conditions; effect 

extends across 

multiple seasons 

Detrimental 

effects may 

eliminate all 

refugia and 

colonization 

sources within the 

catchment and 

affect multiple 

seasons 

X 

Ecosystem 

connectance 

System is highly 

connected in 

space and time, 

at least annually 

Ecosystem 

connectance is 

not impacted 

Slight loss of 

connectance but 

there are 

adequate local 

recolonization 

sources 

Some loss of 

connectance but 

colonization 

sources and 

refugia exist 

within the 

catchment 

Significant loss of 

ecosystem 

connectance is 

evident; 

recolonization 

sources do not 

exist for some 

taxa 

Complete loss of 

ecosystem 

connectance in at 

least one 

dimension (i.e., 

longitudinal, 

lateral, vertical, or 

temporal) lowers 

reproductive 

success of most 

groups; frequent 

failures in 

reproduction & 

recruitment 

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2.1.1 The BCG Attributes 

Taxonomic Composition and Structure: Attributes I – VI 

Attribute I: Historically documented, sensitive, long-lived or regionally endemic taxa. 

“Historically documented” refers to taxa known to have been supported in a waterbody or region prior 

to enactment of the 1972 Clean Water Act, according to historical records compiled by State or federal 

agencies or published scientific literature. 

“Sensitive or regionally endemic taxa” have restricted, geographically isolated distribution patterns 

(occurring only in a locale as opposed to a region), often due to unique life history requirements. They 

may be long-lived, late maturing, low fecundity, limited mobility, or require a mutualist relation with 

other species. They may be among listed Endangered or Threatened (E/T) or special concern species. 

Predictability of occurrence is often low, and therefore requires documented observation. Recorded 

occurrence may be highly dependent on sample methods, site selection, and level of effort. 

Attribute II: Sensitive-rare taxa. 

These are taxa that naturally occur in low numbers relative to total population density but may make up a 

large relative proportion of richness. They may be ubiquitous in occurrence or restricted to certain 

micro-habitats, but because of low density, recorded occurrence is dependent on sample effort. Often 

stenothermic (having a narrow range of thermal tolerance) or cold-water obligates; commonly kstrategists (populations maintained at a fairly constant level; slower development; longer life-span). May 

have specialized food resource needs or feeding strategies. Generally intolerant to significant alteration 

of the physical or chemical environment; are often the first taxa observed to be lost from a community. 

Attribute III: Sensitive ubiquitous taxa. 

“Sensitive” taxa from Attributes II and III are taxa that are intolerant to a given stress; they are the first 

species affected by the specific stressor to which they are “sensitive” and the last to recover following 

restoration. Sensitive ubiquitous taxa are ordinarily common and abundant in natural communities when 

conventional sampling methods are used. They often have a broader range of thermal tolerance than 

Sensitive-rare taxa and comprise a substantial portion of natural communities and often exhibit negative 

response (loss of population, richness) at mild pollution loads or habitat alteration. 

Attribute IV: Taxa of intermediate tolerance. 

Taxa that comprise a substantial portion of natural communities; may be r-strategists (early colonizers 

with rapid turn-over times; e.g.,” boom/bust population characteristics). May be eurythermal (having a 

broad thermal tolerance range). May have generalist or facultative feeding strategies enabling 

utilization of relatively more diversified food types. Readily collected with conventional sample methods. 

May increase in number in waters with moderately increased organic resources and reduced competition 

but are intolerant of excessive pollution loads or habitat alteration. 

Attribute V: Tolerant taxa. 

Taxa that comprise a low proportion of natural communities. Taxa often are tolerant of a broader range 

of environmental conditions and are thus resistant to a variety of pollution or habitat induced stress. 

They may increase in number (sometimes greatly) in the absence of competition. Commonly r-strategists 

(early colonizers with rapid turn-over times: e.g., “boom/bust” population characteristics), able to 

capitalize when stress conditions occur. These taxa are the last survivors in highly disturbed systems. 

Taxa tolerance to stressors (ATTRIBUTES I-V). 

Taxa differ in their sensitivities to stressors. Changes in the numbers, kinds and relative 

abundance of taxa across stressor gradients are important and useful indicators of adverse 

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effects (Cairns 1977, Karr 1981). Sensitivity of taxa to stress can vary among species, as well 

as with stressor. Shifts in taxa as a function of differing sensitivities to aquatic and riparian 

disturbance are well documented (Table 2-2). For perennial streams in temperate zones, 

disturbance tends to select for short-lived, tolerant species and against longer-lived, less 

tolerant species (Pianka 1970, Odum 1985, Rapport et al. 1985). In the highest quality tiers of 

the BCG, locally endemic taxa that are long-lived and ecologically specialized are well 

represented. With increasing stress, assemblage composition shifts towards tolerant species or 

short-lived taxa that can rapidly colonize disturbed environments. Assemblages in the lower 

tiers are dominated by eurytopic taxa (those with wide environmental ranges) with generalist 

or facultative feeding strategies. 

TABLE 2-2. Evidence in support of the depicted changes in ecological attributes in the BCG. 

BCG Attribute Response Case-specific documentation Reference 

Shifts in the numbers 

and kinds of species 

changes in lake diatom species composition in response to 

intentional fertilization 

Zeeb et al. 1974; 

Yang et al. 1996 

present, and in the loss of sculpins downstream of metal mines Mebane et al. 2003 number of individuals 

per species, as a changes in algal species across a nutrient gradient in the 

Florida Everglades 

Stevenson et al. 2002 

function of varying 

tolerances to different 

kinds of aquatic and 

changes in diatom assemblages with increased acidification 

and eutrophication of lakes 

Dixit et al. 1999 

riparian disturbance. shifts in species composition along a gradient of pulp and 

paper mill effluent concentration in a Maine river 

Rabeni et al. 1988 

shifts in damselfly species from specialist species to 

generalist species along a gradient of organic pollution in an 

Italian river 

Solimini et al. 1997 

variable sensitivities of benthic macroinvertebrate species to 

acidic conditions 

Courtney and 

Clements 2000 

changes in fish species composition in an Oregon river with 

increased nutrients and temperature 

Hughes and Gammon 

1987 

differentially tolerant fish species in response to heavy metal 

and dissolved oxygen gradients in two Indian rivers 

Ganasan and Hughes 

1998 

decline in darters, sunfish, and suckers as well as other intolerant 

fishes and increase in tolerant fishes in the Midwest 

Karr et al 1986; Yoder 

and DeShon 2003 

I-V variable responses of stream amphibians to severe siltation Welsh and Ollivier 

1998 

Shifts from K-selected 

strategists to r-selected 

strategists following 

disturbance or in 

response to pollution 

shifts from fragmentation-sensitive to fragmentation-tolerant 

bird species in relation to disturbed riparian habitats 

Croonquist and 

Brooks 1993; Allen 

and O’Connor 2000; 

Bryce et al. 2002 

higher proportion of r-selected species in a flow regulated 

river as compared to a natural flow regime river 

Nilsson et al. 1991 

shift to r-selected, generalist damselfly species along a 

gradient of increasing pollution 

Solimini et al. 1997 

water-level fluctuation in a mesocosm resulted in increased 

proportion of r-strategist species 

Troelstrup and 

Hengenrader 1990 

high pollutional stress correlated with increase in r-selected 

strategists in the same river 21 years apart 

Richardson et al. 2000 

Regional and national 

species attribute lists 

and taxonomic tolerance 

values 

compendium of pollution tolerance, habitat preferences, 

feeding guilds for fish species of the northeastern U.S. 

Halliwell et al. 1998 

compendium of pollution tolerance, habitat preferences, 

feeding guilds for fish species of the Pacific northwest, U.S. 

Zaroban et al. 1999 

organic pollution tolerance ranks for Wisconsin stream insect 

taxa 

Hilsenhoff 1987 

compendium of pollution tolerance, habitat preferences, 

feeding guilds of North American fish and aquatic 

macroinvertebrate taxa 

Barbour et al. 1999 

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TABLE 2-2. Evidence in support of the depicted changes in ecological attributes in the BCG. 

BCG Attribute Response Case-specific documentation Reference 

VI Detrimental effects of 

non-native taxa 

loss of 150-200 endemic species in Lake Victoria following 

intentional introduction of Nile perch (Lates niloticus) and Nile 

tilapia (Oreochromis niloticus) 

Witte et al. 1992 

dominance of many lowland rivers in the western USA by 

non-native fishes and invertebrates 

Moyle 1986, Karr et al 

1986, Miller et al. 

1989 

food web disruption and loss of native mussels from zebra 

mussel invasion 

Whittier et al. 1995 

detrimental changes in non-native taxa in TVArivers where 

Corbicula is present 

Kerans and Karr 1994 

loss of small, soft-finned fish species from Northeast USA 

lakes following predator introductions 

Whittier and Kincaid 

1999 

mid-twentieth century collapse of native salmonid fisheries 

following colonization of the Laurentian Great Lakes by sea 

lamprey (Petromyzon marinus) and alewife (Alosa 

pseudoharengus) 

Smith 1972 

VII Changes in organism 

condition or increase in 

anomalies in response to 

increased fish anomalies in the vicinity of toxic outfalls Hughes and Gammon 

1987, Yoder and 

Rankin 1995b 

pollution gradients altered blood chemistry and mortality in fish associated with 

wetlands that received oil sands effluent 

Bendellyoung et al. 

2000 

changes in growth, organism condition, fecundity, and feeding 

strategies for creek chub (Semotilus atromaculatus) across a 

variety of pressure gradients (urbanization, agriculture, 

temperature) 

Fitzgerald et al. 1999 

the presence of tumors, deformities, lesions, etc. in the fish 

from highly disturbed streams 

Karr et al. 1986, 

Yoder and DeShon 

2003 

VIII ecosystem-level 

disruptions of functional 

integrity 

extinction and succession of littoral lake invertebrate species 

secondary to lake acidification; initially detected by temporal 

changes in taxonomic and density measures but followed by 

top-down and bottom up effects at all trophic levels, caused 

by reduced nutrient cycling. A trophic cascade ultimately 

involved loss of fish and increased biomass of primary 

producers. 

Appelberg et al. 1993 

simplification of global coastal ocean ecosystems to microbial 

domination due to combined effects of historical and current 

overfishing and pollution 

Jackson et al. 2001 

IX influence of spatial and 

temporal scale of 

pressures on biological 

large-scale, multi-state status and trends assessments of 

Pacific salmon influenced the listing of the species under the 

Endangered Species Act 

Nehlsen et al. 1991 

effects and recovery 

potential 

environmental factors operating at different temporal and 

spatial scales influence the production and survivorship of 

juvenile Atlantic salmon 

Poff and Huryn 1998 

past land use activity has long-term effects on aquatic biodiversity Harding et al. 1998 

assessments of stream fish and benthic macroinvertebrate 

assemblages at state and regional scales reveal serious 

alterations in indicators of biological integrity 

U.S. EPA 2000a 

Ocean-wide ecological extinction of large predators from 

historical and current overfishing 

Myers and Worm 

2003 

X ecosystem connectance replacement of 4 native freshwater fish species by 37 marine 

species in the lower Rio Grande following flow diversions that 

caused the lower river to cease flowing and become tidal salt 

water 

Contreras-Balderas et 

al. 2002 

decreased fish species and guilds with decreased riverine 

connectivity with floodplain water bodies 

Aarts et al. 2004 

5 federally listed headwater fish species have had their 

ranges restricted and isolated by mainstem impoundments, 

increasing their susceptibility to local physical and chemical 

habitat degradation 

Freeman et al. 2005 

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TABLE 2-2. Evidence in support of the depicted changes in ecological attributes in the BCG. 

BCG Attribute Response Case-specific documentation Reference 

alteration of natural flow regimes result in changes in 

biological assemblage structure 

Poff et al. 1997, Bunn 

and Arthington 2002 

extirpation of Pacific Northwest salmon following construction 

of impassable dams 

Frissell 1993 

extirpation of Colorado River fishes following dam 

construction 

Holden and Stalnaker 

1975 

Attribute VI: Non-native or intentionally introduced taxa. 

With respect to a particular ecosystem, any species that is not found in that ecosystem. Species 

introduced or spread from one region of the U.S. to another outside their normal range are non-native or 

non-indigenous, as are species introduced from other countries. 

This attribute represents both an effect of human activities and a stressor in the form of 

biological pollution. Although some intentionally introduced species are valued by large 

segments of society (e.g., gamefish), these species may be just as disruptive to native species 

as undesirable opportunistic invaders (e.g., zebra mussels). Many rivers in the U.S. are now 

dominated by non-native fishes and invertebrates (Moyle 1986), and introductions of alien 

species are the second most important factor contributing to fish extinctions in North America 

(Miller et al. 1989). The BCG identifies maintenance of native taxa as an essential 

characteristic of Tier 1 and 2 conditions. The model only allows for the occurrence of nonnative taxa in these tiers if those taxa do not displace native taxa and do not have a detrimental 

effect on native structure and function. Tiers 3 and 4 depict increasing occurrence of nonnative taxa. Extensive replacement of native taxa by tolerant or invasive, non-native taxa can 

occur in Tiers 5 and 6. 

Organism Condition and System Performance: Attributes VII and VIII 

Attribute VII: Organism condition. 

Organism condition is an element of ecosystem function, expressed at the level of anatomical or 

physiological characteristics of individual organisms. 

Organism condition includes direct and indirect indicators such as fecundity, morbidity, 

mortality, growth rates, and anomalies such as lesions, tumors, and deformities and for 

purposes of the BCG, primarily applies to fish and amphibians. Some of these indicators are 

readily observed in the field and laboratory, whereas the assessment of others requires 

specialized expertise and much greater effort. The most common approach for State and 

Tribal programs is to forego complex and demanding direct measures of organism condition 

(e.g., fecundity, morbidity, mortality, growth rates) in favor of indirect or surrogate measures 

(e.g., % of organisms with anomalies, age or size class distributions) (Simon (ed.) 2003). 

Organism anomalies in the BCG vary from naturally occurring incidence in Tiers 1 and 2 to 

higher than expected incidence in Tiers 3 and 4. In Tiers 5 and 6, biomass is reduced, the age 

structure of populations indicates premature mortality or unsuccessful reproduction, and the 

incidence of serious anomalies is high. 

Attribute VIII: Ecosystem function. 

“Function” refers to any processes required for normal performance of a biological system. The term 

may be applied to any level of biological organization. Immigration and emigration are functional 

processes at the population level. Examples of ecosystem functional processes are primary and 

secondary production, respiration, nutrient cycling, and decomposition. 

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The “functional integrity” of an ecosystem refers to the aggregate performance of dynamic 

interactions among an ecosystem’s biological parts (Cairns 1977). The term “ecosystem 

function” includes measures of both the interactions among taxa (food web dynamics) and 

energy and nutrient processing rates (energy and nutrient dynamics). These attributes are 

included in the BCG because ecologists universally recognize their fundamental importance. 

At this time, the level of effort required to directly assess ecosystem function is beyond the 

means of most State and Tribal monitoring programs. Instead, most programs rely on 

taxonomic and structural indicators to make inferences about functional status (Karr et al. 

1986). For example, shifts in the primary source of food may cause changes in trophic guild 

indexes or indicator species. Although direct measures of ecosystem function are currently 

difficult or time consuming, they may become practical in the future (Gessner and Chauvet 

2002). 

Attribute VIII also includes aspects of individual, population, and community condition. 

Altered interactions between individual organisms and their abiotic and biotic environments 

may generate changes in growth rates, reproductive success, movement, or mortality. These 

altered interactions are ultimately expressed at ecosystem-levels of organization (e.g., shifts 

from heterotrophy to autotrophy, onset of eutrophic conditions) and as changes in ecosystem 

process rates (e.g., photosynthesis, respiration, production, decomposition). Maine’s example 

scenario (Table 2-3, located at the end of this chapter) describes a progression of functional 

changes. It depicts a naturally oligotrophic and heterotrophic system with P/R <1 in Tiers 1 

and 2. Tiers 3 and 4 depict functional changes commonly associated with the effects of 

increased temperature and nutrient enrichment (P/R > 1, diurnal sags in dissolved oxygen, 

changes in taxonomic composition and relative abundance, increased algal biomass). Tier 5 

depicts an autotrophic system impacted by excessive algal biomass. 

Scale-dependent Factors: Attributes IX and X 

Attribute IX: Spatial and temporal extent of stressor effects. 

The spatial and temporal extent of stressor effects includes the near-field to far-field range of observable 

effects of the stressor. Patchy islands or periods of unsuitable conditions, within a generally intact 

system, give way to patchy islands or periods of suitable conditions, within a substantially degraded 

system. 

Attribute X: Ecosystem connectance. 

Access or linkage (in space/time) to materials, locations, and conditions required for maintenance of 

interacting populations of aquatic life; the opposite of fragmentation; necessary for metapopulation 

maintenance and natural flows of energy and nutrients across ecosystem boundaries. 

Scale-dependent factors (ATTRIBUTES IX AND X). 

These attributes relate to interactions between the physical environment in all its aspects 

(spatial, temporal, structural, chemical, etc.), and the biota. Attributes IX and X are 

interpreted at different spatial and even temporal scales than the rest of the attributes, i.e., the 

reach, or sampled community perspective has been expanded to consider alterations occurring 

within entire catchments, basins, and regions, or within seasonal and annual cycles. These 

attributes were included in the BCG because the extent of ecosystem alteration has important 

environmental implications in terms of an individual waterbody’s vulnerability to further 

effects from stressors as well as potential for mitigation. For example, ecosystem connectivity 

is fundamental to the successful recruitment and maintenance of organisms into any 

environment. A single impacted stream reach in an otherwise intact watershed has far more 

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Extreme changes in structure; wholesale changes in

taxonomic composition; extreme alterations from

normal densities; organism condition is often poor;

3

2

5

4

6

Sensitive taxa markedly diminished;

conspicuously unbalanced distribution

of major groups from that expected;

organism

1

restoration potential than a similar site in a basin that has undergone extensive land-scape 

alteration (Table 2-2). Tiers 1 and 2 depict a naturally connected or isolated system in which a 

natural disturbance regime, e.g. natural variability, is maintained. Detrimental effects in Tiers 

3 and 4 are limited to the reach or seasonal scale. The two lowest tiers depict a system with 

detrimental effects extending to the catchment scale and affecting multiple seasons. A few 

“islands” of adequate physical/chemical conditions may serve as refugia in Tier 5, but 

extensive loss of connectance and refugia occur in Tier 6. 

2.1.2 The BCG Tiers 

Although the BCG is continuous in concept, it has been divided into six tiers to provide as much 

discrimination of different levels of condition as workgroup members deemed discernable, given current 

assessment methods and robust monitoring information (Figure 2-1). Defining the tiers between 3 and 5 

was a challenge to the workgroup and entailed considerable discussion. The workgroup ultimately agreed 

some States and Tribes may only 

be capable of discriminating 3-4 

tiers, while others might be 

capable of discerning 6 tiers based 

on characteristics of their database 

and monitoring program. 

However the workgroup agreed 

that the important role of the BCG 

model is to be a starting point for 

a State or Tribe to think about 

how to use information to better 

define their designated aquatic life 

uses and to communicate more 

clearly about biological condition. 

There is no expectation that States 

and Tribes establish six tiers of 

use classes. The ultimate number 

of the tiers is a State or Tribal 

determination. 

Condition of the Biotic Com

munity

LOW [Specific to Ecotype] HIG

H

Natural structural, functional, and taxonomic integrity is preserved. 

Structure and function similar to natural community with some additional 

taxa & biomass; no or incidental anomalies; sensitive non-native taxa may be 

present; ecosystem level functions are fully maintained 

Evident changes in structure due to loss of some rare native 

taxa; shifts in relative abundance; ecosystem level functions fully 

maintained through redundant attributes of the system. 

Moderate changes in structure due to replacement of 

sensitive ubiquitous taxa by more tolerant taxa; overall 

balanced distribution of all expected taxa; ecosystem 

functions largely maintained. 

condition shows signs of physiological 

stress; ecosystem function shows reduced 

complexity and redundancy; increased build 

up or export of unused materials. 

anomalies may be frequent; 

ecosystem functions are 

extremely altered. 

1 

LOW Level of Stressors HIGH 

FIGURE 2-1. Conceptual model of the Biological Condition Gradient. 

Tier 1: Natural or native condition. 

Native structural, functional, and taxonomic integrity is preserved; ecosystem function is preserved 

within the range of natural variability. 

Tier 1 represents biological conditions as they existed (or still exist) in the absence of measurable 

effects of stressors. The Tier 1 biological assemblages that occur in a given biogeophysical setting 

are the result of adaptive evolutionary processes and biogeography that selects in favor of survival 

of the observed species. For this reason, the expected Tier 1 assemblage of a stream from the arid 

southwest will be very different from that of a stream in the northern temperate forest. The 

maintenance of native species populations and the expected natural diversity of species are essential 

for Tiers 1 and 2. Non-native taxa (Attribute VI) may be present in Tier 1 if they cause no 

displacement of native taxa, although the practical uncertainties of this provision are acknowledged 

(discussed in Section 2.2). 

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25 
Attributes I and II (e.g., historically documented and sensitive taxa) can be used to help assess the 

status of native taxa and could be a surrogate measure to identify threatened or endangered species 

when classifying a site or assessing its condition. 

Tier 2: Minimal changes in structure of the biotic community and minimal changes in ecosystem 

function. 

Virtually all native taxa are maintained with some changes in biomass and/or abundance; ecosystem 

functions are fully maintained within the range of natural variability. 

Tier 2 represents the earliest changes in densities, species composition, and biomass that occur 

as a result of slight elevation in stressors (such as increased temperature regime or nutrient 

enrichment). There may be some reduction of a small fraction of highly sensitive or 

specialized taxa (Attribute II) or loss of some endemic or rare taxa as a result. Tier 2 can be 

characterized as the first change in condition from natural and it is most often manifested in 

nutrient enriched waters as slightly increased richness and density of sensitive ubiquitous taxa 

and taxa of intermediate tolerance (Attributes III and IV). These early response signals have 

been observed in many State programs as illustrated in Figure 2-2, showing slight to moderate 

increases in conductivity in Maine streams. 

M

a

yfly 

A

b

u

n

d

a

n

ce 

600 

Median 

0-30 30-60 60-100 100-200 >200 

FIGURE 2-2. Response of mayfly density to 

enrichment in Maine streams as indicated by 

500 a gradient of increasing conductivity. 

400 

300 

200 

Non-Outlier Max 

Non-Outlier Min 

75% 

25% 

Outliers 

100 

0 Extremes 

Conductivity 

Tier 3: Evident changes in structure of the biotic community and minimal changes in ecosystem 

function. 

Evident changes in structure due to loss of some rare native taxa; shifts in relative abundance of taxa but 

sensitive-ubiquitous taxa are common and abundant; ecosystem functions are fully maintained through 

redundant attributes of the system. 

Tier 3 represents readily observable changes that, for example, can occur in response to 

organic enrichment or increased temperature. The “evident” change in structure for Tier 3 is 

interpreted to be perceptible and detectable decreases in sensitive-rare or highly sensitive taxa 

(Attribute II) and increases in sensitive-ubiquitous taxa or opportunist organisms (Attributes 

III and IV). Attribute IV taxa (intermediate tolerants) may increase in abundance as an 

opportunistic response to nutrient inputs. 

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Tier 4: Moderate changes in structure of the biotic community with minimal changes in ecosystem 

function. 

Moderate changes in structure due to replacement of some sensitive-ubiquitous taxa by more tolerant 

taxa, but reproducing populations of some sensitive taxa are maintained; overall balanced distribution of 

all expected major groups; ecosystem functions largely maintained through redundant attributes. 

Moderate changes of structure occur as stressor effects increase in Tier 4. A substantial 

reduction of the two sensitive attribute groups (II and III) and replacement by more tolerant 

taxa (Attributes IV and V) may be observed. A key consideration is that some Attribute III 

sensitive taxa are maintained at a reduced level but are still an important functional part of the 

system (function maintained). 

Tier 5: Major changes in structure of the biotic community and moderate changes in ecosystem 

function. 

Sensitive taxa are markedly diminished; conspicuously unbalanced distribution of major groups from 

those expected; organism condition shows signs of physiological stress; ecosystem function shows 

reduced complexity and redundancy; increased build-up or export of unused materials. 

Changes in ecosystem function (as indicated by marked changes in food-web structure and 

guilds) are critical in distinguishing between Tiers 4 and 5. This could include the loss of 

functionally important sensitive taxa and keystone taxa (Attribute I, II and III taxa) such that 

they are no longer important players in the system, though a few individuals may be present. 

Keystone taxa control species composition and trophic interactions, and are often, but not 

always, top predators. As an example, removal of keystone taxa by overfishing has greatly 

altered the structure and function of many coastal ocean ecosystems (Jackson et al. 2001). 

Additionally, tolerant non-native taxa (Attribute VI) may dominate some assemblages and 

changes in organism condition (Attribute VII) may include significantly increased mortality, 

depressed fecundity, and/or increased frequency of lesions, tumors and deformities. 

Tier 6: Severe changes in structure of the biotic community and major loss of ecosystem function. 

Extreme changes in structure; wholesale changes in taxonomic composition; extreme alterations from 

normal densities and distributions; organism condition is often poor; ecosystem functions are severely 

altered. 

Tier 6 systems are taxonomically depauperate (low diversity and/or reduced number of 

organisms) compared to the other tiers. For example, extremely high or low densities of 

organisms caused by excessive organic enrichment or severe toxicity may characterize Tier 6 

systems. 

2.2 How the BCG was developed, tested, and evaluated 

The BCG model was developed and tested by the TALU In developing the BCG, the 

Workgroup. Based on recommendations from the full workgroup, a workgroup believed it was 

steering committee created a matrix that summarized biologists’ important that the model be 

experience and knowledge about how biological attributes change in 

response to stress in aquatic ecosystems (Table 2-1). In developing grounded in sound theory, easy 

the BCG, the workgroup believed it was important that the model be to apply, and meet the needs of 

grounded in sound theory as well as actual empirical observations, practitioners around the country. 

easy to apply, and meet the needs of users around the country. In 

building the model, the workgroup followed an iterative, inductive approach, similar to means-end 

analysis (Martinez 1998). The model was tested by determining how consistently workgroup members 

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27 
assigned samples of macroinvertebrates or fish to the six tiers, the results of which support the contention 

that the BCG represents aspects of biological condition common to all existing assessment methods. 

The workgroup began by testing whether biologists from different parts of the country would draw 

similar conclusions regarding the condition of a waterbody using simple lists of organisms and their 

counts. This approach was based on Maine’s experience, in which expert biologists independently 

assigned samples of macroinvertebrates to a priori defined classes of biological condition defined by 

differences in assemblage attributes (Davies et al. 1995). Decision instructions were provided to 

biologists in the form of a matrix, which outlined expected trajectories of quantifiable aspects of 

invertebrates (See Case Example 3-3 in the next chapter). These corresponded with biological 

expectations for four water quality classes (A, B, C and Non-Attainment; See Appendix A, Tables A-1 and 

A-2). The high level of majority and unanimous agreement (98% and 64% respectively) among experts in 

placing samples into the different classes allowed Maine to develop a predictive statistical model that is 

now used to assess the biological condition of new sites (Courtemanch 1995) (See Case Example 3-3). 

To provide a functional framework for practitioners, the TALU Workgroup described how each of the ten 

attributes varies across six tiers of biological alteration (Table 2-1). The general model was then 

described in terms of the biota of a specific region (Maine). Based on 20 years of biomonitoring data, the 

Maine example describes how the relative densities of specific taxa with varying sensitivities to stressors 

change across the BCG tiers (Table 2-3, located at the end of this chapter). 

To test the general applicability of the BCG to sampling data taken from real ecosystems, the workgroup 

evaluated how consistently individual biologists classified samples of aquatic biota based on the attributes 

incorporated into the BCG. Governmental and research biologists from 23 States and one Tribe 

participated in the data exercise. The full workgroup was divided into breakout groups according to 

regional (Northeast, South-Central, Northwest, Arid Southwest/Great Plains) or assemblage (fish, 

invertebrates) expertise. Samples were selected from invertebrate and fish data sets to span as many of the 

BCG tiers as possible. The invertebrate samples and fish samples used in the tests were collected from six 

different regions within the U.S. (Northeast, Mid-Atlantic, Southeast, Northwest, Southwest, Central) and 

included only basic descriptors of stream physical characteristics (substrate, velocity, width, depth, etc.), 

taxonomic names, densities, and in some cases, metric values. These data represent the basic core 

elements common to nearly all biological monitoring programs. Participants were asked to place each 

sample into one of the six condition tiers, though they were cautioned not to apply a simple relative 

quality ranking since all six tiers did not necessarily occur within the data sets. Biologists relied primarily 

on differences in relative abundances and sensitivities of taxa (i.e., Attributes I-VI) to make tier 

assignments because information needed to evaluate the status of the other Attributes was not available. 

Percent concurrence among the individuals was calculated to assess the level of agreement among 

biologists when applying the BCG to raw data. Perfect concurrence was set to equal the product of the 

number of raters by the number of streams. Case Examples 3-2, 3-3, and 3-7, at the end of Chapter 3, 

outline how Maine and New Jersey biologists described tiers and assigned sites. 

In the first stage of the data exercise, between-biologist differences were evaluated by asking workgroup 

participants to rate a single data set of 6-8 samples. The breakout groups were then asked to classify 

samples from larger and more variable datasets. The groups were also instructed to summarize their 

interpretations and to identify biological responses to changes in conditions not captured by the BCG. 

Finally, the groups identified which tiers corresponded to how they currently assess biological integrity 

and the CWA interim goal for protection and propagation of aquatic life. 

Workgroup members placed 82% of the benthic macroinvertebrate samples and 74% of the fish samples 

into the same BCG tiers. The range of variation among individuals was within one tier’s distance in 

either direction. Tiers were revised following full workgroup discussion so that transitions were more 

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28 
distinct. Each of the breakout groups independently reported that the ecological characteristics 

approximately described by Tiers 4 and above were compatible with how they currently assess the 

CWA’s interim goal for protection and propagation of aquatic life. These groups also identified the 

characteristics described by Tiers 1 and 2 as indicative of biological integrity. 

Workgroup members reported that key concepts were important with respect to classifying samples into 

tiers and identifying the boundaries in between. For Tiers 1 and 2, biologists identified the maintenance 

of native species populations as essential to their understanding of biological integrity. Although many 

participants noted that criteria for distinguishing differences between tiers in Attribute VIII (ecosystem 

function) were poorly defined, most nevertheless identified ecosystem function changes (as indicated by 

marked changes in food-web structure and guilds) as critical in distinguishing between Tiers 4 and 5. 

Discussion following the BCG exercise revealed that participants readily agreed on some of the condition 

attributes, but not others. For example, participants indicated they mostly used Attributes I-V (taxonomic 

composition and tolerance), Attribute VI (non-native taxa, for Tiers 2-6 only) and Attribute VII (organism 

condition) to evaluate biological conditions. In contrast, because Attributes VIII - X (ecosystem function 

and scale-dependent features) are rarely directly assessed by biologists, the evaluation of these attributes 

was accompanied by relatively high uncertainty. Even so, workgroup members strongly advocated 

retaining these attributes in the BCG because of the importance of this information in making restoration 

decisions. 

The presence of non-native taxa in Tier 1 was also the subject of considerable discussion. Knowledge of 

the extensive occurrence of some non-native taxa in otherwise near-pristine systems conflicted with the 

desire by many to maintain a conceptually pure and natural tier. Further discussion resulted in agreement 

that the presence of non-native taxa in Tier 1 is permissible only if they cause no displacement of native 

taxa, although the practical uncertainties of this provision were acknowledged. The resulting tier 

descriptions, which allow for non-native species in the highest tiers as long as there is no detrimental 

effect on the native populations, has practical management implications. For example, introduced 

European brown trout (Salmo trutta) have replaced native brook trout (Salvelinus fontinalis) in many 

eastern U.S. streams. In some catchments, brook trout only persist in stream reaches above waterfalls that 

are barriers to brown trout. The downstream reaches are nearly pristine except for the presence of brown 

trout (D. Lenat, North Carolina Department of Natural Resources, personal communication). In these 

places, if society decided to remove the introduced brown trout and if stream habitat is preserved 

throughout the catchment, brook trout can potentially repopulate downstream reaches. In the use 

designation process, recognizing that the entire catchment has the potential to attain Tier 1 conditions will 

inform the public that a very high quality resource exists. 

Critical gaps in knowledge were uncovered during the development of the BCG. For example, the 

workgroup identified the need for regional evaluations of species tolerance to stressors associated with 

pressure. Tolerance information presented in the current version of the BCG tends to be based on 

generalized taxa responses to a non-specific stressor gradient. At this time, tolerance information is not 

available for most taxa and for many common stressors (temperature, nutrients, sediments). In some 

cases, tolerance values are based on data collected in other geographic regions or for other purposes (e.g., 

van Dam’s European diatom tolerances are used for North American taxa) (van Dam et al. 1994). 

Improved tolerance value information is needed to refine the BCG and improve its precision. 

Additionally, taxa that are considered tolerant to stressors in one region of the country may not be 

similarly classified in another region. For example, long-lived taxa have generally been characterized as 

sensitive to increasing pressure and tend to be replaced by short-lived taxa in stressed systems. As such, 

the presence of long-lived taxa in a waterbody has been used to indicate high quality conditions, whereas 

the predominance of short-lived taxa indicates degradation. However, in small streams in the arid 

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29 
western U.S., extreme changes in hydrology define the natural regime for some systems and an opposite 

trend has been observed: short-lived taxa can dominate the biological community in natural settings. In 

these systems, a shift to long-lived taxa may be an indicator of altered, less variable flow regimes. 

2.3 The relationship between the BCG and designated uses 

The BCG is a model that provides a rational and consistent way to identify and communicate waterbody 

condition. It can thus be used to establish appropriate ALUs in State water quality standards and to assess 

attainment. The ecological condition to support an ALU for a specific waterbody can be described in 

terms of the BCG tiers and can be related to specific use categories such as fishery-based uses. For 

example, the ecological condition needed to support salmon spawning is an exceptional, high-quality 

natural stream and will likely be either a Tier 1 or 2 on the BCG. The ecological attributes that 

characterize the BCG tiers can be measured with methods used by each State, and these condition 

assessments can be directly linked to a State’s ALUs. 

Maine and Ohio are examples of States that have adopted uses based on a biological condition gradient 

into water quality standards (Courtemanch et al. 1989, Yoder and Rankin 1995a). Both of these States 

have incorporated multiple tiers of resource quality in their water quality standards (State of Maine 1985, 

2003; Davies et al. 1995; State of Ohio 2003). As discussed above, the tiers in these States’ TALUs 

describe aquatic-life management goals and attainment criteria for different waterbody types. For 

example, in Maine a waterbody is assigned to one of four management tiers by considering both its 

existing biological condition and its highest attainable condition as determined by a public and legislative 

process. These four tiers of biological quality in Maine’s water quality standards are based on Odum’s 

subsidy stress gradient (Odum et al. 1979, Odum 1985) (See Appendix A, Figure A-2a and Table A-1). 

Attainment of standards is assessed by determining to which tier a sample of macroinvertebrates is most 

similar (Courtemanch et al. 1989). Site-specific taxonomic composition data and other metrics are used 

in a discriminant model to identify the class of a particular waterbody (See Case Examples 3-3 and 3-6 in 

Chapter 3). Maine has found multiple tiers to be useful in 5 ways: 

1) identifying and preserving the highest quality resources, 

2) depicting existing conditions more accurately, 

3) setting realistic and attainable management goals, 

4) preserving incremental improvements, and 

5) determining appropriate management action when conditions decline. 

Over the past thirty years, States have independently developed technical approaches to assess condition 

and set ALUs specific to the biology of the State and its regulatory and political settings (U.S. EPA 

2002a). Although these different approaches have fostered innovative technical approaches, they have 

also complicated the development of a nationally consistent approach to interpreting the condition of 

aquatic resources. Assessment results are often difficult to compare when quantitative outcomes (i.e., 

index or indicator values) represent different qualitative conditions. Additionally, without a common 

interpretative framework, use of different methods can hinder collaboration among natural resource 

agencies that have complementary missions. A consistent approach to interpreting biological condition 

will allow scientists and the public to more effectively evaluate the current and potential conditions of 

specific waters and watersheds and use that information to set appropriate ALUs. 

The BCG can help promote consistent interpretation of scientific data by applying a common framework 

to diverse conditions and different assessment methods at national, regional, state, or watershed levels. 

By providing a means for managers and the public to identify outstanding resources, recognize 

incremental improvements, more appropriately allocate resources and prioritize management actions, 

aquatic and natural resource agencies will be able to coordinate and target resources more effectively. 

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2.4 Key points from Chapter 2 

1.	 The biological condition gradient is a descriptive model predicting biological response to 

increasing levels of stressors. The biological gradient can be thought of a field-based doseresponse curve where dose (x-axis) is level of stressors and response (y-axis) is biological 

condition. 

2.	 The purpose of the Biological Condition Gradient is to provide an ecologically-based model 

about biological condition and to promote clearer understanding of current conditions 

relative to natural conditions. This should result in more meaningful engagement of the public 

in the designation of aquatic life uses in State and Tribal water quality standards programs. 

3.	 The model must be validated with data. The BCG model does not reduce the necessity of 

developing robust methods for the quantitative and statistical validation of biological conditions. 

The list of attributes is intended to organize how we interpret biological information concerning a 

given aquatic community response to increasing levels of stressors. The approach should be 

thought of as seeking to identify a “best fit” tier, which consists of weighing the importance and 

signal-strength of the different attributes as they pertain to a specific waterbody or as used to 

describe a designated use class. 

4.	 The conceptual framework is not defined by any one method. As presented in Chapter 3, the 

attributes have a quantifiable aspect that can potentially be assessed and validated in many 

different ways. The BCG has been designed to be independent of different assessment 

methodologies (i.e. Rapid Biological Assessment, Index of Biological Integrity; RIVPACS, 

multivariate analyses, etc.). The intent is for the ecological premises that support the model to 

reflect the same basis that underlies all successful methods used to quantify biological response to 

increasing levels of stressors. 

5.	 The number of useful tiers is flexible. The purpose of the number of tiers is to provide a highly 

resolved biological condition gradient. There is no expectation that State or Tribal programs 

adopt six tiers, or categories, of designated uses. While step-wise progress toward refinement of 

designated aquatic life uses in State and Tribal water quality standards programs is desired over 

the long term, the ultimate number and type of tiers of uses is a State or Tribal determination. 

6.	 The BCG was designed to facilitate communication of the current biological condition of a 

waterbody compared to natural conditions. For example, the BCG is grounded in natural 

conditions, which can help users and the public understand that current conditions do not 

necessarily represent natural conditions. In areas where natural or near-natural conditions exist, 

people are generally familiar with what is natural and what is altered. But in extensively altered 

regions practitioners and the public alike tend to accept the “best of what is left” as the potential 

for a system. In such places, it is difficult to visualize the natural conditions that were once 

present and designated uses may end up based on a diminished perspective. Natural conditions 

may not be achievable in many places, but an improved understanding of the changes that have 

occurred will result in a more scientifically defensible evaluation of current conditions and what 

can potentially be restored. 

The next chapter provides information on how to adapt the national BCG model to reflect the specific 

ecology and stressor gradient characteristics of a particular state or region, and introduces some ways to 

quantify a biological condition gradient with monitoring data. 

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TABLE 2-3. Biological Condition Gradient: Maine example scenario for a cold-water stream catchment. 1 

Resource 

Condition “Tiers” 

Biological Condition Characteristics (Effects) 

1 

Natural or native 

I Historically documented, sensitive, long-lived, or regionally endemic taxa 

Í Long-lived native species of fish-host specialist or long-term brooder mussels such as Brook floaterAlasmodonta varicosa; Triangle floater- Alasmodonta undulata; Yellow lampmussel- Lampsilis cariosa 

are present in naturally occurring densities 

Í Fishes: Brook stickleback, Swamp darter 

condition II Sensitive- rare taxa 

Native structural, 

functional and 

taxonomic integrity is 

preserved; 

ecosystem function is 

preserved within the 

range of natural 

variability 

Í The proportion of total richness represented by rare, specialist and vulnerable taxa is high, for 

example, without limitation, the following taxa are representative: Plecoptera: Capniidae, 

Taeniopteryx, Isoperla, Perlesta, Pteronarcys, Leuctra; Ephemeroptera: Cinygmula, Rhithrogena, 

Epeorus, Serratella, Leucrocuta; Trichoptera: Glossosoma; Psilotreta; Brachycentrus; Diptera: 

Stempellina, Hexatoma, Probezzia; Coleoptera: Promoresia; Fishes: Slimy sculpin, Longnose sucker; 

Longnose dace 

III Sensitive- ubiquitous taxa 

Í Densities of Sensitive-ubiquitous taxa are as naturally occur. The following taxa are representative of 

this group for Maine: Plecoptera: Acroneuria; Ephemeroptera: Stenonema, Baetis, Ephemerella, 

Pseudocloeon; Fishes: Brook trout, Burbot, Lake chub 

IV Taxa of intermediate tolerance 

Í Densities of intermediate tolerance taxa are as naturally occur. The following taxa are representative 

of this category: Trichoptera: Hydropsychidae, Chimarra, Neureclipsis, Polycentropus; Diptera: 

Tvetenia, Microtendipes, Rheocricotopus, Simulium; Fishes: Common shiner, Fallfish 

V Tolerant taxa 

Í Occurrence and densities of Tolerant taxa are as naturally occur. The following taxa are 

representative of this category: Diptera: Dicrotendipes, Tribelos, Chironomus, Parachironomus; NonInsects: Caecidotea, Isopoda, Physa, Helobdella; Fishes: White sucker, Blacknose dace, Creek chub 

VI Non native or intentionally introduced taxa 

Í Non native taxa such as Brown trout, Rainbow trout, Yellow perch, are absent or, if they occur, their 

presence does not displace native biota or alter native structure and function 

VII Physiological condition of long-lived organisms 

Í Anomalies are absent or rare; any that occur are consistent with naturally occurring incidence and 

characteristics 

VIII Ecosystem Function 

Í Rates and characteristics of life history (e.g., reproduction, immigration, mortality, etc.), and materials 

exchange processes (e.g., production, respiration, nutrient exchange, decomposition, etc.) are 

comparable to that of “natural” systems 

Í The system is predominantly heterotrophic, sustained by leaf litter inputs from intact riparian areas, 

with low algal biomass; P/R<1 (Photosynthesis: Respiration ratio) 

IX Spatial and temporal extent of detrimental effects 

Í Not applicable- disturbance is limited to natural events such as storms, droughts, fire, earth-flows. A 

natural flow regime is maintained. 

X Ecosystem connectance 

Í Reach is highly connected with groundwater, its floodplain, and riparian zone, and other reaches in the 

basin, at least annually. Allows for access to habitats and maintenance of seasonal cycles that are 

necessary for life history requirements, colonization sources and refugia for extreme events. 

1 This scenario presents Maine biologists'summary of the ecological characteristics of the six tiers in the Biological 

Condition Gradient model as observed in Maine (see Appendix A, Sections II and III). It is based on analysis of 

genus/species level benthic macroinvertebrate data (400 samples from rivers and streams spanning conditions from 

near-natural to severely altered) (Davies et al. 1999). 

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2


Minimal changes in 

structure of the 

biotic community 

and minimal 

changes in 

ecosystem function 

Virtually all native 

taxa are maintained 

with some changes in 

biomass and/or 

abundance; 

ecosystem functions 

are fully maintained 

within the range of 

natural variability 

I Historically documented, sensitive, long-lived, regionally endemic taxa 

Í Some regionally endemic, long-lived species (e.g., some mussel species such as the Dwarf 

wedgemussel- Alasmidonta heterodon, and/or fish species, such as the Brook stickleback are absent 

due extirpation from Maine prior to the enactment of the CWA; some mussel species of Special 

Concern in Maine are present (e.g., Brook floater- Alasmodonta varicosa; Triangle floaterAlasmodonta undulata; Yellow lampmussel- Lampsilis cariosa) 

II Sensitive- rare taxa 

Í Richness of rare and/or specialist invertebrate taxa is high though densities may be low (e.g., for 

Maine- Plecoptera: Capniidae, Taeniopteryx, Isoperla, Agnetina, Perlesta, Pteronarcys, Leuctra; 

Ephemeroptera: Cinygmula, Rhithrogena, Epeorus, Serratella, Leucrocuta; Trichoptera: 

Glossosoma, Psilotreta, Brachycentrus; Diptera: Stempellina, Rheopelopia, Hexatoma, Probezzia; 

Coleoptera: Promoresia). Densities of scrapers such as Glossosoma are increased 

Í Fish assemblage is predominantly native including such sensitive fish as Slimy sculpin, Longnose 

sucker, Longnose dace. 

III Sensitive- ubiquitous taxa 

Í Superficial scraper-grazers and collector-gathers are favored due to slightly increased periphyton 

biomass on hard substrates, which results in higher relative abundance of these groups (e.g., 

Ephemeroptera: Stenonema, Stenacron, Baetis, Ephemerella, Pseudocloeon). Predatory stoneflies 

are common (e.g., Acroneuria, Agnetina). Populations of such native fish taxa as Brook trout, Lake 

chub, Burbot are common. 

IV Taxa of intermediate tolerance 

Í Increased biomass of diatom species that respond positively to increased nutrients and temperatures, 

but sensitive diatom species are maintained. Diatom richness is increased; filamentous forms are rare 

or as naturally occur 

Í May be slight increases in densities of macroinvertebrate taxa such as Trichoptera: Hydropsychidae, 

Philopotamidae, Neureclipsis; Diptera: Rheotanytarsus, Microtendipes, Rheocricotopus, Simulium 

Í Common shiner and Fallfish are in good condition 

V Tolerant taxa 

Í May be slight increases in occurrence of tolerant taxa such as Diptera: Polypedilum, Tvetenia, NonInsects: Isopoda, Physa; Fishes: White sucker; Creek chub, Blacknose dace 

VI Non-native or intentionally introduced taxa 

Í Any intentionally introduced fish species (e.g., Brown trout- Salmo trutta, Rainbow troutOncorhynchus mykiss) occupy non-detrimental niche space 

VII Physiological condition of long-lived organisms 

Í Any anomalies on fish are consistent with naturally occurring incidences and characteristics such as 

rare occurrence of gill or anchor parasites, blackspot, etc. 

Í Spawning areas of native fishes are evident during spawning season 

VIII Ecosystem Function 

Í Rates and characteristics of life history (e.g., reproduction; immigration; mortality etc.), and materials 

exchange processes (e.g., production; respiration; nutrient exchange; decomposition etc.) are 

unimpaired and not significantly different from the range of natural variability. 

Í The system is predominantly heterotrophic, sustained by leaf litter inputs from intact riparian areas; 

P/R/ is<1 

IX Spatial and temporal extent of detrimental effects 

Í Extent is limited to small pockets or brief periods 

X Ecosystem connectance 

Í Unimpaired access to habitats and maintenance of seasonal cycles that are necessary to fulfill life 

history requirements, and to provide colonization sources and refugia for extreme events. 

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Evident changes in 

structure of the 

biotic community 

and minimal 

changes in 

ecosystem function 

Some changes in 

structure due to loss 

of some rare native 

taxa; shifts in relative 

abundance of taxa 

but sensitiveubiquitous taxa are 

common and 

abundant; ecosystem 

functions are fully 

maintained through 

redundant attributes 

of the system 

I Historically documented, sensitive, long-lived, or regionally endemic taxa 

Í Brook floater- Alasmodonta varicosa; Triangle floater- Alasmodonta undulata; Yellow lampmusselLampsilis cariosa; are uncommon; Dwarf wedgemussel- Alasmidonta heterodon (and/ or a fish 

species) absent due to extirpation from Maine prior to CWA 

II Sensitive- rare taxa 

Í Some replacement of taxa having narrow or specialized environmental requirements, with functionally 

equivalent sensitive-ubiquitous taxa; coldwater obligate taxa are disadvantaged. Taxa such as 

Plecoptera: Capniidae, Taeniopteryx, Isoperla, Perlesta, Pteronarcys, Leuctra, Agnetina; 

Ephemeroptera: Cinygmula, Rhithrogena, Epeorus, Serratella, Leucrocuta; Trichoptera: 

Glossosoma, Psilotreta, Brachycentrus; Diptera: Stempellina, Rheopelopia; Hexatoma, Probezzia; 

Coleoptera: Promoresia; Fishes: Brook stickleback, Longnose sucker, Longnose dace are 

uncommonly encountered or absent 

III Sensitive- ubiquitous or generalist taxa 

Í Sensitive- ubiquitous or generalist taxa are common and abundant; taxa with broader temperaturetolerance range are favored (e.g., Plecoptera: Acroneuria; Ephemeroptera: Stenonema, Baetis, 

Ephemerella, Pseudocloeon) 

Í Overall mayfly taxonomic richness is reduced relative to the Tier 2 condition, with the preponderance 

of richness represented by sensitive- ubiquitous taxa; densities of remaining taxa are high and are 

sufficient to indicate healthy, reproducing populations 

Í Native Brook trout are significantly reduced due to the introduction of non-native Brown trout and the 

increased temperature regime 

IV Opportunist or facultative taxa of intermediate tolerance 

Í Filter-feeding blackflies (Simulium) and net-spinning caddisflies (e.g., Hydropsyche, Cheumatopsyche, 

Polycentropus, Neureclipsis) show increased densities in response to nutrient enrichment, but relative 

abundance of all expected major groups is well-distributed 

Í Increased temperature and increased available nutrients result in increased algal productivity causing 

an increase in the thickness of the diatom mat. This results in a “slimy” covering on hard substrates. 

Í Fish assemblage exhibits increased occurrence of Common shiner and Fallfish 

V Tolerant taxa 

Í Richness of Diptera: Chironomidae is increased; relative abundance of Diptera and Non-insects is 

somewhat increased but overall relative abundance is well-distributed among taxa from Groups III, IV 

and V, with the majority of taxa represented from Groups III and IV. Blacknose dace and white sucker 

are more common. 

VI Non-native or intentionally introduced taxa 

Í Brown trout have largely replaced native brook trout 

VII Physiological condition of long-lived organisms 

Í Incidence of anomalies such as gill parasites, anchor parasites, blackspot, etc., is low; serious 

anomalies such as tumors or deformities are essentially absent 

Í Environmental quality is sufficient to fully support reproduction of most long-lived species 

VIII Ecosystem Function 

Í Increased temperature and algal metabolism causes small diurnal sags in dissolved oxygen, 

compensated by adequate aeration from turbulence over riffle areas 

Í Algal biomass somewhat exceeds what can be utilized by resident grazers, resulting in evidence of 

die-back and slight downstream export of sloughed material. 

Í Patchy loss of high food quality riparian vegetation (e.g., oak; maple, beech) and elevated 

temperature, results in decreased growth and survival of some specialized shredder taxa 

(Pteronarcidae; Taeniopterygidae) with replacement by shredders capable of utilizing lower quality 

organic matter (Lepidostomatidae; Limnephilidae; Tipulidae). 

IX Spatial and temporal extent of detrimental effects 

Í Filamentous green algae occur in small patches within reaches; low dissolved oxygen levels occur 

only during the high temperature and low flow summer periods. 

Í Interstitial spaces, within the substrate of pools, are filled with fine sediment resulting in localized 

losses of interstitial habitats but riffle areas continue to provide adequate water flow and oxygen 

through interstitial habitats. 

X Ecosystem connectance 

Í Some downcutting has resulted in a patchy decrease in connectance of the stream from its floodplain 

except at unusually high flows. 

Í Thinning and patchy loss of riparian vegetation has altered the microclimate of the surrounding 

landscape causing a decrease in survival and reproductive success of adult mayflies and stoneflies. 

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4


Moderate changes 

in structure of the 

biotic community 

and minimal 

changes in 

ecosystem function 

Moderate changes in 

structure due to 

replacement of some 

Sensitive-ubiquitous 

taxa by more tolerant 

taxa, but reproducing 

populations of some 

Sensitive taxa are 

maintained; overall 

balanced distribution 

of all expected major 

groups; ecosystem 

functions largely 

maintained through 

redundant attributes 

I Historically documented, sensitive, long-lived, regionally endemic taxa 

Í Healthy, reproducing populations of generalist mussel species are present (such as Eastern elliptioEliptio complanata; or Eastern lampmussel- Lampsilis radiata radiata or Eastern floater- Pyganodon 

cataracta) but Brook floater- Alasmodonta varicosa; Triangle floater- Alasmodonta undulata; Yellow 

lampmussel- Lampsilis cariosa are absent. 

II Sensitive- rare, specialist, vulnerable taxa with narrow environmental requirements 

Í Richness of specialist and vulnerable taxa is notably reduced; if present, densities are low (e.g., 

Plecoptera: Capniidae, Taeniopteryx, Isoperla, Perlesta, Pteronarcys, Leuctra; Agnetina; 

Ephemeroptera: Cinygmula, Rhithrogena, Epeorus, Serratella, Leucrocuta; Trichoptera: 

Glossosoma; Psilotreta; Brachycentrus; Diptera: Stempellina, Rheopelopia; Hexatoma, Probezzia; 

Coleoptera: Promoresia, Fishes: Occurrence of Slimy sculpin, Longnose sucker and Longnose dace 

is reduced 

III Sensitive- ubiquitous or generalist taxa 

Í Densities of sensitive- ubiquitous scraper and gatherer insects (e.g., Stenonema, Heptagenia, Baetis, 

Ephemerella, Pseudocloeon) are sufficient to indicate that reproducing populations are present but 

relative abundance is reduced due to increased densities of opportunist invertebrate taxa (Group IV); 

Í Predatory stoneflies are reduced (e.g., Acroneuria) 

IV Opportunist or facultative taxa of intermediate tolerance 

Í Many substrate surfaces are covered by bryophytes and macro-algae responding to increased 

nutrients, resulting in displacement of lithophytic (stone-dwelling) micro-algae in favor of epiphytic 

(plant-dwelling) and filamentous forms (e.g., Cladophora). 

Í Increased loads of suspended particles favor collector-filterer invertebrates resulting in notably 

increased densities and relative abundance of filter-feeding caddisflies and chironomids (e.g., 

Trichoptera: Hydropsychidae, Chimarra, Neureclipsis, Polycentropus; Diptera: Tvetenia, 

Microtendipes, Rheocricotopus, Simulium; Fishes: Common shiner and Fallfish are common and 

abundant 

V Tolerant taxa 

Í There is an increase in the relative abundance of tolerant generalists (for example, Polypedilum, 

Eukeifferiella, Cricoptopus) and/or in numbers of non-insect scrapers and gatherers (e.g., Physa, 

Sphaerium, Asellus, Hyalella) but they do not exhibit significant dominance 

Í Overall relative abundance is well distributed among taxa from Groups III, IV and V, with the majority 

of the total abundance represented from Group IV. 

Í Native fish such as White sucker, Blacknose dace, Creek chub are common. 

VI Non-native or intentionally introduced taxa 

Í Brook trout are absent or transient but such taxa as Smallmouth bass, Golden shiner and 

Yellow perch are common. 

VII Physiological condition of long-lived organisms 

Í Incidence of anomalies such as blackspot and gill and anchor parasites is slightly higher than 

expected 

Í Occurrence of tumors, lesions and deformities is rare 

VIII Ecosystem Function 

Í Increased available nutrients increase algal productivity causing increased diatom, macro-algae and 

macrophyte biomass, and consequently lowering evening dissolved oxygen levels and increasing 

daytime oxygen levels. Invertebrate biomass is high but production has shifted to result in greater 

biomass of intermediate tolerance organisms than sensitive organisms. For example, filter-feeders 

utilizing suspended material shift from mayflies and sensitive mussels and caddisflies (e.g., Isonychia, 

Elliptio, Brachycentrus) to facultative types (e.g., Hydropsychidae, Rheotanytarsus, Sphaeriidae, 

Musculium, Pisidium); grazers of diatoms shift from sensitive mayflies and caddisflies (e.g., 

Heptagenia, Leucrocuta, Glossosomatidae) to facultative scrapers and collector gatherer organisms 

(e.g., Baetis, Callibaetis, Physidae, Leptoceridae). The suspended organic matter load somewhat 

exceeds what can be utilized by resident filterers resulting in increased levels of exported material. 

Sloughing of excess macro-algae and macrophyte biomass results in increased downstream export of 

course particulate organic matter. 

Í The system is becoming more autotrophic due to algal photosynthesis. The P/R ratio shows a slight 

increase. 

IX Spatial and temporal extent of detrimental effects 

Í Increased macrophyte and algal biomass extends downstream beyond the confluence with the next 

tributary; filamentous algae first appears in the stream as temperatures warm in late spring; pools and 

depositional areas are silt-filled; the interstitial spaces in the substrate of runs is becoming obstructed 

by sand and silt 

Í Early morning low dissolved oxygen levels occur occasionally during late spring and fall as well as 

during the mid summer 

X Ecosystem connectance 

Í Filling of interstitial spaces obstructs access to hyporheic zone for early instar stonefly nymphs, 

eliminating nursery areas and refugia for storm-events and low flows. Adult stoneflies from upstream 

reaches continue to oviposit but reproductive success is limited; stonefly nymphs continue to colonize 

by drift, with limited success. 

Í Poorly managed culverts on some tributaries impede fish passage and access to some spawning 

areas. 

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5


Major changes in 

structure of the 

biotic community 

and moderate 

changes in 

ecosystem function 

Sensitive taxa are 

markedly diminished; 

conspicuously 

unbalanced 

distribution of major 

groups from that 

expected; organism 

condition shows 

signs of physiological 

stress; system 

function shows 

reduced complexity 

and redundancy; 

increased build-up or 

export of unused 

materials 

I Historically documented, sensitive, long-lived, or regionally endemic taxa 

Í Mussel fauna, including commonly occurring, generalist taxa (e.g., Eastern lampmussel- Lampsilis 

radiata radiata; Eastern floater- Pyganodon cataracta; Eastern elliptio- Elliptio complanata) is markedly 

diminished due to poor water quality 

II Sensitive- rare taxa 

Í Only the rare occurrence of individual representatives of specialist and vulnerable taxa with no 

evidence of successful reproduction 

III Sensitive- ubiquitous taxa 

Í Either absent or present in very low numbers, indicating impaired recruitment and/or reproduction 

IV Opportunist or facultative taxa of intermediate tolerance 

Í Filter-feeding invertebrates such as Hydropsychid caddisflies (e.g., Cheumatopsyche) and filterfeeding midges (e.g., Rheotanytarsus, Microtendipes) occur in very high numbers 

V Tolerant taxa 

Í Frequent occurrence of tolerant collector-gatherers (e.g., Orthocladiini, Micropsectra, 

Pseudochironomus, Dicrotendipes, Isopoda- Caecidotea; Amphipoda- Hyalella, Gammarus); 

Í Relative abundance of non-insects often equal to or higher than relative abundance of insects 

Í Deposit-feeders such as Oligochaeta are increased 

Í Numbers of tolerant predators are increased (Hirudinea, Thienemannimyia, Cryptochironomus) 

Í Native fish species are essentially absent with the exception of tolerant taxa like White sucker, 

Blacknose dace and Creek chub 

VI Non-native or intentionally introduced taxa 

Í Golden shiner, Smallmouth bass, and Yellow perch are common 

VII Physiological condition of long-lived organisms 

Í Biomass of young of year age classes is low; overall fish biomass is reduced; 

Í Sex ratio of remaining fish does not equal 1 

Í Occurrence of parasitic infestations and disease is common 

Í Incidence of serious anomalies such as tumors and anatomical deformities is higher than expected 

VIII Ecosystem Function 

Í High algal photosynthetic activity results in daytime dissolved oxygen supersaturation accompanied by 

nighttime dissolved oxygen levels less than 4 ppm. Extremely high algal biomass significantly alters 

the habitat structure of the substrate; 

Í The P/R ratio is significantly > 1; the system is predominantly autotrophic 

Í Loss of coarse particulate shredders and alteration of bacterial decomposer community contributes to 

build-up and/or export of unused organic matter; 

Í Mechanisms for nutrient spiraling are significantly simplified and less efficient resulting in increased 

export of nutrients from the system 

IX Spatial and temporal extent of detrimental effects 

Í Substrate has become armored by increased sediment loading, altered flow regime and altered 

channel morphology resulting in compaction of interstitial space habitat, leaving only patches of wellscoured gravel substrate in high-gradient riffle areas; 

Í Armoring is resistant to spring scouring events, preventing annual spring sediment flushing and resorting of substrate; 

Í Near complete canopy removal results in all day insolation of stream and surrounding land surface 

causing abnormally elevated temperature regime in early spring and late fall. This causes unnaturally 

elevated seasonal temperature cues and results in failures of life history requirements. 

X Ecosystem connectance 

Í Lateral connectance to floodplain areas is eliminated except at peak flows, due to altered channel 

morphology caused by human intervention (bank riprapping, dikes) and altered flow regime. 

Í All appropriate high quality spawning gravel in upstream areas is destroyed by silt deposition, 

preventing spawning of white suckers, leaving only mature adults. Culverting is common, contributing 

to impairment of fish passage 

Í Lack of riparian vegetation eliminates habitat for adult flying aquatic insects, reducing survival and 

reproduction of resident organisms and reducing successful recruitment of immigrating organisms (i.e., 

flight dispersal of ovipositing females). 

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6


Severe changes in 

structure of the 

biotic community 

and major loss of 

ecosystem function 

Extreme changes in 

structure; wholesale 

changes in taxonomic 

composition; extreme 

alterations from 

normal densities and 

distributions; 

organism condition is 

often poor; 

ecosystem functions 

are severely altered 

I Historically documented, sensitive, long-lived, regionally endemic taxa 

Í Poor water quality, compaction of substrate, elevated temperature regime and absence of fish hosts 

for reproductive functions preclude the survival of any mussel fauna 

II Sensitive- rare taxa 

Í These taxa are absent due to poor water quality, elevated temperature regime, alteration of habitat, 

loss of riparian zone, etc. 

III Sensitive- ubiquitous taxa 

Í Absent due to above listed factors, though an occasional transient individual, usually in poor condition, 

may be collected. 

IV Taxa of intermediate tolerance 

Í Filter-feeding insects and other macroinvertebrate representatives of this group are severely reduced 

in density and richness, or are absent. 

V Tolerant taxa 

Í Low dissolved oxygen conditions preclude survival of most insect taxa except those with special 

adaptations to deficient oxygen conditions (e.g., Chironomus) 

Í The macroinvertebrate assemblage is dominated by tolerant non-insects (Planariidae, Oligochaeta, 

Hirudinea, Sphaeriidae, etc.) 

VI Non-native or intentionally introduced taxa 

Í Native species are essentially absent 

Í Only very tolerant invasive alien fish taxa are collected (Golden shiner, Yellow perch); 

Í Number of individuals collected is abnormally low 

VII Physiological condition of long-lived organisms 

Í Fish biomass is very low; individuals that are collected appear to be transients and are in poor 

condition 

Í Incidence of parasitic infestations and disease is high; anatomical deformities and/or tumors are 

common 

Í Minimal evidence of recruitment or reproduction except some extremely tolerant groups may have 

high production; young of year age classes are absent 

VIII Ecosystem Function 

Í Water quality has degraded to such an extent that algal photosynthesis is negligible 

Í Decomposition of organic matter creates P/R markedly <1; the system is predominantly heterotrophic 

as a result of high bacterial respiration and minimal photosynthesis 

Í Reproductive success is very low 

Í Recruitment of emigrating organisms into upstream and downstream habitats is impaired due to low 

fecundity and high mortality rates of resident biota. 

IX Spatial and temporal extent of detrimental effects 

Í The reach and all tributaries are affected by widespread alteration of within stream conditions as a 

result of severely altered land-use and poor water quality. 

X Ecosystem connectance 

Í Watershed-wide land use changes and alteration of stream morphology has affected all tributaries 

eliminating sources of recruitment and destroying spawning habitat; 

Í Physical and chemical requirements to fulfill life history functions (e.g., seasonal temperature cues for 

mating behavior and egg development; intact nursery habitats; optimal levels of dissolved gases, etc.) 

are severely disrupted resulting in very low reproductive success and high mortality rates. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 2 – August 10, 2005 

37 
DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 2 – August 10, 2005 

38 
CHAPTER 3. HOW DO YOU DEVELOP AND CALIBRATE A BIOLOGICAL 

CONDITION GRADIENT? 

Figure 3-1 shows the overall approach for calibrating the Biological Condition Gradient, BCG, for a 

specific region. This chapter discusses the technical elements and steps for calibrating a regional BCG. 

The calibration process includes: 

• Identification of defensible biological goals (also see Chapters 1 and 5) 

• Development of the conceptual foundation of the regional BCG (Section 3.1) 

• Assessment and modification, if necessary, of the State's biological monitoring program to 

support quantitative calibration of a regional BCG (Section 3.2) 

• Calibration of a regional quantitative BCG model for operational assessment (Section 3.3) 

EstablishConceptual Foundation of 

Regional BCG Model 

(Section 3.1) 

• Describe native aquatic assemblages 

• Identify regional stressors 

• Describe expected biological response to 

stressors (the BCG) 

Adopt TALUs into Water 

Quality Standards 

(Chapters 5 & 6) 

Policy/Legal Foundations

Determine management objectives

Q uantify and Calibrate 

the Regional B CG 

(Section 3.3) 

• Assemble information 

• Describe quantifiable attributes 

• Describe BCG tiers; assign sites 

• Develop or apply quantitative 

assessment method (index or model) 

Assess Monitoring Program 

(Section 3.2) 

• Biological assemblages 

• Methodology 

• Geographic coverage 

• Database 

Information 

sufficient to 

support BCG? 

NO 

YES 

Modify Monitoring Program 

FIGURE 3-1. Technical components of the Biological Condition Gradient. 

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and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 3 – August 10, 2005 

39 
A State's water management program can support development of tiered aquatic life uses if it is flexible 

with respect to improvements in scientific knowledge and acknowledges that scientific advances may 

support adjustment of biological goals. State and Tribal designated uses form the aquatic life goals and 

water quality criteria (biological, chemical and physical) to protect the uses provide the basis for 

measuring attainment of the goals. 

3.1 Conceptual foundation of a regional BCG model 

The first technical component of calibrating a regional BCG is to adapt the national BCG model to 

regional conditions. Model development includes three components that, together, provide a complete 

ecological description of biological response to stressors that is consistent with ecological theory and 

empirical observation: 

• Describe the native aquatic assemblages under natural, undisturbed conditions 

• Identify the predominate regional stressors 

• Describe the BCG, including the theoretical and empirically observed foundation of assemblage 

response to stressors 

Similar to the national BCG model development process, regional BCG calibration can take place through 

technical panels and workshops that bring together aquatic biologists and ecologists knowledgeable about 

the waterbodies and assemblages in their regions. The technical experts describe native aquatic 

assemblages, regional stressors, and patterns of biological alteration based on both empirical observations 

and theoretical foundation to develop a regional biological condition gradient. The technical experts can 

include scientists from State and federal water quality agencies and natural resource departments, 

interstate river commissions, universities, and the private sector. 

Expert participants in the regional model and calibration exercise should be knowledgeable about the 

assemblages sampled in the applicable monitoring programs (invertebrate biologists, ichthyologists, 

algologists, endangered species experts, etc.). The group should also include scientists involved in 

monitoring programs who are familiar with the sites and the organisms, plus other State, federal, 

university, and private sector biologists with relevant expertise. In some cases, BCGs have been initially 

drafted by a single experienced and knowledgeable individual, followed by a consensus process to 

confirm and modify the model. 

3.1.1 Describe native aquatic assemblages 

The BCG is grounded in natural biological assemblages that are present in ecosystems with no or minimal 

disturbance. Developing the BCG entails specific descriptions of the natural aquatic assemblages. The 

description of natural conditions requires biological knowledge of the region, classification of the natural 

assemblages, and, if available, historical descriptions of the habitats and assemblages. 

Existing information – Information on biota in undisturbed or minimally disturbed habitats is required to 

develop a regional BCG model. If the State has an extensive monitoring program with undisturbed 

reference sites, its existing monitoring data will play an important role in developing the descriptions of 

reference biota. In addition to monitoring data, participants should also consult general references on 

biota of the region, especially references showing the historical and present-day geographic distribution of 

flora and fauna. These references often exist for fish and vascular plants, or may be unpublished reports 

and lists for threatened invertebrates such as mussels, snails, and dragonflies. However, such references 

are often unavailable for benthic macroinvertebrates or algae. 

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Classification – Developing a description of the BCG requires that biologists take into account the natural 

variability in assemblage structure and composition among sites and explain that variability where 

possible. This requires a classification system or model to predict the natural variation among sites (e.g., 

Wright et al. 1984, Barbour et al. 1999, Bailey et al. 2004). In this document, the term "classification" 

refers to identifying consistent differences between biological assemblages from undisturbed or 

minimally disturbed aquatic systems, if information available, and explaining those differences in terms 

of natural environmental gradients. Such natural gradients are encompassed within the regional 

descriptions of the undisturbed or minimally disturbed condition of the stressor gradient (Chapter 4). 

Distributions of the organisms that make up aquatic communities are controlled by the effects of 

temperature, water velocity, light, oxygen, water quantity, dissolved substances (e.g., DOC, alkalinity, 

pH), food resources, cover, reproductive habitat, variability of physical and chemical factors, competitors, 

and predators. These physical and chemical factors vary geographically enabling biologists to 

characterize several community types by geographic location, such as cold water/warm water fish 

communities and low gradient/high gradient invertebrate communities. Scientists have also recognized 

geographic boundaries characterized by geology or vegetation (ecoregions: Omernik 1987; fish 

communities: Hughes and Larsen 1988; macroinvertebrate communities: Gerritsen et al. 2000). Some 

variables, notably measures of stream size (e.g., order, catchment area, length, total flow), have a more 

continuous effect on biological variables (e.g., increase of fish species richness with stream size; Karr et 

al. 1986). 

Reference condition – Closely connected with classification of undisturbed or minimally disturbed 

systems and communities is the definition and measurement of reference condition. Methods for 

establishing reference condition need to be consistent for differing waterbody conditions to be compared 

(Hughes 1985, 1994; Hughes et al. 1986; Moss et al. 1987; Bailey et al. 2004; Stoddard et al. in press). 

Undisturbed or minimally disturbed conditions are comparable to “natural conditions,” e.g. BCG tiers 1 

and 2. Therefore, defining "natural" reference conditions is the starting point for development of a 

regional BCG. Ideally, empirical data assembled from reference sites with no or minimal levels of 

stressors characterize Tiers 1 and 2 of the BCG. This is because Tier 1 biological condition is, by 

definition, an assemblage structure, function, and taxonomic composition that is "naturally derived" from 

a physical environment not effected by stressors (Angermeier and Karr 1994). 

Minimally disturbed sites (as defined by physical, chemical, and landscape measures) can be slightly 

altered from undisturbed condition, but should retain most characteristics of the resident biota in 

undisturbed sites. In many regions of the country where Tier 1 and Tier 2 sites may no longer exist, the 

reference sites used by agencies are considered “least disturbed.” These sites have also been termed as the 

“best available,” or “best existing,” in the region but may be substantially altered from pristine, natural 

conditions. In extensively altered regions where undisturbed or minimally disturbed sites are absent, the 

best means to accurately characterize Tiers 1 or 2 may be through historical records of the taxonomic 

distributions of different assemblages and descriptions of the physical setting of undisturbed conditions 

(see below). 

Historical descriptions – Historical descriptions help reconstruct undisturbed aquatic habitats and may 

help identify present-day sites that approximate historical conditions. This information is especially 

critical in areas where the best existing sites are significantly altered. Sources of historical information 

include early photographs and taxonomic collections, pre-dam and pre-irrigation physical data (USGS 

flow data, BLM data), and the descriptions of pioneers, naturalists, and scientists. Recent compilations 

and summaries of historical information have been developed where local or conservation interest is 

strong (e.g., Kuzelka et al. 1993, Johnson 1994). See Case Example 3-1 on considering historical stream 

characteristics to estimate minimally disturbed conditions and support reference stream selections in 

Kansas. 

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41 
If no undisturbed or minimally disturbed reference sites exist in a region, the stressor gradient provides a 

means for determining the best regional candidates to act as benchmarks for comparison, i.e., “least 

disturbed” or “best available conditions.” Chapter 4 discusses the stressor gradient and a framework to 

organize stressor information derived from measures of the physical, chemical, and landscape variables of 

a sampled site. Applying monitoring information that is organized into the stressor gradient framework 

will help managers evaluate the status of their waters relative to change, or departure, from reference 

condition. 

3.1.2 Identify regional stressors 

A description of regionally dominant stressors will help define expectations for biological responses that 

are likely to occur. This step considers sources of physical and chemical stressors and causes of 

landscape or habitat disturbance (the stressor gradient; Chapter 4). For example, if an ecoregion is 

primarily mountainous, then stressors from extensive row-crop agriculture will be relatively less frequent 

than stressors from other sources. Other examples of regionally important stressors include hydrologic 

alteration from urbanization; effluent-created permanent streams in the arid west; and acid mine drainage 

and related metals contamination in coal mining regions of the Appalachians and metal mining regions of 

the Rocky Mountains. 

Identification of stressors and their sources is the first step in characterizing the stressor gradient (Chapter 

4). The stressor gradient is the combination of causal factors that induce an adverse response in the 

aquatic biota. A conceptual model of fish and macroinvertebrate assemblage response to a regional 

stressor gradient ranging from undisturbed or minimally disturbed conditions to severely altered 

conditions was developed based on empirical observations of assemblage responses to multiple sources in 

Ohio (Figure 3-2). The graphic represents measured assemblage abundance (y-axis) against an 

assemblage index (fish IBI, macroinvertebrate ICI; x-axis) with the generalized response of selected 

metrics. Biological descriptions correspond to the six tiers of the BCG model and include descriptions of 

assemblage characteristics, chemical water quality conditions, physical habitat and flow regime, and 

sources of stress that are typically associated with each. This was modified from an original conceptual 

model by Ohio EPA (1987) and Yoder and Rankin (1995b). It demonstrates that understanding the 

relationship between assemblage responses and stressors is a fundamental aspect of bioassessments. 

3.1.3 Describe the Biological Condition Gradient 

In testing the national BCG model, regional experts calibrated it to specific regional sites and 

assemblages. Biologists familiar with the regions’ natural aquatic communities and their responses to 

stress worked collaboratively to calibrate the BCG model to conditions in the following regions: Maine, 

Kentucky, the Central Great Plains, and selected areas in the arid west (Arizona and eastern Washington). 

Table 2-3 shows the resulting model for Maine. 

The equivalent step in developing a regional BCG model is to develop a local counterpart to the national 

BCG model. The objective is to ground the BCG in local conditions. The regionally calibrated BCG 

describes the undisturbed or minimally disturbed aquatic ecosystems of the region, and the responses of 

the biota to the predominate regional stressor gradient. To the extent possible, the regional model should 

describe undisturbed or minimally disturbed conditions. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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42 
Assemblage 

Abundance

(density, bio

mass) 

Assemblage index (IBI, ICI) 

Unimpacted 

(as naturally 

occurs) 

Least impacted 

(best available) 

Substantially Altered 

(initial enrichment) 

Severely Degraded 

(acutely toxic conditions) 

Highly Altered 

(gross enrichment) 

Condition likely 

beyond scope of 

current indices 

Arrow direction indicates measured value; line thickness indicates strength of signal 

Taxa Richness 

Intolerant Taxa 

%Tolerant Taxa 

%Omnivores 

Specialist Taxa 

%DELTs 

Biological and Stressor Gradient Descriptors 

“As Naturally 

Occurs” 

(Pristine) 

“Least Impacted” 

(Exceptional) 

“Initial 

Enrichment” 

(Good) 

“Moderate 

Enrichment” 

(Fair) 

“Gross 

Enrichment” 

(Poor) 

“Severely 

Altered” 

(Very Poor) 

Assemblage Characteristics 

Native 

assemblages; 

no symptoms of 

stress 

“Best of what’s 

left” 

assemblages; 

high richness; 

intolerants, 

specialists 

predominate 

“Typical” 

assemblages; 

good richness; 

emerging 

symptoms of 

stress in selected 

metrics 

“Impaired” 

assemblages; 

tolerants & 

generalists 

predominate 

numbers/biomass; loss of 

intolerants 

“Degraded”; 

highly tolerant 

taxa predominate; 

reduced 

abundance; 

anomalies 

increasing 

“Severely 

degraded”; very 

low numbers; 

few taxa; very 

high % 

anomalies; toxic 

signatures 

Chemical Water Quality Conditions 

As natural; no 

human-made 

compounds 

present 

“Best reference” 

quality; toxics < 

detection; high 

D.O., low nutrients 

“Background 

reference” quality; 

toxics < chronic; 

adequate D.O., 

nutrients = 

“Enriched” 

quality; toxics < 

chronic; marginal 

D.O. regime, 

nutrients > 

“Degraded” 

quality; toxics > 

chronic; low 

D.O., nutrients 

>> reference 

“Extremely poor” 

quality; toxics > 

acute; very low 

D.O., nutrients >> 

reference; 

reference reference contaminated 

Physical Habitat & Flow Regime sediments 

Natural habitat 

and flow 

regime; no 

human-made 

Excellent 

quality habitat 

& flow regime; 

recovered from 

Good quality 

habitat & flow 

regime; de 

minimis human 

Fair quality 

habitat & flow 

regime; active 

human modifiPoor quality 

habitat & flow 

regime; active 

human modifiSevere modifications; ephemeral 

flows; active human 

modifications; no 

modifications human-made 

modifications 

modifications cations; 

incomplete 

cations; no 

recovery 

recovery potential 

recovery 

Examples of Sources and Activities 

No effects of 

human activity 

are evident 

Point sources 

present, do not 

dominate flows; 

NPS impacts 

buffered by 

extensive 

riparian system 

Point sources 

may dominate 

flows; NPS 

impacts 

buffered by 

good riparian 

zones 

PS/NPS enrichment impacts; 

NPS unbufferd; 

channel modifications; impoundments 

Gross PS/NPS 

enrichment 

impacts inc. 

CSOs; NPS 

unbufferd; channel modifications; 

urbanization 

Severe PS/NPS 

toxic impacts; 

extreme channel 

modifications; 

urbanization; acid 

mine drainage, 

severe thermal 

FIGURE 3-2. Conceptual model of the response of fish and macroinvertebrate 

assemblages to a gradient of impacts in warmwater rivers and streams throughout Ohio 

(modified from Ohio EPA 1987 and Yoder and Rankin 1995b). 

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43 
The BCG model may require some example data from sites to empirically ground-truth conclusions. An 

example regional BCG was described in Chapter 2, the Maine scenario for cold-water, high gradient 

streams (Table 2-3). Ohio also developed a conceptual model of the BCG, shown in Figure 3-2, as part of 

its tiered aquatic life use development. In addition to the description of undisturbed, natural assemblages 

and the predominate stressor gradient in a region, the regional model also requires a narrative description 

of the tiers and their biological attributes. 

A narrative description of the tiers of the BCG for the region – The regional model includes description 

of individual tiers along the gradient of biological response to stressors, including organisms present and 

organisms absent. The descriptions of changes in the attributes corresponding to the different tiers are 

derived from the consensus among technical experts as well as agreement on the number of tiers that can 

be discriminated across the entire gradient. The regional narrative descriptions refine the national 

model’s descriptions of changes across the stressor gradient to reflect local conditions. (e.g., see Maine 

example, Table 2-3 and Ohio example, Figure 3-2). The description of the Ohio BCG is in the row titled 

“Assemblage Characteristics” (Figure 3-2). In Ohio, enrichment occurs at intermediate disturbance 

levels for the metrics (numbers or biomass). 

The descriptions should account for the natural classification that applies to the region. As noted in 

Section 3.1.1, “classification” is defined as the process of stratifying according to natural gradients. It 

may be necessary to develop separate narrative descriptions for major classes of natural gradients if the 

biological expectations differ widely among classes. For example, the biota of low-gradient streams with 

fine, sandy substrates may be dominated by invertebrates adapted to those conditions, such as midges and 

worms. These same organisms are often indicators of degraded conditions in fast-flowing streams with 

coarse substrate, but may be expected to occur under the best conditions in naturally silty streams. 

A narrative description of the ecological attributes that are used to determine the tiers – Ecological 

attributes are measurable characteristics of the system (described in Chapter 2). For bioassessment 

programs that sample biota of target assemblages, the critical attributes are those most closely related to 

taxonomic information contained in the sampled assemblages. Many species can be assigned to an 

attribute group, and the change in the attributes is described in the conceptual model. In the Ohio 

example (Figure 3-2), attributes include intolerants, generalists, specialists, etc. listed in the descriptions 

in the first row (Assemblage Characteristics). 

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44 
3.2 Data needs: Assess and modify technical program 

Consistent, quality assured and controlled (qa/qc) monitoring information is key to developing a 

quantitative assessment system within a BCG framework. Key elements of a biological monitoring 

programs are listed below, correspond to design and data collection elements outlined in Technical 

Guidelines: Technical Elements of a Bioassessment Program (see Appendix C) (Barbour and Yoder 

unpublished manuscript). Elements of a monitoring program for quantitative calibration of the BCG are 

discussed below. 

3.2.1 Biological assemblages 

Development of a quantitative BCG can include one or more biological assemblages (e.g., benthic 

macroinvertebrates, fish, periphyton, phytoplankton). Choice of each of these assemblages, and field 

sampling methods, are discussed in Rapid Bioassessment Protocols for Use in Streams and Wadeable 

Rivers: Periphyton, Benthic Macroinvertebrates and Fish (EPA/841-B-99-002; Barbour et al. 1999). 

3.2.2 Consistent methodology 

Consistent and demonstrated methodology is important for calibration of a regional BCG. 

Methodological consistency includes sampling methods that obtain representative samples of relevant 

biota in the assessment unit, choice and use of sampling equipment, index period, definition of sampling 

site (e.g., stream reach), and allocation of sampling and subsampling effort to obtain representative 

estimates of composition and structure. Field sampling considerations are discussed in Rapid 

Bioassessment Protocols for Use in Streams and Wadeable Rivers: Periphyton, Benthic 

Macroinvertebrates and Fish (EPA/841-B-99-002; Barbour et al. 1999), and statistical considerations are 

discussed in Statistical Guidance for Developing Indicators for Rivers and Streams (Appendix E). 

3.2.3 Geographic coverage 

The monitoring program should have sufficient spatial and temporal coverage to provide adequate 

quantitative information to describe biological community expected undisturbed/minimally disturbed 

conditions (Section 3.1.1). This would include major geographic regions, waterbody types, and 

environmental gradients of pressure and stressors. 

Natural Classifications –There should be sufficient reference site data in the State’s database to classify 

natural conditions and account for natural spatial variability among sites. Classification was discussed in 

Section 3.1.1. 

Stressor gradient – To describe the BCG, examples are used for each of the tiers that occur in the state or 

region. Hence, data must span the entire condition gradient from the least disturbed to the most disturbed 

sites in a particular region, along the entire stressor gradient. 

Geographic information – In addition to routine monitoring data, geographic information helps to 

develop natural classification of waterbodies to refine the expected condition. As noted above, one of the 

requirements for developing a description of the BCG is to have a natural classification of the resource, 

which provides a framework for organizing and interpreting natural variability among sites. Useful 

geographic information includes: 

• Watershed delineations – catchments of the specific sampling sites 

• Physical characteristics of sampling site catchments (catchment area, distance to source, mean 

slope, etc.) 

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In addition to natural characteristics, geographic information should include information for 

characterizing the stressor gradient, the x-axis of the BCG and evaluating whether there are undisturbed 

or least disturbed reference sites. This would include information on discharges, non-point sources of 

pollutants, and watershed and landscape characteristics. 

Reference condition – The no or low stressor end of the stressor gradient, whether undisturbed or least 

disturbed condition, should be well represented as reference sites and reference condition in the database. 

Considerations for establishing reference condition were discussed in Section 3.1.1. 

3.2.4 Database 

A comprehensive and complete database is critical to BCG calibration. The database should include all 

information collected in the monitoring program, as well as stressor and pressure information that may be 

collected on a geographic basis. The data must be organized and made accessible so that expert 

participants can easily view and interpret the data. 

3.2.5 Modify monitoring program 

If the specific data and information from a State monitoring program are not sufficient to support a 

quantitative BCG calibration, then the State may need to strengthen its technical program. Monitoring 

and sampling program design are not covered here. See Technical Guidelines: Technical Elements of a 

Bioassessment Program and Statistical Guidance for Developing Indicators for Rivers and Streams 

(Appendixes C and E). 

3.3 Calibrate a regional BCG model 

The final step in developing an assessment method using the BCG framework is to quantify and calibrate 

a model or system for routine assessment of waterbodies. In this step, the conceptual model that was 

adjusted for regional conditions is further refined and validated with data and, where possible, with 

quantitative relationships. The same expert panel that developed the regional conceptual model is best 

suited to calibrate the BCG model with quantitative information. 

Regional BCG models have been calibrated for routine use in bioassessment and biocriteria programs. 

These calibrations can be used independently as stand-alone assessment methods, or in conjunction with 

existing biotic indexes. The earliest operational development took place in Maine and Ohio (Ohio EPA 

1987, Courtemanch et al. 1989, Davies et al. 1995, Yoder and Rankin 1995a, Davies et al. 1999) and was 

the basis for the development of the national conceptual model. Regional calibration extends beyond 

application of the conceptual model and requires consistent operational rules so that sites can be assigned 

to tiers in a consistent fashion. 

The following sections outline the process of regionally calibrating and developing a BCG model. 

3.3.1 Assemble information 

The information required to complete these tasks includes the database of consistently collected 

biological monitoring data from a subset of sites throughout the region and geographic and historical 

information where available (Section 3.2). If the State or agency has a very large data set from a longstanding monitoring program, then it is not practical to make all of the data available to the regional BCG 

workshop participants. Instead, select a subset of sites that represent the entire stressor gradient, from the 

minimally or least disturbed to the most stressed sites in the state. The objective of the rating exercise is 

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46 
to select a variety of representative sites across the gradient so that all tiers occurring in the region are 

represented in the calibration sample of sites. Some reference sites should be included in this set as well 

as intermediate and severely stressed sites. The data must be organized and made accessible so that 

expert participants can easily view and interpret the data. The following information should be available: 

• A comprehensive species list for each assemblage that is monitored (e.g., macroinvertebrates, 

periphyton, fish), which can be sorted by higher taxonomic categories (order and family). To the 

extent known, tolerance values (to various stressors), trophic status (functional feeding group), 

habit, breeding guild, etc. should be included in each taxa list. 

• Counts of abundance, by taxon, for each sample. If necessary, the database program can adjust 

for unequal effort among samples. 

• Complete habitat data 

• Field notes 

• Complete field physical and chemistry data (e.g., streamflow, pH, conductivity, temperature, 

velocity, etc.) 

• Complete laboratory chemistry results 

• Landscape and hydrologic alteration of the catchments of the sampling sites, if available;


otherwise land use of the smallest hydrologic accounting unit that contains the sampled


catchments


• Site identification (name, ID, location) 

Sites from a comprehensive monitoring program should span the range of water and habitat quality found 

in the state, from the best to the worst. At this point, the data will have passed QA checks and will meet 

the requirements for developing a BCG, outlined briefly in Section 3.2 and in Appendix C, and in greater 

detail in Technical Guidelines: Technical Elements of a Bioassessment Program (Barbour and Yoder 

unpublished manuscript). 

Rather than expecting the expert group to work with stacks of printed data, it is useful to develop a 

spreadsheet that can be manipulated by participants or projected onto a screen for use during group 

discussions. The spreadsheet displays data from a single site at a time and calculates taxa and abundances 

of attribute groups. One person should be assigned responsibility for assembling all relevant data for the 

workshop exercise. If the State data are not well organized (i.e., not housed in a single comprehensive 

database), then assembling the data may require substantial time and effort. 

Classification – In this stage, it may be necessary to develop, refine, or empirically test classification 

schemes proposed in conceptual model development (Section 3.1) if the State does not have a fully tested 

classification scheme for aquatic assemblages in natural waterbodies. The purpose of classification for 

this document was also explained in Section 3.1. Classification is influenced by the components of a 

monitoring design: methods, measured variables, sample size (number of sites), etc. There are several 

quantitative approaches to developing a classification system, including categorical models, continuous 

models, a priori methods (use of existing models), and a posteriori methods (empirical models using data 

in hand). Many references are available to help analysts develop biological classifications of waterbodies 

(bioassessment case studies and methods: Barbour et al. 1999, Wright 2000, Gerritsen et al. 2000, 

Hawkins et al. 2000, Hawkins and Vinson 2000, Smith et al. 2001, Bailey et al. 2004; textbooks: 

Jongman et al. 1987, Ludwig and Reynolds 1988, Legendre and Legendre 1998, Davies et al. unpublished 

manuscript). 

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3.3.2 Describe attributes 

Ecological attributes are measurable characteristics of the system described in Chapter 2. These are the 

measures used to determine a waterbody's position along the BCG. As described in Chapter 2, attributes 

that are derived from taxonomic composition or organism condition (Attributes I to VII) are routinely 

measured and interpreted in State and Tribal water programs. As a practical matter, these are the key 

attributes that need to be quantitatively characterized for routine assessment. 

The technical expert panel should work through the list of taxa collected in the monitoring program and 

assign the taxa to Attributes I through VI. In this process, the specific definitions of the attributes may be 

adjusted to reflect local knowledge. For example, New Jersey biologists redefined Attribute II from 

“sensitive-rare” taxa to “highly sensitive” taxa because rarity was not considered to be related to 

sensitivity to pollution, and sampling methods do not capture rare taxa with any predictable reliability. 

See Case Example 3-2 for further discussion of New Jersey’s tier descriptions for high and low gradient 

streams. 

• Attribute I consists of rare and endemic taxa, which are not often encountered by routine 

biological sampling methods. Their presence may be known from larger-scale surveys designed 

to assess rare species. 

• Attributes II through V are taxonomic groupings organized according to tolerance to pollution, 

where Attribute II taxa are the most sensitive and Attribute V taxa are the most tolerant. These 

four attributes are the quantitative workhorses for assessment on the BCG and must be thoroughly 

characterized to calibrate a regional BCG. The tolerances of these attributes can be initially 

assigned based on existing tolerance estimates, but the panel should consider whether the existing 

tolerance estimates are accurate based on their experience and observations of the organisms. 

• Attribute VI consists of introduced taxa. 

Due to incomplete information, rarity in the database, or lack of knowledge, not all taxa will be assigned 

to an attribute. 

3.3.3 Describe tiers and assign sites to tiers 

Similar to the national BCG model development process, regional development can occur in workshops 

that bring together aquatic biologists and water quality standards experts familiar with streams in their 

regions. Workshop participants are asked to develop both the ecological attributes and the rules for 

assigning sites to tiers along the gradient. Workshops proceed as follows: 

1.	 Participants consider the conceptual model of the BCG to identify specific biological changes that 

can be observed along the stressor gradient in their region. Specific metrics or attributes that can 

be measured within the BCG framework are identified. 

2.	 The groups consider data from selected monitoring sites and assign the sites to tiers in the BCG 

based on the biological monitoring information from each site. Initially there may be 

disagreement among the group members, but as they become familiar with the process, sites are 

rated more consistently. 

3.	 From the discussions and decisions, a set of rules is developed for assigning sites to individual 

tiers in the BCG. 

Using the regionally adapted conceptual model (Section 3.1.3), participants examine data from selected 

sites throughout the region. Sites are selected from the preliminary stressor gradient (See Chapter 4) to 

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48 
represent the gradient as it occurs in the region. The group should consider the biological condition, 

species present and absent, and come to consensus on the tier to which each site should be assigned. 

Experience has shown that assemblages are best kept separate at this stage. The group should describe 

the tiers and assign sites to tiers separately for macroinvertebrates, fish, periphyton, and other 

assemblages. 

Groups typically start with several candidate reference sites in the region in an effort to establish a 

reference baseline. Depending on the completeness of the database, the best sites in that database may 

not reflect undisturbed or minimally disturbed conditions. Additionally, if the ecoregion spans more 

than one state, the best sites might be in a different state or tribal land—and may not be part of the 

database. Ideally, calibration of the BCG in physiographic or ecological regions that cross state 

boundaries should be multi-state and tribal efforts. The important point here is that the best sites are not 

automatically assigned to Tiers 1 or 2. The assemblages from the candidate reference sites should be 

compared to the descriptions of Tier 1 and Tier 2 sites developed in the initial theoretical exercise. The 

following questions should be addressed: 

• Do the candidate reference sites meet the theoretical expectations of Tier 1 or Tier 2? Then, if the 

answer is no, first validate the model’s Tier 1 and 2 expectations by addressing the following 

questions: 

o Are these candidate reference sites minimally disturbed, that is, are there no or negligible 

effects from stressors? 

o Can the level of stressors be documented? 

o Is historical information available that would suggest that they are minimally disturbed? 

• If these three questions are answered “yes” then the theoretical expectations and descriptions of 

Tiers 1 and 2 may need to be reassessed and altered. If the candidate reference sites apparently 

have more then than minimal or negligible levels of stressors, then they do represent examples of 

Tiers 1 and 2, undisturbed or minimally disturbed conditions. In many areas, sites identified as 

reference, especially those that are the “least disturbed,” may be rated Tier 3 or even Tier 4 in the 

BCG. 

Following development of the tier descriptions, participants continue to assign sites to tiers using the 

descriptions they have developed. Both the tier descriptions and the original taxa assignments may be 

revisited and revised in order to resolve any anomalies or issues that arise throughout the assignment 

process. Sites are frequently deemed intermediate (between adjacent tiers), and assigning sites to tiers 

does not require group unanimity. See Case Example 3-3 on Maine’s assignment of stream sites to 

waterbody classes (tiers) using benthic macroinvertebrate metrics. 

Tier assignments can also be tested against stressor gradients from the database. Stressor gradients (e.g., 

toxic metal concentrations, habitat conditions, nutrient concentrations, etc.) can be considered partial 

components of the stressor gradient (Chapter 4). Figure 3-3 shows an example from Ohio, showing 

copper concentration in the BCG tiers. In general, lower tier sites have a greater likelihood of elevated 

copper above the criterion level, although all tiers except the poorest (NA; very poor) included at least 

some sites with copper not exceeding the criterion. 

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49 
I

B

I

O hio E PA Criteria 

FIGURE 3-3. Ohio BCG tiers and copper 

concentration. Each horizontal bar 

50-60 EWH	 approximates the tier shown on the right: 

EWH - exceptional warmwater habitat; 

WWH - warmwater habitat; MWH ­ 40-49 WWH	 modified warmwater habitat; LRW ­

limited resource waters; NA - non30-39 MWH	 attaining (very poor). Shaded areas are 

interquartile ranges of copper 

concentration in each BCG tier. Note that 20-29 LRW 

all sites in the very poor tier had copper 

concentration above the Ohio copper 

12-19 NA	 criterion (dashed line). 

0 20 40 60 80 100 

S tandard T otal

R ecoverable Copper (ug/l)

Setting expectations in significantly altered landscapes 

In some regions, the historical conditions describing Tier 1 and 2 sites no longer exist. Many native 

species have been extirpated or greatly reduced, and the physical and chemical habitat of streams is 

completely different from the pristine, or undisturbed, condition. For example, the breaking up of native 

prairie sod and ongoing agricultural practices has resulted in high sediment and nutrient loads in 

midwestern prairie streams (e.g., Kuzelka et al. 1993). Removal of forest cover in eastern agricultural 

areas (e.g., Corn Belt Plains, Interior Plateau, Southeastern Plains, Riverine Lowlands) has had similar 

effects, although large tracts of forest cover remain or have regrown. In the western Great Plains, 

damming of snowmelt-fed streams and rivers has eliminated annual scouring flows and reduced sediment 

loads of rivers such as the Missouri, Platte, Arkansas, Rio Grande (e.g., Johnson 1994). Biological 

conditions comparable to Tiers 1 and 2 may no longer exist in some ecological regions of the continent. 

Mitigation of the resource to pristine conditions may not be currently possible (See Case Example 3-1). 

3.3.4 Develop quantitative assessment methods 

To developing a regional BCG water quality agencies should consider ecological information critically in 

making assessments. Biological condition tiers are narrative statements on presence, absence, abundance, 

and relative abundance of several groups of taxa, as well as statements on system connectivity and 

ecosystem attributes (e.g., production, material cycling). The statements are consensus best professional 

judgments based on the years of experience of many biologists in a region, and reflect accumulated 

biological knowledge. 

Consistent application of the BCG to routine assessment and ultimately to better define designated aquatic 

life uses in water quality standards, will require an operational system that does not depend on 

reconvening the same group of experts to rate all sites. Assessments should minimize individual 

variability or bias, as might occur if individual assessors then interpret the rules developed by expert 

consensus. 

Accordingly, there are a variety of ways to automate the decision tool, ranging from application of 

existing biotic indexes (multimetric IBI type indexes, RIVPACS indexes, BEAST applications) to 

development of new expert systems that specifically replicate the decision-making of the expert group 

that defined the BCG for the region (Appendix A; Davies et al. unpublished manuscript). Below are 

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50 
discussions of three methods for developing an operational assessment system, two of which use existing 

indexes, and the third of which develops and calibrates a system specifically for identifying tiers of the 

BCG. Other methods are also possible (e.g., expert systems), but the three explained below are currently 

used for operational bioassessment into tiers of the BCG. 

Any quantitative model or procedure that is developed to assign sites to tiers should be tested with 

independent data that were not used to calibrate the model. This applies to all three quantitative model 

approaches discussed here. In general, the models are calibrated using tier assignments developed by the 

expert panel (Section 3.3.3). A second data set of tier assignments (also assigned by the expert panel) is 

then required to test the model. 

Calibrating biotic indexes to the BCG 

Biotic indexes such as IBIs (multimetric approaches under a variety of acronyms; Barbour et al. 1999), 

predictive model indexes (RIVPACS approaches; Wright 2000), and true multivariate indexes (BEAST 

models; Bailey et al. 2004) are all attempts to describe a biological condition gradient. As such, index 

approaches may be suited to identifying tiers in the gradient and for assessment in the context of the 

BCG. 

Simple division of an index scoring range is not recommended because most indexes were not explicitly 

developed on a BCG framework. For example, metrics in an IBI-type index may have been selected 

because of strong responsiveness to stressors, rather than reflecting the conditions expressed in the BCG 

(see Table 2-1). If a State is to develop tiered aquatic life uses based on the national BCG model, it 

therefore may be necessary to recalibrate existing index models to the BCG or develop new biological 

models and can be used to assign sites to tiers. For example, Vermont has designated aquatic life uses as 

differentiated by biological threshold criteria (See Case Example 3-4). 

Through an iterative process, scoring criteria may be developed for existing indexes that correspond with 

biologists’ consensus on narrative descriptions of the tiers in the biological gradient. If tiers are 

established based on other designated uses (e.g., hydrologically modified canals), then each tier or use 

class can be calibrated to an index score reflecting the best potential condition for that use. Ohio used this 

approach to set biological criteria for four use classes (see Chapter 5). 

An existing index may be calibrated to the BCG model at the level of index scores, or by deriving a new 

index that better reflects the BCG. Both approaches require a set of sites that have been assigned to the 

tiers of the BCG that were determined by the expert panel to be appropriate for the specific aquatic 

ecosystem (Section 3.3.3). 

Calibrating index scores – The set of sites that have been assigned to tiers of the BCG are used to 

calibrate index scores. Index scores for the sites are examined (Figure 3-4). If separation of the index 

scores among tiers is good, then index thresholds can be selected to maximize the ability to discriminate 

among the tiers. Figure 3-4 shows a hypothetical example with five tiers (BCG Tiers 2 - 6). Separation 

of scores among tiers is generally good, and the solid lines indicate scoring thresholds between adjacent 

tiers. The exception here is that the index does not discriminate as reliably between Tiers 2 and 3 as it 

does between other pairs of tiers. 

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51 
tlier Max

tlier Min

Non O

Non O

75%

25%

Median

90 

80 

70 

60 

50 

40 

30 

20 

10 

2 3 4 5 6 

- u 

- u 

Assigned Tier 

Tier 6 

FIGURE 3-4. Hypothetical example of biotic index scores 

of sites assigned to BCG tiers, where the index is able to 

Tier 2	 discriminate tiers most of the time. Boxes represent 

interquartile range of each tier; points are medians, Tier 3	 and whiskers represent range of score outside the 

quartiles. Horizontal lines represent thresholds that 

Tier 4	 could be applied to discriminate tiers using the index 

scores. In this example, there are no undisturbed 

Tier 5	 reference conditions in the region. Index Score 

The British Environment Agency recalibrated two RIVPACS indexes in a similar way. Initially, index 

scores were divided into four equal tier categories based on the statistical distribution of reference site 

scores (90% interval; Helmsley-Flint 2000). However, regional field biologists observed that four equal 

categories based on a 90% interval were insufficient to discriminate exceptional from good sites, and poor 

from very poor sites (Helmsley-Flint 2000). Accordingly, the indexes were recalibrated so that categories 

matched those determined by the regional experts. The resultant six categories are similar to the six tiers 

of the BCG (Table 3-4). See Case Example 3-5 for a description of this process. 

Calibrating metrics – However, index scores may show a great deal of variation within BCG tiers, such 

that assigning tiers based on index scores is an inaccurate process (Figure 3-5). In the hypothetical 

example shown in Figure 3-5, the index is unable to discriminate among Tiers 2 through 4. In this 

instance, it would be necessary to revise the index to reflect tiers of the regionally calibrated BCG. 

Revision and recalibration of an IBI, or of other indexes, can be part of a State's routine recalibration 

process that occurs periodically when substantial new data have been collected. 

Tier 5 

15 

10 Tier 6 

5


0


30 

Tiers 2-4 

25 

20 

Index Score 

2 3 4 5 6 

Assigned Tier 

FIGURE 3-5. Hypothetical example of biotic index scores of sites assigned to 

BCG tiers, where the index is not able to discriminate tiers. 

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52 
Model development to support BCG tiers: Discriminant model 

Simple recalibration of index scores to BCG tiers may not yield distinct break-points (or benchmarks) 

between adjacent tiers. This is the case when sites in different tiers (as determined by the expert panel) 

have the same or similar index scores, showing that the index cannot discriminate among tiers of the 

BCG. Development of an operational tiered assessment system may require a separate index or model 

calibrated to the tiers. 

Discriminant analysis may be used to develop a model that will divide, or discriminate, observations 

among two or more classes. A discriminant function model is a linear function combining the input 

variables. It obtains the maximum separation (discrimination) among the classes. The model is 

developed from a "learning" dataset where the classes have been identified. The model is then used to 

determine class membership of new observations where the class is unknown. Thus, a discriminant 

function model can be developed from a biological data set where sites have been assigned to BCG tiers. 

The analysis identifies variables that will discriminate among the tiers. The resultant model is then used 

to identify the tier to which a site should be assigned. Maine uses this method to determine whether 

streams are meeting biological criteria for multiple tiered uses. See Case Example 3-6 on Maine’s 

development of linear discriminant functions to assess tiers. 

Although it requires considerable statistical expertise to develop, the advantage of discriminant analysis is 

that it uses established and well-documented statistical methodology. However, it requires a relatively 

large set of assigned sites to calibrate the model, approximately 20 per tier. Accuracy of the model to the 

expert-assigned calibration and test sites can be as high as 89 - 97% (based on jack-knife tests; Davies et 

al. unpublished manuscript). 

Using a discriminant model to develop biocriteria requires both a set of training data to develop the model 

and confirmation data to test the model. The training and confirmation data may be from the same 

biosurvey, randomly divided into two, or they may be two or more years of survey data. All sites in each 

data set are assigned to BCG tiers by the expert workgroup (Section 3.3.3). 

One or more discriminant function models are developed from the training set to predict tier membership 

from biological data. Once developed, the model is applied to the confirmation data set to determine how 

well it can assign sites to classes using independent data not used to develop the model (See Case 

Example 3-6). More information on discriminant analysis can be found in any textbook on multivariate 

statistics (e.g., Jongman et al. 1987, Ludwig and Reynolds 1988, Legendre and Legendre 1998). 

Quantitative rules for tier assignments 

Tier descriptions in the conceptual model tend to be rather general (e.g., “reduced richness”). To allow 

for consistent assignments of sites to tiers, it is necessary to operationalize, or codify, the general tier 

descriptions into a set of rules that anyone can follow and obtain the same tier assignments as the group of 

experts. 

Operational rules are used to define the tier descriptions (“as naturally occur,” “reduced,” “greatly 

reduced,” etc.) to quantitative or semi-quantitative rules for each attribute (“Attribute II taxa > 50% of 

any other attribute, ± 10%”). These rules preserve the collective professional judgment of the expert 

group and set the stage for the development of models that reliably assign sites to tiers without having to 

reconvene the same group. In essence, the rules and models capture the group’s collective decision 

criteria. 

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53 
Rule development can take place during the expert panel workshop to describe the detailed BCG and 

assign sites to tiers (Section 3.3.3). It requires discussion and documentation of tier assignment decisions 

and the reasoning behind the decisions. During this discussion, facilitators should elicit and record: 

• each participant’s tier decision (“vote”) for the site; 

• the critical or most important information for the decision – for example, the number of taxa of a 

certain attribute, the abundance of an attribute, the presence of indicator taxa, etc.; and 

• any confounding or conflicting information and how this was resolved for the eventual decision. 

See Case Example 3-7 for an example of decision rules developed during New Jersey’s calibration 

exercise (Table 3-6). 

Testing 

Rule development should be iterative. Following the initial development phase, the draft rules should be 

tested by a group of experts to ensure that new data and new sites are assessed in the same way. This 

usually requires a second workshop, during which a set of test sites not used in the initial rule 

development and also spanning the range of stress should be assessed. Any remaining ambiguities and 

inconsistencies from the first iteration can also be resolved. Rules can be used directly for assessments, 

for calibrating one of the previous assessment methods (IBI, discriminant model), or as the basis of an 

expert system. 

Thresholds and uncertainty 

For each of the quantitative models described above, it is possible to estimate predictive uncertainties. 

Index variability is estimated from repeated measures at sites over one or more years, and accuracy of the 

quantitative model to expert consensus is estimated from the number of “correct” calls by the model. 

Several methods exist to estimate overall predictive uncertainty. For uncertainty of the models discussed 

here, see Helmsley-Flint (2000) and Davies et al. (unpublished manuscript). 

Not all uncertainty is statistical, and not all issues of uncertainty can be reduced to a statistical probability. 

Experience with the BCG workgroups suggests that there will always be sites that fall on the border 

between tiers. It is important to recognize that some sites are borderline or intermediate, not that we are 

uncertain about where they are. This is a consequence of forcing a more-or-less continuous gradient into 

discrete management categories. 

While thresholds between tiers do not need to reflect true discontinuities in nature, the tiers should 

represent detectable and consistent differences in assemblages, their taxonomic composition, and 

ecological function. To the extent they are consistent and detectable, they serve to inform management 

on how well we are protecting against degradation and making progress towards restoration goals. 

Disagreement among assemblages 

Once a BCG has been regionally calibrated, a possible scenario in assessment is that two assemblages 

collected at the same site indicate different tiers of the BCG. For example, to what tier should a site be 

assigned if the fish indicate Tier 2 but the macroinvertebrates indicate Tier 4? Options include: 

• averaging the two assemblages (Tier 3 in this example), 

• selecting the lowest assessment among the assemblages (Tier 4), or 

• selecting the highest assessment among the assemblages (Tier 2). 

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54 
In making this decision, it is important to consider the level of rigor in the tier assessments among the 

assemblages, particularly if an assessment is based on an absence, rather than presence, of information 

(absence of evidence is not evidence of absence). This requires considering the strength of evidence for 

each assemblage. Automatic calculation of an average or use of the highest assessment is neither 

conservative nor protective of the resource. Both Ohio EPA and the British Environment Agency have 

chosen to select the lowest assessment among indexes and assemblages for final tier assignments (Yoder 

and Rankin 1995b, Helmsley-Flint 2000). 

3.4 Key points from Chapter 3 

1.	 The conceptual Biological Condition Gradient can be quantified and calibrated to local 

conditions for use in assessment and water quality criteria. The tiers of condition described 

in the BCG conceptual model can be applied to local or regional conditions by regional biological 

experts with a sufficient monitoring database. 

2.	 A quantified BCG is not defined by any one monitored assemblage or methodology. BCGs 

have been developed from different assemblages and methodologies (fish, benthic 

macroinvertebrates, artificial substrates, etc.) and by calibrating different assessment indicators to 

the BCG (IBI, RIVPACS, and multivariate analysis). 

3.	 Quantification and development of a BCG is data driven. A regional monitoring database 

should be used to calibrate a BCG that meets performance requirements and QA requirements. 

The monitoring agency should have access to biological expertise, and should be committed to 

provide sustained support. 

Chapter 3 has discussed transforming the conceptual scientific model of the BCG into a quantified and 

calibrated model for biological assessment. Chapter 4 discusses the Stressor Gradient model, the x-axis 

of the BCG. Chapter 5 discusses key concepts and milestones for developing tiered aquatic life uses in 

water quality standards that two states, Maine and Ohio, have learned based on their experience in 

adopting tiered uses, and is supported by their individual case histories of TALU development 

(Appendixes A and B). Chapter 6 presents examples of how Maine and Ohio have applied tiered uses in 

their water quality management program. 

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55 
Chapter 3 Case Examples 

CASE EXAMPLE 3-1. USING HISTORICAL INFORMATION TO IDENTIFY


REFERENCE STREAMS IN KANSAS


Historical information can be used to reconstruct the pre-settlement biological baseline and estimate 

undisturbed or minimally disturbed conditions. Potential sources of historical data include museum fish 

and shellfish collections, historical notes and writings, journal entries, indigenous knowledge, published 

archeological studies, photographs and maps, and early biological surveys or studies. 

Some knowledge of pre-settlement baseline conditions is needed when planning long-term restoration 

efforts in areas where undisturbed or minimally disturbed reference waterbodies no longer exist. For 

example, in Kansas, few streams have completely escaped the effects of large-scale agricultural and 

livestock practices implemented over the past 150 years. Therefore, biologists within the Kansas 

Department of Health and Environment (KDHE) consider available information on historical stream 

characteristics to estimate minimally disturbed conditions and support contemporary reference stream 

selections. 

KDHE recognizes six general categories TABLE 3-1. Kansas stream biological integrity categories. of aquatic biological responses to 

increasing levels of disturbance (Table 3- Class A: Historical (natural) reference condition 

1). Class A represents natural or pre- Class B: Contemporary (quasi-natural) reference condition 

settlement stream conditions, equivalent 

to Tier 1 in the BCG, in which “native 

Class C: Fully supportive of designated aquatic life use 

structural, functional and taxonomic Class D: Partially supportive of designated aquatic life use 

integrity is preserved; ecosystem function Class E: Non-supportive of designated aquatic life use 

is presented within the range of natural 

variability.” Some indication of the 

Class F: Grossly non-supportive of designated aquatic life use 

native character of streams in the Great Source: Kansas Dept. of Health and Environment 

Plains can be found in the narrative 

accounts of early nineteenth century explorers, including Lewis and Clark, Zebulon Pike, and George 

Sibley, among others. Railroad surveys and other investigations yielded additional information on the 

aquatic flora and fauna and generated maps and the earliest known photographs of many streams. 

Although many of the biological surveys from the mid-1800s were performed after the start of intensive 

agriculture, they still provide valuable documentation of the occurrence of several freshwater species that 

soon disappeared from specific watersheds or the region as a whole. Museum collections and other 

historical records indicate that many creeks and smaller rivers in the Great Plains supported a variety of 

predominately eastern fish and shellfish species, most requiring clear water and relatively stable stream 

bottoms. In fact, this region was once home to more than 50 unionid mussel species. Today, several 

mollusca species are no longer found in most of their original habitats (Figure 3-6). Over the past 150 

years, at least 11 aquatic molluscan taxa have become extinct in Kansas, and an additional 23 species are 

currently designated as endangered, threatened, or vulnerable. 

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56 
FULL SUPPORT (CLASSES B AND C) 

! 

! ! ! ! ! ! ! ! 

! !

! ! 

! 

! ! 

! 

! 

! 

! 

! 

! 

! 

! 

! 

! 

! 

!

! ! ! ! ! ! 

! 

! 

! 

! 

!

! 

! 

! 

! 

!! 

! 

! 

Historical populations

Known extant population

FIGURE 3-6. Decline in geographical distribution of black sandshell mussel in Kansas.

Because typical biological indexes (e.g., IBI) are usually developed from ambient “least disturbed”

reference sites, they may lack sensitivity to discriminate among tiers or levels in the BCG. Surviving

populations of historically occurring key species and indicator taxa can be used to further verify the

minimally disturbed condition. KDHE considers historical fish, mussel, and prosobranch snail

communities, and has created a “mussel loss” indicator metric that compares the taxa richness of the

contemporary and historical unionid mussel assemblage for use in 305(b) and 303(d) list development

(Figure 3-7). Sites retaining 90-100 percent of their pre-settlement species are deemed fully supportive of

the aquatic life use, sites with 75-89 percent are considered partially supportive, and sites retaining 0-74

percent are assigned to the non-supportive category. In establishing long-term restoration goals, KDHE

intends to continue drawing upon historical information sources to help ensure that the projected changes

in aquatic plant and animal assemblages trend toward the pre-settlement biological condition.

There are some challenges and drawbacks when using historical data to reconstruct natural stream

conditions. It takes a great deal of time and commitment to piece together numerous bits of information,

especially considering the limitations and inconsistencies inherent in historical data. Much of the

information is not directly comparable to modern assessment data, largely because results from previous

studies and observations are often based on different sampling methodologies. Sometimes the data are

not applicable because they were obtained after settlers significantly impacted the land, but often such

physical habitat data are missing or incomplete. Finally, some regions settled early in the history of the

nation may simply lack definitive data on the baseline biological condition.

100 FIGURE 3-7. Cumulative frequency NON-SUPPORT (CLASSES E AND F)

80

distribution for Kansas streams with

Cumulative frequency (%)

minimum three-year period-of-record and

five or more species historically.

60

40

20

0

PARTIAL SUPPORT (CLASS D) 

0 20 40 60 80 100

Extirpated mussel species (%)

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and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 3 – August 10, 2005
CASE EXAMPLE 3-2. NEW JERSEY TIER DESCRIPTION 

Aquatic biologists in New Jersey described tiers of the BCG for benthic macroinvertebrate assemblages 

of both high and low gradient streams of the state. The expert panel first assigned invertebrate taxa to 

Attributes I to VI. The panel redefined Attribute II from "sensitive-rare" taxa to "highly sensitive" taxa 

because rarity was not considered to be related to sensitivity to pollution, and sampling methods do not 

capture rare taxa with any predictable reliability. In addition, the panel determined that five tiers are 

applicable to New Jersey high gradient streams, and that four tiers describe the State's low gradient 

streams. For both high and low gradient streams, the panel thought that Tier 1 sites may not exist. 

Table 3-2 shows the attribute matrix for high gradient streams. Attributes VII to X are not measured for 

the invertebrate assemblage at this time, and are not included in the matrix. The group was able to 

distinguish five separate tiers (Tiers 2-6) for high-gradient streams of New Jersey. The first tier described 

in the Maine model (Davies and Jackson in press) was not initially useful because it was not clear to the 

group whether Tier 1 (pristine) sites occur in New Jersey based upon benthic macroinvertebrate data 

alone. Other data sets (i.e. finfish communities and/or rare and endangered species) may be more useful 

in determining whether a site is in Tier 1. The group also determined that several indicator taxa are useful 

in discriminating tiers, in particular the tolerant hydropsychid caddisflies as indicators of moderate 

organic enrichment for Tiers 3 and 4; abundance of tubificid worms as an indicator of extreme enrichment 

and hypoxia for Tier 6; and complete absence of mayflies as an indicator of toxicity, also for Tier 6. 

In contrast to high gradient streams, participants could only distinguish four separate tiers for low gradient 

streams (Tier 2, Tiers 3-4 combined, Tier 5, and Tier 6) (matrix not shown). The best-known sites in the 

Coastal Plain contain moderate numbers of tolerant taxa, which is a consequence of low water velocity 

and absence of cobble habitat rather than poor water quality. As a result, the group concluded that it was 

not feasible to distinguish Tier 3 from Tier 4, and combined them into a single tier. 

In general, participants were able to achieve consensus on tier assignments for the sites reviewed. In 

some cases, there was discussion and some disagreement on which of two adjacent tiers a site should be 

assigned to. These intermediate sites, with characteristics of both adjacent tiers, are to be expected since 

ecological response to stressors is relatively continuous. 

TABLE 3-2. Summary attribute matrix for New Jersey high gradient streams. 

Ecological 

Attributes 

1 

Natural 

2 

Minimal Loss 

3 

Some 

4 

Notable 

5 

Tolerants 

6 

Severe Alter 

Condition Replacement; 

Function 

Replacement 

Function 

Dominant, 

Loss of 

Structure and 

Function 

Maintained Largely 

Maintained 

Function 

I Historically As predicted for As predicted for Some may be Some may be Usually absent Absent 

documented, natural natural absent due to absent due to 

sensitive, occurrence occurrence global extinction global, regional 

long-lived or except for except for or local or local 

regionally global global extirpation extirpation 

endemic taxa extinctions extinctions 

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58 
TABLE 3-2. Summary attribute matrix for New Jersey high gradient streams. 

Ecological 

Attributes 

1 

Natural 

2 

Minimal Loss 

3 

Some 

4 

Notable 

5 

Tolerants 

6 

Severe Alter 

Condition Replacement; 

Function 

Replacement 

Function 

Dominant, 

Loss of 

Structure and 

Function 

Maintained Largely 

Maintained 

Function 

II Highly 

sensitive taxa 

As predicted for 

natural 

Virtually all are 

maintained and 

May be 

markedly 

Significantly 

diminished 

Usually absent Absent 

occurrence, 

with at most 

well 

represented 

diminished (in 

either taxa or 

(taxa and 

abundance) 

minor changes 

from natural 

densities 

(both taxa and 

abundance) 

abundance), 

with replacement by 

functionally 

equivalent 

Sensitive and 

common taxa 

III Sensitive & As predicted for Present and Common and Present with Frequently Absent 

common taxa natural 

occurrence, 

with at most 

may be 

increasingly 

abundant. 

abundant; 

relative 

abundance 

reproducing 

populations 

maintained; 

absent or 

significantly 

diminished (if 

minor changes 

from natural 

greater than 

Highly Sensitive 

some 

replacement by 

present 

incidental) 

densities taxa. Similar to 

good taxa 

functionally 

equivalent taxa 

(sensitive & 

common taxa). 

of intermediate 

tolerance. 

IV Taxa of 

intermediate 

tolerance 

As predicted for 

natural 

occurrence, 

As naturally 

present at low 

abundances 

Often evident 

increases in 

abundance 

Common and 

often abundant; 

relative 

Often exhibit 

excessive 

dominance 

Richness of all 

taxa is low 

with at most abundance 

minor changes 

from natural 

greater than 

Sensitive and 

densities common taxa 

V Tolerant taxa As naturally As naturally May be May be Often occur in Usually 

occur, with at 

most minor 

present at low 

abundances. 

increases in 

abundance of 

common but do 

not exhibit 

high densities 

and may be 

comprise the 

majority of the 

changes from 

natural 

May have 

several taxa at 

functionally 

diverse tolerant 

significant 

dominance 

dominant assemblage; 

often either very 

densities. If 

present, at very 

low 

abundances. 

taxa low or very high 

densities. 

low abundance. 

VI Non-native Non-native Non-native taxa Sensitive or Some Some Often dominant; 

or intentionally 

introduced 

taxa, if present, 

do not displace 

may be present, 

but occurrence 

intentionally 

introduced nonreplacement of sensitive nonassemblages (e.g., fish or 

may be the only 

representative 

taxa native taxa or 

alter native 

has a nondetrimental native taxa may 

dominate some 

native taxa with 

functionally 

macrophytes) 

are dominated 

of some 

assemblages 

structural or 

functional 

effect on native 

taxa 

assemblages 

(e.g. fish or 

diverse 

assemblage of 

by tolerant nonnative taxa (e.g., plants, 

fish, bivalves) 

integrity macrophytes) non-native taxa 

of intermediate 

tolerance 

XI Potential No apparent No apparent Initial response Some response Response of 

Supplemental 

Attributes; 

response of 

indicator taxa 

response of 

indicator taxa 

of indicator 

taxa, (e.g., 

of indicator 

taxa, (e.g. 

indicator taxa 

(e.g., loss of 

Indicator taxa increase of increase of mayflies with 

suspension Caenids with toxic stress) 

feeders with silt, etc.) 

enrichment) 

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59 
CASE EXAMPLE 3-3. MAINE BIOLOGISTS’ ASSIGNMENT OF SITES TO CLASSES (TIERS) 

Maine DEP assembled a panel of three biologists to assign sites to each of Maine's three stream classes 

(A, B, C), and a fourth class representing non-attainment (NA). Each biologist independently reviewed 

biological information for each sampling event, including identities and abundances of taxa occurring in 

the biological sample and computed index values for the biological data (e.g. diversity, richness, EPT, 

etc). Physical habitat information was also reviewed including water depth, velocity, substrate 

composition, canopy cover, etc., in order to evaluate the effects of various habitat conditions on the 

structure of the macroinvertebrate community. Sample information was reviewed for the values of the 

given measures, relative to values for other samples in the data set. The actual classification assignment 

was determined by how closely the biological information conformed to the aquatic life classification 

standards, correcting for habitat effects. Numerical ranges, per se, were not established, a priori, for 

each measure. Instead, the information was reviewed for its compatibility with the mosaic of findings 

expected for each Class, listed in Table 3-3. The biologists did not have any knowledge of the actual 

location of the sampled sites, nor did they have knowledge of any pollution influences. Following the 

independent assignment of classes the biologists established a consensus classification, following an open 

exchange of justifications for each biologist's assignment. 

Each biologist reviewed the sample data for the values of a list of measures of community structure and 

function. Criteria used by biologists to evaluate each measure are listed in Table 3-3. 

In 64% of the cases there was unanimous agreement among the independent raters, and in an additional 

34% of the samples two of the raters were in agreement and one had assigned a different classification. In 

three of the rated samples there was disagreement among all three raters (2%). 

TABLE 3-3. Relative findings chart. 

Measure of Community Relative Findings 

Structure A B C NA 

Total Abundance of Individuals often low often high variable variable: often 

very low or high 

Abundance of Ephemeroptera high high low low to absent 

Abundance of Plecoptera highest some present Low to absent Absent 

Proportion of Ephemeroptera highest variable depending 

on dominance by 

other groups 

low zero 

Proportion of Plecoptera highest variable depending 

on dominance by 

other groups 

low zero 

Proportion of Hydropsychidae intermediate highest variable low to high 

Proportion of Ephemeroptera & 

Plecoptera 

highest variable Low absent 

Proportion of Glossosoma highest low to intermediate very low to 

absent 

absent 

Proportion of Brachycentrus highest low to intermediate very low to 

absent 

absent 

Proportion of Oligochaetes low low low to moderate highest 

Proportion of Hirudinea low variable variable variable to 

highest 

Proportion of Gastropoda low low variable variable to 

highest 

Proportion of Chironomidae lowest variable depending 

on the dominance of 

other groups 

highest variable 

Proportion of Conchapelopia & 

Thienemannimyia 

lowest low to variable variable variable to 

highest 

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60 
TABLE 3-3. Relative findings chart. 

Measure of Community Relative Findings 

Structure A B C NA 

Proportion of Tribelos low to absent low to absent low to variable variable to 

highest 

Proportion of Chironomus low to absent low to absent low to variable variable to 

highest 

Generic Richness variable highest variable lowest 

Ephemeroptera Richness highest high low very low to 

absent 

Plecoptera Richness highest variable low to absent absent 

EPT Richness high highest variable low 

Proportion Ephemeroptera 

Richness 

highest high low low to zero 

Proportion Plecoptera Richness highest variable low zero 

Proportion Diptera Richness low to variable variable highest variable to high 

Proportion Ephemeroptera & 

Plecoptera Richness 

highest high low to variable low to absent 

EPT Richness divided by Diptera 

Richness 

high highest low to variable lowest to zero 

Proportion Non-EPT or 

Chironomid Richness 

high high low lowest 

Percent Predators low low high to variable highest 

Percent Collector, Filterers & 

Gatherers divided by Percent 

Predators & Shredders 

high highest low lowest 

Number of Functional Feeding 

Groups Represented 

variable highest variable lowest 

Shannon-Weiner Generic Diversity low to 

intermediate 

Highest Variable to 

intermediate 

lowest 

Hilsenhoff Biotic Index lowest low intermediate highest 

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61 
e 

CASE EXAMPLE 3-4. VERMONT’S USE OF EXISTING BIOLOGICAL INFORMATION FOR THE BCG 

Vermont used reference condition as the anchor point for assessing biological condition, and tiers of 

biological condition were established and described in terms of deviation from the reference condition. 

Biological narratives were developed, which provided guidance for evaluating degrees of deviation from 

the reference condition. The proposed language was intended to formalize Best Professional Judgment 

(BPJ) assessments by technical experts while remaining close to historical implementation. It was also 

critical that the new classification system maintain consistent assessment results, particularly for nonattainment findings. 

Vermont tapped into more than 20 years worth of biological data collected from wadeable streams to 

develop biocriteria. Existing macroinvertebrate and fish assemblage monitoring data were evaluated for 

“reference” and “non-reference” condition in order to classify wadeable stream ecotypes and define 

biological reference conditions for each. Reference, or minimally disturbed, sites were determined based 

on BPJ. Various macroinvertebrate and fish community metrics were evaluated in order to describe their 

usefulness in detecting responses to disturbance. 

Macroinvertebrate analysis identified four distinct wadeable stream ecotypes exhibiting unique biological 

characteristics: small high-gradient mountain streams; medium-sized high gradient streams and rivers; 

warmwater moderate gradient rivers and streams; low gradient soft bottom rivers and streams. A suite of 

eight macroinvertebrate community metrics was selected for the purpose of setting threshold criteria 

based on responsiveness to disturbance and impact. The eight metrics represent a range of structural and 

functional characteristics and were evaluated to minimize information redundancy. The range of reference 

condition was described for each metric and ecotype. Threshold criteria, based on deviation from the 

reference condition, were established for each ecotype consistent with the language contained in the water 

quality standards for each classification (Figure 3-8). Uncertainties associated with each threshold are 

recognized through the establishment of threshold ranges. The eight metrics are not combined into a 

single index number, but are evaluated separately in a BPJ analysis of use support status. 

natural/

minimally

altered

highly

altered


severely


aaltleterered d

Stressor Gradient 

Biolo

gical C

o

n

dition 

Not meeting CWA 101a uses for protection & 

propagation of aquatic life 

Human Disturbanc

C

s tion; tolerant/intolerant 

forms within the range of reference 

condition. 

Class B2/3: Good - Moderate changes in 

the relative proportions of tolerant, 

intolerant, taxonomic and functional 

components. 

Class A: Excellent - Biota within the 

range of the natural condition 

Non-Support: 

Fair - Very Poor 

1 

hreshold criterion B1 

B

lass B1: Very Good - Minor changes to 

tructure and func

2 

3 

4 

5 

6 

Bio

c

o

n

dition 

Gra

die

nt Tiers 

Threshold criterion A1 

T

Threshold criterion B2/3 

iolo

gical C

o

n

ditio

n

Not meeting CWA 101a uses for protection &

propagation of aquatic life

Human Disturbance

Class B1: Very Good - Minor changes to

structure and function; tolerant/intolerant

forms within the range of reference

condition.

Class B2/3: Good - Moderate changes in

the relative proportions of tolerant,

intolerant, taxonomic and functional

components.

Class A: Excellent - Biota within the

range of the natural condition

Non-Support:

Fair - Very Poor

1

2

3

4

5

6

Bio

c

o

n

ditio

n

Gra

die

nt Tiers

Threshold criterion A1

Threshold criterion B1

Threshold criterion B2/3

FIGURE 3-8. Vermont’s designated aquatic life uses as differentiated by biological threshold criteria. 

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62 
Two fish community indices of biotic integrity differentiating between strictly coldwater and mixed water 

assemblages were developed and calibrated to the Vermont Water Quality Standard narrative thresholds 

based on deviations from the reference condition. The indices combine multiple metrics representing a 

range of structural and functional characteristics into a single index number. 

Since the BCG is continuous, it can be subdivided into any number of categories. The fish and 

macroinvertebrate criteria thresholds used by the Department were able to differentiate four categories of 

“support” status – Class A (near natural condition), high quality Class B1, general Class B2/3, and nonsupport (Figure 3-8). Common narrative descriptors – excellent, very good, good and fair-very poor were 

used to describe the thresholds. A determination of less than good was indicative of aquatic life use nonsupport. Categories of non-support (fair, poor, very poor) were not described. 

When Vermont’s new standards became effective in July 2000, all waters previously designated Class B 

were categorized as general Class B2/3 by default. The idea was to use the watershed planning process to 

propose and implement designated use reclassifications, particularly to the high quality Class B1. VtDEC 

is assembling candidate lists of waterbodies exhibiting high quality biological condition consistent with 

the Class B1 designated use. Final consideration of candidates is made via public process in order to 

ensure compatibility with local watershed plans and interests. Although no reclassifications have been 

made to date, the BCG has provided a clear visualization of the concepts of disturbance and impact, and 

this has been a useful tool in explaining the WQS to the public. 

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63 
CASE EXAMPLE 3-5. DEVELOPING BIOLOGICAL CONDITION TIERS IN GREAT BRITAIN 

In the 1980s, the Environment Agency of the United Kingdom sponsored the development of a 

nationwide monitoring and assessment program based on benthic macroinvertebrates. A four-year 

initiative, aimed at determining whether the macroinvertebrate community at a site could be predicted 

using physical and chemical features, led to the development of RIVPACS (River Invertebrate Prediction 

and Classification System). Other countries, and some states in the U.S. such as Oregon and Illinois, 

have subsequently integrated RIVPACS models into their biological assessment programs. 

Predictive models like RIVPACS base assessments on the compositional similarity between observed and 

expected biota. To create a RIVPACS model for a particular region, standard protocols are followed to 

sample the region’s biota and habitat at a network of reference sites that span the range of that region’s 

environmental conditions. Sites are then classified based on biological similarity. Next, a multivariate 

model relates environmental setting (elevation, watershed area, geology) to the biological classification – 

this is used to estimate, or predict, the probabilities of sites belonging to biologically-defined groups and 

the probabilities of capturing each taxon. The current RIVPACS model, RIVPACS IIIa (Wright 2000), 

estimates two indexes for assessment – one based on the total number of expected taxa and a second 

based on expected average tolerance of the taxa. For both indexes, the model generates a list of taxa 

expected to occur under unstressed conditions, at greater than 50% probability for a particular assessment 

site. This list is then used to estimate the site’s expected average tolerance value, and the probabilities are 

summed to generate the expected number of species. Both the number of predicted taxa that were 

actually observed and the tolerance value actually observed are divided by the expected values to obtain 

the final indexes. These indexes are compared against the model predictions to determine if the values 

are significantly different from the reference condition. Index values close to 1.0 indicate the site is 

similar to reference, and values less than 1.0 indicate deviation from reference. 

Initially, the Environment Agency created four categories for the indexes – the scoring range below the 

5th percentile of the index distribution of reference sites was divided into three equal categories, and the 

range above the 5th percentile made up the fourth. These categories, or grades, correspond to tiers of a 

BCG (Wright et al. 1994, Helmsley-Flint 2000). Review and application of the grades by regional 

biologists revealed that they did not discriminate between “good” and “very good” sites, or between 

“poor” and “very poor” sites (Helmsley-Flint 2000). Through cycles of data analysis and discussions 

with regional biologists, the Environment Agency was able to establish index thresholds for six grades, 

ranging from “very good” to “bad” (Table 3-4). The grades do not represent equal intervals of the index 

scores (Helmsley-Flint 2000). Although the British grades are determined solely by benthic 

macroinvertebrates, there is a distinct similarity between the narrative descriptions of the grades and the 

tiers of the BCG. 

Assignment of a site to a grade is based on both the tolerance and total taxa indexes (Table 3-4). The 

indexes are independently applicable, and the lower of the two index scores determines the site grade. 

For example, if the total taxa index indicates “Good” but the tolerance index indicates “Fair”, the site will 

be rated “Fair.” To achieve the status of “Very Good”, a site must have at least 85% of the expected taxa 

of an equivalent reference site and must have a tolerance index value (average score per taxon) as high as 

the expected value from a reference site. 

Through an iterative process, the British Environment Agency was able to develop scoring criteria for 

existing indexes (RIVPACS N-Taxa and RIVPACS ASPT) that corresponded to regional biologists’ 

consensus on tiers of a biological condition gradient. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 3 – August 10, 2005 

64 
TABLE 3-4. Definitions of six biological grades, developed by regional biologists of the Environment Agency in 

England and Wales (Helmsley-Flint 2000). 

1 RIVPACS Index 

Scores 

Grade Definition 

Tolerance 

Index 

(EQI ASPT) 

Taxa Index 

(EQI N-taxa) 

Grade a 

VERY 

GOOD 

The biology is similar to (or better than) that expected for an 

average and unpolluted river of this size, type and location. There 

is a high diversity of Families, usually with several species in each. 

It is rare to find a dominance of any one Family. 

� 1.0 � 0.85 

Grade b 

GOOD 

The biology shows minor differences from Grade a and falls a little 

short of that expected for an unpolluted river of this size, type and 

location. There may be a small reduction in the number of Families 

that are sensitive to pollution, and a moderate increase in the 

number of individual creatures in the Families that tolerate pollution 

(like worms and midges). This may indicate the first signs of 

organic pollution. 

� 0.90 � 0.70 

Grade c 

FAIRLY 

GOOD 

The biology is worse than that expected for an unpolluted river of 

this size, type and location. Many of the sensitive Families are 

absent or the n umber of individual creatures is reduced, and in 

many cases there is a marked rise in the numbers of individual 

creatures in the Families that tolerate pollution. 

� 0.77 � 0.55 

Grade d 

FAIR 

The biology shows big differences from that expected for an 

unpolluted river of this size, type and location. Sensitive Families 

are scarce and contain only small numbers of individual creatures. 

There may be a range of those Families that tolerate pollution and 

some of these may have high numbers of individual animals. 

� 0.65 � 0.45 

Grade e 

POOR 

The biology is restricted to animals that tolerate pollution, with 

some Families dominant in terms of the numbers of individual 

creatures. Sensitive Families will be rare or absent. 

� 0.50 � 0.30 

Grade f 

BAD 

The biology is limited to a small number of very tolerant families, 

often only worms, midge larvae, leeches, and the water hoglouse. 

These may be present in very high numbers. Even these may be 

missing if the pollution is toxic. In the very worst case there may 

be no life present in the river. 

< 0.50 < 0.30 

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and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 3 – August 10, 2005 

65 
CASE EXAMPLE 3-6. MAINE’S USE OF LINEAR DISCRIMINANT MODELS


TO ASSESS AQUATIC LIFE USE TIERS


Maine identifies three aquatic life use classes for its streams – AA/A, B, and C – and also has a 4th 

category of non-attainment (NA) for streams that do not meet minimum water quality criteria (Table 3-5). 

The Maine Department of Environmental Protection (DEP) has developed a procedure using linear 

discriminant models (LDMs) to classify samples. LDMs are multivariate predictive models that use 

biological variables to determine whether a stream meets the biological criteria for classes A, B, or C, or 

if it falls into the category of non-attainment (Davies et al. 1995). 

TABLE 3-5. Maine water quality classification system for rivers and streams, with associated biological


standards (Davies et al. 1995).


Aquatic 

Life Use 

Class Management Biological Standard 

Discriminant 

Class 

AA High quality water for recreation and 

ecological interests. No discharges or 

impoundments permitted. 

Habitat natural and free flowing. 

Aquatic life as naturally occurs. 

A 

A High quality water with limited human 

interference. Discharges restricted to 

noncontact process water or highly 

treated wastewater equal to or better 

than the receiving water. 

Impoundments allowed. 

Habitat natural. Aquatic life as 

naturally occurs. 

A and AA are 

indistinguishable 

because biota are 

“as naturally 

occurs.” 

B Good quality water. Discharge of welltreated effluent with ample dilution 

permitted. 

Habitat minimally impaired. Ambient 

water quality sufficient to support life 

stages of all indigenous aquatic 

species. Only nondetrimental changes 

in community composition allowed. 

B 

C Lowest water quality. Maintains the 

interim goals of the Federal Clean Water 

Act (fishable/swimmable). Discharge of 

well-treated effluent permitted. 

Ambient water quality sufficient to 

support life stages of all indigenous 

fish species. Change in community 

composition may occur but structure 

and function of the community must be 

maintained. 

C 

NA Not attaining 

Class C 

To calibrate the LDMs, stream biologists from Maine DEP assigned an initial set of streams to the four 

aquatic life categories: A, B, C, and NA. Assignment of samples was based on presence-absence of taxa, 

abundance of taxa, richness, community structure, and ecological theory. Four linear discriminant models 

were calibrated from the initial data set. The four models function as a two-step process to evaluate 

individual sites: 

Step 1: First stage model – Estimates the probability of a site’s membership into each of the four 

classes (4-way test) 

Step 2: Second stage models – Develop more accurate membership probabilities. Each is a twoway discriminant function, which perform better than multi-way models. There are three second 

stage models that estimate the probabilities of membership in a given class(es) versus any lower 

classes (Figure 3-9). 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 3 – August 10, 2005 

66 
First Stage Model 

(4-way test)


A vs. B vs. C vs. NA


"C or Better" Model 

(2-way test) 

A/B/C vs. NA 

"B or Better" Model 

(2-way test) 

A/B vs. C/NA 

"A" Model 

(2-way test) 

A vs. B/C/NA 

* Aquatic life use attainment decisions are based on the three 2-way tests. 

FIGURE 3-9. Series of four linear discriminant models. 

The models use 31 quantitative measures of community structure, including the Hilsenhoff Biotic Index, 

Generic Species Richness, EPT, and EP values to classify sites. In operational assessment, monitored test 

sites are run through the two-step hierarchical models and assigned to one of the four categories based on 

the probability results. Uncertainty is expressed for intermediate sites that fall between two categories. 

The assessment becomes the basis for management action if a site is rated as NA, or if its assessed 

category (B, C, or NA; the result of the LDM) is less than the site’s assigned life use class (A, B, or C). 

Thus, if a site was assigned life use class A, but assessment shows that it only meets life use class B or C 

(model assessment was B or C), then management action may be required. If a site has improved, it 

requires further evaluation as a candidate for reclassification to a higher class. 

Maine’s numeric biocriteria provide an expert system for determining attainment of aquatic life uses. The 

LDMs provide an empirical model for expert judgment, which in turn is ultimately derived from years of 

empirical observations, ecological theory, data analysis, and clearly stated aquatic life management goals. 

They establish a direct relationship between the model’s outcomes and management objectives (the 

aquatic life use classes). Therefore, broad resource goals and objectives can be directly translated to 

scientifically defensible, quantitative thresholds (Table 3-5). The relationship is immediately viable for 

management and enforcement as long as the aquatic life use classes remain the same. If the classes are 

redefined, a complete reassignment of streams and a review of the calibration procedure would be 

necessary. Details of Maine’s approach and statistical analysis procedures are in Shelton and Blocksom 

(2004) and Davies et al. (unpublished manuscript). 

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67 
CASE EXAMPLE 3-7. NEW JERSEY QUANTITATIVE RULE DEVELOPMENT 

After describing the BCG for high gradient streams of New Jersey (Table 3-2), the New Jersey DEP 

workgroup developed decision rules for assigning sites to the tiers (Table 3-6). Biologists in the New 

Jersey workgroup generally preferred to use taxa richness as the first and most important criterion for 

determining site tier assignments. Thus, the number of highly sensitive taxa was most often used to 

distinguish between Tier 2 and Tier 3 sites. Tier 2 should have several highly sensitive taxa (Attribute 2), 

but their richness may be reduced in Tier 3. For example, a preliminary rule for Tier 2 was that highly 

sensitive taxa richness (Attribute 2 taxa richness) should be at least 50% of the richness of any other 

attribute group (3 through 5). Similarly, the difference between Tiers 3 and 4 was viewed primarily as 

changes in the sum of richness of highly sensitive and sensitive-common taxa, such that in Tier 3 sites, 

the sum of taxa richness of the two sensitive groups should be at least 50% of the sum of richness of the 

two more tolerant groups. 

Although taxa richness was generally the first criterion for the higher tiers (Tiers 2 and 3), relative 

abundance could override richness in extreme cases: Tier 3 was required to have more than 25% relative 

abundance of the two sensitive groups combined, and severely reduced abundance (< 50 organisms in the 

total sample, after QA determined that the sample was properly collected and processed) can downgrade a 

site to Tier 6 in combination with signals of potential toxicity. 

Tier 5 was discriminated from Tier 4 by a significant reduction of sensitive taxa (Attributes 2 and 3) to 

the point where they are merely incidental if present and are not a functional part of the community. 

Approximately 10% relative abundance was deemed a functional part of the community. Tier 6 was 

discriminated from Tier 5 by increasing loss of all taxa and dominance by tolerant taxa (Attribute 5). Tier 

6 could also be indicated by extreme low numbers combined with signals of toxicity (complete absence of 

mayflies, presence of Cricotopus), without other Attribute 5 taxa. 

The rules are applied as a downward cascade: for a site to be rated as Tier 2 (the highest defined tier for 

New Jersey), all attributes must meet the Tier 2 condition (Table 3-6). A Tier 3 rating requires one or 

more failures of Tier 2 rules, but the site must meet all remaining Tier 3 rules. These rules cascade to 

Tier 5. Tier 6 has special rules of exceedingly low taxa richness, or abundance, or complete dominance 

of tolerant taxa (Attribute 5). Tier 5 consists of sites that fail Tier 4 conditions, yet also fail Tier 6. 

TABLE 3-6. Proposed decision rules for New Jersey high gradient streams. 

Attributes Tiers 

1 2 3 4 5 6 

All Taxa Low richness 

(<10 taxa) 

Low abundance 

(<50 individuals) 

I Sensitive, (No rules 

regionally determined for 

endemic taxa Attribute 1) 

II Highly Taxa >= 50% of Taxa >=2 May be absent May be absent May be absent 

sensitive taxa any other (" 2 taxa) 

Attribute (" 10)% 

III Sensitive & 

common taxa 

Taxa (2 + 3) >= 

Taxa (4 + 5) 

(" 2 taxa) 

Taxa (2 + 3) > 

50% of Taxa (4 

+ 5) 

(" 10%) 

Taxa (2 + 3) � 3 

(" 2 taxa) 

Abund (2+3) 

>10% 

May be absent; 

abund (2 + 3) 

<10% (or less 

than 3 taxa) ("

5%) 

May be absent 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 3 – August 10, 2005 

68 
TABLE 3-6. Proposed decision rules for New Jersey high gradient streams. 

Attributes Tiers 

1 2 3 4 5 6 

IV Taxa of Taxa (4) ~= 

intermediate Taxa (5) 

tolerance Abund (4) >= 

Abund (5) 

V Tolerant 

taxa 

<20% of total 

abundance ("

5%) 

(if tiers 2 and 3 

<50% of total 

abundance 

(" 10%) 

High density, 

abundance of 

Attributes 4, 5 

Taxa (5) > Taxa 

(4) (" 2 taxa) 

Abund (5) > 

Abund (4) 

ambiguous) 

V.a. Indicator Tolerant Tolerant Hydropsych. Mayflies absent 

taxa Hydropsych. <= Hydropsych. <= may dominate Tubificidae 

10% abundance 50% abundance Tubificidae not dominate Attrib 5 

(" 5%) (" 10)% dominant 

Combinatorial 

rules (RxC 

format) 

(II,2) and 

(III,2) and 

(IV,2) and 

(V.a,2) 

(not (II,2) or 

not (III,2)) and 

(II,3) and 

(III,3) and 

(Not (II,3) or 

Not (III,3)) and 

(III,4) 

Not (III,4) and 

Not (All,6) and 

Not (V,6) 

(All,6) or 

(V,6) 

((V,3) or (V.a,3)) 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 3 – August 10, 2005 

69 
DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 3 – August 10, 2005 

70 
CHAPTER 4. THE X-AXIS: A GENERALIZED STRESSOR GRADIENT 

The x-axis of the Biological Condition Gradient Model (BCG) illustrates how increasing levels of 

stressors in aquatic ecosystems change biological condition. This chapter presents a conceptual model 

that helps characterize stressor gradients by focusing on the progression from sources (changes in key 

environmental processes) to stressors and ultimately to their effects on biotic condition (Figure 4-1). The 

model also looks at the mechanisms through which these biotic components are affected. The stressor 

gradient model can be used to organize data and information on watershed characteristics, hydrologic 

modifications and stressors to thoroughly evaluate these relationships. This information will provide a 

foundation for States and Tribes to use the BCG to address both current conditions and ecological 

potential of their waterbodies, develop realistic restoration options for impaired waters, and communicate 

this information to the public. 

4.1 The scientific foundation for the stressor gradient 

Stressors affect biological assemblages and ecosystem processes both directly and indirectly, including 

altering metabolic pathways, energy availability and behavior of the organisms (Karr et al. 1986, Adams 

1990, Poff et al. 1997). Historically, point source pollution and in-stream hydrological modifications 

were the dominant alterations (see 4.2.1) to fresh waters. While these issues continue today, water quality 

management now faces a wider variety of changes stemming from mining, forest harvest, agriculture, 

urbanization, industry, and even recreation (Richter et al. 1997, Bryce et al. 1999). In addition, noncontaminant related changes to aquatic ecosystem factors (see text box below) commonly impact 

biological conditions (Figure 1-3) and can also influence other stressors (Karr and Dudley 1981, Karr et 

al. 1986, Poff et al. 1997, Slivitzky 2001). Consideration of these factors and their interactions in water 

quality management can lead to greater improvements to biological condition than a focus on 

contaminants alone (Karr et al 1986). 

The influence of each factor on biological 1.Chemical factors (e.g., hardness, nutrients, toxic 

condition in specific waterbodies can be difficult compounds)


to evaluate and quantify because each of these 2.Flow regime (including the timing and amount of


factors reflect both indirect and direct forces. water in the channel; diversions)


Flow regime, for example, affects biological 3.Biotic factors (competition, predation, disease,


condition and the other in-stream factors (e.g., invading species, etc.)


habitat structure, water quality) (Poff et al. 1997). 4.Energy source (photosynthesis, inputs from land, etc.)


Altered stream flows are associated with poor 5.Habitat structure (channel shape and features,


channel habitats, erosion, bank instability, and siltation, etc.) (from Karr et al. 1986, see Figure 1-3)


lower base flows (Poff et al. 1997). Species


distributions, abundances, and competitive interactions all rely on natural flow regimes (Poff and Allan


1995, Greenburg et al. 1996, Reeves et al. 1996, Poff et al. 1997). Stream ecosystem structure and


function (Vannote et al. 1980) and the riverscape concept (Ward 1998, Fausch et al. 2002) integrate the


influences of all stressors. These individual and collective influences, represented by the BCG model’s x-


axis – the Generalized Stressor Gradient (GSG) – drive the biological condition of streams and reveal the


need for a more holistic approach to stream monitoring and management. Because of the dynamic nature


of aquatic ecosystems, however, all of these factors are in a state of constant flux. The natural range of


conditions that native biota are adapted to may be narrow, wide, or seasonally variable, depending on the


climate, topography and ecoregion in which the system occurs. A simplified model, therefore, is needed


to help organize environmental factors and their relationships to stressors and biological responses.


DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 

71 
4.2 The conceptual model for a Generalized Stressor Gradient 

Building upon the Karr conceptual model, the Generalized Stressor Axis model characterizes the 

environmental processes and mechanisms that generate stressors which lead to biological responses 

within waterbodies (Figure 4-1). An event or activity that alters the aquatic system is called a 

disturbance. Ecosystems normally have some level of disturbances that characteristically occur within a 

range of natural variability. Disturbances beyond this range, however, can exert pressure

1 

upon an 

aquatic system by altering fundamental environmental processes and ultimately generating stressors. 

Stressors are physical, chemical or biological factors that cause an adverse response from aquatic biota 

(U.S. EPA 2000b). The term “pressure” conceptually and mechanistically links larger scale landscape 

and hydrological disturbances with the ecological processes that are ultimately changed, leading to 

pressure(s) being “felt” by the aquatic biota. Stressors are what link pressures to effects on biota, via 

exposure mechanisms. A stressor, therefore, can be traced back to its source or tracked forward to the 

biological response, via a causal pathway (Figure 4-1). For example, destabilized stream banks due to 

removal of riparian plants could be the source of excess fine sediment to a stream. Erosion by high flows 

is the mechanism by which the excess fine sediments are generated, and the resulting in-stream siltation is 

the stressor. Smothering of bottom substrate habitat and organism gills by these fine sediments are two 

mechanisms by which biota are exposed and adversely affected. Invertebrate mortality and fish 

emigration could be some of the environmental outcomes or changes in biotic condition. 

Source/activity 

Mechanism 

Unstable Banks 

Erosion of Fine 

Sediments 

Pressure

Rip

arian 

Tre

e

R

e

m

o

v

al 

Stressor In-stream Siltation 

Mechanism 

Smothering of 

larger substrate 

and gills 

Response Fish and Invertebrate 

(Biological Condition) mortality and emigration 

(Biological Condition) 

FIGURE 4-1. Conceptual model illustrating the linkages between pressure and biological 

condition. The specific stressor(s) and their intensity (the BCG x-axis) are created via 

pressure(s) acting through specific mechanisms. An example for each step of the model is 

also shown. 

The effects of stressors on biota, however, depend on the magnitude, frequency, and duration of exposure 

to the stressors. Developing a BCG for a given system characterizes the general relationship between its 

combined stressors (the model’s x-axis) and its overall biological condition (the y-axis). Multiple 

stressors are usually present, and thus the stressor x-axis of the BCG seeks to represent their cumulative 

1 The use of the word pressure in this context has a well-established history in the European environmental 

literature. Pressure is a term originally used by the European Union in its Water Framework Directive (OECD 

1993). SOLEC (State of the Lakes Ecosystem Conference) also used the term pressure and defined it to be the 

outcomes of human activities that have the potential to cause environmental effects (Shear et al. 2005). 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 

72 
influence as a Generalized Stressor Gradient (GSG), much as the y-axis generalizes biological 

condition. 

4.2.1 How the model supports development of a GSG 

The conceptual model provides a theoretical basis for relating single or multiple stressors to biotic 

responses and condition. This concept is taken further in developing a generalized stressor gradient, 

which, as the BCG’s x-axis, is used in relating cumulative stressors to cumulative biotic effects. The 

factors that drive biological condition (Figure 1-3) and how condition is affected by a range of stressor 

intensities are used in defining the gradient. Two example GSGs are provided below. 

Tables 4-1A and 4-1B outline example scenarios for humid-temperate (Table 4-1A) and arid (Table 4-1B) 

regions of the U.S. under differing levels of stressors. The high, medium and no/low stressor levels are 

used only to describe relative differences in magnitude and are not formal categories for classifying 

stressors. The five factors from Figure 1-3 were modified to six factors by separating toxics (e.g., 

copper, cadmium, mercury) from conventional chemical pollutants (e.g., nitrates, phosphorous). 

When stressors are absent or low, natural or near-natural conditions of the aquatic ecosystem prevail. 

However, as stressors increase, one or more of the six factors can deviate from natural conditions. In 

humid temperate regions, for example, the loss of a watershed’s forested landscape generally increases instream stressors by affecting flow, soil erosion, water quality and aquatic habitat structure. In arid 

regions, loss of riparian vegetation and cryptogamic crusts (a tightly bound mesh of lichen, algae and 

lower plants that prevent erosion and provide a hospitable environment for germinating plants) has the 

same kind of effects. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 

73 
DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 

T

A

B

LE 

4-1. E

x

a

m

ple scen

arios for h

u

mid-tem

perate (A) a

nd 

arid (B) regio

ns of the US 

u

n

der three levels of stressors. T

he stre

to 

describe relative differences in 

m

a

g

nitu

de a

nd 

are n

ot form

al categ

ories. K

arr’s five factors (Fig

ure 1-3) were m

o

dified to s

to

xics from co

n

ventio

n

al chemical p

olluta

nts. T

hese scen

arios were written 

prim

arily from the reach-scale perspective, b

oth loc

factors, h

o

wever, are im

p

orta

nt for determining the co

n

dition 

of strea

ms. 

(A) H

u

mid-tem

perate Scen

ario 

Stressor Level Flow 

Regime Ha

bitat Structure Water Q

u

ality 

Toxics & 

Bioen

gineered 

Chemicals E

nergy 

Sourc

N

o/L

ow 

As naturally occurs, 

includes floods & low 

flows at natural rates 

and extent; High 

connectivity with 

ground water 

maintained 

As naturally occurs, varies with size & 

slope, typically large 

wood abundant, coarse substrate, overhanging 

vegetation, and 

undercut banks are present 

As naturally occurs or only 

minimal increase in nutrients & 

sediments; no point sources, includes flood turbidity & 

sum

mer warming; usually cool 

or cold & dissolved oxygen 

(D

O) saturated; sediments & 

nutrients low & pulsed 

seasonally 

As naturally occur, typically 

rare and no toxics in amounts 

toxic to aquatic biota 

As naturally occurs, varies with channel 

width, typically 

dominated by 

riparian woody 

vegetation, 

unless naturally autochthonous 

Medium 

Flashier, increased 

drought frequency; 

some water withdrawals; low to 

moderate wetland 

drainage; dams may reduce annual floods and droughts 

Reduced L

WD in 

channel; fines slightly 

to moderately more abundant than expected 

from stream power; 

pool substrate 

moderately embedded; 

reduced undercut banks, 

overhanging vegetation, 

and habitat complexity; 

some loss of pool 

volume and pool/riffle 

proportions may be 

altered. 

Enriched, turbidity may 

increase, moderate diel warming, small DO sags may 

occur but these rarely violate 

criteria; point sources minor or 

if they exist are treated; fish 

kills rare 

Toxics rarely in amounts toxic to aquatic biota, but Hg 

may be of chronic concern to 

top piscivores due to 

bioaccumulation; sediment contamination may be detectable but not causing 

effects in biota. 

Autochthonous 

production higher than expected in low

order streams; filamentous alg

may be present 

High 

Flashy; highly altered 

drought/flood regime; 

mostly or entirely human controlled in 

urban areas; water 

withdrawals & 

impoundments if 

present, fundamentally alter the nature of the 

ecosystem 

Simplified or manmade; 

wood, undercut banks 

& overhanging 

vegetation absent or 

non-functioning; rubble 

& trash com

mon, 

substrates highly 

armored or embedded. 

Dam impoundments 

often present. 

Highly enriched, turbid, warm; 

large diel DO & temperature 

changes; chemical and point 

sources inadequately treated or 

overwhelmed by untreated diffuse toxic pollution. Dams 

when present produce altered 

thermal regime and nutrient dynamics 

Fish kills may be com

mon in 

low sum

mer flows; toxics 

may be present in chronic or acutely toxic amounts; 

bioengineered chemicals can 

affect growth & reproduction; 

high to extreme sediment 

contamination; fish 

consumption advisories serious 

Mostly autochthonous imported fine particulate 

organic matter 

dissolved organ

matter; may be 

too turbid for 

filamentous alg

74 
T

A

B

LE 

4-1. (B) Arid 

Scen

ario 

Stressor Level Flow 

Regime Ha

bitat Structure Water Q

u

ality 

Toxics & 

Bioen

gineered 

Chemicals E

nergy 

Sourc

N

o/L

ow 

As naturally occurs or only slightly altered, 

includes floods & low 

flows at 10-20 & 20-50 yr intervals, respectively; 

floods flashy; annual 

scouring flows; high 

connectivity with ground 

water. 

As naturally occurs, varies with geology, 

substrate, flow, size, 

slope, soil, latitude, 

elevation & orography; 

relatively stable riparian 

vegetation, L

WD in 

flats. 

As naturally occurs with 

only minimal increase in 

nutrients & sediments, includes flood turbidity & 

sum

mer warming; depending 

on soils, may be naturally saline or alkaline; enriched 

where beaver present; ash 

from 5-20 year fire cycles. 

No point sources 

As naturally occur, typically 

rare, but may be natural 

sources of arsenic & 

selenium. No toxics in 

amounts toxic to aquatic 

biota 

As naturally occurs, varies with channel 

width, typically 

dominated by 

riparian woody 

vegetation in 

small unconstrained channels; heterotrophic & 

autochthonous iwider systems 

Medium 

Altered, increasingly 

flashy; increased drought 

frequency; some water 

withdrawals and wetland 

drainage; flow 

alterations mitigated to 

some extent by 

environmental flow 

releases. 

Minor amounts of 

incision, widening or 

shallowing; reduced 

L

WD in channel; fines 

greater than expected 

from stream power; bed 

coarsening from 

upstream dams; pool 

substrate increasingly 

embedded; reduced aquatic macrophytes, 

undercut banks, & 

overhanging vegetation. 

Enriched, warmer & saltier, 

turbid at low flows, small 

DO sags; point sources if present with treatment. No 

fish kills 

No acute toxicity is 

observed, but chronic 

toxicity is possible due to 

bioaccumulation. Fish 

consumption advisories 

likely for sensitive 

populations 

Mostly allochthonous, 

but increasingly 

autochthonous inarrow streams; 

wide streams 

heterotrophic or 

autochthonous 

with increasing 

amounts of filamentous 

algae. 

High 

Human controlled; large 

inter-basin transfers; 

ground water overdrawn; 

effluent dominated 

streams below cities. 

Highly altered 

drought/flood regime; 

droughts yield more dry 

channels; withdrawals & 

dams severely alter 

nature of the ecosystem. 

Largely manmade; little 

or no L

W

D, undercut 

banks & overhanging 

vegetation; highly 

sedimented; construction rubble & 

trash com

mon. 

Highly enriched, turbid, 

warm; large diel DO 

changes; most point sources 

inadequately treated or 

overwhelmed by untreated diffuse toxic pollution; dams 

produce altered thermal 

regime. 

Fish kills in low sum

mer 

flows or after rains; toxics 

seasonally or always present in acutely toxic amounts; 

mine spills; bioengineered 

chemicals affect growth & 

reproduction. 

Mostly autochthonous oimported fine particulate or 

dissolved organi

matter; 

filamentous alga

com

mon if 

turbidity allows 

it. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 

75 
4.3 How the BCG model and management actions are linked 

Pressure, as used in this document, applies to the environmental processes that can be altered by certain 

activities and the mechanisms from those activities that generate stressors. Many landscape altering 

activities can be quantified with such measures as population density, proportion of land devoted to 

agriculture, total miles of roadway, or quantities of water used /released. These activities, however, may 

or may not generate stressors. Actions can be taken that insulate stream processes from the 

environmental pressure of certain activities, helping to maintain or restore the ecological potential of an 

aquatic system. 

Controls and Best Management Practices (BMPs) are management actions designed to mitigate or reduce 

the levels and effects of stressors that adversely alter stream ecosystem function. BMPs can function in a 

number of ways: they may reduce the stressors being generated by sources, reduce the exposure of biota 

to stressors, or increase the resistance of an aquatic ecosystem to adverse changes. For example, 

urbanization without controlling for the effects of added impervious surface is a pressure that often results 

in reduced biological condition. The typical alteration of water flow (such as more frequent flooding due 

to increased runoff) causes stressors. The mechanism for flow alteration is the creation of large expanses 

of impervious surfaces, characteristic of most cities. Impervious surface speeds up the flow of water over 

the land during rain events often resulting in more frequent and more intense floods. Constructing 

retention ponds to store run-off water is a control measure that doesn’t alter the pressure of urbanization, 

but may reduce the stressors acting on the stream system. Mechanistic processes operate between 

pressures and stressors, and between stressors and biological response (Figure 4-1). Understanding these 

mechanisms, and how they operate, is the key to identifying the likely effect of a particular management 

action and its likelihood to produce the desired response in biological condition. In the retention ponds 

example above, the pressure (urbanization) and mechanism for stressor generation (excessive surface runoff) still exist, but their influence on in-stream stressors has been neutralized by a management action, and 

therefore the exposure mechanism influencing the biological community was reduced or eliminated. 

The basis of the BCG model is that increased pressures can generate increased stressors, and in turn, 

increased stressors are associated with decreasing biological condition (Figure 4-2A through D). Systems 

that are minimally affected by stressors exhibit natural condition (Tables 4-1A and 4-1B). Human 

activities may exert pressure and generate stressors on aquatic systems, resulting in changes from the 

natural state. Typically, the stressors on aquatic systems increase as pressures increase (Figure 4-2A 

dashed line). Effective management practices, however, can alter the effects of pressures and reduce 

stressors. The solid, curved line in Figure 4-2B represents this theoretical relationship graphically. With 

effective controls and/or BMPs, a given amount of pressure (vertical fine dashed arrow rising from the 

pressure axis) results in a lower stressor level (where the dashed arrow intersects the stressor axis). Figure 

4-2B illustrates the influence of effective management in changing the pressure/stressor relationship in 

ways that will subsequently improve the biological condition. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 76 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 
C

Stressors High Low 

A B

Stressors 

No BMP 

BMP 

High Low 

Excellent Biol. Condition Poor Excellent Biol. Condition Poor 

Pressure Pressure 

Low High Low High 

Excellent Excellent 

Biol. Condition 

Stressors Low 

Low High 

High 

Pressure 

Low High 

Pressure Biol. Condition

No BMP 

BMP 

Stressors Low High 

D

Poor Poor 

FIGURE 4-2. Relationship between pressure, stressors, and biological response. 

Figure 4-2C is a 90 degrees clockwise rotation of Figure 4-2A. Stressors (which are shown to increase in 

response to increasing pressure in Figure 4-2A) are now on the x-axis. Biological condition is shown as 

the response variable on the y-axis. This represents the biological condition-stressor relationship 

developed in Chapter 1. In this example, the moderate-high effect of the stressors (dashed arrow rising 

from the stressor axis) results in poor biological condition (the point where the dashed arrow intersects the 

biological condition axis). 

Figure 4-2D shows Figure 4-2B rotated 90 degrees clockwise. As in Figure 4-2C, stressors are on the xaxis, and biological condition is shown as the response variable on the y-axis. The effect of low levels of 

stressors (dashed arrow rising from the stressors axis in Figure 4-2D) results in near excellent biological 

condition (where the dashed arrow intersects the biological condition axis). The pressure-stressor 

relationship has been shaded out. But it reminds us how, together, pressure and management actions (i.e., 

permit limits, BMPs, channel restructuring) can determine stressor levels, and ultimately, the condition of 

the biota. The specific effects of stressors on biological responses will depend on the type, magnitude, 

duration, and frequency with which the stressor occurs. These stressor attributes are, in turn, a result of 

the cumulative pressures exerted on the ecosystem and relevant management decisions to mitigate these 

pressures. 

Different types of disturbances can exert pressure on an ecosystem through altering fundamental 

processes such as water flow, transport of materials, watershed/riparian structural dynamics, channel 

structural dynamics and biological activities. For example, dams and impoundments alter flow, natural 

biological activities and material transport by creating lake conditions in a stream environment, and 

creating barriers to fish movements and migration. Sediment, nutrient and organic matter transport are all 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 77 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 
reduced downstream of impoundments and water quality attributes such as natural temperature 

fluctuations and dissolved oxygen are often altered by dams. When severe enough, these alterations act as 

stressors to the downstream community. 

Tools can be developed that characterize the relationships among pressures, altered processes, the 

stressors they generate, and the resulting biological responses. Information from pressure and stressor 

indicators provides insight on how changes in these fundamental processes may be affecting the 

biological condition of water resources (Table 4-2). Understanding how specific stressors are generated 

and the influence of specific stressors on biological condition, provides the underpinnings for the BCG’s 

stressor axis. Further, it reveals potential opportunities for management actions to reduce stressors and 

counteract the alteration of fundamental processes. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 78 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 
DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005

T

A

B

LE 

4-2. F

u

n

d

a

mental en

viro

n

mental processes ty

pically 

altered 

by 

disturb

a

nces th

at ultim

ately 

generate stressors. F

or ea

mech

a

nisms th

at link 

pressures (pressure in

dicators) to stressors a

nd ty

pical stressor in

dicators for the m

ajor en

viro

n

mental f

listed. M

a

n

a

gement Actio

ns (in

dicated 

by the grey 

b

ar place h

older), w

hen effective, will alter the effect of the pressures, ther

or all of the mech

a

nism for increasing stressors. 

Process 

Pressure 

In

dicators 

(potential for stress) 

Mech

a

nism 

for Stressor 

Pro

d

uction 

Stressor In

dicators 

for each 

M

ajor F

actor C

Flow alteration 

-% im

pervious area 

-road 

density 

-% 

urban 

-pop

ulation-density 

-storm sewer miles 

-# 

diversions 

-# of dams 

-point source 

dischargers 

-acceleration of water flow 

-red

uced grou

n

d

water infiltration 

-increased 

peak flow 

-more freq

uent elevated events 

-red

uced 

base flow 

-suspen

ded fines d

uring floods 

increased su

bseq

uent deposition 

-increased incision and changes to 

chan

nel structure d

ue to increased 

power d

uring flood 

Management Actions (BMPs /Controls)

Flow regime 

-changes in flood freq

uency 

-changes in 

base flow 

-changes in 

drought freq

uency 

-changes in stream 

power 

Alteration of flo

the rate, volu

me 

discharge 

Alteration of wa

materials transp

structure; the co

water q

uality, to

sources (See Ta

Alterations of ha

fish life historie

flow regimes lea

rheop

hils and 

no

lithopelagop

hils 

residents, gener

Habitat Structure 

-increased fines 

-increased armouring 

of su

bstrate 

Water Q

uality 

no 

direct in

dicators 

Toxics no 

direct in

dicators 

E

nergy Source 

no 

direct in

dicators 

Biotic Interactions 

-lose certain fish life histories 

79 
T

A

B

LE 

4-2. F

u

n

d

a

mental en

viro

n

mental processes ty

pically 

altered 

by 

disturb

a

nces th

at ultim

ately 

generate stressors. 

Process 

Pressure 

In

dicators 

(potential for stress) 

Mech

a

nism 

for Stressor 

Pro

d

uction 

Stressor In

dicators 

for each 

M

ajor F

actor 

Alteration 

of materials 

transported 

-point source dischargers 

and 

discharge constituent 

levels 

-km of riparian 

b

uffers 

-% im

pervious surfaces 

-road 

density 

-row crops 

-pop

ulation-density 

-atmosp

heric deposition 

-C

A

F

OS 

-k

m2 of tile drains 

-non-point sources 

-logging 

-# 

mines 

-# septic systems 

-fertilizer use 

-irrigation 

-# 

q

uarries 

-erosion of surface solutes, 

sediments and 

warmer water 

-increased 

discharge of 

chemicals from 

point sources 

-increased algal biomass 

results in greater daytime 

p

hotosy

nthesis and 

night-time 

respiration 

-increased 

material in

p

ut ad

ds 

carbon and 

n

utrients that 

increase biological activity 

Management Actions (BMPs /Controls) 

Flow regime 

See above 

Sediment de

complexity a

floods, remo

materials can 

and 

bioaccu

m

food 

web 

Algal growth 

increased 

n

u

to 

high turbi

changes will 

fu

nctional gr

more filterer

suspen

ded o

grazers if alt

transport are 

Habitat Structure 

See above 

Water Q

uality 

-altered 

n

utrient 

concentrations 

-altered 

TSS 

-altered 

T

DS 

-altered temperature 

-altered turbidity 

-increased coliform 

Toxics -increased contaminants in fish 

-increased 

pesticides 

-increased 

bioaccu

m

ulative 

organics 

-increased 

metals in 

water and 

sediments 

E

nergy Source 

-suspen

ded algae could increase or 

decrease 

Biotic Interactions 

-changes in in

vertebrate 

fu

nctional grou

ps to 

more filterers 

or grazers -sensitive species diminished; % 

tolerant species increased 

-algal com

m

u

nity changes 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005

80 
T

A

B

LE 

4-2. F

u

n

d

a

mental en

viro

n

mental processes ty

pically 

altered 

by 

disturb

a

nces th

at ultim

ately 

generate stressors. 

Process 

Pressure 

In

dicators 

(potential for stress) 

Mech

a

nism 

for Stressor 

Pro

d

uction 

Stressor In

dicators 

for each 

M

ajor F

actor C

C

hanges 

to chan

nel 

structure 

-km chan

nelized 

-# 

dams 

-# culverts 

-density of road 

crossings 

-valley fills 

-diversions 

-levees 

-ban

k-stabilization 

-riprap/ Concrete 

-flood

plain losses 

-snagging of L

WD 

-flow alteration 

-solute sediment transport 

-direct engineering activities 

Management Actions (BMPs /Controls) 

Flow regime 

-changes in 

mean 

velocity 

-changes in 

discharge 

Alteration of n

and 

depth alter

flow of energy 

transport both 

longitu

dinally 

red

uces habitat 

therefore red

uc

diversity. 

Habitat Structure 

-red

uctions in 

n

u

mber of habitat 

ty

pes 

-red

uced 

pool depth 

-red

uced su

bstrate heterogeneity 

-increased embed

ded

ness 

-changes in 

width: depth ratio 

-red

uced 

n

u

mber of snags 

-red

uced 

woody 

debris 

-red

uced off chan

nel habitat 

(inclu

ding 

braiding in

dex) 

-red

uced flood 

plain con

nectivity, 

bank angle/stability 

Water Q

uality 

no 

direct in

dicators 

Toxics no 

direct in

dicators 

E

nergy Source 

-autochthonous allochthonous shift Biotic Interactions 

-red

uced 

pool d

welling organisms 

-loss of specialized insectivores 

-blocked 

migrations 

-red

uced spaw

ning 

habitat 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005

81 
T

A

B

LE 

4-2. F

u

n

d

a

mental en

viro

n

mental processes ty

pically 

altered 

by 

disturb

a

nces th

at ultim

ately 

generate stressors. 

Process 

Pressure 

In

dicators 

(potential for stress) 

Mech

a

nism 

for Stressor 

Pro

d

uction 

Stressor In

dicators 

for each 

M

ajor F

actor 

C

hanges 

to watershed/ 

riparian 

structure 

-% of area developed 

-# trap

ping 

permits 

-levees 

-tile n

u

mberdrains/ditches 

-km of streamside roads 

-surface area of off stream 

pon

ds or 

wetlan

ds 

-valley 

bottom grazing 

-riparian 

width 

-riparian contin

uity 

-aggregate mining 

-devegetation 

-fragmentation 

-lan

dscape alterations 

-clearing of vegetation 

-paving surfaces 

-b

uilding structures 

-agricultural practices 

-draining or filling 

wetlan

ds 

-riparian 

disturbance or 

removal 

-increased algal biomass 

results in greater daytime 

p

hotosy

nthesis and 

night-time 

respiration 

-increased 

material in

p

ut ad

ds 

carbon and 

n

utrients that 

increase biological activity 

Management Actions (BMPs /Controls) 

Flow regime 

-changes in flood severity and response 

time 

Watershe

vegetatio

assimilati

flooding 

and 

n

utrie

periods; t

n

ursery 

h

maintain 

Habitat Structure 

-red

uctions in amou

nt of woody 

debris 

-loss of riparian trees 

-red

uced riparian structural complexity 

-red

uced off chan

nel habitat (inclu

ding 

braiding in

dex) 

-red

uced flood 

plain con

nectivity 

-increased riparian fragmentation 

Water Q

uality 

-increased fine 

-increased sediments 

-increased 

n

utrients 

-increased ions 

Toxics no 

direct in

dicators 

E

nergy Source 

-P/R changes 

-increased algal contrib

utions; 

-shift from allochthonous toward 

autochthonous 

Biotic Interactions 

-loss of sensitive species 

-ad

dition of intermediate species and total 

species 

-changes in in

vertebrate fu

nctional grou

ps 

to 

more filterers or grazers 

-algal com

m

u

nity changes 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005

82 
T

A

B

LE 

4-2. F

u

n

d

a

mental en

viro

n

mental processes ty

pically 

altered 

by 

disturb

a

nces th

at ultim

ately 

generate stressors.

C

o

m

ments 

Loss of species from in

vasives

and stocking 

practices 

Stressor In

dicators

for each

M

ajor F

actor 

Flow regime

-macrop

h

ytes (decreases-> accelerate

flow; increases->red

uce flow)

Ha

bitat Structure

-macrop

h

ytes/algalmats alter su

bstrate

Water Q

uality

-increased 

B

O

D

Toxicsno 

direct in

dicators

E

nergy Source

no 

direct in

dicators 

Biotic Interactions

-NIS (native gamefish 

decline, hatchery

fish increase)

-native fish/benthos and riparian

vegetation and 

birds increasingly replaced

by aliens

-sensitive specialists replaced 

by tolerant

generalists (birds, fish, in

vertebrates,

plants)

-increased fish 

diseases and anomalies

-riparian 

vegetation 

may 

be eliminated 

) sl ort noC/ s P MB( s noit c At ne megana M

Mech

a

nism

for Stressor

Pro

d

uction 

-stocking 

programs

-foraging 

by in

vasive

species (grazing, predation)

-habitat modification 

b

y

in

vasive plants and fish 

Pressure

In

dicators

(potential for stress) 

-# 

non-in

digenous

in

vasive species (NIS)

-# fish stocked (species

in

divid

uals)

-baitfish sales

-fishing licenses

-creel census results

-# 

G

uide licenses 

Process 

C

hanges

inbiological

activity 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 

83 
Temporal Scale

4.3.1 Additional considerations for the stressor axis 

The concepts of spatial and temporal scale are critical issues in adequately defining a stressor axis. 

Stressors may be introduced through diffuse or point sources delivered from upstream in the channel or 

watershed, or laterally from riparian, floodplain or upland sources. Pollutants can also be delivered 

through atmospheric sources from above, or below from groundwater sources. Activities in the watershed 

or along the waterbody corridor will influence the connectivity and integrity of the water resource. 

Stressors are expressed over temporal and spatial scales ranging from a one-time, localized event to 

chronic exposures occurring continuously over vast landscapes. Pressures, stressors, and responses 

operate at different spatial and temporal scales (Figure 4-3). These are not independent of one another in 

either space or time; therefore, consideration of multiple pressures is essential. An additional 

consideration is that any given pressure creates multiple stressors, which in turn affect biological 

condition. The steady accumulation of small pressures in watersheds results in “cumulative impacts,” 

which present added challenges for characterizing, evaluating, and managing stressors. 

Water Regulation 100yr 

10yr 

year 

month 

days 

Climate change; 

Acidification; 

Evolutionary 

Land conversion; processes 

Non-native species; 

Regional Water 

Quality 

Point 

Sources; 

Decomposition 

Point sources; 

Invertebrate 

communities 

Silviculture 

Microbial 

Hurricane; 

production Flooding 

Fish 

communities 

Primary 

production 

and Diversions 

1m 1km 100km 1000km 10,000km 100,000km 

Spatial Scale 

FIGURE 4-3. Perspective of scale for pressure-stressor-response variables (modified from Richards, 

C. and L.B. Johnson. 1998. Landscape perspectives on ecological risk assessment. In Risk Assessment: 

Logic and Measurement, M.C. Newman and C. Strojan (eds.). Ann Arbor Press.). 

The complexity of the relationships between biological condition and stressors at various spatial and 

temporal scales, underscores the importance of using sound information to identify and link these 

stressors back to the pressures that cause them. To a large degree, this is the critical step in gaining 

stakeholder support for restoration and protection actions as well as for changes in activities or behaviors. 

As discussed earlier, fine sediment is commonly identified as a stressor across the United States because 

of the smothering of important habitat. Identifying the relative contributions of various sources of these 

sediments is more challenging (e.g., bank erosion, upland erosion, spatial sources), but also critical to 

remediation efforts. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 84 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 
4.4 How a GSG can be developed and calibrated 

Developing and calibrating a stressor gradient must be based on appropriately classifying aquatic 

resources and establishing reference conditions or other scientifically defensible approaches. 

Classification (e.g., biogeographic regions, basins, biological considerations) is a critical first step so that 

the temporal and spatial scales of the dominant stressor categories and sources can be addressed (Herlihy 

et al. in press, VanSickle and Hughes 2000, McCormick et al. 2000, Waite et al. 2000). Of equal 

importance is establishing the appropriate reference condition for a particular area (Hughes 1985, 1994; 

Hughes et al. 1986; Moss et al. 1987; Stoddard et al. in press), because that is the benchmark against 

which areas to be evaluated will be compared (as discussed in BCG Section 3.1.1). 

Like the biological condition axis, the stressor axis is anchored in the natural, or undisturbed or minimally 

disturbed, condition (i.e., Tier 1 BCG). However, reference may represent minimally-disturbed (i.e., 

nearly natural) or least-disturbed (i.e., best available) conditions depending on the level of disturbance 

that exists across the geographic area of interest (Stoddard et al. in press, Hughes 1994). Linking regional 

factors, pressures, and stressors with biological condition into a BCG will assist States and Tribes in 

identifying levels of disturbance and the primary drivers of biological condition in their watersheds. If no 

undisturbed or minimally disturbed reference sites exist in a region, a stressor axis provides a means for 

determining the best condition or regional candidates to act as benchmarks for comparison, i.e., “least 

disturbed” or “best available conditions.” The stressor axis concept will enable managers to place the 

status of their stream ecosystems into a regional context and prioritize actions. The reference condition 

approach, which describes the potential biological condition of the region’s waters, provides a framework 

to set appropriate restoration endpoints for that resource and region. 

The next step involves quantification of in-stream stressors, riparian condition, landscape characteristics 

and riverscape alterations, as well as point source discharges and other localized pressures. Calibrating 

stressors along natural gradients (waterbody size, catchment area, stream power, elevation, latitude, and 

geology) can improve ability to detect pressure effects by removing the confounding effects of stressor 

gradients with natural gradients (Fausch et al. 1984, Hughes et al. 2004, Kaufmann and Hughes in press). 

There have been many efforts to characterize pressures and incorporate quantitative information into 

environmental assessment programs (Table 4-3). Riparian condition has been widely recognized as 

affecting the physical habitat and biological condition of streams (Naiman and Decamps 1990, Fitzpatrick 

et al. 2001, Lammert and Allan 1999, and Lattin et al. 2004). In some circumstances, watershed 

condition was more important (Roth et al. 1996, Snyder et al. 2003). Wilhelm et al. (unpublished 

manuscript) used both catchment (i.e., watershed) and riparian disturbance for the development of their 

non-wadeable habitat index for streams in Michigan. Wang and others (in press) found that fish 

assemblages were most influenced by local environmental factors in largely undisturbed catchments. 

However, as the level of catchment disturbance increased, the importance of catchment-scale factors 

increased and that of local-scale factors decreased. These studies indicate how important regional and 

local factors are for determining the relationship among sources, stressors, and biological condition and 

the most appropriate scale for addressing these relationships. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 85 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 
TABLE 4-3. Percent variance in biological response (R2

) explained by catchment and riparian land use, and 

percent land use producing poor IBI scores (modified from Hughes et al. unpublished manuscript). 

Location & % Land Use for Authors Response Variable R2 Catchment R2 Riparian N “Poor” rating 

Bryce & Hughes (2002) Fish IBI 0.40 -------- 13 OR/ 50% urban 

Fish IBI 0.35 -------- 16 Appalachia/ 15% urban 

Diatom IBI 0.29-0.36 -------- 16 App./ declines w/ ag. 

Benthos IBI 0.48-0.67 -------- 16 App./ 50% ag., 20% mined 

Fitzpatrick et al. (2001) Fish IBI 0.31 0.58 25 WI/ 70% ag. 

Diatom IBI 0.16 ns 25 WI/ag. 

Benthos IBI ns ns 25 WI/ag. 

Hughes et al. (unpublished) Fish IBI 0.42 0.38 104 OR/ rd. density >1.9 km/km2 

Karr & Chu (2000) Benthos IBI 0.25 --------- 66 WA/ 40% impervious 

Klauda et al. (1998) Fish IBI 0.68 --------- 61 MD/ 60% urban 

Lammert & Allan (1999) Fish IBI 0.01 0.22-0.28 18 MI/ declines w/ riparian ag. 

Benthos IBI ns ns 18 MI/ag. 

Lattin et al. (2004) Fish IBI ns 0.20-0.46 25 OR/20% network riparian ag. 

Leonard & Orth (1986) Fish IBI 0.60 --------- 44 WV/ rd. density >1.7 km/km2 

McCormick et al. (2001) Fish IBI 0.05-.08 --------- 313 App./ declines as deforested 

Mebane et al. (2003) Fish IBI 0.45-0.56 --------- 41 OR/ 25% deforested 

Fish IBI 0.56 --------- 30 ID/ 15% irrigated ag. 

Morley & Karr (2002) Benthos IBI 0.53 0.00-0.82 34 WA/ 45% impervious 

Roth et al. (1996) Fish IBI 0.50 0.02-0.38 21 MI/ 80% ag. 

Snyder et al. (in press) Fish IBI 0.16-0.64 0.02-0.17 20 WV/ 15% urban 

Steedman (1988) Fish IBI 0.64 0.67 10 ONT/ 95% ag., 60% urban 

Wang et al. (1997) Fish IBI 0.48 --------- 134 WI/ declines w/ deforesting 

Wang et al. (2000) Fish IBI 0.34 --------- 47 WI/ 5% impervious 

Wang et al. (2001) Fish IBI 0.04-0.31 0.26-0.34 47 WI/ 5% impervious 

Yoder et al. (2000) Fish IBI 0.41 --------- 101 OH/ 30% urban 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State and 86 

Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 
Once the suite of stressors and pressures are measured or quantified for a given group of waterbodies, the 

next step is to determine if more than one stressor gradient exists and how they are related (i.e., are there 

several gradients based on different pressures, activities or landscapes?). Dealing with these multiple 

stressors and pressures can be complicated. A direct multiple correlation approach was taken by EMAP in 

the mid-Appalachian Highlands where poor quality streams were most often associated with alien fish, 

channel sedimentation, and riparian habitat alteration out of several hundred possible stressors (U.S. EPA 

2000a). Kaufmann and Hughes (in press) used correlation and multiple linear regression analyses to 

determine that low stream IBI values were associated with excess streambed fines, bed instability, higher 

water temperature, higher dissolved nutrient concentrations, and lack of deep pools and cover complexity. 

These stressors were most strongly associated with riparian disturbance and road density. Effects were 

more pronounced in streams draining erodible sedimentary bedrock than in those draining more resistant 

volcanic terrain. States and Tribes could use similar multivariate approaches for identifying the 

stressor(s) most associated with measures of biological condition in their regions 

A method employed in the Great Lakes Environmental Indicators (GLEI) project to characterize 

disturbance to the U.S. Great Lakes coastal region, used principle components analysis to reduce over 200 

GIS variables into a single gradient (Danz et al. 2005). The GLEI approach individually considered six 

different kinds of disturbance: agriculture, atmospheric deposition, land cover, human population, point 

sources, and shoreline alteration. A watershed-based approach was used to reflect the premise that the 

environmental effects of these activities in coastal watersheds can influence environmental conditions in 

(downstream) coastal ecosystems. The first principle component from their analysis explained 73% of 

the variance in the agriculture variables and was interpreted as an overall gradient in stressors across the 

basin (Figure 4-4). Environmental responses such as water quality, fish assemblage metrics, and bird 

abundances were strongly correlated with this stressor gradient. 

FIGURE 4-4. The first principal component of the agricultural 

variables for the U.S. Great Lakes basin. Darker shading indicates 

greater amounts of agriculture. 

When multiple sources and stressors interacted to form the stressor gradient for a given watershed, GLEI 

found it desirable to develop a visual display of PCA axis 1 that subsumes the multiple stressors by 

portraying a single disturbance gradient. While the pressure-stressor model could eventually be 

developed and visualized as a single gradient from low to high levels of stressors (Figure 4-4), different 

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Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 4 – August 10, 2005 
individual and combinations of stressors are expected to dominate in different regions. Furthermore, the 

depiction of individual categories of stress provides important information about potential mechanisms 

affecting the state of the system. The GLEI researchers created a flow diagram (Figure 4-5) that details 

their steps for quantifying a stressor gradient (modified from Danz et al. 2005). 

Organize 

Data 

Define sampling units 

Compile & summarize 

environmental variables 

Evaluate & categorize 

variables 

Generate 

Stressor 

Gradient Remove redundancy with PCA 

Map disturbance gradient 

using PCA axes from using color-coded scheme

each stressor category 

gional 

classification system 

Organize

Data

De

Compute overall stressor 

gradient 

C

Apply re

fine sampling units

Compile & summarize

environmental variables

Evaluate & categorize

variables

Remove redundancy 

(PCA is one method) 

Map disturbance gradient

using color-coded scheme

ompute overall stressor

gradient using PCA axes from

each stressor category

pply regional

classification system

FIGURE 4-5. Flow diagram detailing the steps used by GLEI researchers in 

quantifying their stressor gradient (modified from Danz et al. 2005). 

Whether using a single or multiple stressor gradient, all this information needs to be assembled to develop 

a model that integrates the components of pressures and establishes a baseline for using stressors to 

interpret biological responses. Relationship models that describe the associations among stressors, the 

processes that generate them, and biological conditions (responses) need to be developed. If possible, the 

extent of management actions (e.g., controls/BMPs) needs to be identified and ways to characterize these 

actions need to be considered (although this is an area of active research). The degree of deviation from 

natural conditions and the types of stressors present will affect restoration potential and therefore BMP 

effectiveness. Examples of tools that are currently available for characterizing a suite of pressures are: 

Analytical Tools Interface for Landscape Assessments (ATtiLA), National Land Cover Database 

(NLCD), and air photos. 

Calibrating a stressor axis depends on the scale of the question to be addressed. The stressor axis should 

be developed independently of the biological information to avoid circularity when developing the BCG. 

In the development of their non-wadeable habitat index (NWHI), Wilhelm et al. (unpublished manuscript) 

used catchment and riparian disturbance gradients (CDG and RDG respectively) to select and weight 

habitat metrics at both watershed and reach scales. While the final NWHI was strongly correlated to 

disturbance measures and included habitat metrics that supported this relationship, a true test of the 

relationship between their stream response measure and disturbance measures would require a new, 

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independent data set. The GLEI researchers used a wide range of publicly available data sets to quantify 

five different classes of disturbances. Their stressor axis is currently being calibrated. Stressor 

development and calibration involves using sufficient information to characterize relative positions along 

the axis and, in particular, being able to anchor the upper end (i.e., low or no stressors) and the lower end 

(i.e., high level of stressors) (Whittier et al. in press). This can be accomplished via a combination of 

public consensus, best professional judgment, and empirical approaches (e.g., Areas Of Concern (AOC), 

Great Lakes Environmental Indicators (GLEI) approach, and index development) (Whittier et al. in press, 

Danz et al. 2005, U.S. EPA 2000b). 

4.5 Key points from Chapter 4 

1.	 The stressor gradient provides a framework for organizing and interpreting information about 

watershed characteristics and using those characteristics to predict aquatic ecosystem biological 

responses. It helps us understand the observed biological conditions and the stressors related to 

those conditions. It can help identify the predominant stressors affecting the aquatic biota and 

develop effective management actions to mitigate their effects. 

2.	 Understanding how specific stressors are generated and how they affect biotic condition provides 

the underpinnings for the BCG’s stressor axis and ultimately the basis for interpreting the 

influence of stressors on biological condition. 

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90 
Define and Allocate

Control Responsibilities

Incorporating Tiered Aquatic Life Uses Into 

State and TribalW Q S:Case Exam ples 

As a key component of State and Tribal water quality standards, 

designated uses define the goals for a waterbody, determine the criteria to 

protect it, guide management outputs, and, ultimately, environmental 

outcomes. Aquatic life tiers couple descriptive narratives (tiered uses) 

Tiered aquatic life uses are 

descriptive narratives of 

designated uses that are 

with supporting numeric criteria. The specificity of designated uses supported with numeric 

greatly influences the level of precision at which a water quality biocriteria and chemical and 

management program operates. Incorporating tiered aquatic life uses into 

water quality standards can have a positive effect on water quality 

physical criteria. 

management outcomes. States that have made this transition have 

demonstrated that tiered aquatic life uses promote both the development of more appropriate aquatic life 

use goals and biological criteria to measure attainment of those goals. The data and experience developed 

from tiered uses supported by comprehensive monitoring have multiple uses in the water quality based 

approach to pollution control (Figure 5-1). 

The preceding chapters of this document 

Biological 

defining the biological and physical condition of Monitoring 

waterbodies and their aquatic life uses. These & Assessment 

next two chapters discuss the underlying Enforcement 

principles and processes involved in developing & Compliance Tiered Aquatic Life & Criteria 

describe ways of better characterizing and Chemical 

Establish Uses 

tiered aquatic life uses and applying them in Uses help better 

water quality management based on “lessons define designated 

Source aquatic life uses. Problem ID/Set learned” from State experiences. Maine and Controls/BMPs Priorities Ohio are two States that have adopted tiered 

aquatic life uses in their WQS and have 

implemented them through systematic 

monitoring and assessment. The experiences of 

Maine and Ohio provide a sequence of steps, or 

milestones, that can serve as a template for other FIGURE 5-1. U.S. EPA Water Quality Based Approach to States to follow. These milestones are: Pollution Control based on Chapter 7, Water Quality 

Standards Handbook. 1. Establish conceptual foundation 

2. Merge scientific and policy foundations 

3. Establish monitoring program 

4. Develop and validate quantitative thresholds 

5. Apply tiered uses in water quality management 

Both States developed tiered aquatic life uses for similar reasons: 1) to incorporate ecologically relevant 

outcomes in goal setting; 2) to guide cost-effective, defensible management decisions; 3) to measure 

incremental progress in meeting management goals; and 4) to merge the design and practice of 

monitoring and assessment with the development and implementation of WQS. Chapter 5 captures the 

“lessons learned” by Maine and Ohio in their development of tiered uses (Milestones 1 – 4) and Chapter 6 

presents case examples about how each State has benefited from this approach (Milestone 5). 

Physical 

Define and Allocate Control 

Responsibilities 

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92 
CHAPTER 5.	 KEY CONCEPTS AND MILESTONES IN THE DEVELOPMENT OF 

TIERED AQUATIC LIFE USES 

Tiered aquatic life uses should be derived based on knowledge of the aquatic biota (specifically the 

assemblages used in biological assessments) and the factors that determine their distribution, abundance, 

and composition. Tiered narrative statements and numeric biological criteria can represent measurable 

benchmarks along a regionally calibrated biological condition gradient (BCG). Maine and Ohio have 

determined that these benchmarks represent attainable conditions in their States for the protection or 

restoration of surface waters through implementation of WQS. Since waterbodies are assigned to tiered 

uses based on a comprehensive ecological database (biological, chemical, physical assessments), Maine 

and Ohio are more confident that both the uses themselves and any changes to a waterbody’s condition 

are ecologically relevant. 

5.1 Key concepts for developing tiered aquatic life uses 

Maine and Ohio’s tiered aquatic life uses represent the goals for individual waterbodies. Their tiered uses 

share the following common characteristics: 

• uses are ecologically-based 

• uses include the structural and functional properties of the specific aquatic communities that 

inhabit an aquatic ecosystem 

• attainment is based on measurable biological criteria, which are indexed to a regionally relevant 

reference condition 

• implementation integrates monitoring, assessment, and WQS 

These characteristics are discussed more fully in the Maine and Ohio case histories (Appendixes A and 

B). But, two key concepts that Maine and Ohio have learned are: 

1. Tiered Aquatic Life Uses Should Be Ecologically Based 

Tiered uses should be built on a strong ecological foundation that provides a credible basis for the 

protection and restoration of aquatic resources. Tiered uses should reflect the collective attributes of the 

BCG and encompass the structural and functional attributes and processes of an aquatic ecosystem. As 

discussed previously, Figure 1-4 illustrates how pollution leads to exposures and responses, both 

ecological and human health, which can affect the status of waterbody-specific designated uses. Because 

the designated use is initially stated in narrative and qualitative terms, the challenge is to logically and 

appropriately relate the chemical, physical, and biological criteria to the designated use. The more precise 

the statement of the designated use, the more accurate the associated criteria can be as an indicator of that 

use. 

Linking tiered uses to a regionally calibrated BCG provides the scientific framework for determining the 

biological condition and potential of individual waterbodies, which is the basis for assigning the 

appropriate tier. Tiered use narratives should include explicit references to the protection of aquatic life 

and specify the structural and functional properties that are to be protected. The derivation and 

calibration of numeric biocriteria should assure ecological relevance consistent with the properties of the 

regional aquatic fauna. 

2. Linkage of Tiered Uses to the BCG via Biocriteria 

The BCG attributes are incorporated directly into tiered aquatic life uses through biological assessments 

and with biological criteria. The development of biocriteria is an important part of the process in 

accomplishing this task and should adhere to the technical components of the overall TALU process 

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93 
(Appendixes C, D, and E). Karr et al. (1986) recommended six key elements in the development of 

bioassessment tools and biocriteria: 

1)	 measure(s) must be biological 

2)	 measure(s) should be interpretable at different trophic levels and provide a connection to other 

organisms and assemblages not included in the biological assessment process 

3)	 measure(s) must be sensitive to the environmental conditions being assessed 

4)	 response range must be suitable for the intended application, i.e., encompassing the full range of 

the BCG 

5) measure(s) must be reproducible and precise within acceptable limits for data collected over 

space and through time 

6)	 variability of the measure(s) must be low enough to detect changes along the entirety of the BCG 

Representative indicator assemblages are used to measure attainment of the biocriteria as part of the 

derivation process. As such, biocriteria represent the measurable ecological properties of a tiered aquatic 

life use. 

5.2 Key milestones for developing tiered aquatic life uses 

The Maine and Ohio case histories (Appendixes A and B) reveal conceptually consistent, but technically 

different ways of developing tiered uses including numeric biological criteria and a comprehensive 

monitoring and assessment program. However, the process followed by each demonstrates common tasks 

and milestones that States and Tribes can use as a template for developing tiered uses. These milestones 

and tasks are illustrated in Table 5-1 and consist of five major steps: 

Milestone 1. Establish Conceptual Foundation (Maine and Ohio Case Histories, part I) 

• Establish an interdisciplinary, collaborative approach to the development of tiered uses 

(ecological, technical, and legal) 

• Identify and acquire appropriate staff and management expertise 

Milestone 2. Merge Scientific & Policy Foundations (Maine and Ohio Case Histories, part II) 

• Link management objectives with technical program 

• Evaluate for consistency with existing water quality standards framework 

• Draft or refine narrative aquatic life use descriptions 

Milestone 3. Establish Monitoring Program (Maine and Ohio Case Histories, part III) 

• Develop methods and monitoring design, establish reference conditions, build baseline 

database and database management system 

• Logistics: staffing, facilities, and equipment 

Milestone 4. Develop/Validate Quantitative Thresholds (Maine and Ohio Case Histories, part IV) 

• Program implementation: develop biocriteria and water quality program support 

(initiating the process of using TALUs and biological assessments to support water 

quality management tasks) 

• Validate the accuracy of ecological expectations with empirical data 

• Program maintenance: refine biocriteria and maintain water quality program support 

(maintaining the process of using TALUs and biological assessments including the 

continuous evaluation of tools, criteria, and processes based on what is being learned via 

a systematic approach to monitoring and assessment; includes expansion to other aquatic 

ecotypes) 

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Milestone 5. Application in Water Quality Management (Chapter 6; Maine Case History, part IV) 

• Apply biocriteria to support WQS 

• Integrate tiered biocriteria with other types of chemical and physical criteria 

Milestones 1 - 4 describe the key tasks in the development of tiered aquatic life uses. Milestone 5 

addresses the application of tiered uses in water quality management. Ideally, the milestones can be 

accomplished sequentially, each laying the appropriate scientific or policy foundation for the next step. 

However, many States will have already accomplished some or even a majority of the tasks, particularly 

under Milestone 3 (Establish Monitoring Program). Some may also use biological assessments for 

support functions beyond status assessments, but perhaps lack the formal tiered use framework in their 

WQS or have remaining technical development issues. Maine and Ohio found that capacity for 

conducting biological assessments is an equally important issue and generally included 5-10% of State 

water quality management program resources. They found that this level of funding should make 

available sufficient resources to carry out the development, maintenance, and assessment tasks on a 

statewide basis. 

Table 5-1 and Figure 5-2 include many of the major tasks in the development of a program and they can 

serve as a “road map” to determine where a particular State program stands regarding the goal of 

developing and applying tiered uses in its water management programs. Figure 5-2 can also be used as a 

guide for identifying, prioritizing, and organizing outstanding and remaining tasks. Furthermore, there is 

a transition under Milestone 4 from an emphasis on development of a tiered aquatic life use approach to 

program maintenance. Program maintenance includes ongoing evaluation and “fine tuning” of the 

bioassessment tools and criteria as the program matures. It also includes the further development and 

refinement of assessment and management tools and criteria as data, experience, and knowledge are 

gained via systematic monitoring and assessment. Maine and Ohio initially developed tiered uses and 

biocriteria for streams and wadeable rivers and currently either have developed or are evaluating tiered 

uses and biocriteria for other waterbody types (e.g. nonwadeable rivers, wetlands, lakes and estuaries). 

Program maintenance can also include the development of tiered uses for these other types of 

waterbodies. Evaluating whether there is a need to change existing use designations for specific 

waterbodies is another important task. This is accomplished during the triennial review process with 

decisions based directly on outcomes from systematic watershed monitoring and assessment and historic 

data. 

Milestones 1 - 4 and Figure 5-2 reflect a sequence of strategic steps in the development of tiered aquatic 

life uses. A functional and effective program will emerge if essential theoretical, technical, and legal 

elements are addressed and fully integrated throughout the development process. Table 5-1 shows typical 

tasks associated with each founding element and the type of professional expertise required to accomplish 

them. One of the key “lessons learned” in Maine and Ohio is that problems arise when technical and 

management activities are done in isolation from each other. A collaborative and interdisciplinary 

approach that blends technical and management activities yields better decisions at all levels. 

The triennial review process is readily adaptable to developing and then refining uses on a watershed 

basis, and to making needed adjustments to bioassessment tools and criteria. As the program develops 

and matures over time, and as resources become available, application of a tiered use framework can 

advance from condition assessment to formal incorporation into water quality standards. 

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TABLE 5-1. Expertise and tasks for key TALU milestones. 

Conceptual Foundations Technical Foundations Policy/Legal Foundations 

Professional Expertise Required 

V Senior professional biologists 

V Regional ecological experts 

V Professional biologists 

V Taxonomists 

V Field support staff 

V Statistician 

V Database managers 

Initial concept formulation: 

V Senior professional biologists 

V WQS managers 

Later stages: 

All of the above plus... 

V Senior management 

V State legal counsel 

V Legislature or WQS board 

V Stakeholders 

Milestones 1, 2 and 4 Milestones 3 and 4 Milestones 1, 2 and 4 

Essential Elements 

° Literature review of stress 

ecology studies for locale 

° Develop regional BCG model 

° Determine expected biological 

assemblage response to typical 

stressor scenarios; 

° Identify ecological attributes 

necessary to maintain a 

functioning ecosystem (to help 

establish goals for protection or 

restoration) 

° Clarify classification issues 

(confounding natural gradients of 

locale); 

° Define reference conditions 

° Determine monitoring approach 

and strategy 

° Exploratory data analyses to 

validate/refine BCG model 

° Best available, best tested metrics 

to assess status of ecological 

attributes of interest 

° Set thresholds that correspond to 

BCG tiers, that protect essential 

ecological attributes 

° Determine management objectives; 

° Identify priority aquatic resources 

° Cross-walk BCG to WQS context- (how 

good a fit is provisional BCG/TALU 

conceptual model to existing use classes 

and WQ criteria) 

° Seek early review of the legal standing of 

any proposed changes to WQS- strengthen 

and clarify language 

° Account for public values and economic 

constraints/realities 

Based on the commonalities between Maine and Ohio’s experiences, several important “lessons learned” 

were identified for States and Tribes that are considering developing tiered aquatic life uses. 

• Interdisciplinary approach to development: Development of tiered aquatic life uses is most 

successful when active cooperation and close working relationships exist among the individuals 

charged with technical/scientific development and oversight of water quality standards. 

• Plan enough to be certain of success... and use adaptive management approach: Clear 

knowledge of scientific and legal principles should guide every step of planning and 

development. An adaptive management approach is beneficial throughout the development 

process because new technical information and management understanding are gained as part of 

the process. An adaptive management approach incorporates needed flexibility into a program by 

building on the new knowledge and insights. 

• “Proper” sequencing versus logical decisions: The exact sequence of developmental events is 

not as critical as the necessity of following a plan that is logical for a particular State or Tribe, 

builds on current program strengths and reflects rigorous adherence to scientifically and legally 

sound foundations. 

• Graduated application to support water quality management decisions: Some level of 

condition assessment and regulatory decision-making (application in water management) can 

happen as soon as a credible monitoring program is established and linked to narrative TALU 

goal statements. 

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96 
°

°

° °

°

0-18 MONTHS 

12-24 MONTHS 

18 MO – 6 YEARS 

INITIAL DEVELOPMENT PHASE 

INITIAL IMPLEMENTATION PHASE 

INITIAL ASSESSMENT PHASE 

FULL ASSESSMENT PHASE 

5 – 10+ YEARS 

3. Establish Technical Program 

Start-Up Tasks: Initial 

Technical Development Tasks 

Start-Up Tasks: Initiate 

Monitoring Strategy 

Initiate Field Sampling ° Review spatial designs 

° Develop QA/QC and QAPP 

° Develop sampling plans in 

accordance with monitoring 

strategy 

° Pilot assessments 

Classification Issues 

° Consider spatial stratification 

issues 

° Develop and test reference 

condition approach 

° Select and sample reference 

sites 

° Develop index development 

and calibration strategy 

Program Implementation Program Maintenance 

Acquire Staffing ° Professional biologists with 

taxonomic expertise & training 

° Database manager 

° Interns/technicians (field work, 

lab tasks 

Acquire Facilities & Equipment 

° Outfit laboratory and field facility 

° Office accommodations 

° Database support infrastructure 

Methods Development 

° Review and select candidate 

methods and protocols 

° Consider MQO/DQO needs 

° Test methods for applicability 

° Analyze test results – select 

methods 

4. Develop & Validate Quantitative Thresholds 

Biocriteria Development ° Select candidate metrics and/or 

assessment tools 

° Develop refined uses ­

narratives 

° Test metrics and develop 

calibrated indices 

° Evaluate via bioassessments 

Water Quality Program Support 

° Develop capacity to support 

WQ programs (WQS/UAAs, 

TMDLs, permits, planning) 

° Formalize and increase water 

quality program support as 

capacity is developed 

(biological data should support 

more decisions) 

Biocriteria Development ° Refine metrics and develop 

calibrated indices 

° Develop reference benchmarks 

for calibrated indices according 

to classification scheme and by 

major aquatic ecotype 

° Link to TALUs via BCG 

Water Quality Program Support 

° Fully functioning bioassessment 

program supports WQS (UAAs, 

ALU, biocriteria) and basic 

program needs (305b/303d) 

° Program dev’t should be fully 

initiated – e.g., integrated 

chemical, physical, and 

biological database supports 

tool, criteria, & policy dev’t. 

(ongoing) 

5. Application in WQ Management 

Assessment Issues 

° Use data for “makeable” 

decisions 

° Initiate exploratory analysis of 

biological responses to 

stressors 

1. Establish 

Conceptual 

Foundation 

2. Merge Scientific & 

Policy Foundations 

Science 

Policy 

Link conceptual TALU 

tiers to regional BCG 

conceptual model 

Evaluate for consistency with 

existing WQS framework 

Draft or refine narrative ALU 

descriptions 

Quality Improvement Process Evaluate effectiveness of initial decisions – make needed adjustments 

FIGURE 5-2. TALU and biocriteria program development tasks: Timeline and key milestones. A process of 

sequential tasks and milestones that States can follow in the development and implementation of tiered 

aquatic life uses and attendant biological criteria. 

5.3 Using TALUs to support water quality management 

The adoption of tiered uses should positively influence water quality management outputs and outcomes. 

Tiered uses in State and Tribal water quality standards, coupled with a systematic and comprehensive 

monitoring and assessment program, can provide an essential link among a wide variety of water quality 

management programs. In Maine and Ohio, the end result have supported baseline CWA management 

programs such as NPDES permitting, construction grants, and, more recently, the revolving loan 

program, basin planning (including TMDLs, listings of impaired waters, development of restoration 

plans), and nonpoint source assessment. The comprehensive support of water quality management that 

emerges from systematic monitoring and tiered aquatic life uses in Maine and Ohio is made possible by 

following the milestones shown in Table 5-1 and Figure 5-2 to establish and develop a program. 

Monitoring supports day-to-day water quality management needs and can take place at multiple scales 

including a statewide, regional, watershed, or site-specific basis. 

A sustained monitoring and assessment program naturally incorporates strategic functions and results in 

improved criteria, tools, policies, awareness, and legislation. The aggregated database comprises the 

experience gained by conducting systematic assessments and includes the regular resampling of reference 

sites and long-term monitoring of reference condition. The database allows comprehensive analysis and 

interpretation of spatial and temporal trends and tracking the effectiveness of different water quality 

Continuously evaluate program – develop and implement refinements 

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97 
management programs. The overall program thereby fosters continuous improvement through adaptive 

management because the relevant information and the interpretation of that information is made available 

to managers. 

As an example, full documentation of the results and benefits of improvements in wastewater treatment 

on multiple waterbodies in both Ohio and Maine would not have been possible without a comprehensive 

biological monitoring network and tiered uses to put the results into a communication and management 

context (See Case Example 6-4. Long-term Monitoring and Use Re-establishment in Maine). 

Furthermore, tiered uses allowed the two States to secure and retain the gains made by upgrading some of 

the affected rivers to higher tiers, a development that had not been anticipated before the wastewater 

treatment was improved. These examples also validated the process of setting TALU-based WQS and 

using them to develop regulatory requirements. The outcomes allayed many of the original uncertainties 

about the cost-effectiveness of water quality based permitting and gave regulatory programs the 

confidence to implement new requirements. This was critical in Ohio where the virtues of municipal 

wastewater treatment more stringent than secondary treatment were widely debated and doubted in the 

early 1980s. Advanced treatment (also known as best available demonstrated control technology or 

BADCT) is now widely supported because not only did it work as a treatment technology, but it delivered 

the end outcome of improved biological condition. 

The comprehensive, long-term programs in Ohio and Maine have demonstrated their value by improving 

prioritization of management actions and enabling more effective targeting of resources. Chapter 6 

summarizes several case examples of how biological monitoring and tiered uses contribute to many 

different aspects of the water quality management cycle (Figure 5-1). 

5.4 Key points from Chapter 5 

States that have successfully implemented a TALU approach have found that: 

1.	 The specificity of designated uses greatly influences the level of precision at which a water 

quality management program operates. Incorporating more refined, or tiered, aquatic life uses 

into water quality standards can have a positive effect on water quality management outcomes. 

States that have made this transition have demonstrated that tiered aquatic life uses promote both 

the development of more appropriate aquatic life use goals and biological criteria to measure 

attainment of those goals. 

2.	 Tiered uses in State and Tribal water quality standards, coupled with a systematic and 

comprehensive monitoring and assessment program, can provide comprehensive support to water 

quality management programs. In Maine and Ohio, the end result supports baseline CWA 

management programs such as NPDES permitting, construction grants, and, more recently, the 

revolving loan program, basin planning (including TMDLs, listings of impaired waters, 

development of restoration plans), and nonpoint source assessment. 

3.	 Though based on different technical approaches, their development of tiered aquatic life uses 

followed common tasks and milestones. Development of tiered uses has been most successful 

when there was early and consistent collaboration among their monitoring, criteria, and standards 

programs. 

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Define and Allocate

Control Responsibilities

CHAPTER 6. HOW HAVE STATES AND TRIBES USED TALUS IN WATER 

QUALITY STANDARDS AND MANAGEMENT? 

Tiered aquatic life uses supported by systematic assessments can provide the information needed for 

water quality management at watershed, regional, and statewide scales. A comprehensive monitoring and 

assessment program is a critical aspect of implementation of tiered aquatic life uses. The same data and 

information that provide baseline status assessments also address watershed-specific management needs 

such as the appropriate designation of individual waterbodies, TMDL development, and NPDES permits. 

This chapter presents several case examples in Maine and Ohio of how tiered uses and monitoring 

contribute to all aspects of the water quality based approach to pollution control (Figure 5-1). These 

include setting criteria and standards; problem identification and establishing priorities (stressor 

identification); defining and allocating control responsibilities (source identification); determining source 

controls or BMPs (TMDLs, UAAs, WLAs); and enforcement and compliance (NPDES permits and other 

compliance agreements). The following are case examples of how TALUs, coupled with systematic 

monitoring and assessment, have and can be used to support key water quality management programs and 

functions. These examples further exemplify what can be accomplished by following the developmental 

process described in Chapter 5. Accompanying each case example is a diagram of U.S. EPA’s Water 

Quality Management Cycle (Figure 5-1) with the key component for that particular example shaded. 

Most of the following examples were accomplished during the Program Maintenance phase of the TALU 

development milestones (Figure 5-2) and demonstrate what can be produced as the bioassessment 

program matures; however, some of the initial assessments can be accomplished during the Program 

Implementation phase. 

CASE EXAMPLE 6-1. REFINING WATER QUALITY CRITERIA IN OHIO 

Ohio EPA developed empirical associations between aquatic 

life and ambient stressor levels for parameters such as dissolved 

oxygen from its monitoring program data beginning in the late 

1970s. The known prevalence of organic enrichment from 

point sources and intensive watershed surveys identified 

dissolved oxygen (D.O.) as a major stressor limiting aquatic life 

throughout the 1980s (Ohio EPA 1988, 2000). 

When the Exceptional Warmwater Habitat (EWH) aquatic life 

use was established in 1978, Ohio also established tiered 

dissolved oxygen criteria to protect “highly sensitive aquatic 

organisms; growth and reproduction of recreationally and commercially important species; [and] 

maintenance of populations of imperiled species” (Ohio EPA 1996). This was in contrast to the goal for 

the Warmwater Habitat (WWH) use, which was the “maintenance of typically representative warmwater 

aquatic organisms and recreationally important species” (Ohio EPA 1996). The original single criteria for 

EWH streams of 6 mg/l was largely based on pertinent literature of the time, best professional judgment 

using the knowledge that these streams supported populations of very sensitive aquatic species, and that 

the D.O. criteria should be more stringent than the WWH criterion (5 mg/l daily average, 4 mg/l 

minimum). 

Since the original adoption of the EWH use and associated tiered D.O. criteria, analyses of ambient 

biological and chemical data suggested that the 6 mg/l minimum criterion was over-protective for these 

waters. Both statewide and reach specific data were used to document streams with dissolved oxygen 

concentrations below 6 mg/l (but typically above 5 mg/l) that fully attained the EWH aquatic life use as 

measured by the numeric biocriteria. These results were used to justify a two-number criterion of 6 mg/l 

Enforcement 

& Compliance 

Source 

Controls/BMPs 

Monitoring 

& Assessment 

Establish Uses & Criteria 

Problem ID/Set Priorities 

Chemical 

Physical 

Biological 

Define & Allocate Control 

Responsibilities 

Tiered Aquatic Life 

Uses help better 

define designated 

aquatic life uses. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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99 
I

B

I

R

ange 

IBI average, 5 mg/l minimum for the EWH use (Ohio EPA 1996). Two examples of these data include the

stressor-response relationship between grab sample D.O. data (Figure 6-1) and continuous D.O. data

(Figure 6-2) and the IBI in the E. Corn Belt Plains (ECBP) and Huron/Erie Lake Plain (HELP) ecoregions

of Ohio. Both graphs show an expected gradient of response between D.O. and IBI scores and show that

minimum dissolved oxygen values between 5 and 6 mg/l were commonly associated with IBI scores in

the EWH range.

Figure 6-1 illustrates a relationship that is commonly observed between stressors and biological measures

where multiple stressors are prevalent. On Figure 6-1, to the left of the dashed line at 5.0 mg/l (grab

samples), numerous D.O. values are found associated with low IBI scores, but very few at IBI scores

above 50 (EWH). If D.O. is >5.0 mg/l, IBI scores are much more likely to attain WWH (>40) and EWH

(>50). Figure 6-2 shows continuous D.O. data vs. IBI ranges that correspond to quality tiers ranging from

exceptional to very poor. This also supports a similar conclusion as Figure 6-1, but captures the full range

of D.O. values that occur over a 24-hour period, especially the early morning hours when the diel cycle

yields the lowest values.

60 

D ata - 1994-2001 

ECBP & HELP Ecoregions 

O hio EPA Survey D ata 

Minim um V alues,D atasonde D ata 

50-60 

50 

EWH 

40-49 

40 WWH 

30-39 

30 

20-29 

20 

12-19 

10 

0 2 4 6 8 10 00 22 44 66 88 1

100

D issolved O xygen (m g/l) D issolved O xygen (m g/l) 

IndividualG rab Sam ples [Continuous Monitoring D ata]

FIGURE 6-1. Dissolved oxygen concentrations FIGURE 6-2. Box plots of minimum dissolved oxygen

(individual grab samples) vs. Index of Biotic concentrations by IBI ranges for continuous

Integrity (IBI) values in the Huron/Erie Lake monitoring data at all locations monitored in 1988 and

Plain (HELP) and E. Corn Belt Plains (ECBP) 1994. IBI ranges are: 50-60 (exceptional, EWH); 40­

ecoregions of Ohio. Hatched areas represent 49 (good, WWH), 30-39 (fair); 20-29 (poor); 12-19

Exceptional Warmwater Habitat (EWH) and (very poor).

Warmwater Habitat (WWH) biocriteria for the

ECBP ecoregion.

The key message of this case example is that water quality criteria can be refined to reflect aquatic life

use tiers if sufficient ambient data exists over sufficient spatial and temporal scales. It also provides

more confidence in applying the water quality criterion as a design target for permitting and TMDL

purposes. The previous EWH D.O. criterion (6 mg/l minimum) became a disincentive to redesignate

rivers and streams that were fully attaining the EWH biocriteria because of the difficulty in meeting

the permit limits. The criterion revision, based in part on the analyses presented here, resolved that

situation in the majority of cases and allowed for the redesignation of such rivers and streams to EWH.

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and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 6 – August 10, 2005
Define and Allocate

Control Responsibilities

CASE EXAMPLE 6-2. DEVELOPMENT OF MORE PRECISE TARGETS FOR RESTORATION IN OHIO 

Nutrients have been identified as a major stressor to aquatic life 

across the U.S. (U.S. EPA 2002b). Nutrients are not directly 

Enforcement 

& Compliance 

Source 

Controls/BMPs 

Monitoring 

& Assessment 

Establish Uses & Criteria 

Problem ID/Set Priorities 

Chemical Biological 

Define & Allocate Control 

Responsibilities 

Tiered Aquatic Life 

Uses help better 

define designated 

aquatic life uses. 

Physical 

toxic under most conditions, but rather exert their influence on 

higher organism groups via interactions within energy pathways 

and by influencing D.O. dynamics within streams and rivers. 

Ohio EPA described biological gradients of response to nutrient 

concentrations in streams and rivers (Ohio EPA 1999a). This 

was accomplished by linking the primary nutrients (nitrate, total 

phosphorus) and other parameters to the biocriteria (IBI, ICI, 

etc.) on a statewide, ecoregion, and stream/river size basis. Thus 

ranges of these parameters consistent with attainment of the 

tiered aquatic life uses were accomplished (Ohio EPA 1999a; 

Table 6-1). While the values in Table 6-1 are not explicit water quality criteria, they are used as TMDL 

targets given the direct linkage they have with aquatic life use attainment. In addition to ambient fish and 

invertebrate data, ambient chemical data, and stream habitat data, Ohio is currently collecting information 

on chlorophyll and algal assemblages to improve understanding of the mechanisms of nutrient impact on 

aquatic life (Bob Miltner, Ohio EPA, personnel communication). This work should result in refined 

targets that can be used to determine which restoration activities should be most effective at restoring 

aquatic life. The identification of nutrient targets for each aquatic life use tier provides an appropriate and 

achievable level of protection for specific waterbodies. This application provides restoration targets for 

TMDLs that, if achieved, should result in full attainment of aquatic life uses. 

TABLE 6-1. Statewide total phosphorus targets (mg/L) for Ohio rivers and streams. 

Watershed Size Aquatic Life Use 

EWH WWH MWH 

Headwaters (drainage area <20 mi

2

) 0.05 0.08 0.34 

Wadeable rivers (20 mi 2 <drainage 

area <200 mi 0.05 0.10 0.28 

Small rivers (200 mi 2 <drainage area 

<1,000 mi 0.10 0.17 0.25 

Large rivers (drainage area >1,000 mi 0.15 0.30 0.32 

EWH =Exceptional Warmwater Habitat; WWH =Warmwater Habitat; MWH =Modified Warmwater Habitat 

As for nutrients, Ohio does not have explicit habitat and sediment criteria in the WQS. However, targets 

for habitat and sedimentation outcomes were developed by demonstrating a relationship between specific 

good quality and poor quality attributes and their ratios. Unlike water quality parameters, single numeric 

criteria for habitat and sedimentation do not exist and are inappropriate because 1) there are complexities 

in identifying expected values or ranges of values for specific attributes, 2) the resultant effects on the 

aquatic biota are explained by aggregations of good (warmwater) and poor (modified; see HIMA in Table 

6-2) habitat attributes, and 3) the spatial scale over which these stressors exert their effects on aquatic life 

includes multiple dimensions (Rankin 1995). Rather than generating tiered criteria for habitat and 

sediment attributes, Ohio has developed quantitative habitat and sediment targets for TMDLs based on 

regional stream types (e.g., low vs. high gradient) and stream-size dependent “dose-response” 

relationships with the numeric biocriteria associated with the tiered aquatic life uses (Rankin 1995). The 

Stillwater River TMDL (Ohio EPA 2004) in the E. Corn Belt Plains (ECBP) ecoregion is an example of 

how nutrient, sediment, and habitat targets (“criteria”) were developed and used along with more 

traditional chemical criteria to direct TMDL development in the watershed (Table 6-2). 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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101 
Define and Allocate

Control Responsibilities

TABLE 6-2. Numeric targets for biological, habitat, and water quality parameters for the Stillwater River 

in western Ohio. From Ohio EPA (2004) TMDL report for the Stillwater River watershed. The targets 

and criteria vary in accordance with the tiered uses, which are resolved prior to impaired water 

delineations and TMDL development. 

Aq. Life 

Use 

Biological 

Criteria Habitat Targets Water Quality Criteria Nutrient Targets 

Min. 

ICI 

Min. 

IBI QHEI HIMAa 

Ammonia-N* 

Dissolved 

Oxygen* 

TKNb Nitrate

b TPb Max Mean Min Mean 

MWH 22 24 45 <3 7.3 1.2 3.0 4.0 4.0 3.0 0.30 

WWH 32 36 60 <1 7.3 0.8 4.0 5.0 1.0 1.0 0.08 

EWH 42 46 75 0 4.5 0.8 5.0 6.0 1.0 0.5 0.05 a

HIMA - High Influence Modified Habitat Attributes b

Target values are adopted from Ohio EPA (1999) *

Specific numeric water quality exist in OAC 3745- 1-07, Tables 7-3 through 7-8; target values are guidelines based on the 

75th percentile values of temperature (24o

C) and field pH (8.1) from all samples collected during the 1999 Stillwater survey. 

MWH = Modified Warmwater Habitat; WWH = Warmwater Habitat; EWH = Exceptional Warmwater Habitat 

All of the targets in Table 6-2 were either wholly or partially generated based on responses between the 

parameters, biological assemblage data, and the tiered aquatic uses to which they are related. This is 

important because most of these parameters, habitat in particular, are not amenable to the traditional 

laboratory based derivation. When these parameters are altered from “naturally occurring” conditions, 

they can induce an adverse response for the biota, thus behaving as stressors. Targets for TMDLs or other 

restoration strategies would either be difficult to generate, or lead to potentially incomplete solutions 

without being ground-truthed in ambient data relationships and a tiered aquatic life use framework, the 

latter of which is typically associated with a stressor gradient based on habitat or landscape 

characteristics. Since many of the targets in Table 6-2 were generated directly from ambient stressor and 

response relationships, their interpretations are likely less ambiguous than a rote application of lab 

derived criteria, although causative associations may be weaker. This approach is consistent with a 

recommendation in the NRC TMDL report (NRC 2001) that criteria or targets be positioned as closely as 

possible to the designated use and that indicators representing the full causal chain of events from stress 

to exposure to response be used. 

Understanding the role of habitat as an influence on the biological restoration potential for a waterbody 

may be one of the greatest values of tiered aquatic life uses coupled with a systematic assessment process. 

Habitat and landscape changes compose a common stressor gradient along which States and Tribes may 

derive tiered uses. Tiered uses provide a useful framework for evaluating restoration potential, 

prioritizing management actions, and allocating abatement resources. 

CASE EXAMPLE 6-3. DETERMINING APPROPRIATE LEVELS OF PROTECTION IN OHIO 

Hurford Run is a small stream located in an urban/industrial area Physical 

(steel finishing, petroleum refineries) of Canton, Ohio that drains 

an area of 8.5 square miles (Figures 6-3, 6-4). The entire stream 

has been subjected to direct channel modifications from the 1900s 

up to the time of the study. During the biological surveys in the 

mid 1980s, the stream was severely impaired by chemical 

pollutants, so much so that some sites had no fish. Because of the 

severity of the impairment, the use attainability analysis (UAA) 

relied on the assessment of habitat quality by the Qualitative 

Habitat Evaluation Index (QHEI; Rankin 1995). 

Enforcement 

& Compliance 

Source 

Controls/BMPs 

Monitoring 

& Assessment 

Establish Uses & Criteria 

Problem ID/Set Priorities 

Chemical Biological 

Define & Allocate Control 

Responsibilities 

Tiered Aquatic Life 

Uses help better 

define designated 

aquatic life uses. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 102 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 6 – August 10, 2005 
LRW MWH WWH


#

# # #

#

Canton, Ohio 

d 

N

# #

#

# # # # #

#

US 

77 

LRW 

MWH 

WWH 

Aquatic Life 

Use 

# Bio Sites 

QHEI Sites 

FIGURE 6-4. Map of Hurford Run near Canton, 

Ohio showing Ohio EPA IBI (solid circles) and 

habitat (QHEI, triangles) sampling stations. 

Spatial extent of stream aquatic life use 

designations is denoted along the top. 

FIGURE 6-3. 1986 photograph of Hurford Run near 

Canton, Ohio looking upstream at the reach that is 

classified as a Limited Resource Water. Disturbed 

soil was caused by efforts to remove soils 

contaminated by nearby industrial operations. 

Established relationships between attributes of habitat as measured by the QHEI and levels of biological 

performance consistent with the tiered aquatic life uses provide an important tool to evaluate use 

attainability and assign appropriate uses to specific streams and rivers (Rankin 1989, 1995; Ohio EPA 

1990). For example, Ohio has identified which habitat features may limit aquatic communities and which 

are predictive of streams with warmwater (WWH) and exceptional warmwater (EWH) biological 

communities. Figure 6-5 summarizes the IBI (left) and QHEI scores (right) for Hurford Run from 1985 

to 1998. Very poor habitat quality from recent and historical channelization in the upper reach (RM 1.8 ­

2.5) of Hurford Run and the associated hydrological characteristics (e.g., ephemeral flows) resulted in a 

Limited Resource Waters (LRW) designation for this upper reach. The middle reach beginning at the 

confluence of Domer Ditch (RM 1.7-1.0) was subject to extensive, maintained channel modifications and 

resulted in degraded habitat features (Figure 6-5, right), but water was always present. Channel 

maintenance practices resulting in poor quality substrates, undeveloped pools and riffles, and a lack of 

instream cover preclude biological recovery to assemblages consistent with the WWH use. Following a 

use attainability analysis (UAA), the middle reach was designated as Modified Warmwater Habitat 

(MWH), reflecting the biological restoration potential for a channel-modified stream. 

The lower one mile of Hurford Run, although previously relocated and channelized, naturally recovered 

sufficient warmwater (good) habitat attributes such as coarse substrates and better developed riffle and 

pool features to achieve QHEI scores (>60-70) that are typical of the WWH use for this ecoregion, hence 

this segment was left at WWH. The tiered aquatic life uses that were assigned represent the highest 

attainable potentials given the existing level of sanctioned channel maintenance in this urban stream. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 103 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 6 – August 10, 2005 
LRW MWH WWH LRW MWH WWH 

20 

30 

40 

50 

60 

70 

80 

Upper Middle Lower 

Q

H

EI 

N = 6 

N = 8 N = 7 

10 

20 

30 

40 

50 

60 

1980s19981980s19981980s1998 

IBI 

N = 16 N = 1 N = 3 N = 2 N = 12 N = 2 

Upper Middle Lower Stream Reach 

Stream Reach 

FIGURE 6-5. Box and whisker plots of IBI (left) and QHEI (right) by stream segment in Hurford Run


near Canton, Ohio. Aquatic life use designations for segments are denoted along the top of each plot.


1998 data is separated from the 1980s data for the IBI, but data are combined for the QHEI. Data


collected between 1985 and 1998. Lines are sites with no variability in scores (IBIs = 12). The hatched


bars denote Ohio biocriteria for each tiered use.


All of the designated uses required additional abatement of the major point sources discharging to 

Hurford Run. Following the initial abatement of point source discharges in the late 1980s, data collected 

in 1998 demonstrated recovery of the IBI score near the mouth of the stream to the WWH biocriterion as 

predicted by the QHEI (Figure 6-5, left). Because this reach was designated WWH, it is protected from 

any further alteration below this quality. The MWH designated middle reach and LRW designated upper 

reach of Hurford Run have been subjected to ongoing channel maintenance activities (e.g., dredging, bank 

mowing), which has limited the amount of biological restoration that can be expected. However, even 

these less-than-CWA goal uses are impaired due to unresolved toxic impacts (reflected in very poor IBI 

scores; Figure 6-5, left) presumably from the point sources and/or legacy impacts associated with the 

industrial sites bordering the stream. 

Urban/industrial streams such as Hurford Run present challenges in terms of setting and attaining 

restoration goals. Visually, the lower reach of Hurford Run may not exemplify the classic depiction of a 

natural stream because of its urban/industrial setting and location adjacent to major highways. The 

instream habitat, however, indicated a WWH potential, which was eventually verified as the effects of 

chemical stressors were reduced. The feedback provided by bioassessments based on the systematic 

collection of biological and habitat data, which is essential to using tiered aquatic life uses, is an 

important impetus for achieving water quality goals. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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104 
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Control Responsibilities

CASE EXAMPLE 6-4. LONG-TERM MONITORING AND USE RE-ESTABLISHMENT IN MAINE 

Between 1974 and 1981, an estimated 33 million dollars was Physical 

spent by industry, State, and federal sources to implement 

primary and secondary wastewater treatment technology on 

facilities discharging into a 100 km section of the Penobscot 

River between Millinocket and Costigan, Maine. These 

expenditures resulted in an 80% reduction in loadings of 

biochemical oxygen demand and total suspended solids 

discharged from the kraft and sulfite pulp and paper mills in 

the study area. In 1974, the benthic macroinvertebrate 

community was determined to be highly degraded at three 

stations in closest proximity to pulp and paper effluents (Stas. 

129, 131, 133). An additional two sites, somewhat downstream of pollution outfalls (Stas. 125, 126), 

were determined to be degraded (Rabeni 1977). The benthic community of the study area has been reevaluated several times following major water quality changes in the 1970s, with the conclusion that the 

investments have resulted in dramatic improvements in the river’s ability to support aquatic life. 

Enforcement 

& Compliance 

Source 

Controls/BMPs 

Monitoring 

& Assessment 

Establish Uses & Criteria 

Problem ID/Set Priorities 

Chemical Biological 

Define & Allocate Control 

Responsibilities 

Tiered Aquatic Life 

Uses help better 

define designated 

aquatic life uses. 

Station 129 is located 4 km downstream of the Lincoln Pulp and Paper Company outfall. Figure 6-6 

provides a graphical summary of changes in two metrics of aquatic community structure for the period of 

record at Station 129. Maine DEP uses the metrics shown in a linear discriminant model to assign aquatic 

life classification attainment. In 1974, Station 129 was designated as “highly polluted.” The substrate at 

Station 129 was covered with sewage bacteria (Sphaerotilus) and the invertebrate community was 

restricted to worms, leeches, and pollution tolerant midge larvae. Numbers of individuals were very high, 

indicating a “bloom” of tolerant, opportunist organisms. Diversity and richness values were very low 

(Figure 6-6), and there was a complete absence of pollution-sensitive mayflies and stoneflies. In terms of 

aquatic life classification, this station did not meet minimum State or federal standards. 

Generic Richness 

0 

10 

20 

30 

40 

50 

60 

1974 1981 1983 1985 1992 1995 

Year 

Var02-Generic

Richness 

Generic Diversity 

0 

1 

2 

3 

4 

5 

1974 1981 1990 1992 1993 1994 1995 

Year 

Var05-SW 

Generic

Diversity 

FIGURE 6-6. Scatter plots showing values for two biological community variables, generic richness (left) 

and generic diversity (right), from Sta. 129, the Penobscot River below Lincoln Pulp and Paper, between 

1974 and 1996. 

Dramatic improvements in the benthic macroinvertebrate community were evident by 1981 (Davies 

1987). Total abundance was down, richness and diversity were greatly improved (Figure 6-6), and the 

proportion of tolerant midge larvae was lower. Low numbers of stoneflies and mayflies were also 

present. Overall, attainment had improved to Class C standards. The station has been sampled four times 

since 1981, each time meeting Class B standards and showing continued improvement in community 

structure, including high diversity and richness and healthy stonefly and mayfly populations. This longterm dataset provides a valuable example of the responsiveness of biota to water quality improvements. It 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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105 
Define and Allocate

Control Responsibilities

also highlights the unique usefulness of biological monitoring to document and summarize the real world 

benefits of responsible stewardship of aquatic resources. 

As a result of investment in wastewater control, the Penobscot River improved dramatically, from not 

attaining Class C standards in 1974 to attaining Class B standards throughout most of the river today. As 

a result, Maine upgraded the river from Class C to Class B in two steps. As of 1999, the entire mainstem, 

with the exception of an impounded section, is now Class B and must attain Class B standards. Without 

TALUs, the upgrade could not have taken place and the river would be maintained today as the equivalent 

of Class C. With Maine's TALUs, the river is now protected as Class B, which has been demonstrated to 

be attainable throughout. Documentation of the improvement and subsequent protection of the improved 

conditions is not possible without TALUs. 

In addition to the Penobscot, many other streams in Maine have been upgraded in class as a result of 

effective wastewater treatment or dam removal, which has led to dramatic improvements in biological 

condition and class attainment. 

CASE EXAMPLE 6-5. DEVELOPMENT OF LIMITS FOR NPDES PERMITS IN MAINE 

Decoster Egg Farm, located in Turner, Maine, is the largest 

producer of brown eggs in New England. The Farm has a long 

history of environmental concerns including levels of ammonia 

and nitrates in violation of drinking water standards. This case 

example presents a unique example of the detection of biological 

impacts in a stream attaining surface water quality standards but 

affected by polluted groundwater recharge. Permitting staff had 

recorded nutrient levels in leachate draining poorly managed 

manure and chicken carcass waste piles. Stream violations were 

not sufficiently high to trigger enforcement action based on 

surface water quality violations but the high levels resulted in 

contaminated leachate entering groundwater on the Decoster property. In 1989, the Department brought 

enforcement action against Decoster Egg Farm to prohibit any further spreading of manure on the 

property and to enforce proper management of other animal waste products. 

In 1991, the company was required to evaluate the condition of the aquatic life in streams affected by 

leachate or groundwater upwelling. Two of the streams, Lively Brook and House Brook, were designated 

by the State to maintain Class B water quality conditions. The use designation process had deemed this to 

be an appropriate management goal for these streams based on the tiered use designations of other 

streams of comparable habitat and watershed condition. Field investigations included probes of the 

hyporheic zone (the water flowing through the stream substrate) to measure the conductivity of the 

upwelling groundwater. Conductivity is a measure of the ionic strength of water and is a very good 

means of detecting certain types of pollutants. The streambed investigation uncovered several areas of 

contaminated groundwater recharge to the stream. Aquatic life sampling, completed in 1992, confirmed 

impacts to the benthos at three stations affected by groundwater upwelling on Lively Brook and one 

station on House Brook. Station 188, on House Brook, is located downstream of a failing treatment 

system that receives waste from the egg washing operation. The waste stream is severely contaminated 

by nitrates. This station failed to attain minimum Class C aquatic life standards in 1992. Repeat 

sampling in 1997 demonstrated attainment of Class C standards but the stream still failed to attain its 

assigned Class B status, indicating the need for additional management intervention. Biomonitoring 

information was used to issue a consent order requiring termination of manure spreading practices and 

improved treatment of the products of the egg washing facilities. The egg washing facility was removed. 

Enforcement 

& Compliance 

Source 

Controls/BMPs 

Monitoring 

& Assessment 

Establish Uses & Criteria 

Problem ID/Set Priorities 

Chemical 

Physical 

Biological 

Define & Allocate Control 

Responsibilities 

Tiered Aquatic Life 

Uses help better 

define designated 

aquatic life uses. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 6 – August 10, 2005 

106 
Define and Allocate

Control Responsibilities

The Lively and House Brooks case study illustrates the full water program cycle (Figure 5-1). 

Monitoring and characterization of the habitat and watersheds of the two streams revealed that, with best 

management practices in place, they should be able to attain Class B status, but in fact were not attaining 

minimum Class C status. Problem identification showed that contaminated groundwater due to poor 

management practices was causing the impairment. A set of source controls were applied, the facility 

complied with the controls, and monitoring of the streams’ condition continued. The monitoring showed 

that although the streams had improved to Class C, they were still not attaining their designated Class B 

status. Maine DEP applied further source controls on the facility to achieve Class B status. 

Ongoing monitoring, iterative management intervention, and tiered use goals confirmed that the streams 

had the potential to attain Class B status. Without tiered uses, source controls would have stopped when a 

minimal condition was reached (consistent with a Class C condition) and the two streams would never 

have recovered to Class B. Tiered aquatic life uses create attainable goals and best uses for waterbodies, 

resulting in better quality waters than are possible with a single use. If a general aquatic life use system 

had been in force, it likely would have resulted in a biological quality comparable to Maine’s Class C, 

with no impetus for improvement to the actual potential (Class B). 

CASE EXAMPLE 6-6. NPDES PERMITTING AND USE ATTAINABILITY ANALYSIS IN OHIO 

Ecologically-based TALUs, a systematic approach to 

monitoring and assessment, and a sound UAA process can Physical 

provide substantial benefits for NPDES permitting related to 

both the derivation of permits and assessing the effectiveness of 

a permit in restoring an aquatic life use. A system for 

identification of the attainable potential for the aquatic life of a 

waterbody using a systematic approach can set credible 

restoration goals and support measured responses to 

environmental risks. This case example illustrates the use of 

TALUs, systematic monitoring and assessment, and a consistent 

process for conducting UAAs in support of NPDES permitting 

issues. 

The Ottawa River in northwest Ohio has been heavily polluted for more than a century. The river is 

impacted by the city of Lima, rural communities, and agricultural activities (row crops). Heavy industry 

in Lima was identified as a major source of water pollution since the 1880s (Leeson 1885 c.f. Ohio EPA 

1992) being especially severe in the 1960s “ . . . when more than 37 miles were devoid of fish, including 

the Auglaize River downstream from the Ottawa River” (Ohio EPA 1992). Point sources include one 

major municipal and two major industrial discharges, industrial contributors to the Lima sewer system, 

combined sewer overflows (CSOs), and partial or untreated sewage discharges from semi-rural areas in 

the watershed. The effluent flow from the three major point sources enter the Ottawa River within a 0.8 

mile reach and comprise the majority of the river flow during dry weather months. Improvements 

consistent with CWA technology standards have been made at the major wastewater treatment facilities 

since the late 1970s. The major causes of impairment include organic enrichment and low D.O., general 

toxicity, habitat alterations (impoundments), nutrients, ammonia, heavy metals, oil and grease, and 

chlorine in both the water column and bottom sediments (Ohio EPA 1998). 

This case example focuses on a 25-mile segment of the Ottawa River that is directly impacted by major 

point sources (Figure 6-7) and includes zones of immediate and acute impacts and various phases of 

recovery downstream. Physical habitat in the mainstem downstream from the major point sources is good 

Enforcement 

& Compliance 

Source 

Controls/BMPs 

Monitoring 

& Assessment 

Establish Uses & Criteria 

Problem ID/Set Priorities 

Chemical Biological 

Define & Allocate Control 

Responsibilities 

Tiered Aquatic Life 

Uses help better 

define designated 

aquatic life uses. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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107 
to excellent, and the mainstem is designated WWH as the result of a use attainability analysis and upgrade 

conducted in the late 1980s. Prior to this analysis, most of the river was assigned the Limited Warmwater 

Habitat (LWH) aquatic life use, which was assigned to rivers thought to be so polluted that restoration 

was considered unfeasible. The LWH use was developed and applied prior to the development and 

adoption of TALUs by Ohio EPA and is no longer used. 

Biological sampling site 

Clark Oil 

(BP Oil) 

PCS 

Lima WWTP 

Lima WWTPRR dam 

L-5 

landfill 

Lima WWTPRR dam 

HogCk 

Little Hog Ck 

Lost Creek 

Little Ottawa River 

Zurmehly Creek 

Honey Run 

Leatherwood 

Ditch 

Auglaize River 

PlumCk 

Sugar Ck 

Beaver 

Run 

Dug Run 

Elida 

Shawnee 

WWTP 

Shawnee

WWTP

Rimer 

Kalida 

Gomer 

American Bath 

WWTP 

LIMA 

Community 

Discharger 

CSO or landfill 

Dam location 

FIGURE 6-7. Map of the Ottawa River with magnification of 

two reaches in the Lima, Ohio area (after Ohio EPA 1998). 

Toxic stressors, exposures, and responses reached a maximum in the segment directly impacted by the 

three major point sources (Ohio EPA 1998; Yoder and DeShon 2003). Evidence of multiple toxic 

exposures occurred in the water column chemistry, sediment chemistry, whole effluent toxicity, 

frequency of DELT anomalies, fish tissue contaminants, and biochemical markers (Table 6-3). These 

indicators pointed strongly to impacts of a toxic character and the biological response signatures provided 

the corroborating feedback. Low D.O. can occur in the Ottawa River (Ohio EPA 1998), but the more 

serious toxic effects that are evident in the biological response signatures presently mask its less serious 

effects. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 6 – August 10, 2005 

108 
er

er

er

TABLE 6-3. A matrix of stressor, exposure, and response indicators for the Ottawa River mainstem 

based on data collected in 1996 (after Ohio EPA 1998). The darkness of shading indicates the degree of 

severity of effect or exceedance expressed by an indicator. 

DES. 

USE 

RESPONSE 

INDICATORS 

EXPOSURE INDICATORS STRESSORS 

SEGMENT 

Attainment 

Status 

QHEI IBI MIwb ICI Water 

Chem. 

Sediment 

Chem. 

Toxicity % 

DELT 

Fish 

Tiss. 

Biomarker 

# 

Dams/ 

Pools 

UrbanIndust. 

Landuse 

Cumulative 

Loads Spills CSO 

SSOs 

Ottawa River mainstem- 1996 

Thayer Rd to 

Sugar St. 

FULLPART. 68 FairGood FairGood Good Nitrates Low NA ModHigh Mercury Low Modate Low Low Low Low 

Sugar St. to 

Lima WWTP NON 47 

Poor 

to 

Fair 

Poor 

to 

Fair 

Poor 

to 

M.G. 

CBOD 

TSS 

D.O. 

As,Cr 

Cd,Cu 

Ni,Zn 

Moderate 

High Pesticides 

BUN 

Naph 

B(a)p 

High High Mod-erate Modate High 

Lima WWTP 

Allentown dam 

NON 72 Poor 

Poor 

to 

Fair 

Fair 

to 

Good 

Amm. 

CBOD 

TSS 

D.O. 

Nitrates 

Phos 

Chrom. 

PAH 

Pesticid 

As,Cr 

Cd,Cu 

Ni,Zn 

PAH 

Moderate 

Very 

High 

Selenium 

Pesticides 

EROD 

Naph 

B(a)p 

BUN 

Modate 

High High High High 

Allentown dam 

to Kalida 

PARTIAL 69 Poor 

-Fair 

FairGood Good 

-Exc. 

TSS Low NA High Pesticides Low Low Low High Low Low 

Kalida to mouth FULL 69 Good Good Exc. TSS Low NA Very 

High 

Pesticides Low Low Low High Low Low 

QHEI scores for the Ottawa indicated more than adequate habitat to support the WWH use designation 

(Rankin 1989, 1995). In a growing recovery zone immediately below the impacted reach, the biota 

eventually exhibited recovery to WWH status in the lower reaches of the river. In the impaired sections, 

the biological response signatures strongly indicate general toxicity, which is a fundamentally different 

response than what would occur in response to habitat or low D.O. alone (Figure 6-8; Yoder and Rankin 

1995b; Yoder and DeShon 2003). Results from a similar time period for the Scioto River are shown for 

comparison. This river is impacted by non-toxic causes and sources including organic enrichment and 

oxygen demanding wastes from sources that dominate the low flow of the river and emanate from a 

similar municipal infrastructure and watershed setting. Taken together, these considerations led Ohio 

EPA to redesignate (upgrade) the Ottawa River from LWH to WWH in 1989. The redesignation was 

controversial and resulted in legal actions challenging the WWH use. Plaintiffs contended that the habitat 

could not support a WWH assemblage and further argued that D.O. concentrations consistent with WWH 

criteria were unattainable due to upstream impoundments and the flow regime. The WWH designation 

was upheld because Ohio had a substantial record demonstrating the relationship between habitat 

condition (as QHEI) and attainable biological condition described in the tiered uses. The response 

signatures indicated that the cause of non-attainment in the Ottawa River was primarily toxicity. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 6 – August 10, 2005 

109 
OTTAWA RIVER: FREQUENCY OF DELT ANOMALIES SCIOTO RIVER: FREQUENCY OF DELT ANOMALIES 

0 

10 

20 

30 

40 

50 

60 

70 

PER

CENT 

n = 38 n = 22 n = 54 n = 48 n = 49 

Toxic Resonse 

Threshold (>10%) 

0 

10 

20 

30 

40 

50 

60 

70 

PER

CENT 

n = 30 n = 8 n = 31 n = 18 n = 28 

Toxic Resonse 

Threshold (>10%) 

1985 1987 1989 1991 1996 1981 1986 1988 1991 1996 

OTTAWA RIVER: IBI SCIOTO RIVER: IBI 

20 

30 

40 

50 

60 

IN

n = 38 n = 22 n = 54 n = 48 n = 49 

DEX 

OF BIO

TIC IN

TEG

RITY (IBI)

12 

WWH Biocriterion 

(IBI = 42) 

Toxic Resonse 

Threshold (IBI <22) 

EWH Biocriterion 

(IBI = 48) 

20 

30 

40 

50 

60 

IN

n = 30 n = 8 n = 31 n = 18 n = 28 

DEX 

OF BIO

TIC IN

TEG

RITY (IBI)

12 

WWH Biocriterion 

(IBI = 40) 

Toxic Resonse 

Threshold (IBI <22) 

1985 1987 1989 1991 1996 1981 1986 1988 1991 1996 

FIGURE 6-8. Results for two key fish assemblage measures (%DELT anomalies, upper left panel and IBI, 

lower left panel) showing the thresholds for toxic responses in the Ottawa River study area between 1985 

and 1996. The results are shown with those from the Scioto River between 1981 and 1996 to illustrate the 

different responses shown in a river impacted by non-toxic stressors. 

The WWH redesignation and the subsequent permitting of the three major point sources could have taken 

a significantly different path in the absence of the TALU approach employed by Ohio EPA. Instead of 

keeping the focus on the most limiting problem of complex toxicity, the outcome could have been 

diverted by the initial claims of habitat limitations and D.O. issues. Ohio’s systematic approach to 

monitoring directly tied to its TALUs was upheld in a court case on the redesignation to WWH, which 

has averted subsequent legal actions in other similar permitting cases. This is related to the soundness 

and consistency of the UAA approach and the perception that the TALUs are reasonably attainable and 

protective. 

One tool the NPDES program uses to identify potential problems from dischargers is non-compliance 

with permit terms and conditions. In this case, none of the individual point sources involved were 

considered in non-compliance of their NPDES permits at the time of the assessments. However, their 

cumulative effect on biological condition resulted in severe biological impairment of the river. As a 

result, Ohio EPA imposed controls to significantly improve water quality, including chronic WET limits, 

close scrutiny of intermittent releases and spills, and internal audits conducted by two of the industrial 

facilities involved. In addition, an unregulated landfill leachate was discovered and subsequently required 

remediation. 

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110 
Define and Allocate

Control Responsibilities

Under a tiered system, the biocriteria endpoints vary with the specific use and thus can affect the NPDES 

permit. For example, a WWH designation requires better biological condition (higher IBI, MCI and 

MIwB scores) than the LRW use. Accordingly, LRW waters can tolerate higher nutrients and lower D.O. 

than WWH waters (See Figure 6-2, Table 6-2, and Appendix B), which would affect permit limits. A 

decision that the stream was either habitat limited or dissolved oxygen limited alone would have diverted 

attention away from the severe toxic impacts that were in reality limiting the aquatic life in this river. The 

magnitude of these influences would have been underestimated on the sole basis of administrative 

measures, without the stressor analysis that identified the causes of impairment in the Ottawa River. 

CASE EXAMPLE 6-7. SUPPORT FOR DREDGE AND FILL PERMITTING IN OHIO 

The losses of habitat diversity or habitat-mediated stressors such as Physical 

increased siltation are now the most prevalent causes of aquatic 

impairment in Ohio (Figure 6-9, Ohio EPA 2000). This is also true 

across much of the U.S. (U.S. EPA 2002b). Environmental effects 

of extensive landscape changes and in stream habitat alterations 

are a primary stressor gradient along which the tiered aquatic life 

uses were developed. Some habitat alterations are readily 

restorable while others are essentially permanent either because 

they are continuously maintained for flood control or drainage 

purposes or they exceed the natural capacity for recovery. 

Enforcement 

& Compliance 

Source 

Controls/BMPs 

Monitoring 

& Assessment 

Establish Uses & Criteria 

Problem ID/Set Priorities 

Chemical Biological 

Define & Allocate Control 

Responsibilities 

Tiered Aquatic Life 

Uses help better 

define designated 

aquatic life uses. 

Habitat Alterations 1222 

Siltation 932.7 

O rganic Enrichm ent 783.2 

States can use Sections 401 and 404 of the CWA to 

manage direct alterations to aquatic habitats. Tiered 

aquatic life uses have proved useful in 404 permitting 

and 401 certification of those permits. Those wanting 

to modify a stream that will result in the discharge of 

dredge or fill material into waters of the U.S. must 

obtain a Section 404 permit from the U.S. Army Corps 

N utrients 575.9 

Flow Alteration 537.3 

of Engineers (ACOE) and a Section 401 water quality 

certification from the State. The State must certify that 

proposed activities will comply with, not violate, WQS. 

Metals 413.5 

0 200 400 600 800 1000 1200 1400 

M The existence of biocriteria in the Ohio WQS makes iles Impaired By Cause 

this linkage a valid tool for evaluating the impacts of 

FIGURE 6-9. Six leading causes of aquatic life habitat alterations that are covered under the CWA. 

impairment in Ohio up to the year 2000 (from Ohio EPA used a 20+ year database to develop habitat 

Ohio EPA 2000). stressor gradients along several aspects of habitat 

quality at both site and watershed scales, including 

overall habitat quality as measured by the QHEI and for specific attributes such as substrate and channel 

condition. Examples of these stressor gradients from the E. Corn Belt Plains (ECBP) and Huron/Erie 

Lake Plain (HELP) ecoregions are illustrated in Figure 6-10. 

Tiered aquatic life uses have enabled a range of management responses to dredge and fill projects related 

to the quality and sensitivity of the waterbody in question. Tiered uses are an important consideration in 

the implementation of nationwide permits. Nationwide permits are designed to minimize site-specific 

oversight where ecological risks are assumed to be low. Frequently, however, the criteria for which 

places are eligible can overlook high quality waters and lead to their alteration. The Ohio EWH use 

designation requires high habitat quality and stable hydrological regimes (especially in headwater and 

wadeable streams). Because these essential attributes can be altered by direct modifications to the stream 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 111 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 6 – August 10, 2005 
channel and other habitat features, Ohio requires individual reviews of projects that occur in such high

quality streams. Under a general use system, these would be lumped with all other streams under the

nationwide permit system.

The same information embodied in the tiered aquatic life uses allows Ohio to expend less oversight on

streams that cannot attain the WWH use designation. Such streams are generally ephemeral or

continuously maintained as drainage conveyances. This does not mean that physically degraded streams

are ignored. The attention gained by habitat impacts has prompted the development of mitigation

standards that will take the tiered aquatic life uses into account and require enhancement or restoration

wherever feasible. The stressor-response relationships (Figure 6-10) that have been developed between

biological assemblages and key habitat attributes have been applied to the 401 program in Ohio. For

nationwide 404 permits a series of general and specific exclusions and conditions have been derived that

vary with tiered aquatic life uses (ACOE 2002). These include a general exclusion (of nationwide

permits) for streams that are EWH and for certain antidegradation tiers (State Resource Waters and

Outstanding State Resource Waters), the delineation of which was based primarily on the same biological

assemblage attributes that are in common with Ohio’s tiered aquatic life uses.

D ata by Site AllY ears D ata by Site AllY ears 

ECBP & HELP Ecoregions ECBP & HELP Ecoregions,Wadeable Stream s 

Reference Sites O N LY Reference Sites O N LY 60 60 

50 50 

Mean Watershed Site Specific IBI IBI 40 

30 

40 

30 

20 20 

y = 13 .43 + 0.396x y = 22.7 + 1.1x

2 2 R = 0.52 R = 0.32 

10 10 

100 90 80 70 60 50 40 30 20 25 20 15 10 5 0 

Site Specific QHEI Site Specific QHEI Substrate Score 

D ata by Site AllY ears 

D ata by Huc Watershed - 1994-2001 ECBP & HELP Ecoregions 

ECBP & HELP Ecoregions Reference Sites O N LY 60 60 

y = 10.96 + 0.44x

2 R = 0.52 50 50 

Site Specific

Site Specific IBI IBI 

40 

30 

40 

30 

20 20 

y = 18.1 + 1.49x

2 R = 0.41 10 10 

100 80 60 40 20 0 20 15 10 5 0 

Mean Watershed Site Specific QHEI 

QHEI ChannelScore 

FIGURE 6-10. Examples of habitat stressor gradients vs. IBI for Ohio wadeable

streams in the ECBP and HELP ecoregions.

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 112 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 6 – August 10, 2005
Aside from the general considerations discussed above, tiered uses have also proved useful for specific 

nationwide permits. For example, Nationwide Permit 21 is for surface coal mining activities. Higher 

quality uses such as WWH or EWH and Coldwater Habitat (CWH) require individual 404 permits in all 

cases. Only MWH or LRW uses can be exempted from site-specific review under a nationwide permit 

for mining (and for these there are stream length limitations). Again this is a significant benefit of having 

tiered uses and the knowledge of the relationships between activities (e.g., habitat alterations) and the 

biological responses in the indexes that compose the tiered biocriteria. The 404/401 program in Ohio is 

still evolving. One goal is to move away from a case-by-case review of every permit by developing 

mitigation standards tied directly to the tiered aquatic life uses that will be protective, relatively rapid, 

accurate, and efficient in terms of resource expenditures. Making similar decisions within a single use 

system would be more difficult and require either more case-by-case oversight to account for habitat 

gradients, or risk being over-protective in some cases and under-protective in others. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

and Tribal Water Quality Standards: Tiered Aquatic Life Uses – Chapter 6 – August 10, 2005 

113 
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114 
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Glossary

Ambient Monitoring sampling and evaluation of receiving waters not necessarily associated with 

episodic perturbations 

Allochthonous organic matter that was produced outside the system (e.g., wood, leaves, 

berries, insects etc.) 

Anadromy fish that live most of life in oceans or lakes and migrate to streams to spawn 

Antidegradation Statement statement that protects existing uses, prevents degradation of high quality 

waterbodies unless certain determinations are made, and which protects the 

quality of outstanding national resource waters 

Aquatic Assemblage an association of interacting populations of organisms in a given waterbody, 

for example, fish assemblage or a benthic macroinvertebrate assemblage 

Aquatic Community an association of interacting assemblages in a given waterbody, the biotic 

component of an ecosystem 

Aquatic Life Use a beneficial use designation in which the waterbody provides suitable habitat 

for survival and reproduction of desirable fish, shellfish, and other aquatic 

organisms; classifications specified in State water quality standards relating to 

the level of protection afforded to the resident biological community by the 

State agency 

Attribute measurable part or process of a biological system 

Autochthonous organic matter produced within the system (e.g., algae, macrophytes) 

BEAST used in parts of Canada, the BEAST (BEnthic Assessment of SedimenT) 

multivariate technique uses a probability model based on taxa ordination space 

and the "best fit" of the test site(s) to the probability ellipses constructed 

around the reference site classes 

Beneficial Uses desirable uses that water quality should support. Examples are drinking water 

supply, primary contact recreation (such as swimming), and aquatic life 

support. 

Benthic Macroinvertebrates or Benthos animals without backbones, living in or on the sediments, of a size large 

enough to be seen by the unaided eye and which can be retained by a U.S. 

Standard No. 30 sieve (28 meshes per inch, 0.595 mm openings). Also 

referred to as benthos, infauna, or macrobenthos 

Best Management Practice an engineered structure or management activity, or combination of these, that 

eliminates or reduces an adverse environmental effect of a pollutant 

Biological Assessment or Bioassessment an evaluation of the biological condition of a waterbody using surveys of the 

structure and function of a community of resident biota. 

Biological Criteria or Biocriteria Scientific meaning: quantified values representing the biological condition of 

a waterbody as measured by structure and function of the aquatic communities 

typically at reference condition. 

Regulatory meaning: narrative descriptions or numerical values of the 

structure and function of aquatic communities in a waterbody necessary to 

protect the designated aquatic life use, implemented in, or through water 

quality standards. 

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135 
Biological Diversity or Biodiversity refers to the variety and variability among living organisms and the ecological 

complexes in which they occur. Diversity can be defined as the number of 

different items and their relative frequencies. For biological diversity, these 

items are organized at many levels, ranging from complete ecosystems to the 

biochemical structures that are the molecular basis of heredity. Thus, the term 

encompasses different ecosystems, species, and genes. 

Biological Indicator or Bioindicator an organism, species, assemblage, or community characteristic of a particular 

habitat, or indicative of a particular set of environmental conditions 

Biological Integrity the ability of an aquatic ecosystem to support and maintain a balanced, 

adaptive community of organisms having a species composition, diversity, and 

functional organization comparable to that of natural habitats within a region 

Biological Monitoring or Biomonitoring use of a biological entity as a detector and its response as a measure to 

determine environmental conditions. Ambient biological surveys and toxicity 

tests are common biological monitoring methods. 

Biological Survey or Biosurvey collecting, processing, and analyzing a representative portion of the resident 

aquatic community to determine its structural and/or functional characteristics 

Bioregion any geographical region characterized by a distinctive flora and/or fauna 

Clean Water Act an act passed by the U.S. Congress to control water pollution (formally 

referred to as the Federal Water Pollution Control Act of 1972). Public Law 

92-500, as amended. 33 U.S.C. 1251 et seq. 

Clean Water Act 303(d) This section of the Act requires States, territories, and authorized Tribes to 

develop lists of impaired waters for which applicable water quality standards 

are not being met, even after point sources of pollution have installed the 

minimum required levels of pollution control technology. The law requires 

that these jurisdictions establish priority rankings for waters on the lists and 

develop TMDLs for these waters. States, territories, and authorized Tribes are 

to submit their list of waters on April 1 in every even-numbered year. 

Clean Water Act 305(b) biennial reporting requires description of the quality of the Nation’s surface 

waters, evaluation of progress made in maintaining and restoring water 

quality, and description of the extent of remaining problems 

Cosmopolitan Species species with worldwide distribution or influence where there is suitable habitat 

Criteria limits on a particular pollutant or condition of a waterbody presumed to 

support or protect the designated use or uses of a waterbody. Criteria may be 

narrative or numeric. 

DELT Anomalies percentage of Deformities, Erosions (e.g., fins, barbels), Lesions and Tumors 

on fish assemblages 

Designated Uses those uses specified in water quality standards for each waterbody or segment 

whether or not they are being attained 

Disturbance human activity that alters the natural state and can occur at or across many 

spatial and temporal scales 

Ecological Integrity the condition of an unimpaired ecosystem as measured by combined chemical, 

physical (including physical habitat), and biological attributes. Ecosystems 

have integrity when they have their native components (plants, animals and 

other organisms) and processes (such as growth and reproduction) intact. 

Ecoregion a relatively homogeneous ecological area defined by similarity of climate, 

landform, soil, potential natural vegetation, hydrology, or other ecologically 

relevant variables 

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Ecosystem-level functions 

Existing Uses 

Function 

Heterotrophic 

Hyporheic Zone 

Historical Data 

Historically documented taxa 

Index of Biological/Biotic Integrity 

Invasive species 

Life-history requirements 

Lithophils 

Lithopelagophils 

Maintenance of populations 

Metric 

Multimetric Index 

Multivariate Analysis 

Narrative Biocriteria 

processes performed by ecosystems, including, among other things, primary 

and secondary production; respiration; nutrient cycling; decomposition. See 

discussion concerning how this function is considered in the draft biological 

condition gradient in transmittal memorandum under "outstanding issues" and 

in the file: attribute explanation. 

those uses actually attained in a waterbody on or after November 28, 1975, 

whether or not they are included in the water quality standards (November 28, 

1975 is the date on which U.S. EPA promulgated its first water quality 

standards regulation). Because an existing use has been attained, it cannot be 

removed unless uses are added that require more stringent criteria. 

processes required for normal performance of a biological system (may be 

applied to any level of biological organization) 

obtaining organic matter from other organisms rather than synthesizing it from 

inorganic substrates 

area below the streambed where water percolates through spaces between the 

rocks and cobbles. Also known as the interface between surface water and 

groundwater. 

data sets from previous studies, which can range from handwritten field notes 

to published journal articles 

taxa known to have been supported in a waterbody or region prior to 

enactment of the Clean Water Act, according to historical records compiled by 

state or federal agencies or published scientific literature 

an integrative expression of site condition across multiple metrics. An index 

of biological integrity is often composed of at least seven metrics 

a species whose presence in the environment causes economic or 

environmental harm or harm to human health. Native species or non-native 

species may show invasive traits, although this is rare for native species and 

relatively common for non-native species. (Please note - this term is not 

currently included in the biological condition gradient) 

environmental conditions necessary for completing life cycles (including, 

among other things, reproduction, growth, maturation, migration, dispersal) 

organisms that thrive on rocks or stones 

organisms that spawn in open gravelly areas and have no guarding behavior 

sustained population persistence; associated with locally successful 

reproduction and growth 

a calculated term or enumeration representing some aspect of biological 

assemblage, function, or other measurable aspect and is a characteristic of the 

biota that changes in some predictable way with increased human influence 

an index that combines indicators, or metrics, into a single index value. Each 

metric is tested and calibrated to a scale and transformed into a unitless score 

prior to being aggregated into a multimetric index. Both the index and metrics 

are useful in assessing and diagnosing ecological condition. See Index of 

Biotic Integrity. 

statistical methods (e.g. ordination or discriminant analysis) for analyzing 

physical and biological community data using multiple variables 

written statements describing the structure and function of aquatic 

communities in a waterbody necessary to protect a designated aquatic life use 

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Native an original or indigenous inhabitant of a region; naturally present 

Non-detrimental effect does not displace native taxa 

Non-native or intentionally introduced with respect to a particular ecosystem, any species that is not found in that 

species ecosystem. Species introduced or spread from one region of the U.S. to 

another outside their normal range are non-native or non-indigenous, as are 

species introduced from other continents. 

Numeric Biocriteria specific quantitative measures of the structure and function of aquatic 

communities in a waterbody necessary to protect a designated aquatic life use 

Periphyton a broad organismal assemblage composed of attached algae, bacteria, their 

secretions, associated detritus, and various species of microinvertebrates 

Piscivore predatory fish that eats mainly other fish 

Polyphils organism with no specialized spawning requirements, behavior, or preferred 

habitat 

P/R ratio of photosynthesis to respiration in a system 

Presently Attained Uses those uses actually being attained in a waterbody at the present moment 

Rapid Bioassessment Protocols cost-effective techniques used to survey and evaluate the aquatic community 

to detect aquatic life impairments and their relative severity 

Reference Condition the condition that approximates natural, un-impacted conditions (biological, 

(Biological Integrity) chemical, physical, etc.) for a waterbody. Reference condition (Biological 

Integrity) is best determined by collecting measurements at a number of sites 

in a similar waterbody class or region under undisturbed or minimally 

disturbed conditions (by human activity), if they exist. Since undisturbed or 

minimally disturbed conditions may be difficult or impossible to find, least 

disturbed conditions, combined with historical information, models or other 

methods may be used to approximate reference condition as long as the 

departure from natural or ideal is understood. Reference condition is used as a 

benchmark to determine how much other water bodies depart from this 

condition due to human disturbance. 

Reference Condition Least Disturbed Condition: the best available existing conditions with regard 

(Biological Integrity), cont. to physical, chemical, and biological characteristics or attributes of a 

waterbody within a class or region. These waters have the least amount of 

human disturbance in comparison to others within the waterbody class, region 

or basin. Least disturbed conditions can be readily found, but may depart 

significantly from natural, undisturbed conditions or minimally disturbed 

conditions. Least disturbed condition may change significantly over time as 

human disturbances change. 

Minimally Disturbed Condition: the physical, chemical, and biological 

conditions of a waterbody with very limited, or minimal, human disturbance in 

comparison to others within the waterbody class or region. Minimally 

disturbed conditions can change over time in response to natural processes. 

Best Attainable Condition: a condition that is equivalent to the ecological 

condition of (hypothetical) least disturbed sites where the best possible 

management practices are in use. This condition can be determined using 

techniques such as historical reconstruction, best ecological judgment and 

modeling, restoration experiments, or inference from data distributions 

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Reference Site 

Refugia 

Regional Reference Condition 

Rheophils 

Restoration 

River Invertebrate Prediction and 

Classification System (RIVPACS) 

Sensitive taxa 

Sensitive or regionally endemic taxa 

Sensitive - rare taxa 

Sensitive - ubiquitous taxa 

Spatial and temporal ecosystem 

connectance 

Stressors 

a site selected for comparison with sites being assessed. The type of sites 

selected and the type of comparative measures used will vary with the purpose 

of the comparisons. For the purposes of assessing the ecological condition of 

sites, a reference site is a specific locality on a waterbody that is undisturbed 

or minimally disturbed and is representative of the expected ecological 

integrity of other localities on the same waterbody or nearby waterbodies 

accessible microhabitats or regions within a stream reach or watershed where 

adequate conditions for organism survival are maintained during 

circumstances that threaten survival, e.g., drought, flood, temperature 

extremes, increased chemical stressors, habitat disturbance, etc. 

a description of the chemical, physical, or biological condition based on an 

aggregation of data from reference sites that are representative of a waterbody 

type in an ecoregion, subecoregion, watershed, or political unit 

organisms that flourish in free-flowing water 

the re-establishment of pre-disturbance aquatic functions and related physical, 

chemical, and biological characteristics 

a predictive method developed for use in the United Kingdom to assess water 

quality using a comparison of observed biological species distributions to 

those expected to occur based on a model derived from reference data 

intolerant to a given anthropogenic stress; first species affected by the specific 

stressor to which they are "sensitive" and the last to recover following 

restoration 

taxa with restricted, geographically isolated distribution patterns (occurring 

only in a locale as opposed to a region), often due to unique life history 

requirements. May be long-lived, late maturing, low fecundity, limited 

mobility, or require mutualist relation with other species. May be among 

listed E/T or special concern species. Predictability of occurrence often low, 

therefore, requires documented observation. Recorded occurrence may be 

highly dependent on sample methods, site selection and level of effort. 

naturally occur in low numbers relative to total population density but may 

make up large relative proportion of richness. May be ubiquitous in occurrence 

or may be restricted to certain micro-habitats, but because of low density, 

recorded occurrence is dependent on sample effort. Often stenothermic 

(having a narrow range of thermal tolerance) or cold-water obligates; 

commonly k-strategists (populations maintained at a fairly constant level; 

slower development; longer life-span). May have specialized food resource 

needs or feeding strategies. Generally intolerant to significant alteration of the 

physical or chemical environment; are often the first taxa observed to be lost 

from a community. 

ordinarily common and abundant in natural communities when conventional 

sample methods are used. Often having a broader range of thermal tolerance 

than Sensitive- Rare taxa. These are taxa that comprise a substantial portion of 

natural communities, and that often exhibit negative response (loss of 

population, richness) at mild pollution loads or habitat alteration. 

access or linkage (in space/time) to materials, locations, and conditions 

required for maintenance of interacting populations of aquatic life; the 

opposite of fragmentation; necessary for metapopulation maintenance and 

natural flows of energy and nutrients across ecosystem boundaries 

physical, chemical, and biological factors that adversely affect aquatic 

organisms 

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Structure taxonomic and quantitative attributes of an assemblage or community, 

including species richness and relative abundance structurally & functionally 

redundant attributes of the system = characteristics, qualities, or processes that 

are represented or performed by more than one entity in a biological system 

Subcategorized Uses States and Tribes may adopt subcategories of a use and set the appropriate 

criteria to reflect varying needs of such subcategories of uses, for instance, to 

differentiate between cold water and warm water fisheries 

Taxa a grouping of organisms given a formal taxonomic name such as species, 

genus, family, etc. 

Taxa of intermediate tolerance comprise a substantial portion of natural communities; may be r-strategists 

(early colonizers with rapid turn-over times; "boom/bust population 

characteristics). May be eurythermal (having a broad thermal tolerance range). 

May have generalist or facultative feeding strategies enabling utilization of 

relatively more diversified food types. Readily collected with conventional 

sample methods. May increase in number in waters with moderately increased 

organic resources and reduced competition but are intolerant of excessive 

pollution loads or habitat alteration. 

Tolerant taxa comprise a low proportion of natural communities. Taxa often are tolerant of a 

broader range of environmental conditions and are thus resistant to a variety of 

pollution or habitat induced stress. They may increase in number (sometimes 

greatly) in the absence of competition. Commonly r-strategists (early 

colonizers with rapid turn-over times; "boom/bust" population characteristics), 

able to capitalize when stress conditions occur. Last survivors. 

Total Maximum Daily Load the sum of the allowable loads of a single pollutant from all contributing point 

and nonpoint sources; calculation of the maximum amount of a pollutant a 

waterbody can receive and still meet water quality standards and an allocation 

of that amount to the pollutant’s source 

Use Attainability Analysis structured scientific assessment of the physical, chemical, biological or 

economic factors affecting attainment of the uses of waterbodies 

Water Quality Standards a law or regulation that consists of the designated use or uses of a waterbody, 

the narrative or numerical water quality criteria (including biocriteria) that are 

necessary to protect the use or uses of that particular waterbody, and an 

antidegradation policy 

Water Resource Management 

(Non-Regulatory) 

decisions on management activities relevant to a water resource such as 

problem identification, need for and placement of best management practices, 

pollution abatement actions, and effectiveness of program activity 

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Acronym s

ACOE Army Corps of Engineers 

ALU Aquatic Life Use 

BCG Biological Condition Gradient 

BEAST BEnthic Assessment of SedimenT 

BOD Biological Oxygen Demand 

BPJ Best Professional Judgment 

BMP Best Management Practice 

CDG Catchment Disturbance Gradient 

CAFO Confined Animal Feeding Operation 

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act 

CSO Combined Sewer Overflows 

CWA Clean Water Act 

EPT Ephemeroptera, Plecoptera, Trichoptera 

FWPCA Federal Water Pollution Control Act 

GIS Geographic Information Systems 

GLEI Great Lakes Environmental Indicators 

HDG Human Disturbance Gradient 

HDI Human Disturbance Index 

IBI Index of Biological/Biotic Integrity 

ICI Invertebrate Community Index 

ITFM Intergovernmental Task Force on Monitoring Water Quality 

LDM Linear Discriminant Model 

LWD Large Woody Debris 

NPDES National Pollutant Discharge Elimination System 

NWHI Non-Wadeable Habitat Index 

ONRW Outstanding Natural Resource Waters 

QHEI Qualitative Habitat Evaluation Index 

RBP Rapid Bioassessment Protocols 

RCRA Resource Conservation and Recovery Act 

RDG Riparian Disturbance Gradient 

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RIVPACS River Invertebrate Prediction and Classification System 

TALU Tiered Aquatic Life Use 

TMDL Total Maximum Daily Load 

SCI Stream Condition Index 

STP Sewage Treatment Plants 

UAA Use Attainability Analyses 

WLAs Waste Load Allocations 

WQS Water Quality Standards 

WWTP Wastewater Treatment Plant 

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Appendix A

MAINE TALU IMPLEMENTATION CASE HISTORY1 

I. Establish conceptual foundation 

Since the early 1970s, prior to adoption of the CWA, Maine water quality law has had a tiered structure, 

based on a gradient of water quality conditions. An early articulation of the conceptual basis for a tiered 

approach to establishing aquatic life uses was made by John Cairns and others in a U.S. EPA-sponsored 

symposium on the biological integrity objective of the Clean Water Act (Ballentine and Guarraia 1977), 

with further elaboration in Cairns et al. (1993) and Karr and Chu (2000). The underlying basis depicts 

biological condition declining across a gradient of stressors. 

Maine’s goal-based management classes range from Class AA, the highest water quality standard and 

greatest restrictions on human activity, to Class C (and formerly Class D, discontinued), the lowest 

quality standard with more flexible allowances for human activities (MDEP 2004 305b report). Maine’s 

current water quality classification law for rivers and streams establishes four tiers of aquatic life use 

(ALU) that represent the upper end of a gradient of biological condition that occurs in the State (State of 

Maine 1985, Courtemanch et al. 1989, Courtemanch 1995). Conditions worse than this upper end (i.e., 

worse than Class AA/A, B, or C) are deemed unacceptable. Numeric biocriteria are based on assessment 

of benthic macroinvertebrates (State of Maine 2003, Davies et al. unpublished manuscript). Assessment 

of algal assemblages also occurs in most waterbodies but numeric criteria have not yet been developed. 

Maine relies on the response of benthic macroinvertebrates to human influences for several reasons: 

° Diverse life history strategies and a wide range of pollution tolerance; 

° Relatively long-lived (+/- 1 year) compared to algae and bacteria; 

° Limited mobility diminishes stressor avoidance behavior and emigration; 

° The indigenous fish assemblage in Maine is not very diverse and information is limited to just a 

few species. 

Biologists in Maine and elsewhere have long observed clear-cut differences in community structure and 

composition of benthic macroinvertebrate samples that are collected from waters across a continuum of 

increasing stressors. The conceptual foundation of the Maine Department of Environmental Protection 

(MDEP) Biological Monitoring Program (and resulting biocriteria) was framed by three factors: 1) the 

first-hand observations of such biological response patterns, 2) published empirical and theoretical work 

in aquatic stress ecology, and 3) Maine’s pre-existing water management context. The first two factors 

are discussed in sequence in this section. The water management context is discussed in the next section, 

II. Merge Scientific & Policy Foundations. 

Empirical Observations of Maine Biologists 

Differences in resident biological assemblages are evident even to the untrained eye when there are 

substantial differences in water quality (Figure A-1). This can be illustrated with a very simple example 

based on a gradient of increasing enrichment. In the initial years of biological assessment in Maine, 

biologists observed that minimally disturbed sampling locations tended to support many invertebrate taxa 

(high diversity), but at low to moderate density. In contrast, streams receiving well-treated or well-diluted 

domestic effluents exhibited higher organism densities, though the types of organisms were similar. 

1 Appendix A was written by Susan Davies, Maine Department of Environmental Protection. 

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Streams receiving heavy loadings of sewage or nutrient-laden industrial effluents showed obvious 

differences in taxa and numbers from that expected in minimally disturbed streams. Streams receiving 

toxic amounts of chlorine or industrial waste showed much lower densities and many more hardy types of 

organisms than would be expected in undisturbed areas. 

Undisturbed Watershed Sample Urban Stream Sample 

Dragonflies & 

Midges 

Beetles 

Mayflies 

Stoneflies 

Damselflies Dragonflies 

Caddisflies 

Snails 

Midges 

Scuds 

Beetles Craneflies 

&


Damselflies Leeches


Caddisflies 

1 inch 1 inch 

FIGURE A-1. Differences in numbers and types of organisms that are associated with 

different levels of disturbance can be evident even to the untrained eye. 

Published Empirical and Theoretical Work in Aquatic Stress Ecology 

The very obvious differences in biological responses for Maine streams, described above, are consistent 

with published conceptual models and empirical findings of stress ecology. The subsidy-stress gradient 

model of Reibesell (1974), and further developed by Odum et al. (1979) and Odum (1985), provided 

Maine DEP biologists with a theoretical model of expected patterns of biological change that was 

consistent with their own empirical observations (Figure A-2a and A-2b). Development of numeric 

biocriteria proceeded from this underlying ecological paradigm with the goal to statistically characterize 

the observed biological condition groups to determine aquatic life use class attainment. 

Subsidy 

Natural 

Stress 

Replacement 

Lethal 

Usable Input 

Toxic Input Rel. Variance 

Increasing Perturbation 

Paradox of Enrichment 

FIGURE A-2a. Subsidy-stress gradient: The ecological 

theory basis for Maine’s aquatic life use descriptions 

(Odum et al. 1979). Some disturbances have an 

enriching or subsidizing effect on biological 

assemblages because they provide more than normal 

usable resources (nutrients, organic matter, etc.). 

Inputs in excess of what can be processed by the 

resident community have a detrimental effect 

(increased biochemical oxygen demand, 

accumulation of unusable resources, etc.) and lead to 

negative community response. Toxic or poisonous 

inputs have an immediate detrimental effect. 

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FIGURE A-2b. Empirically observed 

subsidy-stress gradient in Maine 

streams, documented by changes in 

benthic macroinvertebrate density. 

Low levels of conductivity are an 

indicator of slight enrichment while 

high levels are often associated with 

toxic contamination. 

Stress ecology recognizes biological changes in response to increasing levels of stressors (i.e., gradients 

of environmental quality) as distinct from those that occur in responses to natural gradients, such as 

elevation, climate, alkalinity, stream size, and geographic location. While natural and ecoregional 

gradients can and do influence biological expectations in important ways, biological responses from the 

high to the low end of generalized stressor gradients in Maine streams tend to be far more obvious 

(Davies et al. 1999, Davies et al. unpublished manuscript). Odum’s model supported our observation that 

structurally distinct biological groups exist across a gradient of water quality. Identifying predictable, 

characteristic differences among those biological condition groups could serve as the underlying 

conceptual basis for development of tiered aquatic life uses. Four biological condition groups would also 

fit well with the State’s four-tiered standards for dissolved oxygen, bacteria, and habitat described in the 

existing water quality classification law. 

II. Merge scientific and policy foundations 

The narrative aquatic life use statements in Maine’s TALUs describe conditions ranging from “as 

naturally occurs” (Class AA and Class A- the highest ALU designations) to “maintenance of structure and 

function” (Class C- the lowest ALU designation allowed in Maine) (Table A-1). The subsidy-stress 

gradient model helped guide the development of the ecologically-based definitions in the law. These 

specific definitions establish the biological characteristics that are required for attainment of each ALU 

classification (Table A-2). 

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TABLE A-1. Maine's narrative aquatic life and habitat standards for rivers and streams (M.R.S.A Title 38 Article 

4-A § 464-465). 

CLASS MANAGEMENT BIOLOGICAL STANDARD 

AA* High quality water for recreation and ecological 

interests. No discharges or impoundments 

permitted. 

Habitat shall be characterized as natural and free 

flowing. Aquatic life shall be as naturally occurs. 

A High quality water with limited human interference. 

Discharges limited to non-contact process water or 

highly treated wastewater of quality equal to or 

better than the receiving water. Impoundments 

allowed. 

Habitat shall be characterized as natural. Aquatic life 

shall be as naturally occurs 

B Good quality water. Discharge of well-treated 

effluent with ample dilution permitted. 

Impoundments allowed. 

Habitat shall be characterized as unimpaired. 

Discharges shall not cause adverse impacts to aquatic 

life. Receiving water shall be of sufficient quality to 

support all aquatic species indigenous to the receiving 

water without detrimental changes in the resident 

biological community. 

C Acceptable water quality. Maintains the interim 

goals of the Federal Water Quality Act 

(fishable/swimmable). Discharge of well-treated 

effluent permitted. Impoundments allowed. 

Habitat for fish and other aquatic life. Discharges may 

cause some changes to aquatic life, provided that the 

receiving waters shall be of sufficient quality to support 

all species of fish indigenous to the receiving water and 

maintain the structure and function of the resident 

biological community. 

Impoundments Riverine impoundments not classified as Great 

Ponds and managed for hydropower generation 

Support all species of fish indigenous to those waters 

and maintain the structure and function of the resident 

biological community. 

*The narrative aquatic life standard is the same for Class AA and Class A. 

TABLE A-2. Definitions of terms used in Maine’s water classification law. 

1.	 Aquatic life any plants or animals that live at least part of their life cycle in fresh water. 

2.	 As naturally occurs conditions with essentially the same physical, chemical and biological characteristics as 

found in situations with similar habitats, free of measurable effects of human activity. 

3.	 Community function mechanisms of uptake storage and transfer of life-sustaining materials available to a 

biological community, which determine the efficiency of use and the amount of export of the materials from the 

community. 

4.	 Community structure the organization of a biological community based on numbers of individuals within 

different taxonomic groups and the proportion each taxonomic group represents of the total community. 

5.	 Indigenous supported in a reach of water or known to have been supported according to historical records 

compiled by State and Federal agencies or published in scientific literature. 

6.	 Natural living in or as if in, a state of nature not measurably affected by human activity. 

7.	 Resident biological community aquatic life expected to exist in a habitat, which is free from the influence of 

the discharge of any pollutant. This shall be established by accepted biomonitoring techniques. 

8.	 Unimpaired without a diminished capacity to support aquatic life. 

9.	 Without detrimental changes in the resident biological community no significant loss of species or excessive 

dominance by any species or group of species attributable to human activity. 

Consistency with other applicable WQ criteria 

As shown in Figure A-3, MDEP designed the narrative ALUs to be parallel to the tiered dissolved oxygen 

and bacteria standards. This was done because Department biologists recognized that differences in 

allowed human activities and water quality criteria of the different classes (AA, A, B, C) would inevitably 

yield different expectations for aquatic community response. For example, it is unreasonable to expect 

the same biological assemblages to thrive in both Class AA waters (dissolved oxygen: “as naturally 

occurs”- >7 ppm for Maine; dams and discharges prohibited) and Class C waters (minimum dissolved 

oxygen 5 ppm; dams, industrial and municipal discharges allowed). 

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As naturally 

occurs. 

Habitat: “natural” No detrimental change; 

support all indigenous 

species. 

Habitat: “unimpaired” 

Maintain structure 

and function; support 

all indigenous fish 

(salmonids). 

Habitat for fish and 

aquatic life 

NonAttainment 

of minimum 

standards 

Natural 

Very Good 

Sustainable 

Degraded 

Class AA/A 

Class B 

Class C 

NA

Reso

urce C

o

n

dition 

Maine’s Water Quality Management Classes 

CLASS AA CLASS A CLASS B CLASS C NA 

Zero discharge; No alternatives; D/C with ample dilution; DO: 5ppm/60% saturation; 

No hydrologic D/C Equal to or DO: 7ppm/75% saturation; Water quality sufficient to 

alteration; DO better; hydro 9ppm for salmonid ensure salmonid 

and bacteria as allowed; DO: 7ppm/ spawning; Bacteria: spawning/survival; 

natural 75% saturation; 64/100 mil- in the summer Bacteria:142/100 mil 

bacteria as natural 

FIGURE A-3. Relation between Maine TALUs and other water quality standards and criteria. 

The final language of the narrative aquatic life uses was the result of extensive negotiations between 

MDEP biologists and stakeholder biologists, under the purview of a legislative subcommittee. Lawyers 

on both sides weighed in regularly to ensure the fairness and legality of the statute. MDEP biologists 

drafted the narrative standards and definitions with careful attention to retaining a sound foundation in 

ecological theory. Furthermore, careful attention was given to how each biological attribute could be 

quantified (and thus assessed for attainment), with credible and widely accepted biological metrics (Table 

A-3). 

TABLE A-3. Maine tiered uses based on measurable ecological values. 

Narrative Standard Ecological Value Quantifiable Measures 

CLASS A 

natural 

CLASS B 

unimpaired, maintain 

indigenous taxa 

CLASS C 

maintain structure 

and function 

Taxonomic and Numeric 

Equality; Presence of 

Indicator Taxa 

Retention of taxa and 

numbers; Absence of 

hyperdominance; Presence of 

sensitive taxa 

Resistance, Redundancy; 

Resilience; Balanced 

Distribution 

Energy exchange; Resource 

assimilation; Reproduction 

Similarity, Richness, Abundance, 

Diversity; EPT, Indicator Taxa, Biotic 

Index 

Community loss; Richness; Abundance; 

Diversity; Equitability; Evenness; EPT; 

Indicator Taxa, Biotic Index 

Richness; Diversity; Equitability; 

Evenness 

Trophic groups; Richness; Abundance; 

Community loss; Fecundity; Colonization 

rate 

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How do Maine’s tiered aquatic life uses relate to the Biological Condition Gradient? 

Maine’s aquatic life standards specify different levels (tiers) of water quality necessary to maintain 

designated aquatic life uses. These standards correspond to the tiers of the Biological Condition Gradient 

in Figure A-4. 

Nativeornaturalcondition

1

Natural

Biological Con

dition 

Degraded 

Biological Con

dition

SDeveegrrealdy ed

Altered structureandfunction 6

2 Minimal loss of species; some 

density changes may occur 

3 

Some replacement of 

sensitive-rare species; 

functions fully 

maintained 4 

Some sensitive species 

maintained; altered 

distributions; functions 

largely maintained 

5 

Tolerant species show 

increasing dominance; 

sensitive species are rare; 

functions altered Severe alteration of 

2 Minimal loss of species; some

density changes may occur

3

Some replacement of

sensitive-rare species;

functions fully

maintained

4

Some sensitive species

maintained; altered

distributions; functions

largely maintained

5

Tolerant species show

increasing dominance;

sensitive species are rare;

functions altered Severe alteration of

NA 

C 

B 

AA 

A 

NA

C

B

AA

A

L EffectofHumanDisturbance ow Stressor Gradient High

[Stressorgradient]

FIGURE A-4. Maine TALUs in relation to the BCG tiers. 

Class AA and Class A have the same narrative aquatic life uses requiring that aquatic life be “as 

naturally occurs.” This phrase is defined in the statute as “conditions with essentially the same physical, 

chemical, and biological characteristics as found in situations with similar habitats, free of measurable 

effects of human activity.” The stated goal condition for Class AA/A thus conforms to Tier 1 or high Tier 

2 conditions on the BCG. 

Samples attaining MDEP Class A numeric criteria cover a range of conditions, some of which are fully 

consistent with BCG Tier 1 but some of which would have to be interpreted as BCG Tier 2. Examples of 

the latter are mildly enriched locations showing higher abundance of organisms (than “natural” for 

Maine) and increased algal biomass, and Class A locations that are influenced by dams. 

Class B aquatic life standards require that there be “no adverse impacts” and that water quality be 

“sufficient to support all indigenous aquatic species without detrimental changes in the resident biological 

community.” This phrase is defined as “no significant loss of species or excessive dominance by any 

species or group of species attributable to human activity.” This wording was carefully chosen to allow 

for commonly observed increases in measures of biomass, density, and richness that occur in response to 

mild enrichment (as depicted by Odum’s “subsidy hump” in Figure A-2a and A-2b) but to prohibit 

negative biological changes, such as notable loss of indigenous taxa. Thus the expectation for Class B is 

that sensitive taxa should be well represented with community structure comparable to Class A. 

Samples attaining MDEP Class B numeric criteria cover a range of conditions, some of which are fully 

consistent with BCG Tier 2 but some of which would have to be interpreted as BCG Tier 3 because of the 

degree of structural change or the failure to collect Sensitive-Rare taxa. Dams, well-managed landscape 

changes, and well-treated point sources are allowed in Class B waters. These changes may result in 

detectable signals such as absence of migratory taxa, increased algal biomass, higher total abundance of 

organisms, and increased abundance of sensitive-ubiquitous taxa (i.e., higher relative abundance of some 

mayflies and some filter feeders; higher abundance of Perlid stoneflies) resulting in a community 

structure more consistent with Tier 3. 

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Class C aquatic life standards require that structure and function of the resident biological community be 

maintained. Numeric biocriteria in Maine document that waterbody segments meeting Class C dissolved 

oxygen and bacteria standards, but not attaining Class B standards, show obvious differences in biological 

assemblages. In terms of benthic macroinvertebrates, differences can be generally described as lower 

numbers and richness of cold-water obligate taxa and those taxa that have high dissolved oxygen 

requirements (e.g., gill-breathing mayflies and stoneflies), higher densities of filter-feeding organisms, 

and increased densities of some types of chironomid midges and other facultative or tolerant groups. 

Samples attaining MDEP Class C numeric criteria cover a range of biological conditions, most of which 

are fully consistent with BCG Tier 3 and/or Tier 4. About 10% of samples that attain MDEP Class C 

numeric criteria would have to be interpreted as BCG Tier 5 because of the degree of structural change or 

very low numbers of Sensitive taxa (e.g., the mean abundance of Ephemeroptera in sites attaining Class C 

numeric criteria is 86 individuals per sampler but about 10% have less than 10 mayflies). Attainment of 

Class C numeric criteria usually indicates that other community structure attributes are present (e.g., 

evenness of distributions, richness and/or diversity of the assemblage of taxa of intermediate tolerance). 

Hyper-dominance of filter-feeders, complete absence of expected sensitive insect taxa (especially 

stoneflies and mayflies), and high proportions of tolerant taxa signal assemblages that fail to meet Class C 

water quality standards. These conditions represent BCG Tiers 5 and 6. 

III. Establish technical program 

How does Maine DEP collect biological data? 

The MDEP’s Biological Monitoring Program began standardized sampling of river and stream 

macroinvertebrates in 1983 (less rigorously standardized biological assessments had begun at least 10 

years before). Experience gained on the Penobscot River (Davies 1987, Rabeni et al. 1988) had 

demonstrated the practical usefulness and reliability of rock-filled basket artificial substrates (Klemm et 

al. 1990). Maine has adapted the basic design of these devices to enable sampling of waterbody depths 

ranging from as little as 5 cm (using rock-filled mesh bags; Davies et al. 1999) to about 10 meters in large 

riverine impoundments (using boat-retrievable cones; Courtemanch 1984, Davies and Tsomides 2002, 

http://www.state.me.us/dep/blwq/docmonitoring/biological/biorep2000.htm). The success of these 

devices has enabled the MDEP to apply comparable field and analytical methods to nearly all rivers and 

streams of significant regulatory interest (Davies and Tsomides 2002), greatly simplifying the 

development and application of river and stream biocriteria. Further, the physiography of Maine is quite 

homogeneous with roughly 85% of the State falling within just two relatively similar ecoregions 

(Omernik 1987). For this reason stratification by ecoregion was not the critical concern that it is for 

States in some other regions of the country (Davies et al. unpublished manuscript).

2 

In 1999, Maine began an algal monitoring program to strengthen the interpretation of ecological condition 

by providing information from a second biological assemblage. Maine’s fish assemblage is naturally 

depauperate, limiting its suitability as a candidate for bioassessment. The algal monitoring program will 

assist the Department in the development of river and stream nutrient criteria. The Department also has a 

companion biomonitoring program to assess wetland biological condition. 

Database development 

By the late summer of 2004, the Department had established about 800 monitoring stations in all major 

watersheds throughout the State (Figure A-5). Data from macroinvertebrate samples are stored in an 

Oracle

© database and all stations are geo-referenced in the Department's geographic information system 

2

Maine’s southern ecoregion is very small but recent data suggest that some improvement in accuracy of class 

prediction could result from better accounting for ecoregional differences there. 

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FIGURE A-5. Macroinvertebrate sampling 

stations in Maine. 

(ArcInfo©). Data collected in accordance with Maine’s biocriteria protocol are analyzed using statistical 

models that estimate to which of the four water quality classes a sample belongs. Findings of the 

Biological Monitoring Program are used to document existing conditions, identify problems, set water 

management goals, assess the progress of water resource management measures, and trigger needed 

remedial actions. 

Sampling methods 

Samples of benthic macroinvertebrates are collected from 

flowing streams in rock bags (or baskets or cones). At least 

three substrate samplers are exposed in the waterbody for 28 

days during the late summer, low flow period (July 1 to 

September 30). The MDEP usually conducts sampling, but 

others may also perform monitoring to determine attainment of 

classification if done according to a quality assurance plan. 

Laboratory methods 

Samples are retrieved, sorted, and stored for identification by a 

professional freshwater macroinvertebrate taxonomist. 

Organisms are identified to species whenever possible or 

otherwise to the lowest taxonomic level possible. 

Analytical methods 

If a sample satisfies the minimum data requirements (total mean 

abundance of at least 50 individuals, generic richness of at least 

15 taxa for 3 replicate samplers), data are entered into the MDEP’s computer software for further analysis 

through the numeric criteria statistical model. The model is able to take large amounts of information 

generated from a biological sample, describe which variables appear to be most significant in the 

classification decisions, and provide a mathematical summary that integrates the information. The model 

produces probability scores from 0 to 1 that indicate the likelihood that a sample attains each water 

quality class. 

IV. Develop and validate quantitative thresholds 

How does Maine quantify the tiered aquatic life uses so that attainment can be assessed? 

In the late 1980’s, the MDEP quantified the narrative aquatic life goals for each water quality class by 

developing a probability-based statistical model to serve as numeric biocriteria (Courtemanch et al. 1989, 

Courtemanch 1995, Davies et al. unpublished manuscript). The model uses 31 biological variables, many 

of which were specifically chosen because of their utility in measuring some important ecological 

attribute in the narrative standard. The model quantifies and standardizes the expert judgment of 

biologists and it now serves as an expert system for decision-making (See Case Examples 3-3 and 3-6). 

To develop the model, biologists used agreed-upon decision rules and a Delphi technique (Bakus et al. 

1982) to assign an aquatic life attainment classification (A, B, C, or non-attainment) to 144 samples of 

benthic macroinvertebrate data, based on conformity of the sampled community to one of the 3 narrative 

aquatic life standards in Maine’s statute, or to a fourth category representing non-attainment of minimum 

State standards (Shelton and Blocksom 2004, Davies et al. unpublished manuscript). The samples 

evaluated represented 300 distinct taxonomic units and 70,000 organisms collected from rivers, streams, 

and riverine impoundments. Those data and their classification assignments were used as the baseline for 

construction of the expert system, in the form of a linear discriminant model, to evaluate future 

macroinvertebrate samples for water quality classification attainment. The original model was used from 

1992 through 1999 when the model was recalibrated with an additional 229 (for a total of 373) sampling 

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events. The recalibration resulted in relatively minor changes to the structure of the original model, 

involving simplification of the structure of two of the sub-models, the elimination of two poorly 

performing variables, and changes in model coefficients to account for the new data. 

How has Maine established reference conditions? 

Maine has taken a conceptually different approach to establishing baseline reference conditions from 

which to develop numeric biological criteria. Because we determined that detection of four distinct 

biological condition groups, characterized by differences in specified ecological attributes, was our 

management goal, it was also our goal for statistical analysis. We desired to develop numeric criteria that 

would enable us to assign sites to one of those four condition groups (A, B, C, non-attainment). 

Therefore, our task for characterizing reference conditions was to conceptually and then statistically 

define those four groups. Thus in a sense, initially by expert judgment and then by multivariate analysis, 

we created a Class A reference condition (deemed to be close to natural), a Class B reference condition, a 

Class C reference condition, and non-attainment reference conditions. Use of biological information to 

establish a minimally disturbed reference has been criticized due to the dangers of a too circular process. 

We have tested our biology-based a priori assignment of sites to Class A using more traditionally 

identified reference locations (i.e., based on high percent natural landcover) and found good 

correspondence with the biologically-defined Class A sites. 

Adoption of the Numeric Biocriteria Rule 

On April 17, 2003 the Maine Board of Environmental Protection adopted numeric freshwater biocriteria 

in rule. The biocriteria rule describes the process that the MDEP uses to make decisions about attainment 

of aquatic life uses in rivers and streams. The rule describes protocols for biological sampling of benthic 

macroinvertebrates, laboratory analyses, modeling analysis of laboratory data, and selective use of expert 

judgment. Adoption of this rule quantitatively interprets Maine’s existing narrative ‘aquatic life’ 

standards for each riverine water quality classification. 

V. Application in water quality management 

How does the MDEP decide which waterbodies and locations 

to monitor? 

For purposes of biological monitoring, the MDEP divided the 

State into five major river basins, which are sampled on a 5- St. John River 

year rotational schedule (Figure A-6): Androscoggin, 

Kennebec and Mid-Coast, Penobscot, St. Croix and North 

Coastal Rivers, Piscataqua, Saco and Southern Coast, St. John 

and Presumpscot. The decision to monitor specific locations 

on a waterbody can be based on a variety of factors such as: Penobscot River 

St. Croix River 

North Coastal Rivers 

° prior knowledge of human activities that could have a Kennebec Androscoggin River detrimental effect on a waterbody: sampling seeks to River 

detect actual impacts on biological communities; 

° knowledge of future potential threats to a waterbody: 

sampling can be done to collect baseline data before, for 

example, development occurs or a discharge is licensed; Presumpscot 

follow-up sampling can determine the effect, if any, on the River 

Saco River biological community by said development or discharge; Piscataqua River 

° requirement/desire to monitor the effects of remediation 

2002 

2003 

2004 

2005 

2006 

activities or water quality management changes; FIGURE A-6. Maine five-year rotating basin ° desire to expand coverage of the monitoring program and to 

sampling schedule. more fully document natural variability. 

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How are tiered aquatic life uses designated in Maine? 

The quality of Maine’s waters is described in terms of physical, chemical and biological characteristics 

associated with the State's water classification program. As established in Maine statute (38 MRSA 

Sections 464-470), the classification program consists of designated uses (e.g. drinking water supply, 

recreation in and on the water, habitat for fish and other aquatic life), criteria (e.g. bacteria, dissolved 

oxygen and aquatic life), and characteristics (e.g. natural, free flowing) that specify levels of water quality 

necessary to maintain the designated uses. All State waters have a classification assignment (Rivers and 

streams: AA, A, B, C; Lakes: GPA; Marine and estuarine: SA, SB, SC). Tiered narrative aquatic life uses 

specific to wetlands are currently under consideration by MDEP and a supporting wetland biomonitoring 

program is in place. 

The classification system in Maine is goal-based in that assignment of a given waterbody to a use class 

(AA, A, B or C) may not necessarily reflect its current conditions. Rather, it establishes the level of 

quality the State has deemed the waterbody must achieve. Maine’s classification system is also more risk 

based than quality based. Water quality differences among the various classes are not large, however, the 

different levels of restrictions put on human activities associated with each class establishes the level of 

risks that water quality could be degraded resulting in increased threats to designated use attainment. 

Rivers and streams are assigned to a tiered aquatic life use goal (Table A-1: AA and A -“as naturally 

occurs,” B- “no detrimental change,” C- “maintain structure and function and water quality sufficient to 

support salmonids”) that represents the best fit after considering: 

° The current condition in terms of dissolved oxygen, bacteria, and aquatic life (Figure A-3) and 

° The highest attainable goal condition (taking into account ecological and socioeconomic factors). 

The State water quality assessment provided in Maine’s 305b report gives the status of attainment of the 

water resource goals established in the classification program. Thus, some waters may be listed as 

impaired even though they have relatively good water quality (Table A-4), e.g., a Class A river may be 

listed because it does not fully attain the standards of that class but may be of sufficiently good quality to 

attain Class B or C, and the Clean Water Act interim goal. The classification program is reviewed every 

three years (Triennial Review) by the Department and the Board of Environmental Protection (Board). 

The Board may, after opportunity for public review and hearing, make recommendations to the 

Legislature for changes in water quality standards or reclassification of selected waters. The most recent 

revisions to the classification program were completed in 2002-2003 when the Legislature authorized 

classification upgrades to 75 river, stream and coastal segments totaling over 800 miles of waters (Figure 

A-7). 

TABLE A-4. Examples of how numeric biocriteria results determine whether 

or not a waterbody attains designated aquatic life uses in Maine. 

Legislative Class Monitoring Result Attains Class? Next Step 

A A Yes --

C B Yes --

A B No TMDL 

B NA No TMDL 

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Classification Upgrades for Major Rivers in Maine, 1970 to 2004 

Number of River Miles 800 

700 

600 

500 

AA & A 

B 

400 

1970 1979 1986 1990 1999 2004 

Year 

C 

D 

300 

200 

100 

0 

FIGURE A-7. Increased designation of Class AA and Class A uses on major Maine rivers (as shown


by river miles) between 1970 and 2004, as a result of water quality improvements and public


support for the Class AA/A goal in the Triennial Review Process.


What is the management perspective for TALU designations in Maine? 

Class AA waterbodies, as compared to Class A, have significantly greater restrictions on allowed 

activities. For example, no discharge of wastewater and no dams are allowed in Class AA waterbodies. 

Class A waters carry a higher risk of degradation because discharges are allowed, though the risk is small 

because they must be of “equal to or better” water quality than the receiving water. Dams are also 

allowed. Obstructions to flow, whether man-made or natural can alter assemblage structure from freeflowing conditions (Poff et al. 1997, Davies et al. 1999). The definition in water quality standards for the 

term “natural” sought to limit the effects of altered flows to no greater than what could be expected from 

a “natural” obstruction to flow (e.g., a natural hydrological control or a beaver dam). Thus to 

accommodate dams in Class A, “natural” is defined as “occurring in, or as if in, a state of nature not 

measurably affected by human activities.” Assemblages that are characteristic of the waters above and 

below beaver dams or low-head, run-of-river, man-made dams are deemed to pass this standard. Most 

dams in Class A provide for passage of anadromous fish. 

Class B was originally applied as the default ALU for unmonitored waters though current use 

designations are nearly equal in stream miles for Class A and Class B, both of which far exceed Class C 

miles when all rivers and streams in the State are considered (Figure A-8). From the management 

perspective, a Class B designation often applies to waterbody segments exposed to well-treated or welldiluted domestic discharges or to areas subjected to landscape alterations that result in moderate increases 

in the nutrient and organic matter load. 

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Class C narrative aquatic life standards prohibit any


activities that result in the loss of structure and function 2% 6%


of the resident biological community. “Community 

structure” is defined as “the organization of a biological Class AA 

Class A 

different taxonomic groups and the proportion each 47% 

community based on numbers of individuals within 

Class B 45% 

taxonomic group represents of the total community,” Class C 

while community function is defined as “mechanisms of 

uptake storage and transfer of life-sustaining materials 

available to a biological community which determine the 

efficiency of use and the amount of export of the FIGURE A-8. Percent of linear miles of all rivers 

materials from the community.” This management class and streams in each of Maine’s designated use 

is applied to waterbodies that may be impounded, altered classes (year 2000). 

by landscape changes, or that receive industrial 

wastewater. 

What process was used to bring the Maine TALU biocriteria rule through adoption? 

The MDEP Biological Monitoring Program completed provisional numeric biocriteria in 1990. Those 

numeric thresholds were the basis for extensive regulatory and non-regulatory Department decisions 

between 1990 and 2003, e.g., issuance or denial of 401 water quality certificates and recommendations 

for flow management changes, 303d and 305b listings, prioritization of at-risk waterbodies, and problem 

identification. In April 2003, the State formally adopted tiered numeric biocriteria rules that were the 

result of the analysis of 15 years of biological data and the experience gained through 20 years of 

regulatory decision-making based on numeric biocriteria (Table A-5). Remarkably, the biocriteria rule 

was one of the most complicated and important, but least contested water quality rules that the Maine 

Department of Environmental Protection has adopted in the last 15 years. Stakeholders from all sides had 

become convinced of the merits of the approach. 

TABLE A-5. Chronology of Maine’s biocriteria development. 

1983	 The MDEP Biological Monitoring Program began a standardized program of sampling stream invertebrate communities. 

1986	 The revised Water Classification Program, which defined tiered narrative standards for aquatic life, became law. 

1989	 MDEP staff and University of Maine statistical ecologist, Dr. Frank Drummond embarked on the development of numeric 

criteria to support the narrative standards of the law. 

1990	 A technical advisory committee of stakeholder scientists was convened to provide peer review and oversight of the 

biocriteria development process. Over the course of approximately 2 1⁄2 years, MDEP staff, Dr. Drummond, and the 

committee developed a statistical model based on expert judgment and linear discriminant analysis to address the 

scientific goals, as well as the policy and regulatory goals of the new biocriteria program. 

1991- Public informational workshops on the process were held in March 1991, September 1993, and December 1993. 

1993 

1999	 The original statistical model was recalibrated to take advantage of the expanded dataset available at that time. 

2002	 During a formal stakeholder review process, meetings were held in March and April and comments were solicited from 

representatives of the hydropower and paper industry, environmental advocacy groups, other State agency biologists 

(e.g., fish and wildlife), university scientists, and private consultants. 

2002	 A workshop on the rule and its background was held in early October for the Maine Board of Environmental Protection. 

2003	 The Board of Environmental Protection adopted the rule on April 3 and it was subsequently adopted by the Maine State 

Legislature. 

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Appendix B

OHIO TALU IMPLEMENTATION CASE HISTORY1 

In 1990, Ohio EPA adopted numeric biological criteria in the Ohio Water Quality Standards (Ohio WQS; 

Ohio Administrative Code 3745-1). These criteria have been used to guide and enhance water quality 

management programs and assess their environmental outcomes. The numeric biocriteria are an 

outgrowth of an existing framework of tiered aquatic life uses and narrative biological assessment criteria 

that has been in place since 1980. This case history is intended to summarize the evolutionary 

development of the components of the WQS and monitoring and assessment programs that took place in 

the late 1970s and throughout the 1980s and 1990s. 

I. Establish conceptual foundation 

Initially developed and adopted by Ohio EPA in 1978, tiered aquatic life uses represented a major 

revision to the existing general use framework that was adopted in 1974. This level of tiered uses 

recognized the different types of warmwater aquatic assemblages that corresponded to the mosaic of 

natural features of the landscape and nearly two centuries of human-induced changes. The eventual 

development of more refined tiered uses and the attendant numeric biocriteria that are in place today was 

the result of a decade long development process. The important concepts that spurred and guided these 

developments in the Ohio EPA program are described as follows: 

Natural History and Zoogeography 

The empirical evidence used to develop the initial concepts for tiered uses can be found in comprehensive 

works on the natural history and zoogeography of the Midwest such as Fishes of Ohio (Trautman 1957, 

1981) and Fishes of Illinois (Smith 1979). These texts documented the natural and human-induced 

variations in the distribution, composition, and abundance of biological assemblages over space and 

through time. Trautman (1957) not only provides a lesson in Ohio’s natural history, but also describes the 

biological evidence that was used to formulate the initial concepts about biological integrity that emerged 

in the late 1970s and early 1980s. Such works also described the key features of the landscape that 

influence and determine the potential aquatic fauna of waterbodies and were the forerunners of the 

regionalization tools that appeared soon after. As an alternative to a “one-size-fits-all” approach, these 

provided an important foundation for the development of Ohio’s tiered uses. 

Landmark Stream and River Pollution Studies 

The earliest studies of the effects of pollution on biological assemblages were the precursors of the 

approach eventually developed and used by Ohio EPA. Campbell (1939), Brinely (1942), and Wurtz 

(1955) described the classical zones of pollution in flowing waterbodies. Ellis (1937) conducted one of 

the first comprehensive studies of water pollution in the U.S. including an emphasis on the chronic 

impacts of wastewater discharges. Patrick (1950, 1953) employed the concept of species (or taxa) 

diversity as an indicator of the “health and well-being” of aquatic assemblages and described a 

“biodynamic cycle.” Gaufin and Tarzwell (1953) also described pollutional zones using aquatic 

assemblages and were the first to advocate cost-effective assessments of one or two representative 

assemblages (e.g., fish and macroinvertebrates). Subsequent studies of that time included landmark 

pollution investigations of rivers and streams (Krumholz and Minckley 1964; Mills et al. 1966; Tsai 1968, 

1973; Sparks and Starrett 1975; Gammon 1976), some of which introduced standardized approaches to 

1 Appendix B was written by Chris Yoder, Midwest Biodiversity Institute, Columbus, Ohio. 

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biological data collection and analysis. These were the key citations in the original proposal for the 

present-day Ohio EPA biological assessment program (Yoder 1978). Such works also provided the 

impetus for articulating the linkage between ecological symptoms of aquatic health and human-induced 

changes in aquatic ecosystem quality that came later. 

Concepts of Biological Integrity 

The articulation of a practical definition of biological integrity by Karr and Dudley (1981) provided a 

theoretical framework for the development of Ohio’s numeric biological criteria. Key components of this 

framework are: 1) using biological assemblages as a direct measure of aquatic life use attainment status 

(Herricks and Schaeffer 1985, Karr et al. 1986), 2) the development and use of multimetric assessment 

tools (Karr 1981, Karr et al. 1986), 3) derivation of regional reference condition to determine appropriate 

aquatic life use goals and assessment endpoints (Hughes et al. 1986), and 4) systematic monitoring and 

assessment of the State’s waters. This represented a major advancement over previous attempts to define 

and develop a workable framework to address the concept of integrity (Ballentine and Guarraia 1977). 

Embedded in this framework is the recognition that water quality management must be approached from 

an ecological perspective that is grounded in sound ecological theory and validated by empirical 

observation. This means developing monitoring and assessment and WQS to encompass the five factors 

that determine the integrity of a water resource (Figure 1-3; Karr et al. 1986). 

Experiences in Applying Systematic Biological Assessments 

A major aspect of the development of the Ohio biological assessment program and tiered uses is the 

experience gained through the initial and sustained development of systematic bioassessments beginning 

in the late 1970s and through the 1980s. This is where the previously described methods, concepts, and 

theories were applied, tested, and developed, resulting in a tractable system for measuring biological 

quality at multiple spatial scales and through time. An evolutionary process occurred in which 

qualitative, narrative biocriteria were initially used to assess rivers and streams via systematic watershed 

monitoring and assessments. The data and experiences gained in this process provided the raw materials 

for incorporating the concepts of biological integrity that emerged simultaneously. This resulted in 

further refinements to the biological assessment tools and criteria and the tiered uses including how they 

are assigned and assessed. Key to the success of this approach was the initial decisions about indicator 

assemblages and methods. These have remained stable throughout the entire development and 

implementation process, with no major modifications that would have resulted in major disconnections of 

the database. The specific methods, tools, and criteria are described in Section II. 

When numeric biocriteria and refined uses were adopted in 1990, the development process continued with 

adaptations of that system to different waterbody types. A systematic process for classifying and 

assessing wetlands was developed in the early 1990s and narrative biocriteria were adopted in the Ohio 

WQS. Biological assessment methods and indexes were also developed for the Lake Erie near shore and 

lacustuary habitats (Thoma 1999). Routine application of the numeric biocriteria in support of dredge and 

fill permitting and 401 certifications exposed the need to develop new assessment tools for primary 

headwater streams, i.e., those draining less than one square mile. Dealing with these waters required a 

change in indicator groups emphasizing aquatic amphibians and invertebrates and a modified 

classification scheme (Ohio EPA 2003). Finally, the Ohio River Valley Water Sanitation Commission 

(ORSANCO) developed a systematic approach for assessing fish (Emery et al. 2003) and 

macroinvertebrate assemblages of the Ohio River mainstem as a precursor to the adoption of numeric 

biocriteria. Other innovations are expected to follow and include recalibration of the stream and river 

biocriteria following the resampling of reference sites that took place during 1990-1999, urban stream 

classification issues (Yoder et al. 2000, Miltner et al. 2003), and adaptation to level IV ecoregions and 

other geomorphic classification schemes. These are examples of a continuous improvement process that 

naturally follows the adherence to the fundamentals of integrating WQS with systematic monitoring and 

assessment. 

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II. Merge scientific and policy foundations 

From the outset, biological and water quality assessments were intended to play a pivotal role in the 

application of tiered uses. Since designated uses were formulated and described in ecological terms, it 

followed that they should be applied and measured on an ecological basis. At that time, the readily 

available criteria were chemical-specific and the development of practical and systematic biological 

assessments was in pilot testing and development stages. The operational execution of tiered uses (WQS) 

was dependent on developing a more comprehensive and systematic approach to monitoring and 

assessment that supported the watershed and waterbody specific application of tiered uses. However, 

time was required to develop standardized data, tools and criteria, spatial design, and spatial coverage, 

which were part of the monitoring and assessment program that delivered full support for tiered uses (and 

all other water quality management programs). Figure B-1 illustrates the evolutionary and incremental 

process of the development of tiered uses, allied tools and criteria, and the monitoring and assessment 

approach that were necessary to achieve full implementation of TALU in Ohio. 

• General ALU • Narrative TALUs • Narrative TALUs • Refined TALUs 

• Few Specific • More Specific • More Specific • Specific & Complex 

Chemical Criteria Chemical Criteria Chemical Criteria Chemical Criteria 

• Narrative “Free • Initial designation • Narrative Biocriteria • Numerical Biocriteria 

Froms” of specific waters (initial WQ program (BCG implicit) 

• “Pilot” biological 

monitoring program 

(BPJ based; systematic M&A envisioned) 

support) 

• Designation of 

• Physical Habitat 

Assessment 

• Fixed station M&A 

design (chemical 

only; 100+ sites) 

• Fixed station M&A 

design (chemical 

only; 100+ sites) 

specific waters 

based on M&A (UAA 

process) 

• WET Testing 

• Geometric watershed 

design (integration of • “Pilot” biological • Intensive river & biol, chem, and monitoring program watershed surveys physical indicators; 

(10-15 sites/yr.) initiated (integration 400-600 sites/yr.) of biol, chem, and 

physical indicators; • Integrated 

100 -200 sites/yr.) Bioassessments 

(systematic WQ 

program support) 

(1974 - 1978) (1978 - 1980) (1980 - 1987) (1987 - present) 

FIGURE B-1. Evolutionary development of TALU and allied tools, criteria and assessments from the 

baseline of the 1974 WQS based on general uses and few specific water quality criteria to refined 

TALUs and specific chemical, physical, and biological criteria implemented via an integrated 

monitoring and assessment framework. The three time periods beginning with 1978-1980 

approximate the first three phases of biocriteria development and implementation in Figure 5-2. 

Pre-development Phase: 1974-1978 

The first WQS adopted in 1974 were consistent with the technology available at that time consisted of 

general uses, “free from” statements, and few numeric criteria of any kind (chemical, physical, or 

biological). The monitoring and assessment program adhered to contemporary U.S. EPA guidance, 

consisting of a fixed station network (approximately 100 sites, monthly and quarterly chemical sampling) 

and a “pilot” biological program. The baseline water quality management programs (i.e., NPDES 

permitting, funding, planning) were also in their initial stages of development and implementation. A 

comprehensive water quality based approach to pollution abatement and management had not yet been 

developed or envisioned – abatement efforts focused on technology based limitations for major point 

sources. The linkage between WQS and monitoring and assessment had not yet been made, the latter 

being viewed as a less important, optional activity. 

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Initial TALU Development Phase: 1978-1980 

In 1978, tiered aquatic life and other uses (e.g., recreation, water supply) were described and adopted 

along with the development of numeric chemical criteria for parameters such as dissolved oxygen (D.O.), 

temperature, ammonia, and common heavy metals (e.g., copper, cadmium, lead, zinc, iron, chromium, 

and nickel). The tiered uses emanated from recognition of the broader ecological concepts described in 

section I, as well as the belief that a “one-size-fits-all” approach to water quality management (i.e., the 

result of applying general uses) was neither realistic, cost-effective, nor saleable to stakeholders and the 

public. While tiered uses promised more customized and cost-effective management outcomes, the 

integration of WQS and monitoring and assessment, which is necessary before these stated objectives 

could be realized, had not yet taken place. 

Ohio’s First Tiered Use Designations 

Tiered aquatic life uses are articulated as narrative statements describing the ecological attributes that 

should be supported by each tier. The criteria associated with each tier consisted of pollutant-specific, 

single value criteria for a limited set of water quality parameters (i.e., D.O., temperature, ammonia, 

common heavy metals). There were no biological criteria at that time, although the vision was to 

eventually develop a biologically-based assessment process. The tiers included variations on a theme of 

warmwater aquatic assemblages as written in the narrative for the warmwater habitat (WWH) use 

designation: 

“These are waters capable of supporting reproducing populations of fish, normally 

referred to as warmwater species, and associated vertebrate and invertebrate organisms 

and plants on an annual basis. These standards apply outside of the mixing zone.” (Ohio 

Administrative Code 3745-1-07 c. 1978) 

The intent of the exceptional warmwater habitat (EWH) use designation is illustrated by the phrase 

“These are waters capable of supporting exceptional and unusual populations of fish . . . ” In essence, 

the EWH designation required evidence of an exceptional or unusual assemblage of fish or associated 

aquatic organisms and plants on an annual basis. Initially, EWH designations were made based on the 

known locations of self-sustaining populations of fish and other aquatic species that were considered of 

exceptional value, most of which had exhibited historical declines in distribution throughout Ohio and the 

Midwest in response to human-induced changes. These locations also corresponded to a congruence of 

natural landscape features associated with Ohio’s glacial geology that “insulated” these assemblages from 

the cascade of effects from alteration in the landscape that adversely impacted the same species in other 

more vulnerable waterbodies. The result was waters with more intact habitats, less altered hydrological 

characteristics, and water quality that was “much better than most.” As such, a goal of EWH is to protect 

such aquatic habitats as a refuge for rare and sensitive species and is vital to the broader restoration goals 

of the 1972 Federal Water Pollution Control Act (FWPCA) amendments. A greater degree of protection 

was initially afforded to these waters via more stringent water quality criteria for key parameters such as 

D.O., ammonia, and temperature (Ohio Administrative Code 3745-1-07 c. 1978). WWH became the 

default designation for all other waters that lacked such “exceptional and unusual attributes”, but which 

retained or had the potential to exhibit the minimum quality that met the baseline provisions of the 

FWPCA (Sec. 101[a][2]). 

A coldwater habitat (CWH) designation was also developed, but primarily focused on fishery attributes 

(i.e., Salmonids), which are largely artificially propagated and maintained in Ohio. However, the 

possibility of incorporating broader ecological attributes into this use narrative was included in the 

designated use narrative as follows: 

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158 
“These are waters capable of supporting populations of fish, normally referred to as 

coldwater species and associated vertebrate and invertebrate organisms and plants on an 

annual basis. These waters are not necessarily capable of supporting successful 

reproduction of Salmonids and may be stocked periodically. These standards apply 

outside of the mixing zone.” (OAC 3745-1-07) 

The monitoring and assessment program was initially based on fixed stations and emphasized chemical 

assessments, but experimental approaches such as small-scale intensive surveys and biological 

assessments were being developed and tested. There were no empirically derived or narrative biological 

criteria to decide between EWH and WWH. Specific assignments of waters were made using expert 

consensus and best professional judgment based on the known ecological attributes inherent in each 

designation. Thus the assignments of individual water bodies were only as good as the information 

available for such waters, which was later found to be incomplete or inadequate. Other tiers in the Ohio 

aquatic life use designations included seasonal warmwater habitat (SWH) and limited warmwater habitat 

(LWH). Water quality criteria for common chemical parameters were tiered and/or varied for each use 

designation. Criteria were the most stringent for CWH and EWH and the least stringent for LWH, the 

latter use essentially functioning as a temporary variance to WWH. 

Initial TALU Implementation and Development Phase: 1980-1987 

While the tiering provided by EWH and WWH is conceptually consistent with the intent and attributes of 

the biological condition gradient (BCG; Chapters 2 and 3), the tools to quantify and implement the 

associated concepts were lacking in 1978. The inclusion of the concepts of biological integrity (Karr and 

Dudley 1981), operational measures of biological condition (Karr et al. 1986), and the concepts of 

regionalization and reference sites (Hughes et al. 1986, Omernik 1987) led to further refinements of the 

tiered uses in this phase. These refinements resulted in the present day hierarchy of the exceptional 

warmwater, warmwater, modified warmwater, and limited resource waters use designations. The 

narrative descriptions were modified to reflect the operational definition of biological integrity (Karr and 

Dudley 1981), further integrating the parallel development of numeric biological criteria. 

The original tiered uses were devised with an eye toward the eventual development of a biological 

assessment based approach to their implementation. These initial developments took place in the early 

1980s and included narrative (or qualitative) biological “criteria” (Tables B-1 and B-2) supported by 

biological assessments and the implementation of an intensive survey design executed on a mainstem 

river or watershed basis (Ohio EPA 1981). These early biocriteria were based on the experiences and best 

professional judgment of the agency biologists and reflected the analytical and assessment tools of that 

time. At the same time, t chemical criteria were being further developed and whole effluent toxicity 

(WET) testing was being explored. 

The use of monitoring and assessment in support of water quality management programs emphasized 

WQS (assigning tiered uses), construction grants (advanced treatment justifications), and NPDES permits 

(water quality based effluent limits). At the same time, the statewide database that would support the 

eventual and more comprehensive development of biological, chemical, and physical assessment tools 

and criteria was being amassed via the systematic implementation of a an intensive survey and watershed 

assessment process. Comparatively complex chemical-specific criteria were adopted for 126 priority 

pollutants and included chronic, acute, and lethal endpoints for aquatic life; criteria were also adopted for 

human health exposures. Whole effluent toxicity testing was introduced and developed as a water quality 

based permitting tool (Figure B-1). 

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159 
TABLE B-1. Biological criteria (fish) for determining aquatic life use designations and attainment of Clean 

Water Act goals (November, 1980; after Ohio EPA 1981). 

Evaluation “Exceptional” “Good” “Fair” “Poor” 

Class Class I Class II Class III Class IV 

Category (EWH) (WWH) 

1.	 Exceptional or unusual Usual association of Some expected species 

assemblage of species	 expected species absent, or in very low 

abundance 

2.	 Sensitive species Sensitive species present Sensitive species absent, 

abundant	 or in very low 

abundance 

3.	 Exceptionally high High diversity Declining diversity 

diversity 

4.	 Composite index Composite index Composite index 

>9.0 – 9.5 >7.0 – 7.5; <9.0 – 9.5 >4.5 – 5.0; <7.0 – 7.5 

5.	 Outstanding recreational Tolerant species 

Fishery	 increasing, beginning to 

dominate 

6.	 Rare, endangered, or 

threatened species 

present 

Most expected species 

absent 

Sensitive species absent 

Low diversity 

Composite index 

<4.0 – 4.5 

Tolerant species 

dominate 

Conditions: Categories 1, 2, 3, and 4 (if data is available) must be met and 5 or 6 must also be met in order to designated in a 

particular class. 

TABLE B-2. Biological criteria (macroinvertebrates) for determining aquatic life use designations and 

attainment of Clean Water Act goals (November, 1980; after Ohio EPA 1981). 

Evaluation “Exceptional” “Good” “Fair” “Poor” 

Class Class I Class II Class III Class IV 

Category (EWH) (WWH) 

1.	 Pollution sensitive Pollution sensitive Pollution sensitive Pollution sensitive 

species abundant	 species present in species present in low species absent 

moderate numbers numbers 

2.	 Intermediate species Intermediate species Intermediate species Intermediate species 

present in low numbers	 present in moderate abundant present in low numbers 

numbers or absent 

3.	 Tolerant species present Tolerant species present Tolerant species present Tolerant species 

in low numbers	 in low numbers in moderate numbers abundant (all types may 

be absent if extreme 

toxic conditions exist) 

4.	 Number of taxa >301 Number of taxa 25-30 Number of taxa 20-25 Number of taxa <20 

5.	 Exceptional diversity High diversity Moderate diversity Low diversity 

Shannon index <3.5 Shannon index 2.9-3.5 Shannon index 2.3-2.9 Shannon index <2.3 

1

Number of quantitative taxa from artificial substrates 

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160 
A key development that took place during this time period was the pilot testing of ecoregions (Omernik 

1987) and the development of the regional reference condition concept (Hughes et al. 1986). Along with 

the emerging concepts of biological integrity (Gakstatter et al. 1981, Karr and Dudley 1981) and 

multimetric assessment tools (Karr 1981, Karr et al. 1986), these advances represent the foundational 

development of the tools and criteria that emerged out of this phase. During this phase, integrated 

biological, chemical, and physical assessments were emphasized in support of a wider array of 

management issues (including nonpoint sources) in addition to the mainstay priorities of construction 

grants and NPDES permitting. The results of these assessments were documented in Comprehensive 

Water Quality Reports, the production of which included the first true integration of the monitoring and 

assessment, WQS, water quality modeling, and permitting programs. Study teams were formed for each 

project and included staff membership from each program. The analyses and recommendations included 

in these reports provided the basis for WQS use revisions, water quality based NPDES permits (including 

water quality certifications), advanced treatment justifications, and other findings related to the observed 

impacts of nonpoint sources. 

The WQS were modified in 1985 to include a listing of designations by individual waterbody, as opposed 

to default designations or tributary membership (Table B-3). The original listing of individual 

waterbodies in the WQS was based on the Gazetteer of Ohio Rivers and Streams (Ohio Dept. of Natural 

Resources 1960). Waterbodies listed in the Gazetteer that had not been assessed via the biological and 

water quality assessment process were assigned a “default” designation of WWH. Waterbodies that were 

originally designated in 1978, or subsequent to that version of the WQS, retained those uses and this was 

denoted for each waterbody in the rules (Table B-3). Unconfirmed non-WWH uses required validation 

by site-specific monitoring and assessment due to a public notice issued by Ohio EPA in 1981. In reality, 

many “default” WWH designations also required reassessment because the variations in watershed 

settings and stressor gradients had only begun to be recognized. The Gazetteer of Ohio Rivers and 

Streams did not include all jurisdictional streams in the State; thus “unlisted” streams were assigned use 

designations as they became known via the systematic assessment of Ohio watersheds and/or as sitespecific management issues arose. This further emphasized the role of monitoring and assessment in the 

designation of individual waterbodies. 

Ongoing TALU Implementation and Maintenance Phase: 1987- present 

Prompted by the testing and developments that took place in the initial implementation and development 

phase, Ohio EPA proposed and adopted numerical biological criteria (Figure B-2) and further refinements 

to the tiered uses. The narratives of the tiered uses first developed in 1978 were revised and new uses 

were added, both of which were influenced by the developments and the monitoring and assessment 

experience that took place in the preceding time period. The aquatic life use narratives were revised to 

reflect the operational definition of biological integrity (Karr and Dudley 1981) and provided direct 

reference to how the numerical biological criteria were developed and derived. These definitions follow: 

“Warmwater” – these are waters capable of supporting and maintaining a balanced, 

integrated, adaptive community of warmwater aquatic organisms having a species 

composition, diversity, and functional organization comparable to the twenty-fifth 

percentile of the identified reference sites within each of the following ecoregions: the 

interior plateau ecoregion, the Erie/Ontario lake plains ecoregion, the western Allegheny 

plateau ecoregion and the eastern corn belt plains ecoregion. For the Huron/Erie lake 

plains ecoregion, the comparable species composition, diversity and functional 

organization are based on the ninetieth percentile of all sites within the ecoregion. For all 

ecoregions, the attributes of species composition, diversity, and functional organization 

will be measured using the index of biotic integrity, the modified index of well-being, 

and the invertebrate community index as defined in “Biological Criteria for the Protection 

of Aquatic Life: Volume II, Users Manual for Biological Field Assessment of Ohio 

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161 
Surface Waters,” as cited in paragraph (B) of rule 3745-1-03 of the Administrative Code. 

In addition to those water body segments designated in rules 3745-1-08 to 3745-1-32 of 

the Administrative Code, all upground storage reservoirs are designated warmwater 

habitats. Attainment of this use designation (except for upground storage reservoirs) is 

based on the criteria in Table 7-14 of this rule. A temporary variance to the criteria 

associated with this use designation may be granted as described in paragraph (F) of rule 

3745-1-01 of the Administrative Code. 

TABLE B-3. Example of individual stream and/or segment use designations in the Ohio water quality standards 

showing aquatic life, water supply, and recreational use designations. Designation with a “+” means the use has 

been confirmed by monitoring and assessment. Designation with an “*” indicates a “default” designation or 

unverified designation – these waters will eventually be assessed via the rotating basin approach [excerpted from 

Ohio Administrative Code 3745-1-09]. 

Waterbody Segment 

Use Designations 

S Comments R 

W 

Aquatic Life Habitat Water 

Supply 

Recreation 

W 

W 

H 

E 

W 

H 

M 

W 

H 

S 

S 

H 

C 

W 

H 

L 

R 

W 

P 

W 

S 

A 

W 

S 

I 

W 

S 

B 

W 

P 

C 

R 

S 

C 

R 

ú ú ú ú ú ú ú ú

Scioto River – Frank Rd. (RM 127.7) to 

downstream from Bridge St. in 

Chillicothe (RM 70.7) 

- Greenlawn Dam (RM 129.8) to 

Frank Rd. (RM 127.7) 

- Olentangy R. (RM 132.3) to 

Greenlawn Dam (RM 129.8) 

- Dublin Rd. WTP dam (RM 133.4) 

to Olentangy R. (RM 132.3) 

- O’Shaughnessy Dam (RM 148.8) 

To Dublin Rd. WTP dam (RM 

133.4) 

- all other segments 

Scippo Cr. 

Congo Cr. (Scippo Cr. at RM 1.64) 

Unnamed trib. Scippo Cr. (RM 16.31) 

Unnamed trib. Scippo Cr. (RM 18.87) 

Yellowbud Cr. - Ebenhack Rd. (RM 3.0) 

to mouth 

- all other segments 

RCA Tributary (Scioto R. RM 96.5) 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

* 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

* 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

* 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

* 

+ 

+ 

+ 

+ 

+ 

+ 

+ 

ECBP ecoregion 

– impounded 

MWH 

Small 

drainageway 

maintenance 

Small 

drainageway 

maintenance 

SRW = State Resource Water; WWH = Warmwater Habitat; EWH = Exceptional Warmwater Habitat; MWH = Modified Warmwater Habitat; 

SSH = Seasonal Salmonid Habitat; CWH = Coldwater Habitat; LRW = Limited Resource Waters; PWS = Public Water Supply; AWS = Agricultural 

Water Supply; IWS = Industrial Water Supply; BW = Bathing Waters; PCR = Primary Contact Recreation; SCR = Secondary Contact Recreation 

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162 
FIGURE B-2. Numeric biological criteria adopted by Ohio EPA in 1990, showing stratification of


biocriteria by biological assemblage, index, site type, ecoregion for the warmwater habitat (WWH) and


exceptional warmwater habitat (EWH) use designations.


The narrative for the exceptional warmwater habitat (EWH) use designation retained the same application 

language with the following differences (in bold italics): 

“Exceptional warmwater” - these are waters capable of supporting and maintaining an 

exceptional or unusual community of warmwater aquatic organisms having a species 

composition, diversity, and functional organization comparable to the seventy-fifth 

percentile of the identified reference sites on a statewide basis . . . all lakes and 

reservoirs, except upground storage reservoirs, are designated exceptional warmwater 

habitats. Attainment of this use designation (except for lakes and reservoirs) is based on 

the criteria in Table 7-14 of this rule.” 

The narrative for coldwater habitat (CWH) was also revised and reflected a broader application of this use 

for reasons other than the existence of maintenance stocking of Salmonid fish species: 

(i)	 “Coldwater habitat, inland trout streams” – these are waters which support trout


stocking and management under the auspices of the Ohio department of natural


resources, division of wildlife, excluding waters in lake run stocking programs, lake


or reservoir stocking programs, experimental or trial stocking programs, and put and


take programs on waters without, or without the potential restoration of, natural


coldwater attributes of temperature and flow. The director shall designate these


waters in consultation with the Director of the Ohio department of natural resources.


(ii)	 “Coldwater habitat, native fauna” – these are waters capable of supporting


populations of native coldwater fish and associated vertebrate and invertebrate


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163 
organisms and plants on an annual basis. The director shall designate these waters 

based upon the result of use attainability analyses. 

The WWH, EWH, and CWH use designations are considered consistent with the minimum goals of the 

CWA (Section 101[a][2]) and the associated Federal Regulation (40CFR Part 130). However, the public 

notice issued in 1981 by Ohio EPA required that designated uses other than WWH be validated on a 

waterbody specific basis prior to basing permitting requirements on the attendant water quality criteria. 

Furthermore, a waterbody must reflect the capability to attain the EWH biological criteria at a sufficient 

number of sampling locations to be designated EWH (Ohio EPA 1987) and the CWH designation has its 

own set of requirements in the narrative. Such showings are not required for WWH, except that the 

potential to attain must be determined by biological and habitat assessments. 

“Coldwater” – these are waters that meet one or both of the characteristics described in 

paragraphs (B)(1)(f)(i) and (B)(1)(f)(ii) of this rule. A temporary variance to the criteria 

Use designations that do not meet the minimum goals of the CWA, and thus require a use attainability 

analysis on a water body specific and/or segment-by-segment basis include: 

“Modified warmwater” – these are waters that have been the subject of a use attainability 

analysis and have been found to be incapable of supporting and maintaining a balanced, 

integrated, adaptive community of warmwater aquatic organisms due to irretrievable 

modifications of the physical habitat. Such modifications are of a long-lasting duration 

(i.e., twenty years and longer) and may include the following examples: extensive stream 

channel modification activities permitted under sections 401 and 404 of the act or 

Chapter 6131 of the Revised Code, extensive sedimentation resulting from abandoned 

mine land runoff, and extensive, permanent impoundment of free-flowing water bodies. 

The attributes of species composition, diversity and functional organization will be 

measured using the index of biotic integrity, the modified index of well-being, and the 

invertebrate community index as defined in “Biological Criteria for the Protection of 

Aquatic Life: Volume II, Users Manual for Biological Field Assessment of Ohio Surface 

Waters,” as cited in paragraph (B) of rule 3745-1-03 of the Administrative Code. 

Attainment of this use designation is based on the criteria in Table 7-14 of this rule. The 

modified warmwater habitat designation can be applied only to those waters that do not 

attain the warmwater habitat biological criteria in Table 7-14 of this rule because of 

irretrievable modifications of the physical habitat. All water body segments designated 

modified warmwater habitat will be reviewed on a triennial basis (or sooner) to determine 

whether the use designation should be changed. A temporary variance to the criteria 

associated with this use designation may be granted as described in paragraph (F) of rule 

3745-1-01 of the Administrative Code. 

The Limited Resource Waters (LRW) use designation is defined as: 

“Limited resource water – these are waters that have been the subject of a use 

attainability analysis and have been found to lack the potential for any resemblance of 

any other aquatic life habitat as determined by the biological criteria in Table 7-14 of this 

rule. The use attainability analysis must demonstrate that the extant fauna is substantially 

degraded and that the potential for recovery of the fauna to the level characteristic of any 

other aquatic life habitat is realistically precluded due to natural background conditions or 

irretrievable human-induced conditions. All water body segments designated limited 

resource water will be reviewed on a triennial basis (or sooner) to determine whether the 

use designation should be changed. Limited resource waters are also termed nuisance 

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164 
prevention for some water bodies designated in rules 3745-1-08 to 3745-1-30 of the 

Administrative Code. A temporary variance to the criteria associated with this use 

designation may be granted as described in paragraph (F) of rule 3745-1-01 of the 

Administrative Code. Waters designated limited resource water will be assigned one or 

more of the following causative factors. These causative factors will be listed as 

comments in rules 3745-1-08 to 3745-1-30 of the Administrative Code. 

(i)	 “Acid mine drainage” – these are surface waters with sustained pH values below 

4.1 s.u. or with intermittently acidic conditions combined with severe streambed 

siltation, and have a demonstrated biological performance below that of the 

modified warmwater habitat biological criteria. 

(ii)	 “Small drainageway maintenance” – these are highly modified surface water 

drainageways (Usually less than three square miles in drainage area) that do not 

possess the stream morphology and habitat characteristics necessary to support 

any other aquatic life habitat use. The potential for habitat improvements must 

be precluded due to regular stream channel maintenance required for drainage 

purposes. 

(iii)	 Other specified conditions. 

The designation of specific waterbodies as MWH or LRW requires a use attainability analysis (UAA) 

based on a waterbody specific assessment. These do not meet the minimum conditions prescribed by the 

CWA (Section 101[a][2]). All of these were adopted in the Ohio WQS in 1990. 

Relationship of Ohio’s Tiered Uses to the Biological Condition Gradient 

Ohio’s current tiered uses represent refinements to the original tiered uses adopted in 1978 and reflect the 

developments that benefited from ten years of experience in applying a tiered use system. The practical 

impacts of these refined and tiered uses on water quality management are described in Table B-4 and 

include the designated use, the key attributes of that use, why a waterbody would be designated for that 

use, and some of the practical impacts to water quality management. All of the biological criteria and 

some of the chemical/physical criteria associated with each use are tiered in a logical relationship to the 

ecological attributes, which are ascribed by the designated use narrative and the translation of that 

narrative to specific criteria. This is consistent with the concepts of the BCG in that expectations and 

attainment of each use are measured by the biological criteria that are in turn designed to describe and 

measure increments in quality along the BCG (Figure B-3). Chemical-specific and physical parameters 

are cast in the role of stressor and exposure indicators and criteria (i.e., they are best used as design 

criteria in modeling and TMDLs). They directly support the development and implementation of 

abatement and management strategies via water quality management programs by providing the 

translation between associations of cause and effect via monitoring and assessment to enforceable 

controls via permitting and best management practices via TMDLs. The biological criteria are cast in the 

role of response indicators and as the primary criteria for determining use attainment status, measuring 

relative quality, and documenting the effectiveness of abatement and management strategies (Yoder and 

Rankin 1998, Karr and Yoder 2004). The logical relationship between exposure and response follows in 

that some of the key chemical criteria are more stringent for the uses that are representative of the higher 

tiers of the BCG (i.e., EWH) and least stringent for the lowest tiers (i.e., MWH, LRW). These are then 

translated accordingly to wastewater and other water quality management requirements. However, 

criteria that do not demonstrate an empirical relationship along the BCG are not tiered. 

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TABLE B-4. Key features associated with tiered aquatic life uses in the Ohio WQS (OAC 3745-1-07). 

Aquatic Life 

Use Key Attributes 

Why a Waterbody Would Be 

Designated 

Practical Impacts 

(compared to a baseline of WWH) 

Warmwater 

Habitat 

(WWH) 

Balanced assemblages of 

fish/invertebrates comparable to 

least impacted regional reference 

condition 

Either supports biota consistent with 

numeric biocriteria for that ecoregion 

or exhibits the habitat potential to 

support recovery of the aquatic fauna 

Baseline regulatory requirements 

consistent with the CWA “fishable” 

and “protection & propagation” 

goals; criteria consistent with U.S. 

EPA guidance with State/regional 

modifications as appropriate 

Exceptional 

Warmwater 

Habitat 

(EWH) 

Unique and/or diverse 

assemblages; comparable to upper 

quartile of statewide reference 

condition 

Attainment of the EWH biocriteria 

demonstrated by both organism 

groups 

More stringent criteria for D.O., 

temperature, ammonia, and nutrient 

targets; more stringent restrictions 

on dissolved metals translators; 

restrictions on nationwide dredge & 

fill permits; may result in more 

stringent wastewater treatment 

requirements 

Coldwater 

Habitat 

(CWH) 

Sustained presence of Salmonid or 

non-salmonid coldwater aquatic 

organisms; bonafide trout fishery 

Bioassessment reveals coldwater 

species as defined by Ohio EPA 

(1987); put-and-take trout fishery 

managed by Ohio DNR 

Same as above except that common 

metals criteria are more stringent; 

may result in more stringent 

wastewater treatment requirements 

Modified 

Warmwater 

Habitat 

(MWH) 

Warmwater assemblage dominated 

by species tolerant of low D.O., 

excessive nutrients, siltation, 

and/or habitat modifications 

Impairment of the WWH biocriteria; 

existence and/or maintenance of 

hydrological modifications that 

cannot be reversed or abated to attain 

the WWH biocriteria; a use 

attainability analysis is required 

Less stringent criteria for D.O., 

ammonia, and nutrient targets; less 

restrictive applications of dissolved 

metals translators; Nationwide 

permits apply without restrictions or 

exception; may result in less 

restrictive wastewater treatment 

requirements 

Limited 

Resource 

Waters 

(LRW) 

Highly degraded assemblages 

dominated exclusively by tolerant 

species; should not reflect acutely 

toxic conditions 

Extensive physical and hydrological 

modifications that cannot be reversed 

and which preclude attainment of 

higher uses; a use attainability 

analysis is required 

Chemical criteria are based on the 

prevention of acutely lethal 

conditions; may result in less 

restrictive wastewater treatment 

requirements 

FIGURE B-3. The relationship of Ohio’s 

tiered designated uses and numerical 

biological criteria to the Biological 

Condition Gradient. 

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166 
Because of bioaccumulation concerns, many toxicant criteria are designed to protect all aquatic life uses 

even though they may demonstrate a graded response to the numeric biocriteria and tiered uses. For some 

of the heavy metals criteria where translators were developed between dissolved and total forms, concerns 

about the effects of potentially increased discharges of total metals resulted in a risk assessment that 

examined the relationships between the numeric biocriteria and total metals (Ohio EPA 1999a). This led 

to the derivation of “caps” on the amount of additional total metals that are permitted as a result of the 

dissolved metals translator process. These caps varied in accordance with the relationships demonstrated 

with the numeric biocriteria and tiered uses. Other parameters that do not demonstrate an empirical 

relationship along the BCG are not tiered. Future data exploration may well result in tiered chemical or 

physical criteria for stressors that are presently based on fixed, single value criteria. Such refined 

chemical criteria are expected to provide benefits to watershed-based management related to the 

prioritization of BMPs and in the application of emerging tools such as pollutant trading. 

III. Establish technical program 

From the outset, the implementation of tiered uses was intended to include a comprehensive and 

systematic monitoring and assessment program. The integration of the tiered uses with monitoring and 

assessment was an evolutionary development that followed the process outlined in Chapter 5 (Table 5-1; 

Figure 5-2) and Figure B-1. 

How Does Ohio Collect Biological Data? 

Ohio EPA employs a multiple chemical, physical, and biological indicators approach that utilizes each 

according to their most appropriate roles as indicators of stress, exposure, and response (Yoder and Rankin 

1998). This approach leads to more effective regulation of pollution sources, improved assessment of diffuse 

and non-chemical impacts, and improves our ability to implement management strategies for successfully 

protecting and restoring the ecological integrity of watersheds. Key attributes that the biological indicators 

were developed to reflect include: 

1) cost-effective collection of data 

2) readily available science 

3) be indicative of or extend to different trophic levels 

4) integrate multiple effects and exposures 

5) exhibit reasonable response and recovery times 

6) be precise and reproducible 

7) be responsive to a wide range of perturbations 

8) be relevant to managerial and programmatic issues 

Because it is impractical to monitor the entire organism assemblages present in an aquatic ecosystem, 

choices must be made. Ohio’s choice of two organism groups (benthic macroinvertebrates and fish) is 

consistent with the ITFM (1992, 1995) recommendations and was done for a number of reasons. Each 

assemblage has been widely used in assessments and there is abundant information about their life 

histories, distributions, and environmental requirements. The benefit of having two different groups 

independently showing the same result is obvious and lends considerable strength to a bioassessment. 

However, differences in the responses by each group can lead to the definition of problems that might 

otherwise have gone undetected, underrated, or misunderstood in the absence of information from either 

organism group. For example, representatives of one assemblage may be able to tolerate and metabolize 

toxic substances that are highly detrimental to representatives of the other assemblage. The differences in 

recovery rates between each assemblage provide an added dimension to the understanding of how 

abatement processes work and document incremental changes through time. The value of such 

information in a risk management process should be obvious. Comparisons between the performance of 

fish and macroinvertebrates as arbiters of aquatic life use attainment showed non-agreement between 

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167 
assemblages at 33% in non-wadeable rivers, 21.2% in wadeable streams, and 28.2% in headwater streams 

(Yoder and Rankin 1995a). Assessments based on a single group would have overlooked proportions of 

the impairment that actually existed, let alone the loss of signal in diagnosing causal associations. Some 

of the concepts in Appendix C are based on this knowledge and experience. 

Overview of the Technical Approach 

The development and refinement of Ohio’s biological assessment tools and criteria reflects an 

evolutionary process that is summarized in Figure B-1 and in Chapter 5 (Figure 5-2). The standardization 

of sampling and laboratory methods occurred first and illustrates the importance of the initial decisions 

about methods, taxonomic resolution, and professionalism early in the process (Ohio EPA 1987, DeShon 

1995, Rankin 1995, Yoder and Smith 1999). From the outset of the systematic collection of biological data 

in Ohio, choices about sampling methods and laboratory procedures were the most important of the initial 

decisions that were made. These determine the attributes and characteristics of the resulting data and the 

usefulness and accuracy of the analytical tools and criteria that are developed. This, in turn, determines the 

quality of the entire approach including its ability to accurately determine biological impairments and 

discriminate relative quality along the BCG. Because of its primary role as a response indicator, it determines 

our perceptions of environmental quality and the effectiveness of our responses via water quality 

management programs and policies. 

Sampling Methods 

A number of decisions need to be made concerning the adoption of sampling methods. Decisions about 

sampling methods and gear, seasonal considerations, which organism groups to monitor, which parameters to 

measure and record, which level of taxonomy to use, etc. all were made early in the process. This was a 

critical juncture in the process since the decisions made here determined the effectiveness of the 

bioassessment effort. 

The development of standardized sampling methods was the most important initial task in the 

implementation of Ohio’s biological monitoring program. While many sampling methods and techniques 

existed for both macroinvertebrates and fish, many lacked adequate testing or standardization. The primary 

task was the testing, development, and validation of the chosen methods, which involved testing each for its 

ability to deliver good information at a reasonable cost. The goal was to use methods and protocols that 

would require 1-3 hours at a sampling site making it possible to sample several sites each day, tens of sites 

each week, and hundreds of sites each sampling season. A seasonal index period was also established during 

the summer-early fall (mid June to mid October). 

For macroinvertebrates, artificial substrates were the method of choice and this was consistent with the U.S. 

EPA guidance of that time. The application of this method was further tested to refine the general approach 

in the early 1980s. A cluster of five artificial substrates bound to a concrete block are set in detectable current 

for a colonization period of six weeks. A dip net/hand pick sample of the surrounding natural substrates 

including all available habitats is collected at the time of substrate retrieval. This technique, known as 

qualitative sampling, employs a triangular frame dip net and can be used as a stand-alone sampling method. 

A site description data sheet is completed by a crew leader and includes information about the site habitat, 

environmental setting, and other pertinent information. Samples are retrieved, preserved in 10% formalin in 

the field, and transported to the laboratory for later processing. The specific methods are documented in 

written guidance manuals (Ohio EPA 1980, 1987, 1989b) that are codified by reference in the Ohio WQS. 

Fish are collected using various wading and boat-mounted pulsed D.C. electrofishing gears, depending on the 

width and depth of the stream or river. These also had their origin in already available techniques, but the 

stratification of their use in different sizes of waterbodies was an issue that required prior testing and 

development. Sampling is standardized by lineal distance of stream or river and reach lengths were 

determined by sampling standard increments at methods test sites in the early 1980s. Fish samples are 

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168 
processed in the field and include identification to species, enumeration (counts and biomass) by age groups 

(adult, 1+, 0+), and delineation of external anomalies. A qualitative habitat assessment (QHEI; Rankin 1989, 

1995) is completed over the entirety of the electrofishing reach. Fish sites are sampled once, twice, or three 

times within the seasonal index period, the frequency being determined by the complexity of the setting and 

the potential for episodic impacts. The specific methods are documented in written guidance manuals (Ohio 

EPA 1980, 1987, 1989b) that are codified by reference in the Ohio WQS. 

Laboratory Methods 

Each artificial substrate (quantitative) and natural substrate (qualitative) sample is processed in accordance 

with standardized procedures (Ohio EPA 1989b). This includes an initial pre-pick and visual scan for rare 

and large organisms, subsampling by major taxa group (mayflies, stoneflies, caddisflies, midges, others), and 

identification and enumeration to the lowest practicable taxonomic level. Ohio EPA staff perform both field 

sampling and laboratory processing. 

Fish specimens that cannot be verified in the field are preserved in 10% formalin and transported to the 

laboratory for later processing. These are changed to 70% ethyl alcohol and identified to species. 

Verification of difficult specimens is performed by at least one qualified non-Ohio EPA taxonomist. 

Analytical Methods 

Ohio EPA analyzes biological data using routines available in the Ohio ECOS data storage, retrieval, and 

management system. Data is entered into Ohio ECOS following a data validation and QA/QC process to 

eliminate transcription and other errors. The principal indexes are based on multimetric techniques that 

were modified and calibrated for use in Ohio. For fish this includes the Index of Biotic Integrity (IBI; 

Karr 1981, Fausch et al. 1984, Karr et al. 1986) and the Index of Well-Being (IWB; Gammon 1976, 

Gammon et al. 1981). For macroinvertebrates it includes the Invertebrate Community Index (ICI; Ohio 

EPA 1987, DeShon 1995). In addition to the primary indexes, data analyses include the index metric 

values, relative abundance, and other aggregations of the data that exhibit ecologically meaningful 

patterns and information over space and time. This can include the use of multivariate analyses, 

parametric and non-parametric statistical techniques, and data mapping. 

Staffing and Professionalism 

Qualified and regionally experienced staff are employed to carry out the sampling and data analysis activities. 

Skilled and experienced staff direct, manage, and supervise all activities. This includes a high level of 

expertise in the field since many of the critical pieces of information are recorded and, to a degree, interpreted 

here. The same professional staff who collect the field data also interpret and apply the information derived 

from the data in a “cradle to grave” fashion. Thus the same staff who perform the field work also plan that 

work, process the data into information, interpret the results, and apply the results via assessment and 

reporting. Such staff, particularly those with sufficient experience, also contribute to policy and program 

development. The majority of data used by Ohio EPA is collected by agency staff. However, the methods 

and approach can be carried out by other entities and practitioners. Since 1999, Ohio EPA has operated a 

voluntary certification process and this will soon be mandated by the Ohio Credible Data Law. 

How Does Ohio Decide What Waterbodies and Locations to Monitor? 

In 1980, Ohio EPA initiated an intensive watershed survey design that included chemical/physical and 

biological assessments or surveys. A biological and water quality survey, or “biosurvey,” is an 

interdisciplinary monitoring effort coordinated on a waterbody specific or watershed scale. The effort 

may involve a relatively simple setting focusing on one or two small streams, one or two principal 

stressors, and a handful of sampling sites or a much more complex effort including entire drainage basins, 

multiple and overlapping stressors, and tens of sites. Through the 1980s, Ohio EPA conducted 

biosurveys in 6-10 different study areas with an aggregate total of 250-300 sampling sites sampled/year. 

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169 
• Rotating basin approach 

for determining annual 

monitoring activities. 

• Correlated with NPDES 

permit schedule. 

• Supports annual WQS 

use designation rulemaking. 

• Aligned with 15 year 

TMDL schedule in 1998. 

2000 

NWDO NEDO 

SEDO 

SWDO 

CDO 

2001 2003

1999 1999 

2003 

1999 

2004 2001 

2001 2000 

2003 

2002 

2003 

1999 

1999 

2000 

2000

2000 

FIGURE B-4. Five-year basin approach for determining annual 

watershed monitoring and assessment activities and correspondence 

to support major water quality management programs. 

While the purpose of these 

surveys was to support multiple 

program objectives, the schedule 

of water quality management 

program outputs was not always 

coordinated with the biosurvey 

schedule. In 1990, this process 

was formally coordinated 

beginning with a revision to the 

schedule for reissuance of major 

and significant NPDES permits. 

Ohio EPA formally adopted a five 

year basin approach in which 

biosurveys were scheduled two 

years in advance of the reissuance 

of NPDES permits (Figure B-4). 

The rotating basin approach 

proved its utility in two other 

instances. The first was in 

support of Ohio nonpoint source assessment in 1990, and the second when TMDLs became a major 

priority in 1998. The latter was seamlessly integrated into the rotating basin approach (Ohio EPA 1999b). 

In the 1990s, the demand for the watershed assessments increased further with up to 700 sites being 

sampled within 10-12 study areas in some years. The process of program integration was further 

institutionalized with a structured process for selecting watersheds, planning the monitoring, and 

analyzing and reporting the results (Table B-5). 

TABLE B-5. Important timelines and milestones in the planning and execution of the rotating basin approach 

conducted annually and since 1990 by Ohio EPA. 

Milestone Timeline 

December - February: Initial screening of the major hydrologic areas takes place by soliciting input from the various program 

(Months 1-3) offices and other stakeholders. 

February - March: Final prioritization of issues and definition of specific study areas. Resource allocation takes place and 

(Months 3 thru 4) study team assignments are made. 

March - May: Study planning takes place and consists of detailed map reconnaissance, review of historical 

(Months 4 thru 5) monitoring efforts, and initial sampling site selection by the study team. Final study plans are 

reviewed and approved. 

May - June: Final study plans are used to develop logistics for each field crew. Preparations are made for full-scale 

(Months 5 thru 6) field sampling. 

June - October: Field sampling takes place with field crews operating somewhat independently on a day-to-day basis, 

(Months 6 thru 10) but coordinated by the study plan and the team leader. Study team communication takes place as 

necessary, especially to resolve unexpected situations. 

October - February: Laboratory sample analysis takes place for chemical and biological parameters. Raw data is entered 

(Months 10 thru 14) into databases for reduction and analysis. The study team meets to review the information base 

generated by the field sampling and to coordinate the data analysis and reporting effort. 

November - May: Information about indicator levels 3-6 is retrieved, compiled, and used to produce analyses that will 

(Months 11 thru 17) support the evaluation of status and trends and causal associations within the study area. Integration of 

the information (i.e., assessment) is initiated. 

May - December: The assessment process is completed by producing working copies of the assessment for review by the 

(Months 17 thru 24) study team and a final edit for an internal peer review. Final assessment approved by management for 

use within and outside of Ohio EPA. It is used to support 305b /303d, NPDES permitting, water 

quality standards (e.g., use designation revisions), and other programs where surface water quality is of 

concern. 

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170 
Each biosurvey is designed and conducted to meet three major objectives: 

1)	 determine the extent to which use designations assigned in the Ohio WQS are either attained or not 

attained; 

2) determine if use designations assigned to a given waterbody are appropriate and attainable; and 

3) determine if any changes in key ambient biological, chemical, or physical indicators have taken place 

over time, particularly before and after the implementation of point source pollution controls or best 

management practices. 

The data gathered by a biosurvey is 

processed, evaluated, and 

synthesized in a biological and 

water quality report. Each 

biological and water quality study 

contains a summary of major 

findings and recommendations for 

revisions to WQS (e.g., Table B-6), 

future monitoring needs, or other 

actions which may be needed to 

resolve existing impairment(s) of 

designated uses. At the same time, 

the systematic execution of basin 

surveys builds a long-term database 

over space and time, creating and 

sustaining a resource of the 

development and improvement of 

tools, criteria, policies, and 

legislation (Figure B-5). 

The recommendations for use designation revisions are a direct result of the biological and water quality 

assessment. Uses are designated on demonstrated potential to attain a particular use based on the 

following sequence (in order of importance): 

Statewide/Regional 

Applications 

• TMDLs (303d) 

• Status/Trends (305b) 

• Local projects 

• NPS/BMP effectiveness evaluations 

• NAWQA/REMAP 

• Watershed mgmt. 

• SWAP 

• UWA 

• IWI "ground 

truthing" 

• Environmental Indicators 

• Refined & Validated 

WQ Criteria 

• Reference WQ & 

Sediment benchmarks 

• Biological Criteria 

• Biological Response 

Signatures 

• Regional stratification 

(ecoregions, subreg.) 

Program 

Development 

• TMDL Listing/De-listing 

• Refined WQS Uses 

Policy 

Development 

• Antidegradation 

• NPDES (WET, CSOs, 

Stormwater) 

• 404/401 dredge & fill 

• Stream Protection 

• Nutrient management 

• Overall program/policy 

effectiveness 

• Environmental audits 

The systematic accumulation of information 

across spatial and temporal scales 

FIGURE B-5. Strategic support provided over time by systematic 

monitoring and assessment; functions related to the implementation 

of TALUs are italicized and underlined. 

1)	 attainment of the biocriteria (if attaining WWH or higher – attainment of EWH is required to be 

designated as EWH); and 

2)	 if a WWH biocriterion is not met, the habitat potential determined by the Qualitative Habitat 

Evaluation Index (QHEI; Rankin 1989, 1995) and an associated assessment of warmwater: 

modified habitat attributes is used to determine the potential to attain WWH. 

For uses less than WWH (i.e., MWH or LRW), a use attainability analysis is required and includes 

consideration of the factors that essentially preclude WWH attainment including the feasibility of 

restoring the waterbody. A use attainability analysis requires the following information: 

1)	 the present attainment status of the waterbody based on a biological assessment performed in 

accordance with the requirements of the biocriteria, the Ohio WQS, and the Five-Year 

Monitoring Strategy (the latter pertains to adequacy of spatial design); 

2)	 a habitat assessment to evaluate the potential to attain at least WWH; and 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 171 

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3)	 a reasonable relationship between the impaired status and the precluding human-induced 

activities based on an assessment of multiple indicators used in their appropriate indicator roles 

and a demonstration consistent with 40CFR Part 131.10 [g][1-6]. 

In the example from the Big Darby Creek watershed assessment conducted in 2000, all of the streams and 

segments listed in Table B-6 were sampled in accordance with Ohio EPA’s geometric and intensive 

survey design. A number of the streams in Table B-6 were originally assigned aquatic life use 

designations in the 1978 and 1985 WQS based largely on best professional judgment or by tributary 

membership, while others were not yet designated. The current biological assessment methods and 

numerical biocriteria did not exist at that time. Most of the larger tributaries and the mainstem were 

previously designated based on biosurveys of specific segments and streams in 1979, 1981, 1988, and 

1992. The use designations of most of the mainstem and some of the major tributaries were resolved by 

those efforts. However, many of the smaller streams in this watershed were evaluated for the first time 

using a standardized biological approach in 2000. Ultimately, the designations for each stream and river 

segment are based on direct sampling and assessments of each individual waterbody and the processes 

previously described. Extrapolation of sampling results for this and other purposes (e.g., status 

assessment) is minimal and occurs only within individual waterbodies. The application of the geometric 

watershed and intensive survey design included all tributaries and resulted in the addition of 26 

previously unlisted and/or undesignated streams. Of these 26 streams, four were designated EWH, 18 as 

WWH, four as MWH, and two as LRW; an additional five stream segments were simultaneously 

designated CWH. Under the 1978 WQS, all 26 tributaries would have been designated as EWH by virtue 

of their tributary membership in the Big Darby watershed. This was extended to only the 19 named 

tributaries in the 1985 WQS, of which nine were later changed based on earlier biosurvey data. This 

example illustrates the comparative lack of accuracy in extrapolating uses by tributary membership within 

a watershed and the need to sample and assess individual streams for use designation purposes. 

TABLE B-6. Summary of recommendations for use designations in the Big Darby Creek watershed based on a 

biological and water quality assessment completed in 2000. Symbols are listed for the existing 

designation/recommended designation (_ - undesignated; + - verified by biosurvey; * - unverified default 

designation from 1978 or 1985 WQS). 

Water Body Segment 

Use Designations 

S 

R 

W 

Aquatic Life 

Habitat 

Water 

Supply Recreation 

W 

W 

H 

E 

W 

H 

M 

W 

H 

SS 

H 

C 

W 

H 

L 

R 

W 

P 

W 

S 

A 

W 

S 

I 

W 

S 

B 

W 

P 

C 

R 

S 

C 

R 

Big Darby Creek (02-200) a - Headwaters to RM 79.2 

- RM 79.2 to mouth 

Flat Branch (02-223) (RM 78.48)

b 

Tributary to Flat Branch (02–365) (RM 1.5) 

Little Darby Creek (02-251) (RM 78.34) RM 3.5 to mouth 

U.T. to B. Darby Cr. (02-361) (RM 74.91) RM 0.75 to mouth 

Spain Creek (02-222) (RM 74.3) - Headwaters to RM 5.0 

RM 5.0 to mouth 

Pleasant Run (02-221) (RM 72.01) 

* 

+ 

+ 

*+ 

* 

+ 

_+ 

* 

*+ 

*+ 

+ 

_+ 

+ 

+ 

+ 

+ 

*+ 

+ 

+ 

_+ 

_+ 

_+ 

+ 

+ 

+ 

*+ 

+ 

+ 

_+ 

_+ 

_+ 

+ 

+ 

+ 

*+ 

+ 

+ 

_+ 

_+ 

*+ 

*+ 

*+ 

_+ 

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172 
Water Body Segment 

Use Designations 

S 

R 

W 

Aquatic Life 

Habitat 

Water 

Supply Recreation 

W 

W 

H 

E 

W 

H 

M 

W 

H 

SS 

H 

C 

W 

H 

L 

R 

W 

P 

W 

S 

A 

W 

S 

I 

W 

S 

B 

W 

P 

C 

R 

S 

C 

R 

U.T. to Big Darby Creek (02-360) (RM 69.4) RM 1.8 to mouth 

Hay Run (02-220) (RM 67.6) RM 1.1 to mouth 

Prairie Run (02-219) (RM 63.84) 

Buck Run (02-209) (RM 63.74) 

Robinson Run (02-207) (RM 53.69) 

Sweeney Run (02-357) (RM 52.11) RM 1.7 to mouth 

Sugar Run (02-206) (RM 50.92) - Headwaters to RM 7.0 

- RM 7.0 to mouth 

U.T. to Sugar Run (02-358) (RM 7.39) 

Worthington Ditch (02-2356) (RM 50.62) RM 0.4 to mouth 

Ballenger-Jones Ditch (02-355) (RM 49.68) RM 3.72 to mouth 

Yutzy Ditch (02-364) (RM 47.1) RM 1.38 to the mouth 

Fitzgerald Ditch (02-272) (RM 44.96) RM 1.75 to mouth 

Little Darby Cr.(02-210) (RM 34.1) Headwaters to RM 36.9 

Little Darby Cr.(02-210) (RM 34.1) RM 36.9 to mouth 

Clover Run (02-218) (RM 39.8) 

Lake Run (02-216) (RM 36.9) 

Jumping Run (02-217) (RM 3.9) 

Treacle Creek (02-213) (RM 31.3) 

Howard Run (02-215) (RM 5.4) 

Proctor Run (02-214) (RM 3.69) 

Barron Creek (02-212) (RM 24.4) 

Wamp Ditch (02-363) (RM 23.0) 

Spring Fork (02-211) (RM 17.46) 

Bales Ditch (02-362)(RM 3.64) RM 1.72 to mouth 

Smith Ditch (02-353) (RM 31.69) 

Tributary to Smith Ditch (02-354)(RM0.06) 

Gay Run (02-298) (RM 26.48) 

Hellbranch Run (02-204) (RM 26.1) Headwaters to RM 5.0 

Hellbranch Run (02-204) (RM 26.1) RM 5.0 to mouth 

Hamilton Ditch (02-259) (RM 11.19) -Hdwtrs to Feder Rd. 

_+ 

+ 

+ 

_+ 

+ 

_+ 

_+ 

_+ 

_+ 

_+ 

_+ 

_+ 

_+ 

_+ 

_+ 

_+ 

+ 

_+ 

* 

* 

* 

* 

*+ 

*+ 

*+ 

*+ 

*+ 

*+ 

_+ 

_+ 

* 

*+ 

+ 

_+ 

_+ 

+ 

_+ 

_+ 

+ 

_+ 

+ 

+ 

_+ 

+ 

+ 

_+ 

_+ 

_+ 

_+ 

_+ 

+ 

+ 

*+ 

*+ 

*+ 

*+ 

*+ 

*+ 

*+ 

_+ 

*+ 

_+ 

_+ 

_+ 

_+ 

+ 

+ 

*+ 

_+ 

+ 

+ 

+ 

_+ 

+ 

+ 

_+ 

_+ 

_+ 

_+ 

_+ 

+ 

+ 

*+ 

*+ 

*+ 

*+ 

*+ 

*+ 

*+ 

_+ 

*+ 

_+ 

_+ 

_+ 

_+ 

+ 

+ 

*+ 

*+ 

_+ 

*+ 

_+ 

*+ 

*+ 

_+ 

_+ 

_+ 

_+ 

_+ 

+ 

+ 

*+ 

*+ 

*+ 

*+ 

*+ 

*+ 

_+ 

_+ 

_+ 

+ 

*+ 

_+ 

_+ 

_+ 

_+ 

_+ 

_+ 

_+ 

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173 
Water Body Segment 

Use Designations 

S 

R 

W 

Aquatic Life 

Habitat 

Water 

Supply Recreation 

W 

W 

H 

E 

W 

H 

M 

W 

H 

SS 

H 

C 

W 

H 

L 

R 

W 

P 

W 

S 

A 

W 

S 

I 

W 

S 

B 

W 

P 

C 

R 

S 

C 

R 

Feder Rd. to mouth 

Clover Groff Ditch (02-245) (RM 11.19 - Hdwtrs to Feder Rd. 

Feder Rd. to mouth 

Springwater Run (02-203) (RM 24.0) 

U.T. to Big Darby Creek (02-352) (RM 23.77) 

U.T. to Big Darby Creek (02-270) (RM 20.2) 

U.T. to Big Darby Creek (02-366) (RM 18.41) 

Greenbrier Creek (02-202) (RM 16.75) 

Georges Creek (02-201) (RM 14.4) 

Lizard Run (02-273) (RM 12.93) 

_+ 

_+ 

+ 

_+ 

_+ 

_+ 

+ 

+ 

* 

* 

* 

_+ 

_+ 

*+ 

*+ 

*+ 

+ 

_+ 

_+ 

_+ 

+ 

+ 

+ 

*+ 

*+ 

*+ 

+ 

_+ 

_+ 

_+ 

+ 

+ 

+ 

_+ 

_+ 

_+ 

*+ 

_+ 

*+ 

* 

_+ 

_+ 

_+ 

_+ 

a - River code of the river or stream segment; b - River Mile of the confluence point with applicable receiving stream 

While the principal focus of a biosurvey is on AQUATIC LIFE USE CHANGES: 

the status of aquatic life uses, the status of OHIO WQS (1978 - 2001) 

other uses such as recreation and water supply, 300 

1978-1992 

1992-2001 

? 

as well as human health concerns are also 

addressed (Table B-6). The findings and 250 

conclusions of a biological and water quality 

study may factor into regulatory actions taken 

by Ohio EPA (e.g., NPDES permits, Director’s 

Orders, the Ohio Water Quality Standards 

[OAC 3745-1]), and are eventually 

200 

150 

SEG

MEN

TS 

incorporated into Water Quality Permit 

Support Documents (WQPSDs), State Water 

Quality Management Plans, the Ohio Nonpoint 

Source Assessment, and the Integrated Report 

(combined 303[d] and 305[b] report). Periodic 

100 

50 

0 

rulemakings are conducted to incorporate the 

use revision recommendations into the Ohio 

WQS, thus resolving the issue prior to the 

application of water quality management (see 

Figure 5-1, U.S. EPA’s Water Quality 

Management Cycle). Figure B-6 summarizes 

the number of stream and river segments (mostly 

whole streams) where aquatic life uses have 

been revised as the result of a biological and 

water quality assessment in Ohio since 1978. 

This became a routine practice once the 

assessment criteria and decision-making process 

"UPGRADES" "DOWNGRADES" PREVIOUSLY 

UNDESIGNATED 

TYPE OF CHANGE 

FIGURE B-6. The number of individual stream and river 

segments in which aquatic life use designations were 

revised during 1978-1992 and 1992-2001. Cases where 

the use was revised to a higher use are termed 

“upgrades” and cases where a lower use was assigned are 

termed “downgrades”. Previously undesignated refers to 

streams that were not listed in the 1985 WQS, but which 

have been added via the Five-Year Basin Approach to 

monitoring and assessment. 

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174 
for UAAs were established earlier in the assessment process. It required the development of reliable 

tools, particularly for determining status, assessing habitat, and determining causal associations, all of 

which are part of the developmental process described in Figure 5-2. The terms “upgrade” and 

“downgrade” are used figuratively here and in Figure B-6 as descriptors of the direction of change from 

the default use to that produced by a standardized assessment process. The majority of these changes are 

from the baseline of the original designations made in 1978 or 1985 without the benefit of systematic 

monitoring and assessment data, numerical biocriteria, and refinements in the process that occurred in the 

late 1980s. Thus, the original use designations are merely being “corrected” to the appropriate use based 

on a standardized process and more robust criteria and assessments. 

Monitoring and assessment information, when based on a sufficiently comprehensive and rigorous system 

of environmental indicators, is integral to protecting human health, preserving and restoring ecosystem 

integrity, and sustaining a viable economy (ITFM 1992). Such a strategy is intended to achieve a better 

return on public and private investments in environmental protection and natural resources management. 

More and better monitoring and assessment information is needed to answer the fundamental questions 

about the condition of our water resources and to shape the strategies needed to address both existing and 

emerging problems within the context of watershed-based management. These principles have guided the 

development of surface water monitoring and assessment at Ohio EPA for the past 25 years and will 

continue to do so in the future. 

IV. Develop and validate quantitative thresholds 

The lack of adequate and reliable decision criteria for biological assessment has historically limited its 

usefulness, reliability, and wider acceptance in water quality management. In 1980, Ohio EPA developed an 

initial set of decision criteria for fish and macroinvertebrate assemblages that consisted of narrative quality 

ratings based in part on numerical biological index “guidelines” (Tables B-1 and B-2). These were intended 

to more directly reflect and assess the ecological goals espoused by the tiered aquatic life uses adopted in 

1978. These early narrative biocriteria were comprised of contemporary measures such as taxa richness, 

indicator guilds, the Shannon diversity index, and the Index of Well-Being (Gammon 1976). Attainable 

expectations for a set of narrative community attributes were based on Ohio’s experience with sampling 

approximately 150-200 sites statewide. This approach was used between 1980 and 1987 and was applied 

uniformly on a statewide basis. As the technology did not yet exist, no effort was made to account for 

background variability by using landscape partitioning frameworks such as ecoregions. 

The narrative classification system consisted of assigning narrative quality ratings such as exceptional 

(consistent with the Exceptional Warmwater Habitat use), good (Warmwater Habitat use), fair, and poor. 

Exceptional and good met the goals of the Clean Water Act while fair and poor reflected a failure to attain 

those goals (Tables B-1 and B-2). The purpose of this narrative classification system was essentially two 

fold: 1) to provide an objective, systematic basis for assigning aquatic life uses to surface waters; and 2) to 

provide an objective, standardized approach for determining the magnitude and severity of aquatic life 

impairments for assessment purposes. Considerable judgment was used in applying these early narrative 

biological criteria on a site-specific basis and the system was characteristic of between a level 2 and 3 

program (See Appendix C). The aggregate impact of these assessments played a major role in setting and 

evaluating WQS use designations, designing water quality management plans, and developing advanced 

treatment justifications for municipal sewage treatment plants. These criteria also provided a basis for 

designating stream and river segments as attaining, partially attaining, or not attaining designated aquatic life 

uses in the 1982, 1984, and 1986 Ohio EPA 305b reports. They were, however, inherently prone to underestimating impairment (DeShon 1995). 

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175 
Regionally Referenced Numerical Biological Criteria 

In 1986, a major effort was undertaken to develop regionally referenced and calibrated numeric biological 

criteria using a statewide set of regional reference sites. This was spurred by the Ohio Stream 

Regionalization Project in which the application of Omernik’s (1987) ecoregions and the regional reference 

site concept (Hughes et al. 1986) was tested. For the fish assemblage, the Index of Well-Being was modified 

(Ohio EPA 1987) and the Index of Biotic Integrity (IBI; Karr 1981, Karr et al. 1986) was added. For 

macroinvertebrates, the Invertebrate Community Index (ICI; Ohio EPA 1987, DeShon 1995) replaced the 

narrative evaluations used previously. The IBI and ICI consist of metrics that include community production, 

function, tolerance, and reproduction in an aggregated index. This provides for a more rigorous, ecologically 

oriented approach to assessing aquatic community health and well-being. The process of deriving the 

numerical biological criteria is described more extensively in Ohio EPA (1987, 1989a,b) and Yoder and 

Rankin (1995a). 

The derivation of the current numerical biological criteria is based on the biological “performance” that is 

demonstrated at least impacted, regional reference sites. This is consistent with the operational definition of 

biological integrity as defined by Karr and Dudley (1981), which provides the theoretical basis for this 

framework. The numerical biological criteria resulting from the application of this framework represent the 

assemblage performance that can reasonably be attained given contemporary background conditions. 

Although these do not emanate from an attempt to define “pristine,” pre-Columbian conditions, the design 

framework includes a provision to “maintain” the biocriteria by continually resampling the reference sites – 

reference condition is monitored so that all reference sites are resampled once each decade. This promotes 

the periodic and orderly reassessment of reference condition and the database that drives the calibration of 

the biological indexes and the derivation of the numeric biocriteria. Furthermore, the knowledge base used 

in the development of the multimetric indexes includes an awareness of pre-settlement faunas and their 

characteristics. This is entirely consistent with the BCG and the description of attributes from “as naturally 

occurs” to an increasingly disturbed state. Thus, if pristine conditions do return this would be reflected by 

the periodic adjustments to the multimetric indexes, their calibration, and/or the numerical biological 

criteria. 

Biological criteria in Ohio are based on two principal organism groups, fish and macroinvertebrates. 

Numerical biological criteria for rivers and streams were derived by utilizing the results of sampling 

conducted at more than 400 reference sites that represent the “least impacted” conditions within each 

ecoregion (Ohio EPA 1987, 1989a). This information was then merged within the existing framework of 

tiered aquatic life uses to establish attainable, baseline biological assemblage performance expectations on a 

regional basis. Biological criteria vary by ecoregion, aquatic life use designation, site type, and biological 

index (Figure B-2). 

The framework within which biological criteria were established and used to evaluate Ohio rivers and 

streams includes the following major steps: 

• selection of indicator organism groups; 

• establish standardized field sampling, laboratory, and analytical methods; 

• selection and sampling of least impacted reference sites; 

• calibration of multimetric indexes (e.g., IBI, ICI); 

• set numeric biocriteria based on attributes specified by each tiered aquatic life use designation; 

• reference site re-sampling (10% of sites sampled each year beginning in 1990); and, 

• making periodic (i.e., once per 10 years) adjustments to the multi-metric indexes, numeric 

biocriteria, or both as determined by reference site resampling results (Note: this latter step has yet 

to be undertaken by Ohio EPA). 

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176 
Ohio IBI Calibration & Biocriteria Derivation Process

The major steps in the biological criteria calibration, derivation, and application process are summarized in 

Figure B-7. The process integrates the technical process of index derivation and calibration with narrative 

statements about the desired biological assemblage condition and regionalization (e.g., ecoregions). This 

latter step is particularly important as it is needed to stratify regional landscape variability within a tractable 

framework. Figure B-7 portrays the calibration of the IBI for wading sites. A similar stepwise procedure 

was used to calibrate the Invertebrate Community Index for macroinvertebrates (Ohio EPA 1987, DeShon 

1995) and the IBIs for the headwater and boatable site types. Once reference sites are selected and sampled 

(Step 1 in Figure B-7) the biological data is first used to calibrate the IBI (Step 2) and ICI. For fish three 

different IBIs were derived, one each for headwaters, wading (Step 3), and boat sites. The reference site 

IBIs are then used to establish numerical biological criteria (Steps 4 and 5). A notched box-and-whisker 

plot method was used to analyze the distribution of IBIs by ecoregion (Step 4). These plots contain sample 

size, medians, ranges with outliers, and 25th and 75th percentiles. Box plots have one important advantage 

over the use of means and standard deviations (or standard errors) because they do not assume a particular 

distribution of the data. Furthermore, outliers (i.e., data points that are two interquartile ranges beyond the 

25th or 75th percentiles) do not exert an undue influence as they can on means and standard errors. In 

establishing biological criteria for a particular area or ecoregion we attempted to represent the “typical” 

biological community performance, not the extremes and outliers. These can be dealt with on a 

case-by-case or site-specific basis, if necessary. Once numerical biological criteria are determined, they are 

then used in making assessments of specific rivers and streams (Step 6). 

____________________________________________ 

Metric 5 3 1 ____________________________________________ 

Number of Species Varies x Drainage Area 

No. of Darter Spp. Varies x Drainage Area 

No. of Sunfish Spp. >3 2-3 <2 

No. of Sucker Spp. Varies x Drainage Area 

Intolerant Species

>100 sq. mi. >5 3-5 <3 

<100 sq. mi. Varies x Drainage Area 

%Tolerant Species Varies x Drainage Area 

%Omnivores <19 19-34 >34 

%Insectivores 

<30 sq. mi. Varies x Drainage Area 

>30 sq. mi. >55 26-55 <26 

%Top Carnivores >5 1-5 <1 

%Simple Lithophils Varies x Drainage Area

%DELT Anomalies >1.3 0.5-1.3 <0.5 

Relative Abundance >750 200-750 <200 ____________________________________________ 

I. Select & sample

reference sites 

II. Calibration of IBI metrics 

III. Calibrated IBI modified for 

Ohio waters 

IV. Establish ecoregional

patterns/expectations 

V. Derive numeric bio­ criteria: codify in WQS 

VI. Numeric biocriteria are 

used in bioassessments 

FIGURE B-7. The major steps of the Ohio EPA numeric biological criteria calibration and derivation 

process leading to their application in biological and water quality assessments; this example is for the 

Index of Biotic Integrity (IBI) for wading sites. 

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177 
The outcome is a systematic process for measuring the essential products of aquatic structure and function 

that represent symptoms of ecosystem health. BCG derived and calibrated numeric biocriteria provide 

tangible measures of aquatic assemblages by which ecosystem health and well-being can be inferred. The 

tangible products of healthy watersheds are desirable biomass, water quality that is suitable for all uses, and 

an ability to assimilate background inputs that do not alter the key characteristics or processes associated with 

the aquatic assemblages detailed in the BCG (Table B-7). The key indicators of each are biological 

assemblage performance consistent with the designated use (measured by the biological indexes and 

compared to the numeric biocriteria) and chemical and physical quality comparable to least impacted regional 

reference conditions and other acceptable exposure thresholds. 

TABLE B-7. The tangible products that are symptomatic of aquatic ecosystem health and 

the measurable biological, chemical, and physical indicators of healthy and degraded 

aquatic systems. 

Tangible “Products” 

Biomass 

Water Quality 

Assimilative Capacity 

Healthy 

Desirable forms (quality biodiversity, 

game fish, birds, mammals, inverts., 

plants, algae, microbes) 

Comparable to regional reference 

Processes background runoff and 

materials without adverse changes in 

biota 

Degraded 

Undesirable forms (low quality 

biodiversity, nuisance abundances, 

tolerant species dominate) 

Poorer than regional reference 

Inability to process background 

inputs due to reduced capacity to 

biologically and physically process 

excess materials 

Measurable Indicators: 

Biological assemblages 

Chemical indicators 

Physical Indicators 

Meet or exceed numeric biocriteria 

for TALU 

Meets numeric criteria (some are 

TALU based) and is within reference 

thresholds 

Provides essential habitat attributes 

and hydrology 

Does not meet biocriteria for TALU; 

response varies by impact type and 

severity of impairment 

Exceeds numeric criteria and/or 

reference thresholds 

Degraded habitat and altered 

hydrology 

What Process Was Used to Adopt Biocriteria in the Ohio WQS? 

The adoption of numeric biocriteria and tiered uses in the Ohio WQS has been an evolutionary process 

over the preceding 25 years. There were many important events that determined the make-up and 

acceptance of the biocriteria and TALU in Ohio. These milestones are summarized in Table B-8. Some 

of the key events that resulted in a wider acceptance of the present day biocriteria and tiered uses were the 

legal proceedings on the use changes that occurred in the lower Cuyahoga River in 1988 and Ottawa 

River in 1989. Ohio EPA adopted a recommendation that the use designation of the Cuyahoga River 

mainstem be changed from a Limited Warmwater Habitat use designation to Warmwater Habitat based on 

biological and water quality surveys conducted between 1984 and 1987 and the ensuing UAA process. 

The former use was adopted in 1978 as a variance for specific point source derived pollutants. The 

biological assessments concluded that while the mainstem was severely impaired, the potential to attain 

WWH with achievable water quality based management of point sources was supported by the habitat 

assessment that showed a sufficiently intact habitat. This was eventually resolved via a legal process that 

included appeals of the initial decision up to the Ohio Supreme Court. 

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178 
TABLE B-8. Key events and milestones that occurred in the evolutionary development, adoption, and 

implementation of biological assessments, numeric biocriteria, and tiered aquatic life uses in Ohio between 

1974 and the present. 

YEAR MILESTONE DESCRIPTION 

1974 First Ohio WQS General use, few numeric criteria, narrative “free froms” 

1978 Initial TALUs Tiered uses adopted, specific chemical criteria 

1980 Narrative “biocriteria” First organized approach to biological assessment; systematic monitoring & 

assessment 

1983-4 Stream Regionalization Project Testing and validation of Omernik’s ecoregions and reference site concepts in 

Ohio 

1986-7 Derivation of numeric biocriteria Statewide data collected to date was used to develop, derive, and calibrate 

numeric biocriteria based on multimetric indexes; biocriteria “User Manuals” 

published 

1987 Biocriteria proposed in WQS Initial proposal for numeric biocriteria 

1987-89 Hearings on Cuyahoga River use 

change 

Litigation of revision of a segment of the river form LWH to WWH; 

regulated entities Contested basis for the “upgrade”; the first test of the 

technical and policy aspects of the numeric biocriteria and TALU 

implementation; resolved at Ohio Supreme Court 

1989 Hearings on Ottawa River use 

change 

Litigation of revision of a segment of the river from LWH to WWH; 

regulated entities challenged; issue settled after Cuyahoga case ruling; led to 

more stringent regulation of point and nonpoint sources. 

1990 Biocriteria adopted Numeric biocriteria and refinements to TALUs were formally adopted in 

WQS 

1990 Five-Year Basin Approach A rotating basin approach that integrated key WQ management program 

outputs (e.g., NPDES permits) was initiated; use changes processed in annual 

rulemakings 

1991 Internal training and orientation All water program staff receives training in WQS, monitoring & assessment, 

modeling, and permit development and their integration. 

1995 

1998 

Lake Erie Bioassessment 

Wetlands bioassessment methods 

and biocriteria 

Biological assessment methods and indexes developed for application to Lake 

Erie near shore and lacustuary habitats 

Bioassessment methods and narrative criteria were developed for wetlands; 

includes various standardized assessment methods (beyond delineation) and a 

classification scheme. 

1998 TMDL development process & 

schedule 

TMDL development was integrated into the Five-Year Basin Approach ad 

schedule through 2015 

1999 Re-sampling of regional reference 

sites 

First re-sampling of regional reference sites was completed via the Five-Year 

Basin Approach 

2003 Primary Headwater Habitat Assessment and classification scheme for primary headwater streams that are 

not included in the existing numeric biocriteria are developed as a result of 

stream management applications. 

2003 Ohio River ORSANCO develops biological assessment tools and indexes as a precursor 

to numeric biocriteria for the Ohio R. mainstem. 

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179 
Data collected via follow-up monitoring between 1984 and 2000 shows that attainment of the WWH 

biocriteria is increasing in the mainstem and proving the validity of both the WWH designation and the 

water quality based pollution abatement that the redesignation spurred (Figure B-8). A similar case 

involving the Ottawa River was resolved when this legal decision was made. No other appeals of the 

hundreds of use changes that have been made since that time have been filed. The systematic process of 

resolving use designation issues ahead of water quality management actions (permitting, listing, funding, 

planning) has proceeded as one of the most important outcomes of the Five-Year Basin Approach since 

that time. The next major milestone for the program will be the analysis of the first set of reference sites 

re-sampling that took place in the 1990s. In addition, level IV subregions have been delineated, which 

offers an additional level of potential stratification to the biocriteria derivation process. 

The developments that occurred in the late 1990s including biological assessment and classification 

schemes for wetlands, Lake Erie near shore and lacustuary habitats, primary headwater stream habitat, 

and the Ohio River all happened as a result of the ground work laid in the 1980s for streams and rivers. It 

illustrates the natural growth process that can occur once the fundamentals of the approach are developed, 

tested, and adopted. 

0 

10 

20 

30 

40 

50 

60 

CUYAHOGA RIVER: ICI 

1984 1986 1987 1988 1991 1996 2000 

n = 9 n = 5 n = 14 n = 5 n = 10 n = 11 n = 5 

IN

V

E

R

T

E

B

R

A

TE 

C

O

M

M

U

NITY IN

D

EX (ICI)

Toxic Response 

Threshold (ICI <18) 

WWH Biocriterion 

(ICI = 36) 

FIGURE B-8. Box-and-whisker plots of Invertebrate Community Index 

(ICI) results in the mainstem of the Cuyahoga River between Akron and 

Cleveland between 1984 and 2000. 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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180 
Appendix C

Technical Guidelines: Technical Elements 

of a Bioassessment Program 

(SUMMARY OF DRAFT DOCUMENT) 

[This document has undergone review by State and U.S. EPA Regional biologists and managers. Data 

analyses are currently being conducted to refine certain technical elements (e.g., subsampling level, 

taxonomic resolution, spatial array of sites) that determine the level of rigor. A revised version will be 

prepared for a more comprehensive review by States and Tribes prior to finalization. A draft 

document will be available to the public in 2006.] 

What are these technical guidelines and what is the purpose of the document? 

This document is intended primarily for use by State and Tribal program managers and staff responsible 

for monitoring and assessment and WQS programs. States and Tribes can use this information to assess 

and communicate the precision of biological programs and, if deemed necessary, to refine and modify 

those programs. As States and Tribes increasingly use biological assessments and criteria to refine 

designated aquatic life uses, the need to recognize and communicate the level of precision of the 

biological program takes on greater importance. In addition, when the majority of States are in various 

stages of developing and improving their biological assessment programs, States and Tribes can use the 

type of detailed guidelines and milestones provided in this document to evaluate their progress. 

Bioassessment is a major component of monitoring and assessment programs that include other chemical, 

physical, and environmental measures and indicators (ITFM 1992, 1995; Yoder and Rankin 1998). This 

document describes the critical, or key, technical attributes and processes of State and Tribal biological 

assessment programs. State and Tribal monitoring programs can also use the technical information 

presented in this document as a procedural template for evaluating the technical elements of their 

chemical and physical monitoring and assessment approaches. Ultimately, the integration of chemical 

and physical assessment with biological assessment will provide information to help States and Tribes 

better determine priorities and make more informed management decisions. State and Tribal programs 

can achieve appropriate levels of precision 

in their monitoring and assessment programs The 12 Key Technical Elements of a Bioassessment Program 

using currently available methods and 

technologies, and these approaches will Sampling Design Component 

produce a sufficiently accurate, 1. Temporal Periodicity of the sampling 

2. Spatial Coverage of the sites within the area of interest comprehensive, and cost-effective program 3. Natural Classification of the waterbodies as a framework 

capable of supporting all water quality for assessment 

management programs. 4. Regional Reference Condition development 

5. Reference Sites Selection Criteria 

What are the key technical elements of a Methods Component 

bioassessment program? 6. Number and kinds of Indicator Assemblages 

7. Methods for Sample Collection 

There are 12 key technical elements that 8. Methods for Sample Processing 

compose three basic methodological Data Interpretation Component 

components: sampling design, methods, and 9. Attention to Ecological Attributes for indicators 

data interpretation (see box at right). To 

10. Calibration of Biological Endpoints 

11. Diagnostic Capability of the indicators better understand each technical element in a 12. Use of Professional Review of documentation and methods 

bioassessment program, it is important to 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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181 
articulate the underlying rationale for each. The technical elements will be described in detail in the draft 

document that is being prepared for review. 

How do environmental managers use these guidelines to evaluate the precision of their bioassessment 

program? 

Included in the Technical Guidelines document is a checklist that enables managers and technical staff to 

evaluate their program’s level of rigor for each of the 12 key technical elements. The checklist includes 

four levels of rigor, with Level 4 being the most rigorous. For an overall assessment of a water quality 

agency’s bioassessment program, a checklist should be completed for each assemblage and waterbody 

ecotype, as bioassessment programs may have different levels of rigor for different waterbody ecotypes. 

It is important for the water quality agency to determine and reconcile these for management purposes 

since differing levels of rigor provide different levels of confidence in decision-making. 

Evaluation of a program’s level of rigor should be conducted collaboratively with State and Tribal 

technical staff and managers. Documentation will support completion of the checklist regarding aspects 

of the technical elements. Some variation between different elements will likely occur in terms of 

performance level (i.e., one element may receive a Level 4, while another is determined to be Level 2). 

Therefore, a scale that combines the rating of all elements will provide an overall indication of 

bioassessment program rigor. This cumulative evaluation provides a detailed analysis of the strengths 

and weaknesses of the comprehensive bioassessment and biocriteria program. In this rating system, we 

have considered all elements to be of equal weight. However, the data acquisition (sampling, processing) 

and treatment (analysis) phase is the linchpin of any program. One of the questions under discussion in 

preparation of this draft document is how to evaluate the influence of these particularly key elements. 

What are the implications of having a bioassessment program with a high level of rigor? 

The rigor and quality of biological assessments may vary among water resource agencies. The quality of 

the biological data is integral to effectively and accurately answering questions about condition, 

protection, restoration, or other management decisions regarding surface water resources. For example, 

bioassessment data obtained using a low level of rigor may provide a lesser degree of resolution needed to 

differentiate many stressor effects from natural variability. 

The guidelines focus on four levels of rigor, High

where Level 4 is the most rigorous and provides 

the highest quality of data. The lower levels of 

rigor may detect and describe severely altered 

waters, and to a more limited extent, 

waterbodies in the best condition. As the level 

of rigor increases, the ability to discern more 

precisely different levels of biological condition 

increases. Figure C-1 illustrates the theoretical 

performance of the four levels of rigor of 

bioassessment techniques in assessing condition 

and the level of confidence in those assessments. Low

Level of Confidence 

Level 1 

Level 2 

Level 3 

Level 4 

Level of Confidence

Level 1

Level 2

Level 3

Level 4

Detecting and quantifying intermediately 

stressed sites, accurately describing associated 

causes and sources, and measuring along a 

stressor gradient will be done more accurately 

and with more confidence as the level of rigor 

UndisturbedIntermediate Severe

Level of Stress on Ecosystem

FIGURE C-1. Conceptual illustration of confidence in 

detecting different stress levels as a function of assessment 

rigor (Levels 1-4 with 4 being most rigorous). 

DRAFT: Use of Biological Information to Better Define Designated Aquatic Life Uses in State 

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182 
increases. In Figure C-1, Level 4 provides the highest confidence in the biological assessment along the 

stressor gradient. Progressively less rigorous methods provide higher confidence in the assessment at the 

extremes of the stressor continuum, often only useful for status assessments. The difference in levels of 

rigor will be more apparent in applications requiring diagnostic capability. By first identifying the level 

of rigor attained by each of the key elements and the overall approach, States and Tribes can better use the 

data and information. For instance, States and Tribes may need a high level of confidence in an 

assessment, such as that associated with a Level 3 or 4 bioassessment, to determine level of stress along a 

gradient (Figure C-1). Less rigorous methods would not reliably detect disturbance. 

Figure C-2 is a conceptual illustration depicting how increasingly comprehensive bioassessments better 

detect and discriminate differences along the BCG. As currently defined, Level 4 employs numeric 

biocriteria, based on calibrated and refined assessment tools (e.g., calibrated indexes or model output) 

that, in turn, are based on regional reference conditions at a sufficiently detailed level of geographic 

stratification and classification of aquatic ecotypes. This approach can discriminate different condition 

tiers (e.g., as in the Biological Condition Gradient) within a known margin of uncertainty. Level 3 

usually employs a numeric and/or 

narrative assessment methodology that 

discriminates among fewer condition 

categories and reflects an ordinal scale 

of measurement (i.e., excellent, good, 

fair, poor). Assessment programs that 

rate as Level 2 may be unable to 

differentiate more than two broad 

categories or classes of condition. 

This level has a large degree of 

uncertainty about assessing stressors, 

and the pass/fail boundary may reflect 

an under- or over- protective 

threshold. Level 1 functions as a 

general screening tool and may 

identify best conditions from the worst 

in only a very coarse sense. The 

uncertainty with a Level 1 rated 

program precludes resolution to 

many management questions without	 FIGURE C-2. Conceptual illustration of the capability of increasingly 

further monitoring and assessments.	 comprehensive bioassessments to detect and discriminate along the 

biological condition gradient. Shaded areas represent relative degree of 

uncertainty. 

Level 4 

BIOLO

GIC

AL 

C

O

N

DITION 

G

R

A

DIE

NT (B

C

G) 

CAPABILITY TO DETECT STRESSORS 

(RESOLUTION OF ASSESSMENT) HIGHEST LOWEST 

1 

2 

3 

4 

5 

6 

Excellent 

Good 

Fair 

Poor 

Pass 

Fail 

Level 3 Level 2 

100 

0 

Natural 

Condition 

+ 

−

Level 1 

Minimal 

Changes 

Evident 

Changes 

Moderate 

Changes 

Major 

Changes 

Severe 

Changes 

Level 4

BIOLO

GIC

AL C

O

N

DITIO

N

G

R

A

DIE

N

T (B

C

G)

CAPABILITY TO DETECT

(RESOLUTION OF ASSESSMENT) HIGHEST LOWEST

1

2

3

4

5

6

Excellent

Good

Fair

Poor

Pass

Fail

Level 3 Level 2

100

0

Natural

Condition

+

−

Level 1

Minimal

Changes

Evident

Changes

Moderate

Changes

Major

Changes

Severe

Changes

Level 4

BIOLO

GIC

AL C

O

N

DITIO

N

G

R

A

DIE

N

T (B

C

G)

CAPABILITY TO DETECT STRESSORS

(RESOLUTION OF ASSESSMENT) HIGHEST LOWEST

1

2

3

4

5

6

Excellent

Good

Fair

Poor

Pass

Fail

Level 3 Level 2

100

0

Natural

Condition

+

−

Level 1

Minimal

Changes

Evident

Changes

Moderate

Changes

Major

Changes

Severe

Changes

Level 4

BIOLO

GIC

AL C

O

N

DITIO

N

G

R

A

DIE

N

T (B

C

G)

CAPABILITY TO DETECT

(RESOLUTION OF ASSESSMENT) HIGHEST LOWEST

1

2

3

4

5

6

BIOLO

GIC

AL C

O

N

DITIO

N

G

R

A

DIE

N

BIOLO

GIC

AL C

O

Excellent

Good

Fair

Poor

Pass

Fail

Level 3 Level 2

100

0

Natural

Condition

+

−

Level 1

Minimal

Changes

Evident

Changes

Moderate

Changes

Major

Changes

Severe

Changes

Level 4

T (B

C

G)

CAPABILITY TO DETECT STRESSORS

(RESOLUTION OF ASSESSMENT) HIGHEST LOWEST

1

2

3

4

5

6

Excellent

Good

Fair

Poor

Pass

Fail

Level 3 Level 2

100

0

Natural

Condition

+

−

Level 1

Minimal

Changes

Evident

Changes

Moderate

Changes

Major

Changes

Severe

Changes

Level 4

N

DITIO

N

G

R

A

DIE

N

T (B

C

G)

CAPABILITY TO DETECT

(RESOLUTION OF ASSESSMENT) HIGHEST LOWEST

1

2

3

4

5

6

Excellent

Good

Fair

Poor

Pass

Fail

Level 3 Level 2

100

0

Natural

Condition

+

−

Level 1

Minimal

Changes

Evident

Changes

Moderate

Changes

Major

Changes

Severe

Changes

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183 
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184 
Appendix D

The Role of Reference Condition in Biological Assessment and Criteria 

(INTRODUCTION TO DRAFT DOCUMENT ON DEVELOPMENT AND 

APPLICATION OF THE REFERENCE CONDITION CONCEPT) 

The Clean Water Act’s biological integrity objective and fishable swimmable goals pose significant 

challenges to States and Tribes charged with evaluating whether aquatic resources under their 

management achieve the objective and goals. One of the critical challenges is the development of a 

standard or benchmark by which to judge whether particular water bodies are in accord with the objective 

and goals. The concept of a “reference condition” and its implementation form the foundation on which 

to make such judgments. 

This document provides States, Tribes, and other practitioners with guidelines on the reference condition 

concept and how to apply it in their water management programs, particularly for assessing the condition 

of aquatic resources. These guidelines are intended to broaden the implementation of biological 

monitoring and assessment, to increase the consistency among States and Tribes, and to improve the 

success of individual programs. 

States, Tribes, and others have developed and implemented the concept of reference condition in a variety 

of ways to meet their individual needs, without comprehensive guidance from the U.S. EPA. This 

“bottom-up” approach has both advantages and disadvantages. Advantages include the exploration of a 

variety of interpretations of the concept and their implementation, yielding information on successes and 

difficulties. From these experiences comes an evaluation of what works and what does not. 

Disadvantages include the diversity of opinions about the concept and its role, leading to potential 

confusion and sometimes contradictory interpretation and implementation. The technical and policy 

challenges inherent in this effort have resulted in considerable variation in how individual States and 

Tribes define and use the concept. Establishing and using the reference condition concept appropriately is 

critical to implementing biological criteria and tiered aquatic life uses to protect and restore water 

resource quality. Part of the purpose of this document is to encourage consistency, both in the language 

that is used to express the concept, and in its everyday application. 

This document will cover the following topics: a description of the concept of reference condition as well 

as related terms and concepts (including minimally disturbed, least disturbed, and best attainable 

conditions); methods for characterizing reference and related conditions; using water body classification 

to partition natural variability; setting thresholds to determine achievement of a target condition; and 

application of the concept in heavily modified regions (e.g., urban landscapes, agricultural regions) and 

waterbodies (reservoirs, regulated rivers). Both technical and implementation issues are addressed to 

increase the understanding of the concepts. A section on frequently asked questions and answers is 

included to address topics of particular concern to practitioners. Throughout the document, examples are 

drawn from existing State and Tribal programs to illustrate specific applications that are consistent with 

the guidelines. 

In April 2003, U.S. EPA’s Office of Water sponsored a National Biological Assessment and Criteria 

Workshop in Coeur d’Alene, Idaho. This workshop contained sessions on a variety of related topics 

including sessions on the reference condition concept, water quality standards, biocriteria, tiered aquatic 

life uses, and index development. A CD that contains many of the presentations at this workshop is 

included as an appendix to provide a snapshot of the state of the science at that time, and a means to flesh 

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out some of the issues not addressed in detail in the body of this document. Material in this document 

supersedes any contradictory material presented on the CD because thinking has evolved since that time. 

Technical and implementation issues 

A principal technical challenge facing States and Tribes is accurately determining a reference or related 

condition from the range of historical and current ecological conditions. This may involve the analysis of 

data from existing reference sites and/or the modeling of historical information and expert opinion. 

Technical issues include understanding and taking into account natural variability through classification 

and/or modeling of natural gradients. Both classification and modeling need to be ecologically valid, yet 

practical for States and Tribes. A related issue is determining whether an existing condition is 

significantly (both ecologically and statistically) different from a specified condition (e.g., as specified in 

water quality standards). Scientific rigor is necessary, tempered by ease of understanding and 

implementation. 

Implementation issues revolve around how States and Tribes can apply the reference condition concept to 

protect and improve an existing biological condition through application in water quality standards, 

including: 

° Refinement of aquatic life uses through a) setting condition thresholds, b) interpreting/translating 

narrative aquatic life uses, and c) establishing subcategories of tiered aquatic life uses; 

° Establishment of numeric biological criteria; 

° Quantitative biological description of existing designated uses through bioassessments; and 

° Determination of departure of existing condition from biological integrity. 

U.S. EPA guidance on the implementation of the reference condition concept balances the need for 

scientific rigor and the need for practical application, that together result in the protection and 

improvement of water quality. 

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Appendix E

Statistical Guidance for Developing Indicators for Rivers and Streams:


A Guide for Constructing Multimetric and Multivariate Predictive


Bioassessment Models


(SUMMARY OF DRAFT DOCUMENT) 

[This document has undergone various levels of review by a technical workgroup and U.S. EPA 

representatives. The current version is being prepared for a more comprehensive review prior to 

finalization. The final document is anticipated in 2005.] 

States are faced with the challenges of not only developing tools that are both appropriate and costeffective (Barbour 1997), but also the ability to translate scientific data for making sound management 

decisions regarding water resources. The approach to analysis of biological (and other ecological) data 

should be straightforward to facilitate a translation for management application. This is not meant to 

reduce the rigor of data analysis but to ensure its place in making crucial decisions regarding the 

protection, mitigation, and management of the nation’s aquatic resources. In fact, biological monitoring 

should combine biological insight with statistical power (Karr 1987). Karr and Chu (1999) state that 

knowledge of regional biology and natural history (not a search for statistical relationships and 

significance) should drive both sampling design and analytical protocol. 

A central premise of biological assessment is comparison of the biological resources of a waterbody to an 

expected reference condition. The condition of the waterbody is evaluated by its departure from the 

expected condition. Biological assessment of waterbodies depends on our ability to define, measure, and 

compare an assessment endpoint between similar systems. This guidance outlines analytical 

methodologies to perform two tasks: 

• Characterize biological expectation. 

• Determine whether a site deviates from that expectation. 

The methods considered here use the same general approach: sites are assessed by comparing the 

assemblage of organisms found at a site to an expectation derived from observations of many relatively 

undisturbed reference sites. The expectations are modified by classifying the reference sites to account 

for natural variability. Biological variables are tested for response to stressors by comparison of 

undisturbed or minimally disturbed reference sites and disturbed sites. A set of “rules” is developed from 

this information, which are then used to determine if the biota of a site deviate from the expectation, 

indicating the degree to which the site is impacted. 

Several analytical methods have been developed to assess the condition of water resources from 

biological data, beginning with the saprobien system in the early 20th century to present-day development 

of biological markers (Cairns and Pratt 1993). This document provides guidance for two methods for 

analyzing and assessing waterbody condition from assemblage and community-level biological 

information: 

1.	 Multimetric assessment using an index that is the sum of several metrics. This is the basis of the 

Index of Biotic Integrity (IBI) (Karr et al. 1986), the Invertebrate Community Index (ICI) (Ohio 

EPA 1990); the Rapid Bioassessment Protocol (Plafkin et al. 1989); and State indexes developed 

from these (e.g., Southerland and Stribling 1995, Barbour et al. 1996a, Barbour et al. 1996b). 

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2.	 Assessment comparing actual species composition at a site to an idealized reference site predicted 

from a multivariate statistical model. This is the basis of the River InVertebrate Prediction And 

Classification System (RIVPACS; Wright et al. 1984, Furse et al. 1984, Moss et al. 1987, Wright 

1995, Wright 2000) and the AUStralian RIVer Assessment System (AUSRIVAS; Davies 2000, 

Simpson and Norris 2000). 

Many other methods are possible, as well as permutations of the two methods above, all of which are 

beyond the scope of this document. The two approaches were selected because: 

• They use community and assemblage data. 

• The methods are not restricted to any one assemblage. The examples all use freshwater benthic 

macroinvertebrates, but any other assemblage could also be used, such as fish phytoplankton, 

zooplankton or macrophytes. 

• The methods are general, and have been used by several agencies in many areas. The examples 

used to illustrate the methods have also been carried out over wide geographic areas with many 

sites, demonstrating the generality of the methods. 

• The methods have been fully documented and illustrated with case examples. 

• These analysis methodologies are cost-effective and easy to communicate to managers and the 

public. 

Once the framework for bioassessment is in place, conducting bioassessments becomes relatively 

straightforward. Either a targeted design that focuses on site-specific problems or a probability-based 

design, which has a component of randomness and is appropriate for 305(b), area-wide, and watershed 

monitoring, can be done efficiently. Routine monitoring of reference sites may be based on a probability 

design, which will allow cost efficiencies in sampling while monitoring the status of the reference 

condition of a State’s streams. Potential reference sites of each stream class would be randomly selected 

for sampling, so that an unbiased estimate of reference condition can be developed. A randomized subset 

of reference sites can be resampled at some regular interval (e.g., a 4-year cycle) to provide information 

on trends in reference sites. 

This document outlines the steps required to complete multimetric and multivariate predictive assessment 

models. It includes sections briefly covering the conceptual principles behind each step and then uses an 

example dataset that demonstrates the practical application of those principles step by step. It begins with 

a discussion of some concepts and approaches common to both techniques and then moves into 

multimetric and multivariate predictive models. At the end, it concludes with a discussion of how 

biocriteria can be developed from either of the approaches. 

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United States Environmental Protection Agency 

Office ofWater 

Washington,DC20460 

(4304T) 

EPA-822-R-05-001

August 2005