United States Environmental

Protection Agency

Office of Water

Washington, DC 20460

EPA 822-R-02-016

March 2002

Methods for evaluating wetland condition

#6 Developing Metrics and Indexes

of Biological Integrity
United States Environmental

Protection Agency

Office of Water

Washington, DC 20460

EPA 822-R-02-016

March 2002

Methods for evaluating wetland condition

#6 Developing Metrics and Indexes

of Biological Integrity

Major Contributors

Natural Resources Conservation Service, Wetland Science Institute

Billy M. Teels

Oregon State University

Paul Adamus

Prepared jointly by:

The U.S. Environmental Protection Agency

Health and Ecological Criteria Division (Office of Science and Technology)

and

Wetlands Division (Office of Wetlands, Oceans, and Watersheds)
United States Environmental

Protection Agency

Office of Water

Washington, DC 20460

EPA 822-R-02-016

March 2002

Notice

The material in this document has been subjected to U.S. Environmental Protection Agency (EPA)

technical review and has been approved for publication as an EPA document. The information

contained herein is offered to the reader as a review of the “state of the science” concerning wetland

bioassessment and nutrient enrichment and is not intended to be prescriptive guidance or firm advice.

Mention of trade names, products or services does not convey, and should not be interpreted as

conveying official EPA approval, endorsement, or recommendation.

Appropriate Citation

U.S. EPA. 2002. Methods for Evaluating Wetland Condition: Developing Metrics and Indexes

of Biological Integrity. Office of Water, U.S. Environmental Protection Agency, Washington, DC.

EPA-822-R-02-016.

Acknowledgments

EPA acknowledges the contributions of the following people in the writing of this module:

Billy M. Teels (Natural Resources Conservation Service, Wetland Science Institute), Paul Adamus

(Oregon State University), Mark Brown (University of Florida), Dave Cowen (Duke Engineering &

Services), Chris Faulkner (U.S. Environmental Protection Agency), Ric Hauer (University of Montana),

and Jan Smith (Massachusetts Bays National Estuary Program).

This entire document can be downloaded from the following U.S. EPA websites:

http://www.epa.gov/ost/standards

http://www.epa.gov/owow/wetlands/bawwg

ii
iii

Contents

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

List of “ Methods of Evaluating Wetland

 Condition” Modules ....................................................................................... vi

Summary .................................................................................................................1

Purpose..................................................................................................................1

Introduction.........................................................................................................1

Identify Regional Wetland Flora and Fauna ..............................................3

Assign Taxa into Biological Attributes .......................................................5

Classify Wetlands into Regional Classes ............................................. 11

Target Selection of Sample Sites .............................................................. 13

Collect Land-use and Habitat Information ............................................. 14

Establish Gradient of Human Disturbance .............................................. 15

Sample Within the Wetland .......................................................................... 21

Summarize Sample Data by Biological Attributes .................................. 23

Evaluate Attribute Performance Across a

Gradient of Human Disturbance .................................................................. 24

Select Metrics from Best Performing Attributes ................................ 25

Score Each Individual Metric ...................................................................... 28

Calculate Total IBI Score for All Sites.................................................. 28

Interpret IBI and Report Data ...................................................................... 30

References ........................................................................................................ 32

Glossary ............................................................................................................. 36
i v

List of Tables

Table 1: Current Pilot Projects Developing Wetland

Bioassessment Methods and Assemblages .......................... 2

Table 2: Assumed Effects of Environmental Degradation on

Biological Assemblages in Streams ....................................... 7

Table 3: Invertebrate Metrics and Scoring for a Wetlands

Invertebrate Index of Biological Integrity (IBI) ............... 12

Table 4: Individual Metric Scores for

Invertebrate Metrics ................................................................ 29

Table 5: Total IBI Scores, Integrity Classes, and Their

Attributes for Streams in a Regional Reference............. 31

List of Figures

Figure 1: Sequence of Activities in Developing Metrics

and IBI ............................................................................................... 4

Figure 2: Minnesota Wetland Disturbance Analysis ......................... 17

Figure 3: Species/Area Curves for Wetland

Invertebrate Samples ............................................................... 22

Figure 4: Evaluation of Metric Performance...................................... 26

Figure 5: Scatter Plot Illustrating Metric (Grasslike Taxa

Richness) Response to a Single Variable (Zinc

Concentrations) Representing the Gradient of

Human Disturbance .................................................................... 26

Figure 6: Evaluation of Attribute Performance Over

a Combined Set of Disturbances ........................................... 27

Figure 7: Scatter Plot Demonstrating Close Correlation Between

a Wetland Macroinvertebrate IBI and a Disturbance

Gradient Derived From a Combination of

Human Disturbances .................................................................. 27

Figure 8: Example of Wetland Index of Biological

Integrity Scores ......................................................................... 30
v

Foreword

In 1999, the U.S. Environmental Protection Agency (EPA) began work on this series of reports entitled

Methods for Evaluating Wetland Condition. The purpose of these reports is to help States and

Tribes develop methods to evaluate (1) the overall ecological condition of wetlands using biological

assessments and (2) nutrient enrichment of wetlands, which is one of the primary stressors damaging

wetlands in many parts of the country. This information is intended to serve as a starting point for States

and Tribes to eventually establish biological and nutrient water quality criteria specifically refined for

wetland waterbodies.

This purpose was to be accomplished by providing a series of “state of the science” modules concerning

wetland bioassessment as well as the nutrient enrichment of wetlands. The individual module format

was used instead of one large publication to facilitate the addition of other reports as wetland science

progresses and wetlands are further incorporated into water quality programs. Also, this modular

approach allows EPA to revise reports without having to reprint them all. A list of the inaugural set of

20 modules can be found at the end of this section.

This series of reports is the product of a collaborative effort between EPA’s Health and Ecological

Criteria Division of the Office of Science and Technology (OST) and the Wetlands Division of the

Office of Wetlands, Oceans and Watersheds (OWOW). The reports were initiated with the support

and oversight of Thomas J. Danielson (OWOW), Amanda K. Parker and Susan K. Jackson (OST),

and seen to completion by Douglas G. Hoskins (OWOW) and Ifeyinwa F. Davis (OST). EPA relied

heavily on the input, recommendations, and energy of three panels of experts, which unfortunately have

too many members to list individually:

n Biological Assessment of Wetlands Workgroup

n New England Biological Assessment of Wetlands Workgroup

n Wetlands Nutrient Criteria Workgroup

More information about biological and nutrient criteria is available at the following EPA website:

http://www.epa.gov/ost/standards

More information about wetland biological assessments is available at the following EPA website:

http://www.epa.gov/owow/wetlands/bawwg
v i

List of “Methods for Evaluating Wetland

Condition” Modules

1 ................. Introduction to Wetland Biological Assessment

2 ................. Introduction to Wetland Nutrient Assessment

3 ................. The State of Wetland Science

4 ................. Study Design for Monitoring Wetlands

5 ................. Administrative Framework for the Implementation of a

Wetland Bioassessment Program

6 ................. Developing Metrics and Indexes of Biological Integrity

7 ................. Wetlands Classification

8 ................. Volunteers and Wetland Biomonitoring

9 ................. Developing an Invertebrate Index of Biological

Integrity for Wetlands

10............... Using Vegetation to Assess Environmental Conditions

in Wetlands

11 ............... Using Algae to Assess Environmental Conditions in

Wetlands

12 ............... Using amphibians in Bioassessments of Wetlands

13 ............... Biological Assessment Methods for Birds

14 ............... Wetland Bioassessment Case Studies

15 ............... Bioassessment Methods for Fish

16 ............... Vegetation-Based Indicators of Wetland Nutrient

Enrichment

17 ............... Land-Use Characterization for Nutrient and Sediment

Risk Assessment

18 ............... Biogeochemical Indicators

19 ............... Nutrient Load Estimation

20 .............. Sustainable Nutrient Loading

Module # Module Title
1

Summary

M

ultimetric indexes, such as Indexes of

Biological Integrity (IBIs) are powerful

tools for informed management decisions related

to wetlands and wetland health. A number of

States are currently developing wetland

bioassessments by adapting bioassessment

frameworks originally developed for streams.

Although many aspects of stream bioassessment

may apply, wetland floral and faunal assemblages

are unique, and specific data from those assemblages are required to construct an IBI for

wetlands. The information in this module is

designed to provide a framework for the development of IBIs using specific examples from

wetlands. The module describes a step-by-step

process to propose, evaluate, and ultimately

select metrics into the IBI that will best reflect the

biological condition of wetlands.

Purpose

T

he purpose of this module is to provide a

framework to help wetland and water quality

professionals develop metrics and IBIs for

wetlands.

Introduction

A

s discussed in Module 1: Introduction to

Wetland Biological Assessment, biological assessments (bioassessments) are designed to evaluate the health or biological integrity of wetlands.

Many of the States currently developing wetland

bioassessments are adapting bioassessment frameworks originally developed for streams. This reliance on stream information is in part due to the comparatively abundant body of knowledge and literature that has accompanied the development of

stream IBIs over the past two decades. However,

the floral and faunal assemblages of wetlands as well

as the ecological processes that occur within them

(Wissinger 1999) are unique. Therefore, although

many aspects of stream bioassessment may apply

to wetland bioassessment, specific information from

wetland biological assemblages is required to construct an IBI for wetlands.

Of the 10 States currently developing

bioassessment methods for wetlands, 9 are attempting to use IBIs (Table 1). Maine and Montana use

advanced statistical tests (e.g., canonical correspondence analysis) in addition to IBI (multimetric)

analyses to analyze algal data (Danielson 1998,

Apfelbeck 1999). Multimetric and statistical methods are both valid, and the framework provided by

this module can benefit the development of both

methods. This module, however, focuses on the

development of IBIs. Consult Chapter 9 of the

Rapid Bioassessment Protocols for Use in

Streams and Wadeable Rivers: Periphyton,

Benthic Macroinvertebrates, and Fish (Barbour

et al. 1999) for a detailed description of statistical

analysis.

Multimetric indexes are numbers that integrate

several biological metrics to indicate a site’s condition. They can be designed to be sensitive to a

range of factors (physical, chemical, and biological) that stress biological systems, and they are relatively easy to measure and interpret (Karr and Chu

1999). Through a multimetric approach, each metric is given a rating according to whether its value

approximates, deviates somewhat from, or deviates strongly from values measured in least-disturbed

ecosystems of a particular type within a region.

These ratings (e.g., excellent, moderate, fair, and

poor) can be used to make decisions about whether

the wetland condition indicates that aquatic life is

being supported.

Because wetlands vary so widely geographically,

hydrologically, biologically, and by wetland class, it

is unrealistic to expect a single “off-the-shelf”

multimetric index to be applicable everywhere.

Even though techniques may vary, those that adhere to some basic biological, sampling, and statistical principles maintain the strengths of a multimetric
2

Sponsoring Organization Type(s) of Wetlands Assemblage(s)

Minnesota Pollution Control Agency

Depressional

Starting riparian and would like

to do Vernal Pools next.

Macroinvertebrates

Plants

Ohio EPA Depressional

Riparian

Macroinvertebrates

Plants

Amphibians

North Dakota Department of Health Depressional

Riparian

Plants

Macroinvertebrates

Montana Department of Environmental

Quality Depressional

Macroinvertebrates

Algae

Some plant work

Florida Department of Environmental

Protection Depressional & Others Macroinvertebrates

Plants

Massachusetts Coastal Zone Management Coastal Marshes (salt and fresh)

Macroinvertebrates

Plants

Birds

Maine Department of Environmental

Protection

Casco Bay Watershed

(depressional, fringe, riparian)

Macroinvertebrates

Algae

(some plant work)

Vermont DEC Vernal Pools

White Cedar Swamps

Macroinvertebrates

Amphibians

Plants

Wisconsin DNR Great Lake Fringe Wetlands Macroinvertebrates

Fish

Duke University Southeast forested swamps and

Everglades

Macroinvertebrates

Michigan State University Great Lake Fringe Wetlands Fish

Macroinvertebrates

USGS Patuxent Wildlife Research Center

Restored depressional wetlands

on Delmarva Peninsula (MD &

DE)

Macroinvertebrates

Plants Birds

Amphibians

Penn State Cooperative Wetlands Center

All types focusing first in

Juniata Watershed and then

expanding to whole state.

Macroinvertebrates

Plants Amphibians

Birds

Volunteer Project - Mass Bays Salt marshes

Plants

Macroinvertebrates

Birds

Volunteer Project - King County, WA Depressional Wetlands Amphibians

Volunteer Project - MPCA,Minnesota

Audubon, and Dakota County, MN Depressional Wetlands PlantsMacroinvertebrates

Table 1: Current pilot projects developing wetland

bioassessment methods and assemblages

Note: Data compiled from information contained in EPA, Biological Assessment of Wetlands Workgroup

website, www.epa.gov/owow/wetlands/bawwg/.
3

assessment approach as well as reflect the reality

of regional variation in biological condition (Miller

et al. 1988). The goal of a multimetric index is not

to measure every biological attribute; indeed, doing

so is impossible. Rather, the goal is, first, to identify

those biological attributes that respond reliably to

human activities, are minimally affected by natural

variability, and are cost-effective to measure and,

second, to formulate them as “metrics” and combine them into a regionally appropriate index (Karr

and Chu 1999).

Figure 1 provides a framework that describes how

attributes are derived, evaluated, and ultimately incorporated into an IBI as metrics. However, the

first and most important step is to define the objectives for developing an IBI, which may influence

several steps in the development process (see Module 5: Administrative Framework for Implementation of a Wetland Bioassessment Program). Do

not expect all the steps in IBI development to follow this sequence exactly. Undoubtedly, each

project will deviate from the path and will require

revisiting steps on the basis of individual circumstances. However, this framework provides a useful way to organize actions and ensure that all major steps in developing an IBI are addressed. In

Figure 1, the upper left portion shows the steps related to the establishment of a gradient of human

disturbance (the dose), and the upper right shows

the steps for developing attributes that will, at least

predictably, respond to that gradient (the response).

The column of steps in the lower middle shows the

process by which the dose-response relationship is

analyzed to select and score the best performing

metrics for the IBI. The remainder of this report

follows the framework provided in Figure 1 and

includes small icons to help track progress through

the sequence of activities.

Identify Regional

Wetland Flora

and Fauna

The success of multimetric indexes is largely dependent on

choosing metrics that reflect diverse responses of biological systems to human actions (Karr and

Chu 1999). Therefore, the best

multimetric indexes combine measures of condition in individuals,

populations, communities, ecosystems, and landscapes. Work

with stream bioassessments indicates that valuable

multimetric indexes typically use one or more assemblages for evaluating stream condition, such as

macroinvertebrates, fish, and/or periphyton

(Barbour et al. 1999). Professionals implementing

stream bioassessments have found that monitoring

more than one assemblage greatly increases the

power of their assessment methods. Assemblages

sometimes differ in their sensitivity to environmental

stressors, such as sedimentation and eutrophication. Having more than one assemblage provides

sensitivity to a wider range of stressors and increases

confidence in management decisions. Although

more investigations are needed to confirm the relationship, preliminary results from wetland IBI development indicate that monitoring a combination

of assemblages (e.g., plants and macro-invertebrates) may similarly increase the power of

bioassessments in wetlands (Gernes and Helgen

1999).

Current wetland bioassessment projects are exploring the use of several assemblages, including

algae, amphibians, birds, fish, macroinvertebrates,

and vascular plants (Table 1). It is not yet clear

which assemblages will work best in wetland

bioassessments. It is entirely likely that specific as-
4

Figure 1: Sequence of activities in developing metrics and IBI,

adapted from Karr et al. 1986.
5

semblages may be appropriate in some wetlands

and not in others because of the wide variety of

wetland types (e.g., salt marsh, bog, and forested

swamp). For example, using wetland fish communities in bioassessments may be effective in only a

small number of wetlands, such as wetlands on the

fringes of large bodies of water. It is also likely that

some assemblages will work in some parts of the

country and not in others. For example, wetland

amphibian communities are naturally less diverse in

western states, and there simply may be too few

species to develop a typical IBI. One of the first

steps in developing an IBI, however, is carefully

considering the advantages and disadvantages of

sampling any particular assemblage (See other modules in this series to assist in the appropriate choice.)

After selecting an assemblage, it is very helpful to

make a list of the taxa (e.g., species, genera, and

families) in that assemblage that are expected to

occur in the study area. Such lists may be based on

pre-project sampling or on previous studies from a

particular regional wetland class (Sparling et al.

1996). This list will help with identifying organisms

and with the next step of assigning taxa to biological attributes. Such lists should accommodate new

species findings, which will result from additional

sampling.

Assign Taxa into

Biological Attributes

Attributes, in the context of

bioassessments, are defined as

measurable components of a biological system (Karr and Chu

1999). They include the ecological processes or characteristics of

an individual or assemblage of

species that may or may not provide useful information regarding

response to human disturbances.

Attributes for most IBIs are commonly placed in the following four general categories: species richness and composition, tolerance

and intolerance to human disturbances, trophic composition, and population characteristics (including

health and condition of individuals). After defining

the list of taxa, list the attributes within these categories that will change in value along a gradient of

human disturbance from least impaired to severly

damaged wetlands. Also, predict whether each attribute will increase or decrease in value as wetlands become more damaged. This list of predictions will be tested later to identify metrics, that is,

attributes empirically shown to change in value along

a gradient of human disturbance. Examples include

a change in species richness or a change in the relative abundance of tolerant organisms. (For an example, see Module 9: Developing an Invertebrate

Index of Biological Integrity for Wetlands.) The list

of useful attributes will differ for any wetland type

depending on the assemblage monitored. Consult

other modules for more detailed discussions of potential wetland attributes for algae, birds,

macroinvertebrates, amphibians, and vascular

plants. The ultimate goal in the selection process is

to test the many attributes and from these identify 8

to 12 metrics that show strong relationships across

a gradient of human disturbance. Through the process of evaluation, many of the predicted attributes

will display limited value for detecting human disturbance. Expect only about one-third of the initial

predictions to actually be good metrics.

Each attribute considered for an IBI should be

based on sound ecological theory. Although theory

can be a good guide for selecting metrics, it must

be tested with real-world data before a metric is

used. Even if the underlying theory is sound, many

variables control an attribute’s response to human

disturbance, which in turn affects its utility. For example, an attribute that works in one type of wetland may not work in another type because of differences in ecological function and the prevailing

human disturbance. In stream fish IBIs, for example,

the “anomalies metric” (percentage of individuals

with lesions, tumors, or eroded fins) may function

in only extremely degraded conditions. It provides

valuable information to a region if at least some of
6

the streams are severely degraded but little information if all streams are only moderately degraded

or unimpaired. There may even be inherent differences in how an attribute responds biologically to

human disturbances. In the case of stream fishes,

the number of species typically declines with added

human disturbance; however, in some coldwater

streams, the effect may be reversed because increased nutrients and temperatures may result in

increased species numbers. Thus, it is necessary to

test attributes and their underlying assumptions not

only to validate the existence of an empirical doseresponse relationship, but also to be able to understand and predict the nature of that relationship. The

primary underlying assumptions that have been used

in stream IBIs are presented in Table 2. Although

not all of those assumptions have been extensively

tested in wetlands, at least some appear to be applicable to wetlands.

Attribute Categories

Because development of multimetric indexes for

wetlands is relatively new, no one group of organisms has proven superior to another for

bioassessment. In fact, several taxa or taxa groups

show promise. Regardless of the taxonomic groups

sampled, as previously stated, several studies suggest that attributes and metrics can be conveniently

grouped into the following categories:

n Species richness and composition

n Tolerance and intolerance to human

disturbances

n Trophic composition

n Population characteristics (including health and

condition of individuals)

Because most multimetric studies have been conducted in streams, there may be metric categories

that are yet to be considered in wetlands. Therefore, this categorization is meant as a general guide

to the development of attributes and metrics. A

properly constructed IBI, as defined by Karr and

Chu (1999), will have some metrics from each of

these metric categories.

Species richness and composition

Attributes in this category are usually the most

common feature of IBIs. In general, these attributes

display a declining response to added human disturbance (Karr 1981). Normally, a population must

be viable at a site for some period of time before

one can consistently detect a species presence

(Karr and Chu 1999). The absence of a species at

a site (especially a species with low dispersal abilities) may suggest that viable populations are not

being maintained. Over time, species assemblages

have evolved that are capable of withstanding or

rapidly recovering from most natural perturbations.

For example, invertebrates often adapt to tolerate

the frequent drying that is typical in many wetland

habitats (Sharitz and Batzer 1999). However,

changes in the chemical, physical, and biological environment caused by humans often cannot be tolerated; thus one or more species declines in abundance or becomes extirpated (Karr et al. 1986,

Euliss and Mushet 1999, King and Brazner 1999).

This observation is true particularly for the most intolerant taxa of an assemblage. For example, in a

Minnesota study, impairment to wetlands resulted

in a reduction in the number of kinds of dragonflies,

damselflies, mayflies, caddisflies, and chironomids

(midges), with very few intolerant taxa being observed at the most impaired sites (Gernes and Helgen

1999).

Attributes within this category generally include

overall taxa richness as well as richness for taxa

that are particularly sensitive to specific kinds of

degradation (e.g., impairments to benthic habitats)

(Kerans and Karr 1994, Fore et al. 1996). Groupings may include taxon (or taxa) (e.g., number of

dragonfly and damselfly genera), specialized habitat (e.g., submerged aquatic plant species), or a

combination of both. Attributes within the category

have often been refined by restricting the groupings
7

Table 2: Assumed effects of environmental degradation on

biological assemblages in streams

Source: Modified from Hughes and Oberdorff 1999.

Note: Effects on wetland biological assemblages may be different.

Number of native species, and those in specialized taxa or guilds,

declines*

• Number of sensitive species declines

• Percent of trophic and habitat specialists declines

• Total number of individuals declines*

• Percent of large individuals and the number of size classes decrease

• Percent of alien or nonnative species or individuals increases

• Percent of tolerant individuals increases

• Percent of trophic and habitat generalists increases

• Percent individuals with anomalies increases

* In some instances, particularly in oligotrophic environments, reverse

relationships may be observed.
8

to native species. However, the taxonomy and geographic origin of many wetland organisms is poorly

known, which may limit the use of certain taxa in

this regard.

Tolerance and intolerance to

human disturbances

Tolerance, as it relates to IBI development, implies a general tolerance of a species, or group of

species, to several human disturbances, rather than

tolerance to a specific variable. Therefore, in attribute development, a concept can be applied in

several ways to any organism, or group, that displays these tendencies. Metrics such as percentage of exotic species, number of intolerant species,

and percentage of dominant species are ways of

expressing characteristics that sometimes are related to tolerance. Some taxa are very intolerant

(i.e., are very sensitive) to a variety of perturbations, whereas others are adept at exploiting particular types of disturbances. For example, in Minnesota wetlands, increasing levels of impairment

resulted in fewer intolerant plant species, such as

iris (Iris sp.), slender riccia (Riccia fluitans), and

common bladderwort (Utricularia macrorhiza),

and increased coverage of tolerant species, such as

reed canarygrass (Phalaris arundinacea), duckweed (Lemna sp.), and cattail (Typha sp.) (Gernes

and Helgen 1999).

Intolerant species may be among the first to be

decimated after perturbation and the last to recolonize after normal conditions have returned (Karr et

al. 1986). Endangered or threatened species should

not automatically be considered intolerants, because

their low numbers may be due to factors other than

human disturbance. They might, for example, be

glacial relics (Karr et al. 1986). Trends (increases

or decreases) in distribution or abundance from historical data can be examined to help assign taxa to

these attributes. Tolerance rankings may also be

based on factors that indicate the ecological conservatism of taxa (those taxa adapted to a specific

narrow range of biotic and abiotic factors) (Wilhelm

and Ladd 1988, Andreas and Lichvar 1995). However, because of a lack of information for many

wetland taxa, empirical, rather than theoretical, approaches may be necessary or preferred to establish tolerance rankings. For example, taxa that are

represented in the least impaired sites and tend to

disappear in the most impaired sites would be

empirically defined as intolerant. Similarly, taxa that

tend to increase in disturbed sites would be defined

as tolerant (Gernes and Helgen 1999).

The mere presence of intolerant taxa is a strong

indicator of good biological condition. The relative

abundance of these taxa, in contrast, is often difficult to estimate accurately without extensive and

costly sampling efforts (Karr and Chu 1999).

Therefore, intolerant taxa should be represented

simply as the number of intolerant species per unit

sample effort. In contrast to intolerant taxa, the presence alone of tolerant taxa says little about biological condition, because tolerant groups inhabit a wide

range of places and conditions. However, note that

many wetland organisms can tolerate the stressful

levels produced by a variety of natural environmental

disturbances (Wissinger 1997, Euliss et al. 1999,

Higgins and Merritt 1999), and care should be taken

to base tolerance designations on human disturbances and not natural ones.

Tolerance attributes should be expressed as the

percentage of tolerant individuals from either a single

species or a grouping of highly tolerant species.

Note that if a high number of tolerant or intolerant

species is included in the composition of attributes,

the usefulness of those attributes will be diminished.

In general, it is recommended that only about 10%

(no fewer than 5% or no more than 15%) of taxa in

a region should be classed as intolerant or tolerant.

The point of these metrics is to highlight the strong

signal coming from the lowest and highest ends of

the biological integrity continuum, without being

swamped by the weak or intermediate signals from

in between (Karr and Chu 1999).
9

Trophic composition

Because the food base is central to the maintenance of a community, information about trophic

composition may be important to an IBI. All organisms require a reliable source of energy. The

dominance of trophic generalists occurs as specific

components of the food base become less reliable,

and the opportunistic foraging habits of the generalists make them more successful than trophic specialists (Karr et al. 1986). Sometimes entire groups

of specialized organisms have been reduced or extirpated from ecosystems as a result of human disturbances. For example, top carnivores such as

ospreys and bald eagles have disappeared from

regions as a result of eggshell thinning and reproductive failure associated with the bioaccumulation

of chlorinated hydrocarbon pesticides from aquatic

food webs (Carson 1962, Rudd 1964, Thomann

1989). Depending on the type of disturbance, primary producers and invertebrates of wetlands may

also respond as the ecosystem begins to function

improperly. Some wetland invertebrates will respond to both bottom-up (e.g., enrichment, exotic

plants) and top-down (e.g., heavy metal

biomagnification, exotic fish) alterations in the food

web (Rader 1999). For example, the benthic communities of contaminated Louisiana bayous supported a “poor trophic mix” of macrobenthic invertebrates, and fewer predatory invertebrates and

suspension feeders were found at those sites than

elsewhere (Gaston 1999). Thus, the trophic structure of a community can provide information on

patterns of consuming and producing organisms that

are affected by impairment.

In general, attributes in this category can be designed to assess trophic balance and structure. For

example, the biota of stream ecosystems in good

condition usually will not be overly dominated by

omnivores or trophic generalists and will normally

contain at least some trophic specialists, including

top carnivores that form the apex of many aquatic

food pyramids (Karr et al. 1986). However, manipulations of top carnivores have been shown to

have little effect in some ecosystems, such as wetlands (Batzer 1998), whereas such manipulations

have had a significant effect in others, such as lakes

(Carpenter et al. 1987). Furthermore, surface water levels in most natural wetlands fluctuate widely.

Such variation also affects water and substrate

chemistry, nutrient availability, vegetation, primary

production, detritus processing, and the presence

of vertebrate predators (Wissinger 1999). Therefore, caution should be exercised in developing

trophic attributes for wetlands, and particular attention should be paid to those attributes involving

functional feeding groups. Karr and Chu (1999)

observe that despite widely accepted theory,

metrics pertaining to functional feeding groups

among benthic macroinvertebrates may or may not

be good indicators; their dose-response relationship to human influences must be carefully tested

and established for multiple data sets and circumstances before they are used in a multimetric index.

Population attributes

The attributes in this category assess characteristics of populations such as reproduction, growth,

and condition of individual organisms within the

populations (Fore et al. 1996). Ecosystems can

maintain themselves only if the populations of organisms that characterize the ecosystems are able

to compensate for loss of members by reproducing. Human disturbances that negatively affect reproduction are ordinarily indicated by an accompanying reduction in the proportion of reproductive

specialists. In addition, conditions must be favorable for the young of a population to survive, disperse, and grow to sexual maturity (Pickett and

White 1985, Wissinger and Gallagher 1999). For

example, the eggs of some species, such as fairy

shrimp, require aerated soil for development; therefore, these species rely on the drying up of temporary ponds for reproduction. Any alterations of the

frequency and duration of ponding in wetlands that

contain these species would greatly influence the

viability of populations. In another example, certain invertebrates have become extremely special-
10

ized in their dependence on the fluid of pitcher plants

(e.g., Sarrecinia purpurea) to reproduce and carry

out their life cycle. At least some of these inquilines

(organisms that live within the abode of another

species) are poor dispersers and may be slow to

colonize isolated wetland habitats that have become

fragmented as a result of human disturbance

(Giberson and Hardwick 1999). Therefore, attributes that characterize population structure and

patch dynamics can be effective indicators of human disturbance.

Certain structural and functional attributes of wetland vegetation and algae are also included in this

category. Many of these attributes have been used

in and out of the context of IBI to assess a wide

variety of human disturbances (e.g., hydrologic

changes, nutrient enrichment, sediment loading, and

accumulation of heavy metals). For example, increased algae biomass is one of the most widely

used indicators of eutrophication in aquatic ecosystems (see Module 11: Using Algae To Assess

Environmental Conditions in Wetlands). Likewise,

the percent coverage of submerged aquatic vegetation has been a useful indicator of nutrient enrichment in many estuarine environments (see Module 16: Vegetation-Based Indicators of Nutrient

Enrichment in Freshwater and Estuarine Wetlands).

Minnesota has used increased persistent plant litter, resulting from human-induced changes in the

composition of the plant community, as an IBI attribute to indicate reduced detrital energy to drive

wetland ecosystems (Gernes and Helgen 1999).

Individual abundance is a common surrogate for

system productivity, and some types of highly degraded sites are expected to support fewer individuals than are high-quality sites (Karr 1981).

However, Karr and Chu (1999) suggest that abundance may be a poor candidate for a multimetric

index because it varies too much, even when human disturbance is minimal, and it is also difficult to

measure and score. Recognizing the tendency for

moderate levels of nutrient and thermal enrichment

to elevate fish abundance, Oberdorff and Hughes

(1992) scored this metric so that very high abundances received lower metric scores than moderate numbers did; only very low abundances received

the lowest score. This scoring adaptation is an example of the need to evaluate metric performance

along disturbance gradients before applying the IBI

in resource assessments (Hughes and Oberdorff

1999).

Sites with especially severe degradation often yield

a high number of individuals in poor health (Mills et

al. 1966, Brown et al. 1973, Baumann et al. 1982,

Sanders et al. 1999). Parasitism has been shown

to reflect both poor environmental condition and

reduction in reproductive capacity (sterility) in fish

(Mahon 1976). Indications of poor health include

individuals with tumors; limb, mouthpart, or other

structural malformations; heavy infestations of parasites; and discoloration, excessive mucus, edema,

rash, or hemorrhaging. For example, malformation

in chironomid mouthparts has been used to indicate

impairments to water from sedimentation, eutrophication, and contamination (Warwick 1980). Recently, increasing numbers of amphibian populations

with unusually high frequencies of morphological

abnormalities (>5%) have been reported throughout North America; however, the ecological significance of these observations remain poorly understood (Ouellet 2000, Helgen et al. 2000). Leonard

and Orth (1986) found increases in the incidence

of disease and anomalies in stream fish only after

substantial degradation was evident, indicating that

this metric may be sensitive at only the most severely impaired sites. In cases in which only low to

moderate levels of impairment occur, the metric has

been dropped; however, it should be considered

wherever the possibility exists for changes in the

incidence of diseased or deformed organisms

(Hughes and Oberdorff 1999).
11

Lessons Learned from the

Biological Assessment of

Wetlands Working Group

These lessons should be treated as general rules of

thumb and not absolutes. Nature keeps reminding

us that when dealing with biology and ecology, there

are always exceptions to the rules. The following

lessons on attributes and metrics are based on the

experience of the Biological Assessment of Wetlands Working Group (BAWWG) members:

n Explicitly define attributes. To aid in testing attributes and to improve communication with

others, it is very important to explicitly define

attributes. There are many ways to examine an

attribute. For example, tolerance can be described in the following ways:

• Number of tolerant individuals

• Percentage of tolerant individuals (number

of tolerant individuals/total number of individuals)

• Number of tolerant species or taxa

• Percentage of tolerant species, or taxa

(number of tolerant taxa/total number of tolerant taxa)

n Be careful in using measures of abundance. Although Karr and Chu (1999) suggest that abundance may be a poor candidate for a multimetric

index, BAWWG members have found some

exceptions to this rule. For example, the abundance, or biomass, of algae may be a useful

attribute, but further testing is needed.

n Avoid combining attributes. In general, restrict

ratios to relative abundance or proportions in

which the total number of individuals or taxa is

used as the denominator. Avoid using attributes

such as the number of water boatmen taxa divided by the number of midge taxa. Also be

careful about adding attributes together, such

as the number of sedge taxa plus the number of

rush taxa plus the number of grass taxa. Ratios

and sums of attributes can hide valuable signals, can be difficult to interpret, and are often

more variable than the individual attributes (Karr

and Chu 1999). It may be more effective to

test each attribute independently. However,

BAWWG members have found some exceptions to this rule. For example, Minnesota uses

a metric that combines the number of mayfly

and caddisfly genera plus the presence of dragonflies and fingernail clams (Table 3).

Classify Wetlands

into Regional Classes

Successful biological monitoring begins with a judicious classification of sites. Classification

is an essential step in developing bioassessment methods.

Biological assemblages are influenced by natural variations in

wetland types (e.g., landscape

position, source of water) and

by variations in the amount and

type of human disturbances. Classification is a way

to account for the effects of natural environmental

influences on wetlands and helps avoid comparing

wetlands of unlike classes. Yet, excessive emphasis on classification, or inappropriate classification,

can impede development of cost-effective and sensible monitoring programs. Using too few classes

fails to recognize important distinctions among places

and can produce insensitive metrics; using too many

adds unnecessary costs to the development of

biocriteria. The challenge is to create a system with

only as many classes as needed to represent the

range of relevant biological variation in a region and

the level appropriate for detecting and defining the

biological effects of human activity in that place (Karr

and Chu 1999).

It is important to remember that for the purpose

of developing bioassessment methods, classification is a way to help minimize “noise” and make it

easier to identify signals of human disturbance. Clas-
12

Metric Description Range Score Ref Ag SW

Richness metrics

Total taxa

# Genera chironomids, caddisflies, mayflies, damselflies,

dragonflies, leeches, snails,

macrocrustaceans, presence

of Chaoborus and clams

28 - 46 5 5 3

20 - 27 3 1 3 6

12 - 19 1 2 4

Chironomid # of genera of Chironomidae

larvae

13 - >20 5 3

6 - 12 3 2 5 6

> 70% 1 4 5

ETSD

# Genera of Ephemeroptera,

Trichoptera, plus presence of

Sphaeriidae and Dragonflies

4 or more 5 6

2 - 3 3 3 6

> 70% 1 5 5

Leech taxa # Genera of Hirudinidae found

in BT and DN samples

4 - 5 5 4 2 2

2 - 3 3 2 5 8

0 - 1 1 1 1

Odonata # Genera of Dragonfly &

Damselfly larvae

4 - 6 5 5

3 3 1 4 3

0 - 2 1 4 8

Snails # Taxa of snails to

species most cases

5 - 7 5 4 1 1

3 - 4 3 1 5 6

0 - 2 1 1 2 4

Tolerance/Intolerance metrics

Intolerant

Taxa

# Intolerant taxa:

Leucorrhinia,

Libellula, Tanytarsus, Procladius, Triaenodes, Oecetis

4 or more 5 5

2 - 3 3 1

0 - 1 1 8 11

Proportion metrics

Corixidae % Corixidae of Hemiptera plus

Coleoptera from BT samples.

< 30% 5 5 2 1

30 - 70% 3 1 2 5

> 70% 1 3 4

Erpobdella

% Erpobdella in BT and DN

samples of the total

abundance in DN samples.

0 - 11% 5 6 3 6

>11 - 22% 3 2 3

> 70% 1 3 2

3 Dominants % top 3 dominants of total

abundance in DN samples

34 - 55% 5 5 1

> 55 - 80% 3 6 9

> 70% 1 1 1 2

Table 3: Invertebrate metrics and scoring for a wetlands invertebrate

index of biological Integrity (IBI)

Abbreviations: BT, bottletrap; DN, dipnet; number of sites scoring in range is given for Reference sites (Ref),

agricultural (Ag) and stormwater (SW) influenced wetlands (Gernes and Helgen 1999).
13

sification is not the end product, and there is no

perfect classification system. Also, classification is

an iterative process. Try applying an existing classification system (e.g., Cowardin et al. 1979, USDA

1981, Brinson 1993, Omernik 1995, Omernik and

Bailey 1997) and then lump and split as needed to

produce groups of biologically similar wetlands that

respond in similar ways to anthropogenic influences.

For further discussion of classification issues and

approaches, including some wetland bioassessment

examples, see Module 7: Wetlands Classification.

Target Selection of

Sample Sites

After wetlands are classified,

sample sites should be selected.

Module 4: Study Design for

Monitoring Wetlands describes

the options for developing sampling schemes for a wetlands

monitoring program, including random sampling, targeted sampling,

and before/after or control/impact

designs. The members of

BAWWG recommend the use of a targeted sampling design when developing bioassessment methods for wetlands. They have found that random

sampling often fails to capture enough least impaired

reference wetlands or enough of the severely degraded wetlands. Also, random sampling may not

consider important factors such as accessibility to

sites and the selection of relatively permanent reference sites that will not be subjected to a great

deal of future human disturbance. The process of

testing attributes and selecting metrics depends on

plotting data on a graph with an attribute value on

the y-axis and a gradient of human disturbance on

the x-axis. It is very important to select enough

reference wetlands and severely damaged wetlands

to anchor both ends of the disturbance gradient. It

is also important to select enough wetlands with

varying degrees of human disturbance in order to

reveal a signal in the attribute if there is one. Based

on the experience of the BAWWG members, targeted sampling is probably the best way to ensure

that this is accomplished. The development of human disturbance gradients is discussed further in

this module in the sections “Collect Land Use and

Habitat Information” and “Establish Gradient of

Human Disturbance.”

One challenge to the characterization of reference

conditions is that there are few, if any, places left

that have not been influenced by human actions. In

many regions, what are described as least impaired

wetlands may in fact be very degraded, because

accessible less-degraded sites cannot be found.

This may complicate the development of an IBI but

does not prohibit it. A common pitfall is the failure

to canvass a wide enough area for sites that may be

less impaired. It may be advantageous to survey

neighboring areas and expand the geographic range

to find similar wetlands in better condition. Another failure is to not include an adequate number

of most impaired sites. Sampling only from the least

impaired end of the gradient creates problems because it does not represent the full range of site degradation and it prohibits analysis of the relationship

between biological attributes and highly negative

human influences.

Biological communities in wetlands with a high

proportion of degrading land uses (e.g., commercial, residential, agricultural) in their vicinity or watersheds can sometimes be assumed, for purposes

of developing an IBI, to be potentially stressed.

However, forested wetlands, and in particular, forested wetlands with dense canopies, should not

automatically be considered the least impaired. This

is because in some regions, some wetlands are normally dominated by herbaceous vegetation due to

persistently high water table levels and/or other natural influences. Some of these herbaceous vegetation sites may in fact be in better condition than are

forested wetlands. However, if herbaceous wetlands historically prevailed in an area, their invasion

by woody vegetation could be a sign of stress, not

an indication of good health.
14

As mentioned previously, it is important to select

sites that are minimally impaired reference sites and

severely damaged sites as well as some in between

to represent the full gradient of human disturbance.

The number of sites that are needed depends on

the number of wetland types within a given class,

the ecological variability of the wetland types, the

kinds and amount of human disturbances, and the

size of the region. The number of sites should be

sufficient to show a gradient of human disturbance

for each wetland class in the region. See Module

7: Wetlands Classification for more detail on classifying wetland types. Sampling an adequate number of sites will provide confidence in the sensitivity

of the metrics showing a response.

Collect Land-Use and

Habitat Information

Before starting the field sampling,

gather information about the study

sites through published sources

and field reconnaissance. The

overall goal of this step is to collect information to help verify that

wetlands are classified correctly,

provide data for constructing human disturbance gradients, and

provide insights into why biological communities are damaged during the IBI interpretation phase. A wealth of information can be collected about sites without even

leaving the office. Information sources include the

following:

n U.S. Geological Survey quadrangle topographic

maps. These maps can provide baseline information on slope, elevation, land use, and the

hydrological network in the vicinity of the study

wetland.

n National Resource Conservation Service soil

surveys. These surveys are an invaluable source

of information on wetland soils and their characteristics. Hydric soils are mapped and descriptions of soil characteristics and how they

vary by soil horizons are provided.

n National Wetland Inventory maps. These maps

are useful for identifying the presence of wetlands and estimating wetland size. They also

include the Cowardin et al. (1979) classification.

n U.S. Department of Agriculture aerial photos.

If available, these photos are very useful for

gathering information on the landscape surrounding wetlands. They can also be used to reconstruct historical changes in land use by analyzing a series of photos taken over past years.

n Geographic Information System (GIS) databases. Many state and local units of government have digital land-use and other information available on GIS databases. Often, this

information can be linked to other available data

(e.g., percent impervious surface and point

source discharges) to locate and display geographically referenced sources of impairment.

Such information is also increasingly available

from many online websites. The layering and

interactive features of GIS databases greatly

enhance landscape-level assessments (see

Module 17: Land-Use Characterization for

Nutrient and Sediment Risk Assessment).

However, the scale and quality of GIS information should be closely examined in view of

the intended use. Other information, such as

low-altitude photographs, may be needed to

supplement GIS information in order to derive

a meaningful estimate of the gradient of human

disturbance.

In addition to landscape features, onsite wetland

characteristics are important in establishing gradients of human disturbance. Onsite investigations

should provide general information on landscape

setting, hydrologic features, and vegetative cover

of the wetland. Such observations can generally be

made from visual assessments from the wetland’s

edge. Obvious stressors, such as hydrologic alter-
15

ations (e.g., ditches and dikes), should be identified. The extent of vegetation cover and the characteristics of buffer areas should be noted. Buffer

areas should also be clearly defined (e.g., the 100

m of land surrounding the wetland boundary at full

pool), and land uses within those buffers should be

described. Examples of other data that should be

recorded at each site include the following:

n Topography and landscape features that surround the site. Many characteristics should be

recorded, including the shape of the wetland;

adjacent land use; the general distribution of

wetland vegetation and open water; the interspersion of plant communities; the type of buffer;

hydrological features, including surface water

inflows and outflows; and human-made water

control structures. This information should be

included on a site sketch map.

n Patterns in the vegetation community, such as

the number of community types and their location in relation to each other, the vegetation

strata present, the dominant species, and presence of nonnative or invasive species.

n Evidence of human disturbance (if any). One

way to approach this question is to prepare a

stressor checklist that can be used to survey

each site (see “Establish Gradient of Human

Disturbance” below for potential stressors).

n An estimate of the size of the wetland.

n Photographs of the site.

Establish

Gradient of

Human

Disturbance

Once sites have been classified by

natural factors, it is essential to categorize the same sites according to

degrees of human disturbance.

This step is important to ensure that

metrics are sensitive. Human disturbance serves as

the gradient along the x-axis to which biological attribute data along the y-axis are compared. Determining the human factor and the likely range of the

gradient must be done before sampling begins, not

as an afterthought, because post hoc categorization

may reveal that the full range of human disturbance

was not captured, thus requiring additional sampling to develop a useful IBI.

To help establish sampling sites that reflect the full

range of human disturbance, it can be useful to first

identify and perhaps prioritize the main types of disturbances in a region, such as hydrologic modification, eutrophication, sedimentation, and chemical

contamination. U.S. Environmental Protection

Agency (EPA) and State reports (305b, 303d) can

be used with other sources, particularly interviews

with local conservation groups and resource agencies, to obtain an initial indication of watersheds

whose wetlands might be candidates for designation as least or most impaired sites. In rare instances,

detailed descriptions may exist of a wetland’s biological communities before its alteration and development of the surrounding watershed. In such instances, the historic condition can be used to define

the least impaired reference condition.

In some cases, human disturbance may comprise

a single impairment, such as vegetation removal by

grazing. For example, Montana used a simple discrete disturbance gradient based on grazing and

farming for wetlands in a rural landscape (Apfelbeck

1999). Three classes were identified: wetlands that

are currently grazed or farmed, wetlands that were

grazed or farmed but not within the recent past,

and wetlands that have either never been grazed or

never been farmed or at least not within recent history. In most circumstances, diverse and often

subtle human activities interact to affect conditions

in watersheds, bodies of water, or wetlands. As a

result, it may be advantageous to develop a gradient that integrates several human disturbances to

account for multiple stressors.
16

Where there is adequate information, the development and use of an index may greatly enhance

the establishment of the gradient of human disturbance. Such an index incorporates values that represent the various degrees and combinations of prevailing human disturbances for all sites, not just the

least and most impaired, as illustrated in the Minnesota Wetland Disturbance Analysis (Figure 2). Although there is no standard protocol for constructing such an index, human disturbance should not be

represented simply by a single score from a single

source of disturbance. Instead, it should be developed by combining scores from several prevailing

disturbances from both the landscape and the wetland. Possible landscape-level disturbances in an

index include the following:

n Percentage of the watershed within impairing

land uses (e.g., cropland, pastureland, and urban land)

n Presence, condition, and width of wetland

buffer

n Proximity of wetland to other natural habitats

(e.g., wetlands, natural grasslands, and forest)

n Percentage of other natural habitats in close

proximity (e.g., a 1-km radius) of the wetland

n Impoundment of runoff or flow by dams or

berms located upstream or upslope

Possible local human disturbance factors in an index include the following:

n Impoundment of runoff or flow by excavations

(pits) within wetlands

n Redirection of runoff or flow within wetlands

n Extraction of water from the wetland (e.g., for

irrigation)

n Removal of vegetation (e.g., through logging,

grazing, mowing, and controlled burning)

n Flattening of wetland microtopography

n Steepening of wetland topography (especially

shorelines)

n Persistent disturbance of wetland soils or

vegetation through compaction, tillage, or

trampling

n Drainage of wetlands through ditching or tiling

n Water or atmospheric deposition

n Simplification of shoreline complexity

n Pollution (e.g., thermal and chemical)

The type of land cover that surrounds a wetland

is generally one of the most dominant influences on

wetland condition (see Module 17: Land-Use

Characterization for Nutrient and Sediment Risk

Assessment). GIS information can be useful in

mapping and analyzing land-use patterns and other

spatial relationships that broadly affect wetlands.

For example, several recent GIS studies have found

significant negative correlations between watershedwide agricultural or urban land uses and stream IBIs

(Lenat and Crawford 1994, Richards et al. 1996,

Roth et al. 1996, Wang et al. 1997). When considering the influence of particular land uses, it is important to consider their distance from a wetland,

the intervening slope, and the time period (current

or recent or distant past) at which they occurred.

Land use of the surrounding landscape should be

assessed within a meaningful radius around the wetland (e.g., 300 m), with greater weight given to land

use in areas upstream or upslope of a site, that is,

the “contributing watershed.” Although GIS information can be a powerful tool for defining a disturbance gradient, it is not a replacement, or a good

surrogate, for the IBI itself or for biological monitoring (Karr and Chu 1999). To supplement GIS

mapping data, onsite visits are generally required to

improve the assessment of human disturbances.

Several states (i.e., Ohio, Oregon, Florida, and

Maryland) have prepared data forms to assist in

the assessment of onsite conditions for rapid field

assessment of environmental risks or disturbances
17

Figure 2: Minnesota Wetland Disturbance Analysis

PRELIMINARY DRAFT RATING FORM (2/08/01)

The forms shown below are presented to show the concepts and framework under development

in Minnesota for rating the degree of human disturbance to wetlands and their immediate landscape. These forms are to be completed while referencing various, current digitized spatial

information, such as land use, wetland border, aerial photos, digital raster graphs, hydrologic data

themes and field notes from site visits. These forms and the corresponding evaluation method are

likely to be considerably revised and changed as the scores and method are further tested against

additional data sets (Helgen and Gernes in press).

Site: Study: Raters: Date:

points

Factor 1. Buffer landscape disturbance

Extent and Intensity

Best--as expected for reference site, no evidence of disturbance (0)

Mod.--predominately undisturbed, some human use disturbance (6)

Fair--significant human disturbance, buffer area nearly filled with human use (12)

Poor--nearly all or all of the buffer human use, intensive land use surrounding wetland (18)

BEST MOD.

Mature (>20 yr.) woodlot,

forested Old field, CRP or rangeland,

Mature prairie Restored prairie (<10 yr.)

Other long recovered area Young (<20 yr.) second growth woodlot

Other wetlands Shrubland

FAIR POOR

Residential with unmowed areas Urban development

Active pasture Industrial development

Less intensive agriculture Intensive residential/mowed

Turf park, Golf course Intensive agriculture

Newly fallowed fields Mining in or adjacent to wetland

High road density in buffer area

or impervious surfaces Active construction activity

Remarks or comments:
18

BEST MOD.

Mature (>20 yr.) woodlot,

forested Old field, CRP or rangeland,

Mature prairie Restored prairie (<10 yr.)

Other long recovered area Young (<20 yr.) second growth woodlot

Other wetlands Shrubland

FAIR POOR

Residential with unmowed areas Urban development

Active pasture Industrial development

Less intensive agriculture Intensive residential/mowed

Turf park, Golf course Intensive agriculture

Newly fallowed fields Mining in or adjacent to wetland

High road density or impervious

surfaces in immediate landscape Active construction activity

points

Factor 2. Landscape (immediate) Disturbance

Extent and Intensity

Best--landscape natural, as expected for reference site, no evidence of disturbance (0)

Mod.--predominately undisturbed, some human use disturbance (6)

Fair--significant human disturbance, landscape area nearly filled with human use (12)

Poor--nearly all or all of the landscape in human use, isolating the wetland (18)

points

Factor 3. Habitat alteration—immediate landscape

(within and beyond buffer)

Severity and extent of alteration

Best--as expected for reference, no evidence of disturbance (0)

Mod.--low-intensity alteration or past alteration that is not currently affecting wetland (6)

Fair--highly altered, but some recovery if previously altered (12)

Poor--almost no natural habitat present, highly altered habitat (18)
19

Vegetation removal disturbances

Mowed, Grazed Shrub removal

Tree plantations Course woody debris removal

Tree removal Removal of emergent vegetation

Substrate/soil disturbances and sedimentation

Grading/bulldozing Vehicle use

Filling Sediments input (from inflow or

erosional)

Dredging Livestock hooves

Other

Other

Fish stocking or rearing Other

Remarks or comments:

points

Factor 4. Hydrologic alteration

Severity and degree of alteration

Best--as expected for reference, no evidence of disturbance (0)

Mod.--low-intensity alteration or past alteration that is not currently affecting wetland (7)

Fair--less intense than "poor," but current or active alteration (14)

Poor--currently active and major disturbance to natural hydrology (21)

Ditch inlet Berm or dam

Tile inlet Road bed or RR bed

Point source input Levee

Installed outlet, weir Unnaturally connected to other waters

Dredged Dewatering in or near wetland

Graded or fill Source water changes

Other Drainage

Remarks or comments:
20

points

Factor 5. Chemical pollution

Severity and degree of pollution

Best--chemical data as expected for reference and no evidence of chemical input (0)

Mod.--selected chemical data in low range, little or no evidence of chemical input (7)

Fair--selected chemical date in mid range, high potential for chemical input (14)

Poor--chemical input is recognized as high, with a high potential for biological harm (21)

Checklist:

High C1 conc. (water) Known MMCD treatment

High P conc. (water) Evidence of altered DO regime

High N conc. (water) Other treatment

High Cu conc. (sediment) High input potential

High Zn conc. (sediment) Other

Remarks or comments:

Additional factors and concerns

points Used in exceptional cases as described below

Maximum of (4) additional points added to the cumulative disturbance

total for reasons described below. Apply on factors 4 and 5.

Factor 1 - Buffer and landscape

Factor 2 - Landscape (immediate disturbance)

Factor 3 - Habitat alteration

Factor 4 - Hydrologic alteration

Factor 5 - Chemical pollution

Additional factors

Total final disturbance score

Site:
21

to wetlands (e.g., the Ohio Rapid Assessment for

Method for Wetlands) (Ohio EPA 2001). Independent observers should be able to repeat the assessments of disturbances and obtain the same results, that is, the assessments should be highly precise. Nonetheless, a relatively high degree of judgment usually is required to assess, a priori, the relative level of human disturbance a site is likely to be

enduring. Many impairments are not clearly visible

or assumable (e.g., subsurface drainage tile and

chemical contamination).

Sample Within the

Wetland

After wetlands have been properly classified and selected, sampling within a wetland may begin.

One approach for sampling is to

collect data from all habitat zones.

Another approach is to find a

single zonal transition area that

may be indicative of the entire

wetland (a wetland equivalent to

the riffle zone used in streams).

The goal is not to measure every attribute of a wetland, but rather to find efficient indicators of health

that are expressed adequately with a minimal amount

of sampling. For example, a Minnesota study collected data from the nearshore shallow emergent

zone and based all comparisons on that area. That

approach led to accurate assessments without the

need for the more time-consuming sampling from

each zone. In addition, human access to some parts

of wetlands may be difficult or impossible, which

would preclude sampling from every zone.

Although sampling from a single zone may, in certain instances, provide enough information to accurately assess wetland health, there are instances

when it will not. For example, in streams, it is often

necessary to survey several habitats (e.g., riffles,

pools, runs, and backwater areas) to collect the

variety of taxa needed for IBIs to be sensitive to

the array of possible impairments. If the decision is

made to sample several zones, the number of

samples that need to be collected will increase as

the area of the wetland and its heterogeneity increase. At a minimum, samples should be collected

from the following zones if they are present: permanently inundated areas, seasonally inundated areas, and areas saturated but seldom inundated. For

purposes of IBI development, within these three

zones, samples should be collected in a manner that

will yield unbiased data from the widest variety of

disturbance conditions and seral stages. For quantitative metrics (such as relative abundance and percent cover) to be used in multimetric indexes, random or systematic (grid- or transect-based) location of sampling or observation points within zones

may be justified, and a much larger number of

samples will be necessary. The sampling strategy

must be clearly described and the number of samples

must be adequate to capture the variablity of the

attribute being measured. For more detail on sampling, see Module 4:Study Design for Monitoring

Wetlands.

In general, the number of samples or observations per zone should be roughly proportional to

the area of the zone if the goal is to characterize the

wetland as the assessment unit. (However, a fixed

number of samples should be taken to avoid problems with increasing species richness with increasing sample numbers.) One approach to address

sample adequacy is to construct species/area curves

to determine the number of samples required to

produce diminishing returns (an asymptotic curve)

in the cumulative number of species of the target

taxa (De Vos and Mosby 1969) (Figure 3). Another approach is to plot the cumulative coefficient

of variation (in, e.g., the diameters of trees that were

measured) against the number of samples (e.g., the

number of trees measured). Other approaches for

estimating sampling adequacy may be preferred,

depending on assessment objectives (see Elliott

1970). Also, the boundaries of the unit to which
22

the collected data will be extrapolated need to be

clearly defined and stated. For example, will a few

samples collected on the fringe of a large roadside

wetland be claimed to represent the entire wetland

or only the roadside fringe?

A basic premise of IBI is that the biota have been

sampled in their true relative abundance without bias

toward taxa or size (Karr et al. 1986). As this

assumption is relaxed, the reliability of inferences

based on the IBI is reduced. However, with any

single method, there are inherent biases that affect

the tendency to capture or notice particular organisms. Therefore, method limitations should be well

understood. Standard sampling protocols should be

adhered to, and the resulting metrics should be tailored to the known limitations of the methods, protocols, and sampling equipment. In addition, data

collected by one sampling method should not be

mixed or compared with data collected by another

method.

Temporal variations may also affect the quality of

the sample or limit its comparison with other data.

This may be true particularly in temporary or seasonal wetlands that support organisms that are

equally as periodic in nature. Therefore, it is important to know the best time of the year for the

collection of certain taxa and to specifically relate

that information to the protocols that govern sampling. When sampling assemblages or habitats with

specific sampling periods tied to weather conditions,

such as amphibians in vernal pools, it may be important to maintain flexibility in sampling periods to

be able to adjust to the time of emergence. Other

sections of this document discuss this in greater detail.

Several methods may be appropriate for sampling

the biota of wetlands, and it is important to be able

to duplicate these methods from site to site and to

be as consistent as possible. Sampling should always be conducted in a way that maintains both

precision and accuracy (see Module 4: Study Design for Monitoring Wetlands).

0

5

10

15

20

25

30

0 3 6 9 12 15

Number of Samples

Cumulative Number of Species

Site 1

Site 2

Figure 3: Species/area curves for wetland

invertebrate samples.

Demonstrates the asymptotic relationship (leveling of the curve) that should be considered for the determining

the level of sampling effort (preliminary data from Sparling et al.).
23

In addition to sampling the biota, most projects

involving the development of bioassessment methods also sample some physical and chemical attributes of the study sites (Sparling et al. 1996;

Fennessy et al. 1998; Gernes and Helgen 1999).

This information is particularly useful for verifying

that wetlands are classified properly and for investigating how a wetland is damaged. Data or methods from existing functional assessments may be

useful for helping to characterize the structural characteristics of wetlands. For example, the

hydrogeomorphic approach (Brinson 1993) or state

rapid assessments can provide valuable information to support the development of IBIs for wetlands. Ohio EPA (2001), for example, uses information from its Ohio Rapid Assessment Survey to

gather information on structural characteristics of

wetlands. Ohio EPA also collects additional information from water quality tests. Collecting physical and chemical information for wetlands that can

be useful for developing IBIs should include hydrological indicators and soil characteristics.

Hydrological indicators include the following:

n Presence of conducted stormwater or agricultural drainage

n Water marks, stained leaves, sediment deposits, or soil saturation in the top 30 cm (see U.S.

Army Corps of Engineers 1987)

n Water chemistry parameters (If the system is

seasonally flooded and water chemistry data

are required, this information must be taken into

account when developing the sampling design.

It may be necessary to sample water chemistry

at different times than vegetation sampling. Parameters to analyze might include pH, dissolved

oxygen, conductivity, total phosphorus, nitrogen, total suspended solids, chloride, metals (in

some instances), and total organic carbon)

n Percent salinity and conductivity

n HGM class, for data on site hydrology

n Temporal and spatial patterns of water area and

depth

Soils can be easily characterized using a standard soil probe. The following soil data should

be recorded in each vegetation community type:

n Thickness of the organic layer

n Soil texture

n Color as determined by a Munsell Color (1975)

soil chart

n Presence of mottles and their size and color as

well as the presence of oxidized root channels

Depending on the study goals, it may be necessary to collect soil samples for analysis. Standard

analysis includes pH, percent organic matter, nutrients, and perhaps metals. Total phosphorus can be

a good indicator of disturbance and the deposition

of heavy sediment loads. Also, calcium levels in

the soil may be a good index of stress severity.

Summarize Sample

Data by Biological

Attributes

A spreadsheet or database is useful at this point to summarize

sample data. Many spreadsheet

applications (e.g., Lotus 1-2-3

and Microsoft Excel) are easy to

learn, but they can be cumbersome and difficult to use for exploratory analysis. Database applications are more difficult to

learn, but they offer more features

and flexibility for conducting exploratory analysis

and constructing lists based on certain parameters.

Some states use a combination of spreadsheets, databases, and statistical software. Regardless of the

type of computer software used, the data from field
24

data sheets must be entered into a computer and

summarized on the basis of the list of attributes. Field

data sheets often include a list of species or taxa

with a number next to those found at a site. The

number depends on the assemblages monitored

(e.g., the number of individuals or the percent cover

of a species). After the data are entered into the

computer, they must be summarized based on the

attributes.

Evaluate Attribute

Performance Across a

Gradient of Human

Disturbance

The need to test and validate biological responses of attributes and

metrics across degrees of human

disturbance is a core assumption

of the IBI (Karr and Chu 1999).

Ideally, metrics that are incorporated into a multimetric index

should be relatively easy to measure and interpret. They should

change in a predictable fashion.

The metric should be sensitive to a range of biological disturbances and not narrowly focused on

one particular aspect of the community (e.g., species richness). Most importantly, metrics must be

able to discriminate between human disturbances

and the background “noise” of natural variability.

Human impact should be the focus of biological

monitoring (Karr and Chu 1999).

The process for selecting metrics for use in a

multimetric index involves testing a large set of biological attributes (candidate metrics) and then selecting the ones that are most sensitive to various

aspects of human disturbance. Although large numbers of attributes may need to be explored while

developing a multimetric index, it is inevitable that

there will be spurious relationships when considering large numbers of disturbance-attribute pairings.

A good metric will show a strong signal (response)

to increased disturbance and does not give mixed

signals. Attributes that show large variation (extremely wide ranges in response when data from a

variety of sites are plotted) will have less utility. For

example, the following simplified graphs show some

acceptable relationship for metrics:

X-Axis = Increasing Human 

X-Axis = Increasing Human 

The simplified graphs below show relationships that have limited acceptability. Exceptions are noted with

the two middle two panels, which indicate peak attribute responses with intermediate levels of disturbance.

Attributes with such responses may make appropriate metrics with proper adjustments in metric scoring.

X-Axis = Increasing Human Disturbance

Y-Axis = Attribute Value

X-Axis = Increasing Human Disturbance

Y-Axis = Attribute Value
25

Select Metrics from

Best Performing

Attributes

For most taxa, at least 5 metrics

(but preferably 8–12) should be

defined and selected to construct

a multimetric index. Each metric

should reflect the quality of a different aspect of biota that responds in a different manner to

disturbances to wetlands

(Margalev 1963, Fausch et al.

1990, Hughes and Noss 1992).

Therefore, whenever possible,

care should be taken to select metrics from several

different metric categories (e.g., species composition and richness, tolerance and intolerance, trophic

composition, and population characteristics) to ensure that response is derived from a range of influences and that redundancies are minimized. In general, the wider the range of environmental influences

represented by the metrics the better (Table 2). For

example, if long-lived taxa requiring years to mature are present, one can infer that the spatial and

temporal components they require are also present.

Excessive production of herbivorous species may

be indicative of excessive nutrients. High levels of

toxic substances may be inferred from the frequent

occurrence of individuals with disease or other

anomalies (Karr and Chu 1999).

The performance of each attribute should be evaluated by assessing how well it does the following:

(1) increases or decreases along a gradient of human disturbance, (2) separates the least from the

most impaired sites, (3) provides similar values for

similarly impaired sites, and (4) provides a unique

(nonredundant) discriminatory response (Karr et al.

1997). Several graphical approaches and statistical tests may be used to evaluate attribute performance. Each may be used either individually or in

concert with another to screen out attributes that

do not perform acceptably and retain those that do.

One frequently used approach is to create bar graphs

or box plots showing means or medians and variances of a particular attribute at sites believed to be

least and most impaired (Mundahl and Simon

1999). Several commercial software programs can

do this. The degree of separation between the least

and most impaired sites can then form the basis for

retaining or discarding the attribute for subsequent

analyses (Figure 4). The statistical significance of

the separation can be confirmed using standard statistical tests such as t tests.

Another frequently used approach is to compare

attribute data not just from the extreme sites, but

from all sites across the spectrum of human disturbance. For that comparison, the disturbance gradient can be based on a single variable representing

one or more human disturbances or several variables or an index representing multiple human

disturbances (Figures 5 and 6). The relationship

can be expressed either graphically (scatter plot)

or by a comparison of correlation coefficients, such

as Pearson’s correlation coefficient (Figure 5).

Based on the degree of correlation, certain attributes

may be retained and others may be eliminated

(Figure 7).

Attributes that contain many of the same taxa may

be considered redundant, and although some redundancy is acceptable, seek to reduce double

counting or using the same taxa over and over. Redundancy can be tested statistically, for example,

through factor analyses (Hatcher 1994) or by simply examining similarities in the taxa groupings that

form each attribute. Simple tables can be constructed to compare metric performance over the

various tests.
26

0

5

10

15

20

25

30

35

40

% Odonates % Exotic

Plants

% Trophic

Generalists

Least-disturbed

Most-disturbed

Figure 4: Evaluation of

metric performance.

Examples of bar graphs illustrating the

degree to which attributes separate

least- from most-disturbed sites

(expressed in mean percentages).

Based on degree of separation two of

the attributes may be retained for

further evaluation (% Odonates and

% Exotic Plants) while the other may

be eliminated (% Trophic Generalists)

(hypothetical).

0

2

4

6

8

10

12

14

16

1 1.2 1.4 1.6 1.8 2 2.2 2.4

Log Zn (sediments)

Grasslike Taxa Richness

Ref

Ag

Urb

R

2

 = 0.36

Figure 5: Scatter plot illustrating metric (grasslike taxa

richness) response to a single variable (zinc concentrations)

representing the gradient of human disturbance.

R

2 = Pearson’s correlation coefficient; Ref = reference wetlands; Ag = wetlands with agricultural

impairments; Urb = wetlands with urban impairments (Helgen and Gernes in press).
27

Figure 6: Evaluation

of attribute

performance over a

combined set of

disturbances.

Ref = reference wetlands; AgLo =

wetlands with low levels of

agricultural impairment; SwMo =

wetlands with moderate levels of

stormwater impairment; AgHi =

wetlands with high levels of

agricultural impairment; and SwHi

= wetlands with high levels of

stormwater impairment. Based on

the relationship, one attribute

(number of Odonate genera) may be

retained, while the other (number of

leech genera) may be eliminated

(Gernes and Helgen 1999).

Invertebrate IBI and Disturbance

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100

Disturbance Score

Invertebrate IBI

Ref

Ag

Urb

Figure 7: Scatter

plot demonstrating

close correlation

between a wetland

macroinvertebrate IBI

and a disturbance

gradient derived from

a combination of

human disturbances.

 Ref = reference wetlands; Ag =

wetlands with agricultural

impairments; Urb = wetlands with

urban impairments (Helgen and

Gernes in press).

 Odonata and Influence Categories

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6

Influence Category

Genera of Odonata

Ref

AgLo

SWMo

AgHi

SWHi

 Leech Genera and Influence Categories

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Influence Category

Leech Genera

Ref

AgLo

SWMo

AgHi

SWHi

Leech Genera and Disturbance Categories

Disturbance Category

Disturbance Category
28

Score Each Individual

Metric

The metric evaluation process

should cull attributes, even

those that may show some relationship to the gradient of human disturbance, to select

those few metrics that are

highly sensitive to impairments

yet not redundant, to form the

IBI. The selected metrics then

can be scored by assigning values, such as 5, 3, or 1, depending on whether the data they represent are comparable to, deviate somewhat from, or deviate greatly

from values exhibited by the least impaired wetlands (Karr et al. 1986). Some metrics will decrease with added human disturbance (positive

metrics) and others will increase (negative metrics);

each should be scored accordingly. Several techniques have been used to score metrics, each with

the objective of assigning relative values to reflect

the degree to which each metric departs from expected conditions. Scoring may be accomplished

by determining the range in values (minimum and

maximum) for each metric and then dividing those

data into equal thirds. Metric values falling in the

higher third of the range are assigned a score of 5,

those in the middle third scored a 3, and those in

the lower third scored a 1; if the data are negatively

correlated, the scoring is reversed (Table 3).

Another scoring alternative has been used in

streams, in which a variable, such as size of stream

drainage, is known to influence a metric’s response.

In such cases, a trisection technique is used to divide and score scatter plot data (size of stream drainage vs. metric value) to account for the influence of

the variable (Lyons 1992). Although yet to be documented for wetlands, it is possible that similar influences exist and should be taken into consideration

when individual metrics are scored. Maximum species richness lines or lines that represent the upper

limit of scoring for other metrics can be calculated

though regression analysis; species/area curve plotting; or by best-fit lines, using professional judgment. Care should be taken to avoid outliers in

data that may skew the scoring. This process should

be as objective as possible; rules should be designed for the scoring procedure. Note that scoring should apply only to wetlands in the same class.

For example, take care to avoid having the best

bog receive a score of 25 out of 50 and the best

marsh a 49 out of 50, which would incorrectly imply that bogs are not as healthy as marshes. A pristine bog should receive a 50 compared with other

bogs, and a pristine marsh should receive a 50 compared with other marshes.

Calculate Total IBI

Score for All Sites

An IBI is composed of the

summed response signatures of

the individual metrics that collectively provide a relative measure of biological condition and

individually point to likely

causes of degradation at different sites (Karr et al. 1986,

Yoder and Rankin 1995). An

IBI score can be calculated for

each site by applying the scoring criteria to the data

from each site (Table 4). If the metrics selected are

closely correlated to the gradient of human disturbance, then the IBI that is derived from the composite of those metrics will be also (Figure 7). Once

metric scores have been totaled, various interpretations can be made. For example, the same application can be used for other wetlands in the region

and before and after studies can be performed to

assess the relative effect of various conservation

practices on wetlands. Biological criteria can be

established to help support water quality objectives.

Or, analyses can be performed to determine which
29

Site Chiro Odon Corix% Leech ETSD Erp% TaxTot Intol 3Dom% SnailTx Type IBI Condition

1 5 5 5 5 5 5 5 5 5 5 Ref 50 Exc

2 5 5 5 5 5 5 3 5 5 5 Ref 48 Exc

3 3 3 5 5 5 5 5 5 3 5 Ref 44 Exc

4 3 5 3 5 5 5 5 3 5 5 Ref 44 Exc

5 5 5 5 3 5 5 3 5 5 1 Ref 42 Exc

6 1 5 5 3 5 5 3 5 3 3 Ref 38 Exc

7 3 3 5 5 3 3 1 1 5 5 Ag 34 Mod

8 1 3 5 5 3 5 5 1 3 1 Ag 32 Mod

9 3 3 5 3 1 3 3 1 3 3 Ag 28 Mod

10 3 1 3 3 3 1 5 1 3 3 Ag 26 Mod

11 3 1 1 3 3 3 3 1 3 5 SW 26 Mod

12 3 3 3 1 3 5 3 1 3 1 SW 26 Mod

13 3 1 1 3 3 5 3 1 3 3 SW 26 Mod

14 1 3 5 5 1 5 3 1 1 1 SW 26 Mod

15 3 1 3 3 3 5 1 1 3 3 SW 26 Mod

16 3 1 1 5 1 5 3 1 1 3 SW 24 Mod

17 3 1 3 3 1 5 3 1 1 3 Ag 24 Mod

18 3 1 3 3 1 3 5 1 1 1 SW 22 Poor

19 1 1 3 3 3 5 3 1 1 1 SW 22 Poor

20 1 3 3 3 3 3 1 1 1 3 SW 22 Poor

21 3 1 1 3 1 5 1 1 1 3 Ag 20 Poor

22 1 3 1 1 1 1 3 1 3 3 Ag 18 Poor

23 1 1 1 3 1 1 3 1 1 3 SW 16 Poor

24 1 1 1 3 1 1 1 1 3 3 SW 16 Poor

25 1 1 1 3 1 1 1 1 3 1 Ag 14 Poor

Chiro, Chironomid genera; Odon, Odonata genera; Corix%, Corixidae proportion; Leech, leech genera; ETSD, ; Erp%, Erpobdella proportion; TaxTot,

total taxa; Intol, # of intolerant taxa; 3Dom%, proportion of dominant 3 taxa; Snail Tx, snail taxa. Type Ref, reference wetland; Ag, agriculturalinfluenced wetland; SW, stormwater-influenced wetland. Exc, excellent; Mod, moderate

Table 4: Individual metric scores for invertebrate metrics

Note: Condition classification = 37-50 as excellent, 24-36 as moderate, and 10-23 as poor (Gernes and Helgen

1999).
30

metrics are contributing most heavily to sites with

low scores, thus helping to diagnose causes of impairments for particular sites (Figure 8).

Interpret IBI and

Report Data

Perhaps the greatest benefit of

an IBI is that it summarizes and

presents complex biological information in a format that is easily communicated to managers

and the public. Most people

can understand plant and animal IBIs more easily than they

can understand complex statistical calculations or abstract

chemical and physical wetland

functions. To help with the interpretations, integrity

classes can be developed to classify sites, along

with narrative descriptions of relative biological condition (Table 5). Although an IBI score is helpful

for quickly communicating the overall condition of

a wetland, most of the valuable information lies in

the individual metrics. When bioassessment results

are reported, the IBI score should be accompanied by (1) a narrative description of overall biotic

condition in comparison to reference wetlands of

the same region and wetland type, (2) numeric values of each metric, and (3) narrative descriptions

of each metric in comparison to reference conditions of the same region and wetland type. For more

information about how IBIs can be used to improve

wetland management, refer to Module 5: Administrative Framework for Implementation of Wetland

Bioassessment Program.

0

10

20

30

40

50

Reno Crow Orchard Winter

Wetlands

WIBI Score

# Snail Taxa

# Odonata Taxa

# Leech Taxa

# Intolerant Taxa

# ETSD

# Midge Taxa

% 3 Dominants

% Erpobdella

% Water Boatmen

Total # Taxa

Range of Possible

Scores

Figure 8: Example of Wetland Index of Biological

Integrity scores.

From a Minnesota study for wetlands showing the range in scores and contribution of each metric

(Gernes and Helgen 1999). Reno and Crow are reference sites, Orchard receives urban stormwater,

Winter has heavy influences from agriculture.
31

Total IBI score

(sum for 12

Integritymetric

ratings)

Class Attributes

50-60 Excellent

Comparable to the best situations in the regional subclass without human

disturbance; contains all species expected for the region, including the most

intolerant forms; exhibits balanced trophic structure and reproductive success.

40-49 Good

Species richness somewhat below expectation, especially due to the loss of themost

intolerant forms; some species are present with less than optimal abundances; trophic

structure and reproduction shows some sign of stress. Presence of some invasive or

non-native species.

30-39 Fair

Signs of additional deterioration include loss of intolerant forms, fewer species, highly

skewed trophic structure (e.g., increasing frequency of omnivores or tolerant species);

older age classes or top predators may be rare.

20-29 Poor

Dominated by omnivores, tolerant forms, and habitat generalists; few top carnivores;

reproductive and condition factors commonly depressed; hybrids or diseased

individuals often present. Invasive or non-native species abundant.

10-20 Very Poor

Dominated by highly tolerant forms or invasive species; hybrids may be common;

disease, lesions, parasites, and other anomalies may be regular. Complete absence of

less tolerant forms.

Table 5: Total IBI scores, integrity classes, and their attributes

for streams in a regional reference

Source: Modified from Karr et al. 1986.

Note: Narrative description of integrity classes may differ substantially for wetlands.
32

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Glossary

Composition (structure) The composition of the

taxonomic grouping, such as fish, algae, or

macroinvertebrates, relating primarily to the kinds

and number of organisms in the group.

Continuum A gradient of change.

Disturbance “Any discrete event in time that disrupts ecosystems, communities, or population

structure and changes resources, substrate availability or the physical environment” (Picket and

White 1985). Examples of natural disturbances are

fire, drought, and floods. Human-caused disturbances are referred to as “human influence” and

tend to be more persistent over time, e.g., plowing,

clearcutting of forests, conducting urban stormwater

into wetlands.

Diversity A combination of the number of taxa

(see taxa richness) and the relative abundance of

those taxa. A variety of diversity indexes have been

developed to calculate diversity.

Dominance The relative increase in abundance

of one or more species in relation to the abundance of other species in samples from a habitat.

Ecosystem The community plus its habitat; the

connotation is of an interacting system.

Ecoregion A region defined by similarity of climate, landform, soil, potential natural vegetation,

hydrology, and other ecologically relevant variables.

Functional feeding groups (FFGs) Groupings

of different invertebrates based on the mode of food

acquisition rather than the category of food eaten.

The groupings relate to the morphological structures, behaviors, and life history attributes that determine the mode of feeding by invertebrates. Examples of invertebrate FFGs are shredders, which

chew live plant tissue or plant litter, and scrapers,

which scrape periphyton and associated matter from

substrates (see Merritt and Cummins 1996a,b).

Assemblage An association of interacting populations of organisms in a wetland or other habitat.

Examples of assemblages used for biological assessments include algae, amphibians, birds, fish,

macroinvertebrates (e.g., insects, crayfish, clams,

snails), and vascular plants.

Attribute A measurable component of a biological assemblage. In the context of biological assessments, attributes include the ecological processes or characteristics of an individual or assemblage of species that are expected, but not empirically shown, to respond to a gradient of human disturbance.

Benthos The bottom fauna of bodies of water.

Biological assessment Using biomonitoring data

of samples of living organisms to evaluate the condition or health of a place (e.g., a stream, wetland,

or woodlot).

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”

(Karr and Dudley, 1981).

Biological magnification The increase in concentration of some material in organisms compared

with its concentration in the environment.

Biological monitoring Sampling the biota of a

place (e.g., a stream, a woodlot, or a wetland).

Biota The plants and animals living in a habitat.

Community All the groups of organisms living

together in the same area, usually interacting or depending on each other for existence.

Competition Utilization by different species of

limited resources of food or nutrients, refugia, space,

ovipositioning sites, or other resources necessary

for reproduction, growth, and survival.
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Functional groups A means of dividing organisms into groups, often based on their method of

feeding (e.g., shredder, scraper, filterer, predator),

type of food (e.g., fruit, seeds, nectar, insects), or

habits (e.g., burrower, climber, clinger).

Gradient of human influence The relative ranking of sample sites within a regional wetland class

based on the estimation of degree of human disturbance (e.g., pollution and physical alteration of

habitats).

Habitat The sum of the physical, chemical, and

biological environment occupied by individuals of a

particular species, population, or community.

Hydrology The science of dealing with the properties, distribution, and circulation of water both on

the surface and under the earth.

Impact A change in the chemical, physical (including habitat), or biological quality or condition

of a body of water caused by external forces.

Impairment Adverse changes occurring to an ecosystem or habitat. An impaired wetland has some

degree of human influence affecting it.

Index of Biologic Integrity (IBI) An integrative

expression of the biological condition that is composed of multiple metrics. It is similar to economic

indexes used for expressing the condition of the

economy.

Intolerant taxa Taxa that tend to decrease in

wetlands or other habitats that have higher levels of

human disturbances, such as chemical pollution or

siltation.

Least impaired site Sample sites within a regional wetland class that exhibit the least degree of

detrimental effect. Such sites help anchor gradients

of human disturbance and are commonly referred

to as reference sites.

Macroinvertebrates Animals without backbones that are caught with a 500-800 micron

mesh net. Macroinvertebrates do not include

zooplankton or ostracods, which are generally

smaller than 200 microns in size.

Metric An attribute with empirical change in value

along a gradient of human disturbance.

Most impaired site Sample sites within a regional wetland class that exhibit the greatest degree

of detrimental effect. Such sites help anchor gradients of human disturbance and serve as important

references, although they are not typically referred

to as reference sites. Such sites may be referred to

as impaired or disturbed sites.

Munsell color The color of soil based on its

chroma and hue as determined by a chart in the

book Munsell Soil Color Charts (Munsell Color

1975).

Mottles Spots or blotches of different color or

shades of color interspersed within the dominant

color in a soil layer, usually resulting from the presence of periodic reducing soil conditions.

Omnivores Organisms that consume both plant

and animal material.

Population A set of organisms belonging to the

same species and occupying a particular area at the

same time.

Predator An animal that feeds on other animals.

Reference site As used with an Index of Biological Integrity, a minimally impaired site that

is representative of the expected ecological conditions and integrity of other sites of the same type

and region.

Taxa A grouping of organisms given a formal taxonomic name, such as species, genus, and family.

The singular form is taxon.

Taxa richness The number of distinct species or

taxa that are found in an assemblage, community,

or sample.
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Tolerance The biological ability of different

species or populations to survive successfully

within a certain range of environmental conditions.

Tolerance (range of) The set of conditions within

which an organism, taxa, or population can survive.

Tolerant taxa Taxa that tend to increase in wetlands or other habitats that have higher levels of

human disturbances, such as chemical pollution or

siltation.

Trophic Feeding; thus, pertaining to energy transfers.

Wetland(s) (1) Those areas that are inundated

or saturated by surface or groundwater at a

frequency and duration sufficient to support, and

that under normal circumstances do support, a

prevalence of vegetation typically adapted for life

in saturated soil conditions [EPA, 40 C.F.R.§

230.3 (t) / USACE, 33 C.F.R. § 328.3 (b)]. (2)

Wetlands are lands transitional between terrestrial

and aquatic systems where the water table is

usually at or near the surface or the land is

covered by shallow water. For the purposes of

this classification, wetlands must have one or

more of the following three attributes: (a) at least

periodically, the land supports predominantly

hydrophytes, (b) the substrate is predominantly

undrained hydric soil, and (c) the substrate is

nonsoil and is saturated with water or covered by

shallow water at some time during the growing

season of each year (Cowardin et al. 1979). (3)

The term “wetland” except when such term is part

of the term “converted wetland,” means land that

(a) has a predominance of hydric soils, (b) is

inundated or saturated by surface or ground

water at a frequency and duration sufficient to

support a prevalence of hydrophytic vegetation

typically adapted for life in saturated soil

conditions, and (c) under normal circumstances

does support a prevalence of such vegetation.

For purposes of this Act and any other Act, this

term shall not include lands in Alaska identified as

having a high potential for agricultural development which have a predominance of permafrost

soils [Food Security Act, 16 U.S.C. 801(a)(16)].