United States

Environmental Protection

Agency

Office of Water

4304

EPA 822-B-00-019

December 2000

Ambient Water Quality

Criteria Recommendations

Information Supporting the Development

of State and Tribal Nutrient Criteria

Rivers and Streams in 

Nutrient Ecoregion IX
EPA -822-B-00-019

 AMBIENT WATER QUALITY CRITERIA RECOMMENDATIONS

INFORMATION SUPPORTING THE DEVELOPMENT OF STATE AND TRIBAL

NUTRIENT CRITERIA

FOR

RIVERS AND STREAMS IN NUTRIENT ECOREGION IX

Southeastern Temperate Forested Plains and Hills

including all or parts of the States of

Maryland, Pennsylvania, Virginia, North Carolina, South Carolina, Georgia, Florida, Alabama,

Mississippi, Tennessee, Kentucky, Indiana, Illinois, Iowa, Missouri, Kansas, Oklahoma,

Arkansas, Louisiana, Texas 

and the authorized Tribes within the Ecoregion

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF WATER

OFFICE OF SCIENCE AND TECHNOLOGY

HEALTH AND ECOLOGICAL CRITERIA DIVISION

WASHINGTON, D.C.

DECEMBER 2000
ii

FOREWORD

This document presents EPA’s nutrient criteria for Rivers and Streams in Nutrient

Ecoregion IX. These criteria provide EPA’s recommendations to States and authorized Tribes

for use in establishing their water quality standards consistent with section 303(c) of CWA. 

Under section 303(c) of the CWA, States and authorized Tribes have the primary responsibility

for adopting water quality standards as State or Tribal law or regulation. The standards must

contain scientifically defensible water quality criteria that are protective of designated uses. 

EPA’s recommended section 304(a) criteria are not laws or regulations – they are guidance that

States and Tribes may use as a starting point for the criteria for their water quality standards. 

The term “water quality criteria” is used in two sections of the Clean Water Act, Section

304(a)(1) and Section 303(c)(2). The term has a different impact in each section. In Section 304,

the term represents a scientific assessment of ecological and human health effects that EPA

recommends to States and authorized Tribes for establishing water quality standards that

ultimately provide a basis for controlling discharges or releases of pollutants or related

parameters. Ambient water quality criteria associated with specific waterbody uses when

adopted as State or Tribal water quality standards under Section 303 define the level of a

pollutant (or, in the case of nutrients, a condition) necessary to protect designated uses in ambient

waters. Quantified water quality criteria contained within State or Tribal water quality standards

are essential to a water quality-based approach to pollution control. Whether expressed as

numeric criteria or quantified translations of narrative criteria within State or Tribal water quality

standards, quantified criteria serve as a critical basis for assessing attainment of designated uses

and measuring progress toward meeting the water quality goals of the Clean Water Act.

EPA is developing section 304(a) water quality criteria for nutrients because States and

Tribes consistently identify excessive levels of nutrients as a major reason why as much as half of

the surface waters surveyed in this country do not meet water quality objectives, such as full

support of aquatic life. EPA expects to develop nutrient criteria that cover four major types of

waterbodies – lakes and reservoirs, rivers and streams, estuarine and coastal areas, and wetlands –

across fourteen major ecoregions of the United States. EPA’s section 304(a) criteria are

intended to provide for the protection and propagation of aquatic life and recreation. To support

the development of nutrient criteria, EPA is publishing Technical Guidance Manuals that describe

a process for assessing nutrient conditions in the four waterbody types. 

EPA’s section 304(a) water quality criteria for nutrients provide numeric water quality

criteria, as well as procedures by which to translate narrative criteria within State or Tribal water

quality standards. In the case of nutrients, EPA section 304(a) criteria establish values for causal

variables (e.g., total nitrogen and total phosphorus) and response variables (e.g., turbidity and

chlorophyll a). EPA believes that State and Tribal water quality standards need to include

quantified endpoints for causal and response variables to provide sufficient protection of uses and

to maintain downstream uses. These quantified endpoints will most often be expressed as

numeric water quality criteria or as procedures to translate a State or Tribal narrative criterion

into a quantified endpoint.
iii

EPA will work with States and authorized Tribes as they adopt water quality criteria for

nutrients into their water quality standards. EPA recognizes that States and authorized Tribes

require flexibility in adopting numeric nutrient criteria into State and Tribal water quality

standards. States and authorized Tribes have several options available to them. EPA

recommends the following approaches, in order of preference:

(1) Wherever possible, develop nutrient criteria that fully reflect localized conditions and

protect specific designated uses using the process described in EPA’s Technical Guidance

Manuals for nutrient criteria development. Such criteria may be expressed either as

numeric criteria or as procedures to translate a State or Tribal narrative criterion into a

quantified endpoint in State or Tribal water quality standards.

(2) Adopt EPA’s section 304(a) water quality criteria for nutrients, either as numeric

criteria or as procedures to translate a State or Tribal narrative nutrient criterion into a

quantified endpoint.

(3) Develop nutrient criteria protective of designated uses using other scientifically

defensible methods and appropriate water quality data.

 

Geoffrey H. Grubbs, Director

Office of Science and Technology
iv

DISCLAIMER

This document provides technical guidance and recommendations to States, authorized

Tribes, and other authorized jurisdictions to develop water quality criteria and water quality

standards under the Clean Water Act (CWA) to protect against the adverse effects of nutrient

overenrichment. Under the CWA, States and authorized Tribes are to establish water quality

criteria to protect designated uses. State and Tribal decision-makers retain the discretion to adopt

approaches on a case-by-case basis that differ from this guidance when appropriate and

scientifically defensible. While this document contains EPA’s scientific recommendations

regarding ambient concentrations of nutrients that protect aquatic resource quality, it does not

substitute for the CWA or EPA regulations; nor is it a regulation itself. Thus it cannot impose

legally binding requirements on EPA, States, authorized Tribes, or the regulated community, and

it might not apply to a particular situation or circumstance. EPA may change this guidance in the

future.
v

EXECUTIVE SUMMARY

 

Nutrient Program Goals

EPA developed the National Strategy for the Development of Regional Nutrient Criteria

(National Strategy) in June 1998. The strategy presents EPA’s intentions to develop technical

guidance manuals for four types of waters (lakes and reservoirs, rivers and streams, estuaries and

coastal waters, and wetlands) and produce section 304(a) criteria for specific nutrient ecoregions

by 2000. In addition, the Agency formed Regional Technical Assistance Groups (RTAGs) which

include State and Tribal representatives working to develop more refined and more localized

nutrient criteria based on approaches described in the waterbody guidance manuals. This

document presents EPA’s current recommended criteria for total phosphorus, total nitrogen,

chlorophyll a, and turbidity for rivers and streams in Nutrient Ecoregion IX (Southeastern

Temperate Forested Plains and Hills) which were derived using the procedures described in the

Rivers and Streams Nutrient Criteria Technical Guidance Manual (2000b). 

EPA’s ecoregional nutrient criteria are intended to address cultural eutrophication-- the

adverse effects of excess nutrient inputs. The criteria are empirically derived to represent

conditions of surface waters that are minimally impacted by human activities and protective of

aquatic life and recreational uses. The information contained in this document represent starting

points for States and Tribes to develop (with assistance from EPA) more refined nutrient criteria.

In developing these criteria recommendations, EPA followed a process which included, to

the extent they were readily available, the following elements critical to criterion derivation: 

• Historical and recent nutrient data in Nutrient Ecoregion IX. 

Data sets from Legacy STORET, NASQAN, NAWQA, Auburn University, and EPA

Regions 3, 5 and 7 were used to assess nutrient conditions from 1990 to 1998.

• Reference sites/reference conditions in Nutrient Ecoregion IX.

Reference conditions presented are based on 25th percentiles of all nutrient data including a 

comparison of reference condition for the aggregate ecoregion versus the subecoregions. 

States and Tribes are urged to determine their own reference sites for rivers and streams

within the ecoregion at different geographic scales and to compare them to EPA’s

reference conditions.

• Models employed for prediction or validation.

EPA did not identify any specific models used in the ecoregion to develop nutrient 

criteria. States and Tribes are encouraged to identify and apply appropriate models to

support nutrient criteria development.

• RTAG expert review and consensus.

EPA recommends that when States and Tribes prepare their nutrient criteria, they obtain 

the expert review and consent of the RTAG.
vi

• Downstream effects of criteria.

EPA encourages the RTAG to assess the potential effects of the proposed criteria on

downstream water quality and uses.

In addition, EPA followed specific QA/QC procedures during data collection and

analysis: All data were reviewed for duplications. All data are from ambient waters that were not

located directly outside a permitted discharger. The following States indicated that their data

were sampled and analyzed using either Standard methods or EPA approved methods: Florida,

Georgia, Illinois, Indiana, Iowa, Maryland, Missouri, North Carolina, South Carolina, and

Tennessee.

The following tables contain a summary of Aggregate and level III ecoregion values for

TN, TP, water column chl a, and turbidity:

BASED ON 25th PERCENTILE ONLY

Nutrient Parameters Aggregate Nutrient Ecoregion IX

Reference Conditions

Total phosphorus (μg/L) 36.56

Total nitrogen (mg/L) 0.69

Chlorophyll a (μg/L) (Spectrophotometric

method)

0.93

Periphyton Chlorophyll a (mg/m2) 20.35

Turbidity (FTU) 5.7

For subecoregions, 29,33, 35, 37, 40, 45, 64, 65, 71, 72, and 74, the ranges of nutrient parameter

reference conditions are:

BASED ON 25th PERCENTILE ONLY

Nutrient Parameters Range of Level III Subecoregions

Reference Conditions

Total phosphorus (μg/L) 22.5 - 100.00

Total nitrogen (mg/L) 0.07 - 1.0

Chlorophyll a (μg/L) 0.05 - 5.74

Periphyton Chlorophyll a (mg/m2) 3.13 - 20.35

Turbidity (FTU) 3.15 - 13.5
vii

NOTICE OF DOCUMENT AVAILABILITY

This document is available electronically to the public through the INTERNET at:

(http://www.epa.gov/OST/standards/nutrient.html). Requests for hard copies of the document

should be made to EPA’s National Service Center for Environmental Publications (NSCEP),

11029 Kenwood Road, Cincinnati, OH 45242 or (513) 489-8190, or toll free (800) 490-9198. 

Please refer to EPA document number EPA-822-B-00-019.
viii

ACKNOWLEDGMENTS

The authors thankfully acknowledge the contributions of the following State and Federal

reviewers: EPA Regions 1, 2, 3, 4, 5, 6 and 7; the States of Maryland, Pennsylvania, Virginia,

North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, Tennessee, Kentucky,

Indiana, Illinois, Iowa, Missouri, Kansas, Oklahoma, Arkansas, Louisiana and Texas; the Tribes

within the Ecoregion; EPA Headquarters personnel from the Office of Wetlands, Oceans and

Watersheds, Office of Wastewater Management, Office of General Counsel, Office of Research

and Development, and the Office of Science and Technology. EPA also acknowledges the

external peer review efforts of Eugene Welch (University of Washington), Robert Carlson (Kent

State University), Steve Heiskary (Minnesota Pollution Control Agency), Greg Denton and

Sherry Wang (Tennessee Department of Environment and Conservation), and Gerhard Kuhn

(U.S. Geological Survey). 
ix

LISTS OF TABLES AND FIGURES

Figures

Figure 1 Aggregate Ecoregion IX ........................................... 7

Figure 2 Aggregate Ecoregion IX with level III ecoregions shown ................. 8

Figure 3 Sampling locations within each level III ecoregion ...................... 13

Figure 4a Illustration of data reduction process for stream data .................... 25

Figure 4b Illustration of reference condition calculation .......................... 26

Tables

Table 1 Rivers and Streams records for Aggregate Ecoregion IX– Southeastern Temperate

Forested Plains and Hills .......................................... 14

Table 2 Reference conditions for Aggregate Ecoregion IX streams ............... 17

Table 3a-k Reference conditions for level III ecoregion streams .................... 18
x

TABLE OF CONTENTS

Foreword ................................................................. ii

Disclaimer ............................................................... iv

Executive Summary .......................................................... v

Notice of Document Availability ............................................... vii

Acknowledgments ........................................................ viii

List of Tables and Figures .................................................... ix

Table of Contents ........................................................... x

1.0 Introduction ............................................................ 1

2.0 Best Use of this Information ............................................... 4

3.0 Area Covered by This Document (waterbody type and ecoregion) .................. 6

3.1 Description of Aggregate Ecoregion IX– Southeastern Temperate Forested Plains

and Hills ............................................................ 6

3.2 Geographical Boundaries of Aggregate Ecoregion IX ...................... 7

3.3 Level III Ecoregions within Aggregate Ecoregion IX ...................... 8

4.0 Data Review for Rivers and Streams in Aggregate Ecoregion IX .................. 10

4.1 Data Sources ................................................... 11

4.2 Historical Data from Aggregate Ecoregion IX (TP, TN, Chl a, Turbidity) ...... 11

4.3 QA/QC of Data Sources ........................................... 11

4.4 Data for All Rivers/Streams within Aggregate Ecoregion IX ................ 11

4.5 Statistical Analysis of Data ......................................... 11

4.6 Classification of River/Stream Type .................................. 16

4.7. Summary of Data Reduction Methods ................................. 16

5.0 Reference Sites and Conditions in Aggregate Ecoregion IX ...................... 28

6.0 Models Used to Predict or Verify Response Parameters ......................... 28

7.0 Framework for Refining Recommended Nutrient Criteria for Rivers and Streams in 

 Aggregate Ecoregion IX ................................................. 28

7.1 Example Worksheet for Developing Aggregate Ecoregion and Subecoregion Nutrient 

 Criteria ........................................................ 29
xi

7.2 Tables of Refined Nutrient Water Quality Criteria for Aggregate Ecoregion IX and 

 Level III Subecoregions ............................................ 30

7.3 Setting Seasonal Criteria ........................................... 31

7.4 When Data/Reference Conditions Are Lacking .......................... 32

7.5 Site-Specific Criteria Development ................................... 32

8.0 Literature Cited ....................................................... 32

9.0 Appendices ........................................................... 33
1

1.0 INTRODUCTION

Background

Nutrients are essential to the health and diversity of our surface waters. However, in

excessive amounts, nutrients cause hypereutrophication, which results in overgrowth of plant life

and decline of the biological community. Excessive nutrients can also result in potential human

health risks, such as the growth of harmful algal blooms - most recently manifested in the

Pfiesteria outbreaks of the Gulf and East Coasts. Chronic nutrient overenrichment of a

waterbody can lead to the following consequences: low dissolved oxygen, fish kills, algal blooms,

overabundance of macrophytes, likely increased sediment accumulation rates, and species shifts of

both flora and fauna. 

Historically, National Water Quality Inventories have repeatedly shown that nutrients are a

major cause of ambient water quality use impairments. EPA’s 1996 National Water Quality

Inventory report identifies excessive nutrients as the leading cause of impairment in lakes and the

second leading cause of impairment in rivers (behind siltation). In addition, nutrients were the

second leading cause of impairments reported by the States in their 1998 lists of impaired waters. 

Where use impairment is documented, nutrients contribute roughly 25-50% of the impairment

nationally. The Clean Water Act establishes a national goal to achieve, wherever attainable, water

quality which provides for the protection and propagation of fish, shellfish, and wildlife and

recreation in and on the water. In adopting water quality standards, States and Tribes designate

uses for their waters in consideration of the Clean Water Act goals, and establish water quality

criteria that contain sufficient parameters to protect those uses. To date, EPA has not published

information and recommendations under section 304(a) for nutrients to assist States and Tribes in

establishing numeric nutrient criteria to protect uses when adopting water quality standards.

In 1995, EPA gathered a set of national experts and asked the experts how to best deal

with the national nutrient problem. The experts recommended that the Agency not develop single

criteria values for phosphorus or nitrogen applicable to all water bodies and regions of the

country. Rather, the experts recommended that EPA put a premium on regionalization, develop

guidance (assessment tools and control measures) for specific waterbodies and ecological regions

across the country, and use reference conditions (conditions that reflect pristine or minimally

impacted waters) as a basis for developing nutrient criteria.

With these suggestions as starting points, EPA developed the National Strategy for the

Development of Regional Nutrient Criteria (National Strategy), published in June 1998. This

strategy presented EPA’s intentions to develop technical guidance manuals for four types of

waters (lakes and reservoirs, rivers and streams, estuaries and coastal waters, and wetlands) and,

thereafter, to publish section 304(a) criteria recommendations for specific nutrient ecoregions. 

Technical guidance manuals for lakes/reservoirs and rivers/streams were published in April 2000

and July 2000, respectively. The technical guidance manual for estuaries/coastal waters will be

published in spring 2000 and the draft wetlands technical guidance manual will be published by

December 2001. Each manual presents EPA’s recommended approach for developing nutrient

criteria values for a specific waterbody type. In addition, EPA is committed to working with
2

States and Tribes to develop more refined and more localized nutrient criteria based on

approaches described in the waterbody guidance manuals and this document. 

Overview of the Nutrient Criteria Development Process

For each Nutrient Ecoregion, EPA developed a set of recommendations for two causal

variables (total nitrogen and total phosphorus) and two early indicator response variables

(chlorophyll a and some measure of turbidity). Other indicators such as dissolved oxygen and

macrophyte growth or speciation, and other fauna and flora changes are also deemed useful. 

However, the first four are considered to be the best suited for protecting designated uses.

The technical guidance manuals describe a process for developing nutrient criteria that

involves consideration of five factors. The first of these is the Regional Technical Assistance

Group (RTAG), which is a body of qualified regional specialists able to objectively evaluate all of

the available evidence and select the value(s) appropriate to nutrient control in the water bodies of

concern. These specialists may come from such disciplines as limnology, biology, natural

resources management-- especially water resource management, chemistry, and ecology. The

RTAG evaluates and recommends appropriate classification techniques for criteria determination,

usually physical within an ecoregional construct.

The second factor is the historical information available to establish a perspective of the

resource base. This is usually data and anecdotal information available within the past ten-twenty

five years. This information gives evidence about the background and enrichment trend of the

resource.

The third factor is the present reference condition. A selection of reference sites chosen to

represent the least culturally impacted waters of the class existing at the present time. The data

from these sites is combined and a value from the distribution of these observations is selected to

represent the reference condition, or best attainable, most natural condition of the resource base at

this time.

A fourth factor often employed is theoretical or empirical models of the historical and

reference condition data to better understand the condition of the resource.

The RTAG comprehensively evaluates the other three elements to propose a candidate

criterion (initially one each for TP, TN, chl a, and some measure of turbidity).

The last and final element of the criteria development process is the assessment by the

RTAG of the likely downstream effects of the criterion. Will there be a negative, positive, or

neutral effect on the downstream waterbody? If the RTAG judges that a negative effect is likely,

then the proposed State/Tribal water quality criteria should be revised to ameliorate the potential

for any adverse downstream effects.
3

While States and authorized Tribes would not necessarily need to incorporate all five

elements into their water quality criteria setting process (e.g., modeling may be significant in only

some instances), the best assurance of a representative and effective criterion for nutrient

management decision making is the balanced incorporation of all five elements, or at least all

elements except modeling.

Because some parts of the country have naturally higher soil and parent material

enrichment, and different precipitation regimes, the application of the criterion development

process has to be adjusted by region. Therefore, an ecoregional approach was chosen to develop

nutrient criteria appropriate to each of the different geographical and climatological areas of the

country. Initially, the continental U.S. was divided into 14 separate ecoregions of similar

geographical characteristics. Ecoregions are defined as regions of relative homogeneity in

ecological systems; they depict areas within which the mosaic of ecosystem components (biotic

and abiotic as well as terrestrial and aquatic) is different than adjacent areas in a holistic sense. 

Geographic phenomena such as soils, vegetation, climate, geology, land cover, and physiology

that are associated with spatial differences in the quantity and quality of ecosystem components

are relatively similar within each ecoregion. 

The Nutrient ecoregions are aggregates of U.S. EPA=s hierarchal level III ecoregions. As

such, they are more generalized and less defined than level III ecoregions. EPA determined that

setting ecoregional criteria for the large scale aggregates is not without its drawbacks - variability

is high due to the lumping of many waterbody classes, seasons, and years worth of multipurpose

data over a large geographic area. For these reasons, the Agency recommends that States and

Tribes develop nutrient criteria at the level III ecoregional scale and at the waterbody class scale

where those data are readily available. Data analyses and recommendations on both the large

aggregate ecoregion scale as well as more refined scales (level III ecoregions and waterbody

classes), where data were available to make such assessments, are presented for comparison

purposes and completeness of analysis. 

Relationship of Nutrient Criteria to Biological Criteria

Biological criteria are quantitative expressions of the desired condition of the aquatic

community. Such criteria can be based on an aggregation of data from sites that represent the

least-impacted and attainable condition for a particular waterbody type in an ecoregion,

subecoregion, or watershed. EPA’s nutrient criteria recommendations and biological criteria

recommendations have many similarities in the basic approach to their development and data

requirements. Both are empirically derived from statistical analysis of field collected data and

expert evaluation of current reference conditions and historical information. Both utilize direct

measurements from the environment to integrate the effects of complex processes that vary

according to type and location of waterbody. The resulting criteria recommendations, in both

cases, are efficient and holistic indicators of water quality necessary to protect uses.

States and authorized Tribes can develop and apply nutrient criteria and biological criteria

in tandem, with each providing important and useful information to interpret both the nutrient

enrichment levels and the biological condition of sampled waterbodies. For example, using the
4

same reference sites for both types of criteria can lead to efficiencies in both sample design and

data analysis. In one effort, environmental managers can obtain information to support

assessment of biological and nutrient condition, either through evaluating existing data sets or

through designing and conducting a common sampling program. The traditional biological

criteria variables of benthic invertebrate and fish sampling can be readily incorporated to

supplement a nutrient assessment. To demonstrate the effectiveness of this tandem approach,

EPA has initiated pilot projects in both freshwater and marine environments to investigate the

relationship between nutrient overenrichment and apparent declines in diversity indices of benthic

invertebrates and fish.

2.0 BEST USE OF THIS INFORMATION

EPA recommendations published under section 304(a) of the CWA serve several

purposes, including providing guidance to States and Tribes in adopting water quality standards

for nutrients that ultimately provide a basis for controlling discharges or releases of pollutants. 

The recommendations also provide guidance to EPA when promulgating Federal water quality

standards under section 303(c) when such action is necessary. Other uses include identification of

overenrichment problems, management planning, project evaluation, and determination of status

and trends of water resources. 

State water quality inventories and listings of impaired waters consistently rank nutrient

overenrichment as a top contributor to use impairments. EPA’s water quality standards

regulations at 40 CFR §131.11(a) require States and Tribes to adopt criteria that contain

sufficient parameters and constituents to protect the designated uses of their waters. In addition,

States and Tribes need quantifiable targets for nutrients in their standards to assess attainment of

uses, develop water quality-based permit limits and source control plans, and establish targets for

total maximum daily loads (TMDLs).

EPA expects States and Tribes to address nutrient overenrichment in their water quality

standards, and to build on existing State and Tribal initiated efforts where possible. States and

Tribes can address nutrient overenrichment through establishment of numerical criteria or through

use of new or existing narrative criteria statements (e.g., free from excess nutrients that cause or

contribute to undesirable or nuisance aquatic life or produce adverse physiological response in

humans, animals, or plants). In the case of narrative criteria, EPA expects that States and Tribes

establish procedures to quantitatively translate these statements for both assessment and source

control purposes. 

The intent of developing ecoregional nutrient criteria is to represent conditions of surface

waters that are minimally impacted by human activities and thus protect against the adverse

effects of nutrient overenrichment from cultural eutrophication. EPA’s recommended process for

developing such criteria includes physical classification of waterbodies, determination of current

reference conditions, evaluation of historical data and other information (such as published

literature), use of models to simulate physical and ecological processes or determine empirical

relationships among causal and response variables (if necessary), expert judgement, and

evaluation of downstream effects. To the extent allowed by the information available, EPA has
5

used elements of this process to produce the information contained in this document. The values

for both causal (total nitrogen, total phosphorus) and biological and physical response

(chlorophyll a, turbidity) variables represent a set of starting points for States and Tribes to use in

establishing their own criteria in standards to protect uses.

In its water quality standards regulations, EPA recommends that States and Tribes

establish numerical criteria based on section 304(a) guidance, section 304(a) guidance modified to

reflect site-specific conditions, or other scientifically defensible methods. For many pollutants,

such as toxic chemicals, EPA expects that section 304(a) guidance will provide an appropriate

level of protection without further modification in most cases. EPA has also published methods

for modifying 304(a) criteria on a site-specific basis, such as the water effect ratio, where sitespecific conditions warrant modification to achieve the intended level of protection. For nutrients,

however, EPA expects that, in most cases, it will be necessary for States and authorized Tribes to

identify with greater precision the nutrient levels that protect aquatic life and recreational uses. 

This can be achieved through development of criteria modified to reflect conditions at a smaller

geographic scale than an ecoregion such as a subecoregion, the State or Tribe level, or specific

class of waterbodies. Criteria refinement can occur by grouping data or performing data analyses

at these smaller geographic scales. Refinement can also occur through further consideration of

other elements of criteria development, such as published literature or models.

The values presented in this document generally represent nutrient levels that protect

against the adverse effects of nutrient overenrichment and are based on information available to

the Agency at the time of this publication. However, States and Tribes should critically evaluate

this information in light of the specific designated uses that need to be protected. For example,

more sensitive uses may require more stringent values as criteria to ensure adequate protection. 

On the other hand, overly stringent levels of protection against the adverse effects of cultural

eutrophication may actually fall below levels that represent the natural load of nutrients for certain

waterbodies. In cases such as these, the level of nutrients specified may not be sufficient to

support a productive fishery. In the criteria derivation process, it is important to distinguish

between the natural load associated with a specific waterbody and current reference conditions,

using historical data and expert judgement. These elements of the nutrient criteria derivation

process are best addressed by States and Tribes with access to information and local expertise. 

Therefore, EPA strongly encourages States and Tribes to use the information contained in this

document and to develop more refined criteria according to the methods described in EPA’s

technical guidance manuals for specific waterbody types.

To assist in the process of further refinement of nutrient criteria, EPA has established ten

Regional Technical Advisory Groups (experts from EPA Regional Offices and States/Tribes). In

the process of refining criteria, States and authorized Tribes need to provide documentation of

data and analyses, along with a defensible rationale, for any new or revised nutrient criteria they

submit to EPA for review and approval. As part of EPA’s review of State and Tribal standards,

EPA intends to seek assurance from the RTAG that proposed criteria are sufficient to protect

uses.
6

In the process of using the information and recommendations contained in this document,

as well as additional information, to develop numerical criteria or procedures to translate narrative

criteria, EPA encourages States and Tribes to:

C Address both chemical causal variables and early indicator response variables. Causal

variables are necessary to provide sufficient protection of uses before impairment occurs

and to maintain downstream uses. Early response variables are necessary to provide

warning signs of possible impairment and to integrate the effects of variable and

potentially unmeasured nutrient loads.

C Include variables that can be measured to determine if standards are met, and variables

that can be related to the ultimate sources of excess nutrients.

C Identify appropriate periods of duration (i.e., how long) and frequency (i.e., how often) of

occurrence in addition to magnitude (i.e., how much). EPA does not recommend

identifying nutrient concentrations that must be met at all times, rather a seasonal or

annual averaging period (e.g., based on weekly measurements) is considered appropriate. 

However, these seasonal or annual central tendency measures should apply each season or

each year, except under the most extraordinary of conditions (e.g., a 100 year flood).

3.0 AREA COVERED BY THIS DOCUMENT

The following sections provide a general description of the aggregate ecoregion and its

geographical boundaries. Descriptions of the level III ecoregions contained within the aggregate

ecoregion are also provided.

3.1 Description of Aggregate Ecoregion IX - Southeastern Temperate Forested Plains

and Hills

Region IX is composed of irregular plains and hills. Originally, the Southeastern

Temperate Forested Plains and Hills (IX) was mostly forested in contrast to the South Central

Cultivated Great Plains (V); areas of savannah and grassland also occurred. Today, Region IX is

a mosaic of forest, cropland, and pasture. The Southeastern Temperate Forested Plains and Hills

(IX) is not as arable as the South Central Cultivated Great Plains (V) or the Corn Belt and

Northern Great Plains (VI). However, there is much more cropland than in the more rugged

Central and Eastern Forested Uplands (XI). Lateritic soils are common and are a contrast to the

soils of the surrounding regions. Areas of depleted soils are found in Region IX. Major poultry

and aquaculture operations occur locally in the Southeastern Temperate Forested Plains and Hills

(IX). Stream quality in the Southeastern Temperate Forested Plains and Hills (IX) has been

significantly affected by urban, suburban, and industrial development as well as by poultry,

livestock, silviculture, and aquaculture operations. Downstream of sewage treatment plants,

poultry farms, and hog operations, nutrient levels and fecal coliform bacteria concentrations can

be very high. There are a large number of intensive chicken, turkey, and hog operations in Region

IX; effluent from intensive livestock production poses a substantial eutrophication threat to

surface waters. In contrast, streams draining relatively undisturbed and forested watersheds have

low median concentrations of fecal coliform bacteria, sulfate, dissolved solids, and phosphorus. 

Silviculture, agriculture, and urban development have impacted suspended sediment levels in
7

streams especially where soils are highly erodible. Coal mining has degraded water quality and

affected aquatic biota in several areas including southern Iowa, northern Missouri, and eastern

Pennsylvania. Excessive PCB and DDT concentrations have been detected in the Schuylkill River

of Pennsylvania and have led to advisories against local fish consumption.

3.2 Geographical Boundaries of Aggregate Ecoregion IX

Ecoregion IX is an expansive region encompassing parts of twenty States (Figure 1). The

region’s northeastern border is the southeastern corner of Pennsylvania. The region runs

southward through the States of Maryland, Virginia, North Carolina, South Carolina, Georgia and

Florida. Only the northwestern corner of Florida is included in the region. West of Georgia, the

region includes parts of Alabama, Mississippi, Louisiana and Texas. The region runs north up

through the middle of the country to include parts of Oklahoma, Arkansas, Kansas, Missouri,

Tennessee, Kentucky, Iowa, Illinois and Indiana. The northwestern boundary of the region is

approximately described by the southeastern corner of Iowa, the southern half of Illinois and the

southwestern third of Indiana.

Figure 1. Aggregate Ecoregion IX
8

3.3 Level III Ecoregions Within Aggregate Ecoregion IX

There are eleven Level III ecoregions contained within Aggregate Ecoregion IX (Figure 2). The

following provides brief descriptions of the climate, vegetation cover, topography, and other

ecological information pertaining to these subecoregions.

29. Central Oklahoma/Texas Plains

The Central Oklahoma/Texas Plains ecoregion is a transition area between the once prairie, now

winter wheat growing regions to the west, and the forested low mountains of eastern Oklahoma. 

The region does not possess the arability and suitability for crops such as corn and soybeans that

are common in the Central Irregular Plains to the northeast. Transitional “cross-timbers” (little

bluestem grassland with scattered blackjack oak and post oak trees) is the native vegetation, and

presently rangeland and pastureland comprise the predominant land cover. Oil extraction has

been a major activity in this region for over eighty years.

33. East Central Texas Plains

Also called the Claypan Area, this region of irregular plains was originally covered by a post oak

savanna vegetation, in contrast to the more open prairie-type regions to the north, south and west

and the piney woods to the east. The bulk of this region is now used for pasture and range.

Figure 2. Aggregate Ecoregion IX with level III ecoregions shown.
9

35. South Central Plains

Locally termed the “piney woods”, this region of mostly irregular plains was once blanketed by

oak-hickory-pine forests, but is now predominantly in loblolly and shortleaf pine. Only about one

sixth of the region is in cropland, whereas about two thirds is in forests and woodland. Lumber

and pulpwood production are major economic activities

37. Arkansas Valley

A region of mostly forested valleys and ridges, the physiography of the Arkansas Valley is much

less irregular than that of the Boston Mountains to the north and the Ouachita Mountains to the

south, but is more irregular than the ecological regions to the west and east. About one fourth of

the region is grazed and roughly one tenth is cropland. In the Arkansas Valley, even streams that

have been relatively unimpacted by human activities have considerably lower dissolved oxygen

levels, and hence support different biological communities, than those of most of the adjacent

regions.

40. Central Irregular Plains

The Central Irregular Plains has a mix of land use types and tends to be topographically more

irregular than the Western Corn Belt Plains to the north, where most of the land is in crops;

however, the region is less irregular and less forest covered than the ecoregions to the south and

east. The potential natural vegetation of this ecological region is a grassland/forest mosaic with

wider forested strips along the streams compared to the region to the north. The mix of land use

activities in the Central Irregular Plains also includes mining operations of high-sulfur bituminous

coal. The disturbance of these coal strata in southern Iowa and northern Missouri has degraded

water quality and affected aquatic biota.

45. Piedmont

Considered the nonmountainous portion of the old Appalachians Highland by physiographers, the

northeast-southwest trending Piedmont ecoregion comprises a transitional area between the

mostly mountainous ecoregions of the Appalachians to the northwest and the flat coastal plain to

the southeast. Once largely cultivated, much of this region has reverted to pine and hardwood

woodlands.

64. Northern Piedmont

The Northern Piedmont is transitional region of low rounded hills, irregular plains, and open

valleys in contrast to the low mountains of ecoregions to the north and west and the flat coastal

plains of the ecoregion to the east. Potential natural vegetation here was predominantly

Appalachian oak forest as compared to the mostly oak-hickory-pine forests of the Piedmont

ecoregion to the southwest. 

65. Southeastern Plains

These irregular plains have a mosaic of cropland, pasture, woodland, and forest. Natural

vegetation is mostly oak-hickory-pine and Southern mixed forest. The Cretaceous or Tertiaryage sands, silts, and clays of the region contrast geologically to the older igneous and

metamorphic rocks of the Piedmont, and the older limestone, chert, and shale found in the Interior

Plateau. Streams in this area are relatively low-gradient and sandy-bottomed.
10

71. Interior Plateau

The Interior Plateau is a diverse ecoregion extending from southern Indiana and Ohio to northern

Alabama. Rock types are distinctly different from the coastal plain sands and alluvial deposits to

the west, and elevations are lower than the Appalachian ecoregions to the east. Mississippian to

Ordovician-age limestone, chert, sandstone, siltstone and shale compose the

landforms of open hills, irregular plains, and tablelands. The natural vegetation is primarily oakhickory forest, with some areas of bluestem prairie and cedar glades. The region has a diverse

fish fauna.

72. Interior River Lowland

The Interior River Lowland is made up of many wide, flat-bottomed terraced valleys, forested

valley walls, and dissected glacial till plains. In contrast to the generally rolling to slightly

irregular plains in adjacent ecological regions to the north, east and west, where most of the land

is cultivated for corn and soybeans, a little less than half of this area is in cropland, about 30

percent is in pasture, and the remainder is in pasture. 

74. Mississippi Valley Loess Plains

This ecoregion stretches from near the Ohio River in western Kentucky to Louisiana. It consists

primarily of irregular plains, with oak-hickory and oak-hickory-pine natural vegetation. Thick

loess tends to be the distinguishing characteristic. With flatter topography than the Southeastern

Plains ecoregion to the east, streams tend to have less gradient and more silty substrates. 

Agriculture is the dominant land use in the Kentucky and Tennessee portion of the region, while

in Mississippi there is a mosaic of forest and cropland.

Suggested ecoregional subdivisions or adjustments.

EPA recommends that the RTAG evaluate the adequacy of EPA nutrient ecoregional and

subecoregional boundaries and refine them as needed to reflect local conditions. 

4.0 DATA REVIEW FOR RIVERS AND STREAMS IN AGGREGATE ECOREGION

IX

The following section describes the nutrient data EPA has collected and analyzed for this

Ecoregion, including an assessment of data quantity and quality. The data tables present the data

for each causal parameter-- total phosphorus and total nitrogen (both reported and calculated

from TKN and nitrite/nitrate), and the primary response variables-- some measure of turbidity 

and chlorophyll a. These are the parameters which EPA considers essential to nutrient assessment

because the first two are the main causative agents of enrichment and the two response variables

are the early indicators of system enrichment for most of the surface waters (see Chapter 3 of the

Rivers and Streams Nutrient Criteria Technical Guidance Manual [U.S. EPA, 2000b] for a

complete discussion on choosing causal and response variables.)
11

4.1 Data Sources 

Data sets from Legacy STORET, NASQAN, NAWQA, Auburn University, and EPA

Regions 3, 5, and were used to assess nutrient conditions from1990 to1999. EPA recommends

that the RTAGs identify additional data sources that can be used to supplement the data sets listed

above. In addition, the RTAGs may utilize published literature values to support quantitative and

qualitative analyses.

4.2 Historical Data from Aggregate Ecoregion IX (TP, TN, Chl a and Turbidity)

EPA recommends that States/Tribes assess long-term trends observed over the past 50

years. This information may be obtained from scientific literature or documentation of historical

trends. To gain additional perspective on more recent trends, it is recommended that States and

Tribes assess nutrient trends over the last 10 years (e.g., what do seasonal trends indicate?)

4.3 QA/QC of Data Sources

An initial quality screen of data was conducted using the rules presented in Appendix C. 

Data remaining after screening for duplications and other QA measures (.e.g., poor or unreported

analytical records, sampling errors or omissions, stations associated with outfalls, storm water

sewers, hazardous waste sites) is the data used in statistical analyses.

The following States indicated that their data were sampled and analyzed using either

Standard methods or EPA approved methods: Florida, Georgia, Illinois, Iowa, Indiana,

Maryland, Missouri, North Carolina, South Carolina, Tennessee. Other States in Ecoregion IX

did not provide information at this time.

4.4 Data for All Rivers and Streams Within Aggregate Ecoregion IX 

Figure 3 shows the location of the sampling stations within each subecoregion. Table 1

presents all data records for all parameters for Aggregate Ecoregion IX and subecoregions within

the Aggregate Ecoregion. 

4.5 Statistical Analysis of Data

EPA’s Technical Guidance Manual for Developing Nutrient Criteria for Rivers and

Streams describes two ways of establishing a reference condition. One method is to choose the

upper 25th percentile (75th percentile) of a reference population of streams. This is the preferred

method to establish a reference condition. The 75th percentile was chosen by EPA since it is likely

associated with minimally impacted conditions, will be protective of designated uses, and provides

management flexibility. When reference streams are not identified, the second method is to

determine the lower 25th percentile of the population of all streams within a region. The 25th

percentile of the entire population was chosen by EPA to represent a surrogate for an actual

reference population. Data analyses to date indicate that the lower 25th percentile from an entire

population roughly approximates the 75th percentile for a reference population (see case studies
12

for Minnesota lakes in the Lakes and Reservoirs Nutrient Criteria Technical Guidance Document

[U.S. EPA, 2000a], the case study for Tennessee streams in the Rivers and Streams Nutrient

Criteria Technical Guidance Document [U.S. EPA, 2000b], and the letter from Tennessee

Department of Environment and Conservation to Geoffrey Grubbs [TNDEC, 2000]). New York

State has also presented evidence that the 25th percentile and the 75th percentile compare well

based on user perceptions of water resources (NYSDEC, 2000). 
13

Figure 3 Map of sampling locations within each level III ecoregion.
14

 Table 1. Rivers and Streams records for Aggregate Ecoregion IX - Southeastern Temperate Forested Plains and

Hills

Aggregate

Ecoregion

IX

Sub

ecoR 29

Sub

ecoR 33

Sub

ecoR 35

Sub

ecoR 37

Sub

ecoR 40

Sub

ecoR 45

# of Stream names 3,278 160 44 286 56 220 639

# of Stream Stations 256 73 465 93 445 1,298

Key Nutrient Parameters

(listed below)

 - # of records for Turbidity

(all methods)

115,125 1,631 203 8,137 2,226 3,569 36,404

- # of records for

Chlorophyll a (all methods)

+ Periphyton

16,756 698 521 889 2 229 858

- # of records for Total

Kjeldahl Nitrogen (TKN)

116,104 2,173 856 6,808 1,215 2,522 31,205

- # of records for Nitrate +

Nitrite (NO2 + NO3)

117,925 1,334 469 9,184 2,469 3,015 29,898

- # of records for Total

Nitrogen (TN)

13,749 351 80 317 123 390 1,014

- # of records for Total

Phosphorus (TP)

164,145 2,412 981 10,173 2,421 5,305 42,948

Total # of records for key

nutrient parameters 

543,804 8,599 3,110 35,508 8,456 15,030 142,327
15

Table 1(continued). Rivers and Streams records for Aggregate Ecoregion IX -

Southeastern Temperate Forested Plains and Hills

Sub 

ecoR 64

Sub 

ecoR 65

Sub 

ecoR 71

Sub 

ecoR 72

Sub 

ecoR 74

# of Stream names 284 1,001 213 309 103

# of Stream Stations 880 1,870 429 550 162

Key Nutrient Parameters (listed

below)

 - # of records for

Turbidity (all methods)

8,325 40,234 3,574 9,772 1,050

- # of records for

Chlorophyll a (all

methods) + Periphyton

3,397 9,336 606 194 24

- # of records for Total

Kjeldahl Nitrogen (TKN)

14,572 41,353 3,709 7,801 3,890

- # of records for Nitrate +

Nitrite (NO2 + NO3)

6,407 37,963 6,640 13,823 6,723

- # of records for Total

Nitrogen (TN)

2,396 6,382 206 2,424 66

- # of records for Total

Phosphorus (TP)

17,541 52,744 6,454 16,108 7,058

Total # of records for key

nutrient parameters 

52,638 180,012 21,189 50,122 18,811
16

Definitions used in filling Table 1

1. # of records refers to the total count of observations for that

parameter over the entire decade (1990-1999) for that particular

aggregate or subecoregion. These are counts for all seasons over

that decade.

2. # of stream stations refers to the total number of river and

stream stations within the aggregate or subecoregion from which

nutrient data was collected. Since streams and rivers can cross

ecoregional boundaries, it is important to note that only those

portions of a river or stream (and data associated with those

stations) that exist within the ecoregion are included within this

table.

Tables 2 and 3a-k present potential reference conditions for both the aggregate ecoregion

and the subecoregions using both methods. However, the reference stream column is left blank

because EPA does not have reference data and anticipates that States/Tribes will provide

information on reference streams. Appendix A provides a complete presentation of all descriptive

statistics for both the aggregate ecoregion and the level III subecoregion. 

4.6. Classification of River/Stream Type

It is anticipated that assessing the data by stream type will further reduce the variability in

the data analysis. There were no readily available classification data in the National datasets used

to develop these criteria. States and Tribes are strongly encouraged to classify their streams

before developing a final criterion. 

4.7. Summary of Data Reduction Methods

All descriptive statistics were calculated using the medians for each stream within

ecoregion IX, for which data existed. For example, if one stream had 300 observations for

phosphorus over the decade or one year’s time, one median resulted. Each median from each

stream was then used in calculating the percentiles for phosphorus for the aggregate nutrient

ecoregion/subecoregion (level III ecoregion) by season and year (Figure 4a & b).
17

 Table 2. Reference conditions for aggregate ecoregion IX streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 1,609 0 4.825 0.3

NO2 + NO3 (mg/L) 1,671 0 9.78 0.125

TN (mg/L) - calculated NA 0 15.60 0.425

TN (mg/L) - reported 274 0.24 12.4 0.692

TP (ug/L) 2,104 0 2,400 36.56

Turbidity (NTU) 476 0.175 162.5 7.02

Turbidity (FTU) 1,143 0.475 148 5.7

Turbidity (JCU) 97 0.713 164.5 3.53

Chlorophyll a (ug/L) -F 71 0.225 36.73 2.25

Chlorophyll a (ug/L) -S 235 0 78.9 0.93

Chlorophyll a (ug/L) -T 70 0 93.92 0.53

Periphyton Chl a (mg/m2) 6 11 62 20.35

 P25: 25th percentile of all data

P75: 75th percentile of all data

** as determined by the Regional Technical Assistance Groups (RTAGs)

+ Median for all seasons’ 25th percentiles. E.g. this value was calculated from

four seasons’ 25th percentiles. If the seasonal 25th percentile (P25) TP values

are - spring 10ug/L, summer 15ug/L, fall 12ug/L, and winter 5ug/L, the

median value of all seasons P25 will be 11ug/L. 

++ N = largest value reported for a decade / Season.

TN calculated is based on the sum of TKN + NO2+NO3. 

TN reported is actual TN value reported in the database for one sample.

F Chlorophyll a measured by Fluorometric method with acid correction.

S Chlorophyll a measured by Spectrophotometric method with acid correction.

T Chlorophyll a b c measured by Trichromatic method.

NA Not Applicable 

zz calculated medians from less than 3 seasons’ data.

Table(s) 3a.-k. present the potential reference conditions for rivers and streams in the

Level III subecoregions within the Aggregate Ecoregion. The footnotes for Table 2 apply to

tables 3a-k.
18

 Table 3a. Reference conditions for level III ecoregion 29 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 93 W 0.05 2.058 0.4

NO2 + NO3 (mg/L) 78 W 0.01 4.7 0.078

TN (mg/L) - calculated NA 0.06 6.758 0.478

TN (mg/L) - reported 20 0.39 3.228 0.68

TP (ug/L) 100 W 2.5 1,332.5 37.5

Turbidity (NTU) 6 2.738 27.4 3.713

Turbidity (FTU) 53 F 0.9 95.5 8.825

Turbidity (JCU) 17 2 164.5 9.125

Chlorophyll a (ug/L) -F 1 z 13 13 13 zz

Chlorophyll a (ug/L) -S 32 0.25 33.8 1.238

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) -- – – –

Table 3b. Reference conditions for level III ecoregion 33 streams. 

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 30 0.285 2.48 0.543

NO2 + NO3 (mg/L) 21 0.04 7.582 0.138

TN (mg/L) - calculated NA 0.325 10.062 0.681

TN (mg/L) - reported 3 0.935 5.688 0.935

TP (ug/L) 28 45 1,880 100

Turbidity (NTU) 1 z 0.5 0.5 0.5 zz

Turbidity (FTU) 7 4.3 90.25 10.9

Turbidity (JCU) 0 – – –

Chlorophyll a (ug/L) -F 0 – – –

Chlorophyll a (ug/L) -S 24 0.25 21.15 0.733 

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) -- – – –
19

 Table 3c. Reference conditions for level III ecoregion 35 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 124 0.05 3.213 0.44

NO2 + NO3 (mg/L) 140 0.005 6.245 0.067

TN (mg/L) - calculated NA 0.055 9.458 0.507

TN (mg/L) - reported 19 0.33 3.738 0.385

TP (ug/L) 164 2.5 1900 50

Turbidity (NTU) 82 2.863 106.5 9.513

Turbidity (FTU) 57 S/W 2 69.375 6.938

Turbidity (JCU) 8 z 3.5 127 13

Chlorophyll a (ug/L) -F 0 – – –

Chlorophyll a (ug/L) -S 44 0.25 34.213 0.566

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) 2 z 3.13 5.85 3.13 zz

Table 3d. Reference conditions for level III ecoregion 37 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 26 0.23 2.315 0.53

NO2 + NO3 (mg/L) 37 0.015 6.479 0.075

TN (mg/L) - calculated NA 0.245 8.794 0.605

TN (mg/L) - reported 8 0.55 1.75 0.683

TP (ug/L) 39 5 1410 42.5

Turbidity (NTU) 23 3.15 71.5 6.95

Turbidity (FTU) 17 S/W 5.15 53.5 13.5

Turbidity (JCU) 7 2 61.5 15.25

Chlorophyll a (ug/L) -F 0 – – --

Chlorophyll a (ug/L) -S 1 z 4.5 4.5 4.5 zz

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) -- – – –
20

Table 3e. Reference conditions for level III ecoregion 40 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 81 0.184 4.175 0.625

NO2 + NO3 (mg/L) 137 0.003 9.203 0.23

TN (mg/L) - calculated NA 0.187 13.378 0.855

TN (mg/L) - reported 31 0.28 6.225 0.712

TP (ug/L) 146 10 2090 92.5

Turbidity (NTU) 53 7.825 96.575 15.5

Turbidity (FTU) 78 2.2 73.625 12.25

Turbidity (JCU) 19 4.9 115.25 10.5

Chlorophyll a (ug/L) -F 12 0.65 24.8 2.75 zz

Chlorophyll a (ug/L) -S 16 2.025 22.55 5.488

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) -- – – –

Table 3f. Reference conditions for level III ecoregion 45 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+

P75 - all seasons

TKN (mg/L) 338 0.025 3.1 0.234

NO2 + NO3 (mg/L) 327 0.003 8.813 0.177

TN (mg/L) - calculated NA 0.028 11.913 0.411

TN (mg/L) - reported 18 0.238 2.57 0.615

TP (ug/L) 436 0 1425 30

Turbidity (NTU) 35 2.25 35.45 5.713

Turbidity (FTU) 356 1.125 108 7.488

Turbidity (JCU) 10 1.9 26.05 5.95

Chlorophyll a (ug/L) -F 33 1 36.725 3.3

Chlorophyll a (ug/L) -S 11 1.8 25 3.493

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) -- – – –
21

Table 3g. Reference conditions for level III ecoregion 64 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 125 0.05 2.843 0.3

NO2 + NO3 (mg/L) 77 0.225 8.362 0.995

TN (mg/L) - calculated NA 0.275 11.205 1.295

TN (mg/L) - reported 76 0.56 12.4 2.225

TP (ug/L) 181 1.25 1545 40

Turbidity (NTU) 33 1.05 23 2.825

Turbidity (FTU) 46 F 0.625 13.088 3.15

Turbidity (JCU) 2 4.4 5.425 4.4

Chlorophyll a (ug/L) -F 0 – – –

Chlorophyll a (ug/L) -S 18 0.443 8.41 1.205

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) 6 F 17 62 20.35

Table 3h. Reference conditions for level III ecoregion 65 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 554 0 4.138 0.3

NO2 + NO3 (mg/L) 518 0 5.077 0.095

TN (mg/L) - calculated NA 0 9.215 0.395

TN (mg/L) - reported 65 0.33 2.938 0.618

TP (ug/L) 650 0 1735 22.5

Turbidity (NTU) 173 0.25 100 6.2

Turbidity (FTU) 426 0.475 88.75 4.338

Turbidity (JCU) 21 S 1.875 88 6.55

Chlorophyll a (ug/L) -F 14 0.25 8.8 1.438

Chlorophyll a (ug/L) -S 74 0 65.552 0.049

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) -- – – –
22

Table 3i. Reference conditions for level III ecoregion 71 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 65 0.05 2.045 0.284

NO2 + NO3 (mg/L) 109 0.008 5.373 0.345

TN (mg/L) - calculated NA 0.058 7.418 0.629

TN (mg/L) - reported 10 0.625 4.35 0.8

TP (ug/L) 117 2.5 1280 30

Turbidity (NTU) 47 0.875 104.138 6.975

Turbidity (FTU) 22 1.8 44.075 7.3

Turbidity (JCU) 21 S 0.813 15.75 1.325

Chlorophyll a (ug/L) -F 9 2.6 15.4 3.85

Chlorophyll a (ug/L) -S 14 0.25 7.75 1.5

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) -- – – –

Table 3j. Reference conditions for level III ecoregion 72 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 154 0.025 4.318 0.539

NO2 + NO3 (mg/L) 173 0.003 8.625 0.215

TN (mg/L) - calculated NA 0.028 12.943 0.754

TN (mg/L) - reported 21 0.47 7.088 1.669

TP (ug/L) 183 1.25 1,600 83.125

Turbidity (NTU) 5 13.5 39 15

Turbidity (FTU) 118 1.15 126.75 6.263

Turbidity (JCU) 3 29.75 37 29.75

Chlorophyll a (ug/L) -F 2 z 1.5 6.55 1.5 zz

Chlorophyll a (ug/L) -S 1 5.74 5.74 5.74

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) -- – – –
23

Table 3k. Reference conditions for level III ecoregion 74 streams.

 Parameter

No. of

Streams 

 N ++

Reported values 25th Percentiles based

on all seasons data for

the Decade

Reference Streams **

Min Max P25-all seasons+ P75 - all seasons

TKN (mg/L) 31 0.137 2.875 0.364

NO2 + NO3 (mg/L) 65 0.022 2.515 0.14

TN (mg/L) - calculated NA 0.159 5.39 0.504

TN (mg/L) - reported 3 0.6 1.25 0.6

TP (ug/L) 70 2.5 1,162.5 75

Turbidity (NTU) 18 6.3 91.75 16.25

Turbidity (FTU) 11 3.25 78.375 13.5

Turbidity (JCU) 5 1.775 18.25 7.55

Chlorophyll a (ug/L) -F 2 F z 2 2.1 2 zz

Chlorophyll a (ug/L) -S 0 – – –

Chlorophyll a (ug/L) -T -- – – –

Periphyton Chl a (mg/m2) -- – – –
24

Definitions used in filling Tables 2 and 3 - Reference Condition tables

Definitions used in filling Tables 2 and 3 - Reference Condition tables

1. Number of Streams in Table 2 refers to the largest number of streams and rivers for which data existed

for a given season within an aggregate nutrient ecoregion.

2. Number of Streams in Table 3 refers to the number of streams and rivers for which data existed for the

summer months since summer is generally when the greatest amount of nutrient sampling is conducted. If

another season greatly predominates, notification is made (s=spring, f=fall, w=winter).

3. Medians. All values (min, max, and 25th percentiles) included in the table are based on waterbody

medians. All data for a particular parameter within a stream for the decade were reduced to one median for

that stream. This prevents over-representation of individual waterbodies with a great deal of data versus those

with fewer data points within the statistical analysis.

4. 25th percentile for all seasons is calculated by taking the median of the 4 seasonal 25th percentiles. If a

season is missing, the median was calculated with 3 seasons of data. If less than 3 seasons were used to

derive the median, the entry is flagged (z).

5. A 25th percentile for a season is best derived with data from a minimum of 4 streams/season. However,

this table provides 25th percentiles that were derived with less than 4 streams/season in order to retain all

information for all seasons. In calculating the 25th percentile for a season with less than 4 stream medians,

the statistical program automatically used the minimum value within the less-than-4 population. If less than

4 streams were used in developing a seasonal quartile and or all-seasons median, the entry is flagged (zz).
25

Figure 4a. Illustration of data reduction process for stream data.
26

Select 25th Percentile

from Distribution

of Median

Values

25th 25% 25% 25%

Winter Spring Summer Fall

Calculate Median

Value of the

25th Percentiles

for the Four Seasons

Half values

Below Median

Half values

Above Median

25%

Season D

25%

Season A

25%

Season B

25%

Season C

Median = Reference Condition for the Ecoregion

TP

TN

TKN

NO2+NO3

Chl a

Turbidity

} 25%

} 25%

Figure 4b. Illustration of reference condition calculation.
27

Preferred Data Choices and Recommendations When Data Are Missing

1. Where data are missing or are very low in total records for a given parameter, use 25th

percentiles for parameters within an adjacent, similar subecoregion within the same aggregate

nutrient ecoregion or when a similar subecoregion can not be determined, use the the 25th

percentile for the Aggregate ecoregion or consider the lowest 25th percentile from a subecoregion

(level III) within the aggregate nutrient ecoregion. The rationale being that without data, one may

assume that the subecoregion in question may be as sensitive as the most sensitive subecoregion

within the aggregate.

2. TN calculated: When reported Total Nitrogen (TN) median values are lacking or very low in

comparison to TKN and Nitrate/Nitrite-N values, the medians for TKN and nitrite/nitrate-N were

added, resulting in a calculated TN value. The number of samples (N) for calculated TN is not

filled in since it is represented by two subsamples of data: TKN and nitrite/nitrate-N. Therefore,

N/A is placed in this box. 

3. TN reported: This is the median based on reported values for TN from the database.

4. Chlorophyll a: Medians based on all methods are reported, however, the acid corrected

medians are preferred to the uncorrected medians. In developing a reference condition from a

particular method, it is recommended that the method with the most observations be used. 

Fluorometric and Spectrophotometric are preferred over all other methods. However, when no 

data exist for Fluorometric and Spectrophotometric methods, Trichromatic values may be used.

Data from the variance techniques are not interchangeable.

5. Periphyton: Where periphyton data exist, record them separately For periphyton-dominated

streams, a measure of periphyton chlorophyll is a more appropriate response variable than

planktonic chlorophyll a. See Table 4, p. 101 of the Rivers and Streams Nutrient Technical

Guidance Manual (U. S. EPA, 2000b) for values of periphyton and planktonic chlorophyll a

related to eutrophy in streams.

6. Secchi depth: The 75th percentile is reported for Secchi depth since this is the only variable

for which the value of the parameter increases with greater clarity. (For lakes and reservoirs

only.)

7. Turbidity units: All turbidity units from all methods are reported. FTUs and NTUs are

preferred over JCUs. If FTUs and NTUs do not exist, use JCUs. These units are not

interchangeable. Turbidity is chosen as a response variable in streams since it can be an indicator

of increasing algal biomass due to nutrient enrichment. See pages 32 -33 of the Rivers and

Streams Nutrient Technical Guidance Manual for a discussion of turbidity and correlations with

algal growth.

8. Lack of data: A dash (-) represents missing, inadequate, or inconclusive data. A zero (0) is

reported if the reported median for a parameter is 0 or if the component value is below detection. 
28

5.0 REFERENCE SITES AND CONDITIONS IN AGGREGATE ECOREGION IX

Reference conditions represent the natural, least impacted conditions or what is

considered to be the most attainable conditions. This section compares the different reference

conditions determined from the two methods and establishes which reference condition is most

appropriate.

A priori determination of reference sites. The preferred method for establishing reference

condition is to choose the upper percentile of an a priori population of reference streams. States

and Tribes are encouraged to identify reference conditions based on this method.

Statistical determination of reference conditions (25th percentile of entire database.) See Tables 2

and 3a-k in section 4.0. 

RTAG discussion and rationale for selection of reference sites and conditions in Ecoregion IX.

The RTAG should compare the results derived from the two methods described above and

present a rationale for the final selection of reference sites. 

6.0 MODELS USED TO PREDICT OR VERIFY RESPONSE PARAMETERS

The RTAG is encouraged to identify and apply relevant models to support nutrient criteria

development. The following are three scenarios under which models may be used to derive

criteria or support criteria development.

C Models for predicting correlations between causal and response variables

C Models used to verify reference conditions based on percentiles

C Regression models used to predict reference conditions in impacted areas

7.0 FRAMEWORK FOR REFINING RECOMMENDED NUTRIENT CRITERIA

FOR RIVERS AND STREAMS IN AGGREGATE ECOREGION IX

Information on each of the following six weight of evidence factors is important to refine the

criteria presented in this document. All elements should be addressed in developing criteria, as is

expressed in our nutrient criteria technical guidance manuals. It is our expectation that EPA

Regions, States, and Tribes (as RTAGs) will consider these elements as States/Tribes develop

their criteria. This section should be viewed as a work sheet (sections are left blank for this

purpose) to assist in the refinement of nutrient criteria. If many of these elements are ultimately

unaddressed, EPA may rely on the proposed reference conditions presented in Tables 3a-k and

other literature and information readily available to the HQ nutrient team to develop nutrient

water quality recommendations for this ecoregion.
29

7.1 Example Worksheet for Developing Aggregate Ecoregion and Subecoregion

Nutrient Criteria 

C Literature sources

C Historical data and trends

C Reference condition

C Models

C RTAG expert review and consensus

C Downstream effects
30

7.2 Tables of Refined Nutrient Water Quality Criteria for Aggregate Ecoregion IX and

Level III Subecoregions for TP, TN, Chl a, Turbidity (where sufficient data exist)

Aggregate Ecoregion IX- Southeastern

Temperate Forested Hills and Plains

Proposed Criterion

Total Phosphorus (μg/L)

Total Nitrogen (mg/L)

Chlorophyll a (μg/L or mg/m2))

Turbidity (NTU or other units)

Other (Index; other parameter such as DO)

C Literature sources

C Historical data and trends

C Reference condition

C Models

C RTAG expert review and consensus
31

C Downstream effects

Ecoregion #29 Central Oklahoma/Texas

Plains

Proposed Criterion

Total Phosphorus (μg/L)

Total Nitrogen (mg/L)

Chlorophyll a (μg/L or mg/m2))

Turbidity (NTU or other units)

Other (Index; other parameter such as DO)

7.3 Setting Seasonal Criteria

The recommendations presented in this document are based in part on medians of all the

25th percentile seasonal data (decadal), and as such are reflective of all seasons and not one

particular season or year. It is recommended that States and Tribes monitor in all seasons to best

assess compliance with the resulting criterion. States/Tribes may choose to develop criteria which

reflect each particular season or a given year when there is significant variability between

seasons/years or designated uses that are specifically tied to one or more seasons of the year (e.g.,

recreation, fishing). Using the tables in Appendix A and B, one can set reference conditions based

on a particular season or year and then develop a criterion based on each individual season. 

Obviously, this option is season-specific and would also require increased monitoring within each

season to assess compliance. 
32

7.4 When Data/Reference Conditions are Lacking

When data are unavailable to develop a reference condition for a particular parameter(s)

within a subecoregion, EPA recommends one of three options: 1. Use data from a similar

neighboring subecoregion. E.g., If data are few or nonexistent for the northern cascades, consider

using the data and reference condition developed for the cascades; or 2. Use the 25th perecentiles

for the Aggregate ecoregion or 3. Consider using the lowest of the yearly medians for that

parameter calculated for all the subecoregions within the Aggregate Ecoregion.

7.5 Site-specific Criteria Development 

Criteria may be refined in a number of ways. The best way to refine criteria is to follow

the critical elements of criteria development as well as to refer to the Rivers and Streams Nutrient

Criteria Technical Guidance Manual (U.S. EPA, 2000b).

The Technical Guidance Manual presents sections on each of the following factors to

consider in setting criteria

- refinements to ecoregions (Section 2.3)

- classification of waterbodies (Chapter 2)

- setting seasonal criteria to reflect major seasonal climate differences and accounting for 

significant or cyclical precipitation events (high flow/low flow conditions) (Chapter 4).

8.0 LITERATURE CITED

NYSDEC (New York State Department of Environment and Conservation). 2000. 

Memorandum from Scott Kishbaugh to Jay Bloomfield, September 26, 2000, regarding

reference lakes for nutrient criteria.

TNDEC (Tennessee Department of Environment and Conservation). 2000. Letter to

Geoff Grubbs, October 5, 2000, containing comments on draft nutrient criteria

recommendations.

U.S. EPA. 2000a. Nutrient Criteria Technical Guidance Manual: Lakes and Reservoirs,

U.S. Environmental Protection Agency, Washington, DC. EPA-822-B00-001.

U.S. EPA. 2000b. Nutrient Criteria Technical Guidance Manual: Rivers and Streams,

U.S. Environmental Protection Agency, Washington, DC. EPA-822-B00-002.
33

9.0 APPENDICES

A. Descriptive Statistics Data Tables for Aggregate Ecoregion

B. Descriptive Statistics Data Tables for Level III Subecoregions within Aggregate Ecoregion 

C. Quality Control/Quality Assurance Rules
APPENDIX A

Descriptive Statistics Data Tables for Aggregate Ecoregion
 

 Aggregate Nutrient Ecoregion: IX 1

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Fluo_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 54 8.03 .250 36.35 9.19 1.25 114 0.40 1.80 4.10 8.80 29.8

 SPRING 37 8.27 .000 37.10 8.19 1.35 99 0.25 2.70 4.50 11.7 24.5

 SUMMER 71 10.7 .625 95.10 12.9 1.53 120 1.00 3.65 7.00 12.8 26.8

 WINTER 18 4.40 .200 13.90 3.92 0.92 89 0.20 1.10 3.40 7.90 13.9

 Aggregate Nutrient Ecoregion: IX 2

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_C_F_ug_L_Med

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1 3.40 3.40 3.40 . . . 3.40 3.40 3.40 3.40 3.40

 SPRING 2 6.68 1.90 11.45 6.75 4.78 101 1.90 1.90 6.68 11.5 11.5

 SUMMER 1 9.60 9.60 9.60 . . . 9.60 9.60 9.60 9.60 9.60

 WINTER 1 0.78 .775 0.78 . . . 0.78 0.78 0.78 0.78 0.78

 Aggregate Nutrient Ecoregion: IX 3

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_A_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 187 6.03 .000 78.60 9.79 0.72 162 0.25 0.90 2.85 7.50 19.8

 SPRING 206 6.54 .000 98.52 11.1 0.77 170 0.00 0.97 3.38 7.95 25.0

 SUMMER 235 7.44 .000 79.20 11.5 0.75 154 0.00 1.03 3.48 9.00 25.4

 WINTER 178 3.13 .000 34.80 4.80 0.36 153 0.00 0.25 1.65 3.48 12.0

 Aggregate Nutrient Ecoregion: IX 4

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_U_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1 0.03 .025 0.03 . . . 0.03 0.03 0.03 0.03 0.03

 SPRING 1 4.37 4.37 4.37 . . . 4.37 4.37 4.37 4.37 4.37

 SUMMER 1 0.02 .021 0.02 . . . 0.02 0.02 0.02 0.02 0.02

 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 5

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Tric_U_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 48 9.75 .000 97.78 18.2 2.63 187 0.00 1.06 1.91 10.5 43.4

 SPRING 44 9.22 .000 95.06 17.2 2.59 186 0.00 1.60 3.47 7.11 40.8

 
 

 SUMMER 70 12.0 .000 92.78 19.9 2.38 166 0.00 0.00 3.94 13.0 63.9

 WINTER 50 2.09 .000 16.90 3.76 0.53 180 0.00 0.00 1.08 2.34 12.5

 Aggregate Nutrient Ecoregion: IX 6

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chlb_Phyto_C_F_ug_L_Med

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1 0.40 .400 0.40 . . . 0.40 0.40 0.40 0.40 0.40

 SPRING 2 0.31 .200 0.43 0.16 0.11 51 0.20 0.20 0.31 0.43 0.43

 SUMMER 1 0.70 .700 0.70 . . . 0.70 0.70 0.70 0.70 0.70

 WINTER 1 0.05 .050 0.05 . . . 0.05 0.05 0.05 0.05 0.05

 Aggregate Nutrient Ecoregion: IX 7

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chlb_Phyto_Spec_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 0 . . . . . . . . . . .

 SPRING 1 0.24 .236 0.24 . . . 0.24 0.24 0.24 0.24 0.24

 SUMMER 0 . . . . . . . . . . .

 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 8

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter DIP_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 217 175 .000 9600.00 742 50.4 423 5.00 16.3 50.0 115 568

 SPRING 180 64.1 .000 812.00 115 8.58 180 5.00 10.0 30.0 70.0 224

 SUMMER 230 65.9 .000 930.00 102 6.70 154 5.00 12.5 37.3 81.5 183

 WINTER 170 63.3 .000 1000.00 108 8.29 171 5.00 13.8 35.0 75.0 200

 Aggregate Nutrient Ecoregion: IX 9

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter DO_mg_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1437 7.73 .000 17.88 1.87 0.05 24 4.30 6.75 8.00 8.75 10.4

 SPRING 1417 8.57 1.80 13.80 1.61 0.04 19 5.83 7.60 8.60 9.50 11.2

 SUMMER 1579 6.83 .000 13.50 1.67 0.04 24 3.50 6.00 7.10 7.83 9.10

 WINTER 1240 10.5 2.90 14.70 1.60 0.05 15 7.73 9.64 10.5 11.6 13.0

 
 

 Aggregate Nutrient Ecoregion: IX 10

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter NO2_NO3_mg_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1527 0.74 .000 10.00 1.30 0.03 175 0.01 0.09 0.27 0.74 3.20

 SPRING 1529 0.71 .000 9.80 1.15 0.03 161 0.03 0.14 0.32 0.73 2.95

 SUMMER 1671 0.73 .000 9.03 1.20 0.03 165 0.01 0.12 0.29 0.74 3.11

 WINTER 1378 0.83 .000 9.76 1.28 0.03 155 0.03 0.14 0.36 0.90 3.41

 Aggregate Nutrient Ecoregion: IX 11

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Org_P_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 15 70.4 22.5 188.30 50.2 13.0 71 22.5 37.6 51.1 84.1 188

 SPRING 0 . . . . . . . . . . .

 SUMMER 15 52.4 6.77 115.44 28.5 7.37 54 6.77 27.4 48.7 66.3 115

 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 12

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Orthophosphate_T_as_P_ug_L_Med

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 100 117 5.00 1600.00 261 26.1 223 5.00 17.5 40.0 98.8 490

 SPRING 103 82.9 5.00 1095.00 162 15.9 195 5.00 17.5 37.5 80.0 238

 SUMMER 103 104 5.00 1307.50 202 19.9 194 5.00 16.3 41.3 103 310

 WINTER 101 77.6 5.00 815.00 113 11.3 146 5.00 20.0 40.0 100 225

 Aggregate Nutrient Ecoregion: IX 13

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter TKN_mg_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1404 0.62 .000 5.40 0.55 0.01 89 0.13 0.30 0.50 0.78 1.50

 SPRING 1452 0.60 .000 5.00 0.53 0.01 88 0.12 0.30 0.48 0.73 1.47

 SUMMER 1609 0.64 .000 4.30 0.48 0.01 74 0.15 0.35 0.53 0.81 1.45

 WINTER 1397 0.53 .000 4.65 0.43 0.01 80 0.12 0.30 0.44 0.65 1.20

 Aggregate Nutrient Ecoregion: IX 14

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter TN_mg_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 213 1.87 .180 12.50 2.06 0.14 110 0.35 0.67 1.17 2.20 6.03

 SPRING 204 2.02 .300 11.00 1.98 0.14 98 0.51 0.71 1.26 2.27 6.55

 
 

 SUMMER 274 2.31 .200 12.30 2.47 0.15 107 0.38 0.72 1.37 3.03 8.62

 WINTER 211 1.95 .275 13.00 2.05 0.14 105 0.40 0.67 1.20 2.30 6.16

 Aggregate Nutrient Ecoregion: IX 15

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter TP_ug_L_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1811 157 .000 2420.00 255 5.99 163 5.00 35.0 75.0 160 645

 SPRING 1864 131 .000 2360.00 234 5.42 178 5.00 38.1 70.0 130 465

 SUMMER 2104 148 .000 2400.00 226 4.92 152 7.50 40.0 80.0 160 530

 WINTER 1685 122 .000 2400.00 199 4.86 163 5.00 30.0 65.0 125 430

 Aggregate Nutrient Ecoregion: IX 16

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Turb_FTU_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 1059 11.0 .000 180.00 13.4 0.41 122 2.00 4.55 7.70 12.8 29.5

 SPRING 1113 14.1 .650 123.00 13.5 0.40 95 2.50 6.40 11.0 16.8 38.9

 SUMMER 1143 14.6 .800 160.00 15.6 0.46 106 2.50 5.85 10.0 17.0 45.2

 WINTER 991 14.5 .300 136.00 15.4 0.49 106 2.25 5.55 9.70 18.0 43.0

 Aggregate Nutrient Ecoregion: IX 17

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Turb_JCU_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 89 21.9 .600 171.00 31.9 3.38 145 1.10 3.25 11.0 24.0 90.0

 SPRING 88 20.1 .700 158.00 28.9 3.08 144 1.50 3.46 10.7 23.5 88.8

 SUMMER 97 25.8 .725 173.00 36.6 3.72 142 1.05 3.60 11.3 30.0 127

 WINTER 92 18.9 1.10 96.00 18.8 1.96 100 1.50 6.70 13.5 21.5 60.8

 Aggregate Nutrient Ecoregion: IX 18

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Turb_NTU_Median

 SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 FALL 366 15.1 .250 113.00 16.4 0.86 109 2.00 5.50 9.55 19.0 55.0

 SPRING 379 20.5 .100 175.00 20.4 1.05 99 2.25 8.70 15.0 25.0 57.0

 SUMMER 476 20.2 .000 212.00 25.2 1.16 125 2.00 6.20 12.3 24.0 72.5

 WINTER 323 19.6 .250 150.00 20.2 1.12 103 2.00 7.85 14.0 24.5 55.0

 
APPENDIX B

Descriptive Statistics Data Tables for Level III Subecoregions within Aggregate Ecoregion
 Aggregate Nutrient Ecoregion: IX 1

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Fluo_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 1 15.6 15.6 15.60 . . . 15.6 15.6 15.6 15.6 15.6

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 1 10.4 10.4 10.40 . . . 10.4 10.4 10.4 10.4 10.4

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 11 4.44 .400 26.40 7.48 2.25 169 0.40 0.90 1.60 4.20 26.4

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 12 11.1 .900 23.20 7.19 2.07 65 0.90 4.60 12.4 16.9 23.2

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 26 11.4 1.00 36.35 10.9 2.14 96 1.10 3.00 8.20 16.5 32.0

 45 SPRING 23 10.9 1.00 37.10 9.22 1.92 84 1.13 2.70 10.5 15.8 24.5

 45 SUMMER 33 10.6 .625 41.00 9.61 1.67 91 1.00 3.60 9.00 11.5 30.9

 45 WINTER 6 7.99 1.50 13.90 3.96 1.62 50 1.50 7.50 8.03 9.00 13.9

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 0 . . . . . . . . . . .

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 9 3.18 .250 8.00 3.10 1.03 98 0.25 0.63 2.20 6.30 8.00

 65 SPRING 12 3.70 .250 8.80 2.33 0.67 63 0.25 2.25 4.06 4.70 8.80

 65 SUMMER 14 13.0 1.00 95.10 24.0 6.42 184 1.00 4.00 6.59 8.00 95.1

 Aggregate Nutrient Ecoregion: IX 2

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Fluo_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 12 2.61 .200 8.80 2.46 0.71 94 0.20 0.63 2.30 3.75 8.80

 71 FALL 2 11.9 8.30 15.40 5.02 3.55 42 8.30 8.30 11.9 15.4 15.4

 71 SPRING 2 4.95 .000 9.90 7.00 4.95 141 0.00 0.00 4.95 9.90 9.90

 71 SUMMER 9 8.52 2.60 20.20 6.29 2.10 74 2.60 3.85 6.35 11.5 20.2

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 3 5.77 1.80 8.80 3.59 2.07 62 1.80 1.80 6.70 8.80 8.80
 72 SPRING 0 . . . . . . . . . . .

 72 SUMMER 2 2.75 1.20 4.30 2.19 1.55 80 1.20 1.20 2.75 4.30 4.30

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 2 2.05 2.00 2.10 0.07 0.05 3 2.00 2.00 2.05 2.10 2.10

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 3

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_C_F_ug_L_Med

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 0 . . . . . . . . . . .

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 0 . . . . . . . . . . .

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 0 . . . . . . . . . . .

 45 SPRING 0 . . . . . . . . . . .

 45 SUMMER 0 . . . . . . . . . . .

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 0 . . . . . . . . . . .

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 0 . . . . . . . . . . .

 65 SPRING 0 . . . . . . . . . . .

 65 SUMMER 0 . . . . . . . . . . .
 Aggregate Nutrient Ecoregion: IX 4

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_C_F_ug_L_Med

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 0 . . . . . . . . . . .

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 1 1.90 1.90 1.90 . . . 1.90 1.90 1.90 1.90 1.90

 71 SUMMER 0 . . . . . . . . . . .

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 1 3.40 3.40 3.40 . . . 3.40 3.40 3.40 3.40 3.40

 72 SPRING 1 11.5 11.5 11.45 . . . 11.5 11.5 11.5 11.5 11.5

 72 SUMMER 1 9.60 9.60 9.60 . . . 9.60 9.60 9.60 9.60 9.60

 72 WINTER 1 0.78 .775 0.78 . . . 0.78 0.78 0.78 0.78 0.78

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 5

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_A_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 25 4.84 .250 19.20 5.37 1.07 111 0.25 1.00 3.18 5.15 16.6

 29 SPRING 29 8.68 .250 32.80 9.76 1.81 112 0.25 1.33 5.28 11.3 30.6

 29 SUMMER 32 9.99 .250 54.50 11.5 2.03 115 0.25 3.73 7.36 12.4 44.3

 29 WINTER 30 6.35 .250 34.80 8.71 1.59 137 0.25 1.15 3.33 7.80 27.8

 33 FALL 22 6.62 .250 47.00 11.1 2.37 168 0.25 0.68 1.92 5.98 23.0

 33 SPRING 24 4.37 .250 15.00 4.32 0.88 99 0.25 1.01 2.53 8.49 11.0

 33 SUMMER 24 6.04 .250 27.30 7.49 1.53 124 0.25 0.44 3.19 10.8 20.1

 33 WINTER 21 2.85 .250 9.38 2.68 0.58 94 0.25 0.79 1.78 5.28 7.11

 35 FALL 41 5.59 .250 78.60 12.3 1.93 221 0.25 0.25 2.28 6.86 12.8

 35 SPRING 41 4.42 .250 18.90 4.38 0.68 99 0.25 1.16 4.15 5.89 11.4

 35 SUMMER 44 5.47 .250 49.53 8.24 1.24 151 0.25 0.88 2.73 7.10 17.4

 35 WINTER 38 2.79 .250 13.60 3.40 0.55 122 0.25 0.25 1.92 3.19 12.8

 37 FALL 1 6.00 6.00 6.00 . . . 6.00 6.00 6.00 6.00 6.00

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 1 3.00 3.00 3.00 . . . 3.00 3.00 3.00 3.00 3.00

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 11 10.1 2.45 18.90 5.58 1.68 55 2.45 5.45 9.95 15.4 18.9

 40 SPRING 11 11.3 3.80 26.20 7.74 2.33 68 3.80 5.53 7.98 15.9 26.2

 40 SUMMER 16 11.9 1.60 26.40 7.41 1.85 62 1.60 6.80 11.8 15.8 26.4

 40 WINTER 6 3.50 1.40 10.10 3.29 1.34 94 1.40 1.50 2.55 2.90 10.1

 45 FALL 4 7.90 2.60 19.80 7.99 4.00 101 2.60 3.49 4.60 12.3 19.8

 45 SPRING 6 12.0 1.80 25.00 7.69 3.14 64 1.80 9.43 10.4 15.1 25.0

 45 SUMMER 11 20.7 .800 67.93 22.4 6.75 108 0.80 3.00 15.7 22.0 67.9

 45 WINTER 0 . . . . . . . . . . .
 64 FALL 21 2.56 .635 9.43 2.43 0.53 95 0.67 0.94 1.50 3.00 7.63

 64 SPRING 21 5.80 1.50 47.53 10.2 2.23 176 1.87 2.29 2.54 4.00 19.0

 64 SUMMER 18 2.36 .250 7.39 1.68 0.40 71 0.25 1.41 1.79 3.00 7.39

 64 WINTER 18 1.56 .250 4.13 0.92 0.22 59 0.25 1.00 1.20 1.89 4.13

 65 FALL 49 7.67 .000 51.90 12.1 1.72 157 0.00 0.48 3.00 8.05 38.3

 65 SPRING 64 7.30 .000 98.52 16.6 2.08 227 0.00 0.10 2.20 5.74 35.9

 65 SUMMER 74 6.75 .000 79.20 13.3 1.55 198 0.00 0.00 2.01 7.00 31.0

 Aggregate Nutrient Ecoregion: IX 6

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_A_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 59 2.45 .000 14.55 3.77 0.49 154 0.00 0.00 0.59 3.18 12.0

 71 FALL 12 3.74 .250 10.00 3.16 0.91 84 0.25 1.50 2.50 5.31 10.0

 71 SPRING 9 2.53 .250 5.50 1.55 0.52 61 0.25 1.50 3.00 3.00 5.50

 71 SUMMER 14 5.35 .625 21.00 5.20 1.39 97 0.63 2.00 4.25 6.00 21.0

 71 WINTER 6 1.13 .250 2.00 0.59 0.24 52 0.25 1.00 1.00 1.50 2.00

 72 FALL 1 8.00 8.00 8.00 . . . 8.00 8.00 8.00 8.00 8.00

 72 SPRING 1 0.50 .500 0.50 . . . 0.50 0.50 0.50 0.50 0.50

 72 SUMMER 1 5.74 5.74 5.74 . . . 5.74 5.74 5.74 5.74 5.74

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 7

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_U_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .
 40 FALL 0 . . . . . . . . . . .

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 0 . . . . . . . . . . .

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 0 . . . . . . . . . . .

 45 SPRING 0 . . . . . . . . . . .

 45 SUMMER 0 . . . . . . . . . . .

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 1 0.03 .025 0.03 . . . 0.03 0.03 0.03 0.03 0.03

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 1 0.02 .021 0.02 . . . 0.02 0.02 0.02 0.02 0.02

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 0 . . . . . . . . . . .

 65 SPRING 1 4.37 4.37 4.37 . . . 4.37 4.37 4.37 4.37 4.37

 65 SUMMER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 8

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Phyto_Spec_U_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 0 . . . . . . . . . . .

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 0 . . . . . . . . . . .

 71 SUMMER 0 . . . . . . . . . . .

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 0 . . . . . . . . . . .

 72 SPRING 0 . . . . . . . . . . .

 72 SUMMER 0 . . . . . . . . . . .

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 9

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Tric_U_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .
 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 3 4.17 1.25 10.00 5.05 2.92 121 1.25 1.25 1.25 10.0 10.0

 40 SPRING 2 3.79 1.25 6.33 3.59 2.54 95 1.25 1.25 3.79 6.33 6.33

 40 SUMMER 5 15.9 8.50 28.00 8.48 3.79 53 8.50 8.50 13.5 21.0 28.0

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 4 18.2 3.69 40.90 16.6 8.32 92 3.69 5.91 14.0 30.4 40.9

 45 SPRING 5 19.9 2.50 37.50 14.2 6.36 71 2.50 13.7 14.7 31.4 37.5

 45 SUMMER 10 31.8 3.09 92.78 31.3 9.89 98 3.09 5.90 26.8 34.1 92.8

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 14 1.83 1.00 4.19 0.82 0.22 45 1.00 1.35 1.60 2.03 4.19

 64 SPRING 14 3.24 1.86 5.20 0.98 0.26 30 1.86 2.65 3.02 3.94 5.20

 64 SUMMER 14 3.46 1.28 10.99 2.57 0.69 74 1.28 2.08 2.71 3.34 11.0

 64 WINTER 14 1.53 .960 3.02 0.55 0.15 36 0.96 1.19 1.31 1.93 3.02

 65 FALL 23 14.4 .000 97.78 23.8 4.96 166 0.00 0.00 4.07 14.8 58.4

 65 SPRING 22 11.1 .000 95.06 22.5 4.80 203 0.00 0.00 3.47 7.65 45.4

 65 SUMMER 37 9.21 .000 76.55 18.7 3.08 203 0.00 0.00 0.00 9.33 63.9

 Aggregate Nutrient Ecoregion: IX 10

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chla_Tric_U_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 34 1.87 .000 16.68 3.75 0.64 200 0.00 0.00 0.00 2.53 12.5

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 0 . . . . . . . . . . .

 71 SUMMER 2 8.27 7.62 8.92 0.92 0.65 11 7.62 7.62 8.27 8.92 8.92

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 1 27.1 27.1 27.10 . . . 27.1 27.1 27.1 27.1 27.1

 72 SPRING 0 . . . . . . . . . . .

 72 SUMMER 1 25.1 25.1 25.10 . . . 25.1 25.1 25.1 25.1 25.1

 72 WINTER 1 16.9 16.9 16.90 . . . 16.9 16.9 16.9 16.9 16.9

 74 FALL 3 0.09 .065 0.12 0.03 0.01 27 0.07 0.07 0.10 0.12 0.12

 74 SPRING 1 8.97 8.97 8.97 . . . 8.97 8.97 8.97 8.97 8.97

 74 SUMMER 1 10.2 10.2 10.20 . . . 10.2 10.2 10.2 10.2 10.2

 74 WINTER 1 2.41 2.41 2.41 . . . 2.41 2.41 2.41 2.41 2.41
 Aggregate Nutrient Ecoregion: IX 11

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chlb_Phyto_C_F_ug_L_Med

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 0 . . . . . . . . . . .

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 0 . . . . . . . . . . .

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 0 . . . . . . . . . . .

 45 SPRING 0 . . . . . . . . . . .

 45 SUMMER 0 . . . . . . . . . . .

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 0 . . . . . . . . . . .

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 0 . . . . . . . . . . .

 65 SPRING 0 . . . . . . . . . . .

 65 SUMMER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 12

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chlb_Phyto_C_F_ug_L_Med

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 0 . . . . . . . . . . .

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 1 0.20 .200 0.20 . . . 0.20 0.20 0.20 0.20 0.20

 71 SUMMER 0 . . . . . . . . . . .

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 1 0.40 .400 0.40 . . . 0.40 0.40 0.40 0.40 0.40
 72 SPRING 1 0.43 .425 0.43 . . . 0.43 0.43 0.43 0.43 0.43

 72 SUMMER 1 0.70 .700 0.70 . . . 0.70 0.70 0.70 0.70 0.70

 72 WINTER 1 0.05 .050 0.05 . . . 0.05 0.05 0.05 0.05 0.05

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 13

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chlb_Phyto_Spec_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 0 . . . . . . . . . . .

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 0 . . . . . . . . . . .

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 0 . . . . . . . . . . .

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 0 . . . . . . . . . . .

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 0 . . . . . . . . . . .

 45 SPRING 0 . . . . . . . . . . .

 45 SUMMER 0 . . . . . . . . . . .

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 0 . . . . . . . . . . .

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 0 . . . . . . . . . . .

 65 SPRING 1 0.24 .236 0.24 . . . 0.24 0.24 0.24 0.24 0.24

 65 SUMMER 0 . . . . . . . . . . .
 Aggregate Nutrient Ecoregion: IX 14

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Chlb_Phyto_Spec_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 0 . . . . . . . . . . .

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 0 . . . . . . . . . . .

 71 SUMMER 0 . . . . . . . . . . .

 71 WINTER 0 . . . . . . . . . . .

 72 FALL 0 . . . . . . . . . . .

 72 SPRING 0 . . . . . . . . . . .

 72 SUMMER 0 . . . . . . . . . . .

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 15

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter DIP_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 11 45.3 .000 135.00 44.3 13.4 98 0.00 10.0 35.0 65.0 135

 29 SPRING 9 30.1 5.00 80.00 24.5 8.16 81 5.00 10.0 25.0 35.0 80.0

 29 SUMMER 10 27.8 5.00 92.50 28.1 8.89 101 5.00 6.25 18.8 40.0 92.5

 29 WINTER 9 30.1 5.00 70.00 24.8 8.25 82 5.00 7.50 25.0 55.0 70.0

 33 FALL 4 676 60.0 1412.50 683 342 101 60.0 95.0 615 1256 1413

 33 SPRING 4 323 92.5 750.00 310 155 96 92.5 93.8 225 553 750

 33 SUMMER 4 365 82.5 837.50 342 171 94 82.5 116 270 614 838

 33 WINTER 4 483 52.5 1000.00 479 239 99 52.5 76.3 440 890 1000

 35 FALL 11 146 5.00 790.00 281 84.6 192 5.00 5.00 20.0 65.0 790

 35 SPRING 12 48.4 5.00 295.00 83.0 24.0 171 5.00 10.6 13.8 53.8 295

 35 SUMMER 12 109 5.00 930.00 264 76.2 242 5.00 10.0 12.5 51.3 930

 35 WINTER 12 60.4 6.25 360.00 102 29.6 170 6.25 13.8 20.0 47.5 360

 37 FALL 3 45.0 20.0 70.00 25.0 14.4 56 20.0 20.0 45.0 70.0 70.0

 37 SPRING 3 47.5 12.5 100.00 46.3 26.7 97 12.5 12.5 30.0 100 100

 37 SUMMER 3 84.2 42.5 165.00 70.0 40.4 83 42.5 42.5 45.0 165 165

 37 WINTER 3 98.3 25.0 202.50 92.7 53.5 94 25.0 25.0 67.5 203 203

 40 FALL 22 58.0 18.7 293.02 56.3 12.0 97 18.9 26.1 47.6 65.0 87.5

 40 SPRING 11 60.5 12.5 120.00 30.6 9.24 51 12.5 35.0 65.0 82.5 120

 40 SUMMER 23 59.1 4.30 176.33 48.4 10.1 82 7.41 18.1 47.5 100 145

 40 WINTER 11 81.5 23.8 215.00 62.0 18.7 76 23.8 25.0 70.0 125 215

 45 FALL 16 44.0 5.00 275.00 68.0 17.0 155 5.00 8.75 15.0 62.5 275

 45 SPRING 16 25.2 5.00 102.50 28.5 7.12 113 5.00 5.00 12.5 32.5 103

 45 SUMMER 16 50.9 5.00 362.50 87.8 21.9 173 5.00 8.13 25.0 43.8 363
 45 WINTER 16 25.7 5.00 125.00 29.6 7.39 115 5.00 7.50 18.1 34.8 125

 64 FALL 48 516 5.00 9600.00 1512 218 293 15.0 70.0 143 285 1551

 64 SPRING 25 171 5.00 812.00 221 44.2 129 5.00 37.0 75.0 204 752

 64 SUMMER 62 68.3 4.25 412.50 68.2 8.66 100 7.00 21.0 50.0 96.0 183

 64 WINTER 18 103 16.8 310.25 82.1 19.4 80 16.8 40.0 86.3 133 310

 65 FALL 45 33.0 5.00 250.00 50.9 7.59 154 5.00 5.00 12.5 25.0 115

 65 SPRING 45 24.8 5.00 205.00 35.8 5.33 144 5.00 7.50 10.0 25.0 80.0

 65 SUMMER 45 34.6 5.00 360.00 60.1 8.96 174 5.00 7.50 12.5 30.0 120

 Aggregate Nutrient Ecoregion: IX 16

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter DIP_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 45 22.8 5.00 150.00 30.3 4.52 133 5.00 5.00 12.5 22.5 65.0

 71 FALL 13 94.1 7.50 295.00 87.9 24.4 93 7.50 35.0 56.3 135 295

 71 SPRING 13 48.2 7.50 162.50 46.9 13.0 97 7.50 15.0 30.0 55.0 163

 71 SUMMER 13 80.6 10.0 322.50 85.7 23.8 106 10.0 20.0 60.0 80.0 323

 71 WINTER 12 65.4 17.5 200.00 59.2 17.1 91 17.5 30.0 40.0 85.0 200

 72 FALL 41 86.0 .000 240.00 66.6 10.4 78 5.00 35.2 70.0 128 220

 72 SPRING 39 52.9 .000 160.00 35.6 5.69 67 0.00 30.0 50.0 70.0 125

 72 SUMMER 39 70.0 .000 185.50 45.6 7.30 65 4.00 35.0 62.5 95.0 170

 72 WINTER 37 66.9 .000 140.00 38.4 6.32 57 1.00 40.0 60.0 93.5 135

 74 FALL 3 38.3 5.00 75.00 35.1 20.3 92 5.00 5.00 35.0 75.0 75.0

 74 SPRING 3 33.3 15.0 47.50 16.6 9.61 50 15.0 15.0 37.5 47.5 47.5

 74 SUMMER 3 38.8 11.3 60.00 25.0 14.4 64 11.3 11.3 45.0 60.0 60.0

 74 WINTER 3 30.0 5.00 50.00 22.9 13.2 76 5.00 5.00 35.0 50.0 50.0

 Aggregate Nutrient Ecoregion: IX 17

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter DO_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 83 7.88 4.50 10.70 1.36 0.15 17 5.55 7.00 7.95 8.85 9.75

 29 SPRING 82 8.19 4.00 11.45 1.31 0.14 16 6.10 7.60 8.20 8.80 10.4

 29 SUMMER 87 6.91 3.60 9.45 1.21 0.13 17 4.85 6.00 7.00 7.80 8.40

 29 WINTER 98 11.3 2.90 14.70 1.76 0.18 16 8.10 10.4 11.5 12.5 14.1

 33 FALL 26 7.24 2.90 9.45 1.44 0.28 20 4.88 6.20 7.45 8.15 9.30

 33 SPRING 31 7.54 5.00 9.90 1.15 0.21 15 5.20 6.88 7.65 8.35 9.40

 33 SUMMER 26 6.55 3.40 10.60 1.69 0.33 26 3.80 5.70 6.60 7.40 9.75

 33 WINTER 30 9.76 8.10 12.20 1.02 0.19 10 8.25 9.00 9.60 10.3 11.7

 35 FALL 151 6.62 1.20 11.10 1.75 0.14 27 3.40 5.68 6.70 7.70 9.30

 35 SPRING 144 7.56 2.80 11.80 1.61 0.13 21 5.40 6.69 7.40 8.48 10.6

 35 SUMMER 146 5.58 1.20 9.60 1.66 0.14 30 2.40 4.55 5.75 6.80 7.95

 35 WINTER 139 9.52 4.55 13.30 1.53 0.13 16 6.90 8.60 9.50 10.3 12.5

 37 FALL 33 6.72 2.50 9.60 1.71 0.30 26 3.43 6.00 6.60 7.83 9.60

 37 SPRING 27 8.15 6.15 10.53 1.22 0.24 15 6.63 7.35 7.90 9.25 10.3

 37 SUMMER 32 5.94 2.20 8.45 1.53 0.27 26 2.60 5.18 6.08 6.85 8.40
 37 WINTER 28 10.6 6.20 13.80 1.58 0.30 15 7.48 9.80 10.9 11.7 12.3

 40 FALL 104 7.37 1.25 17.88 2.20 0.22 30 4.10 5.96 7.41 8.58 10.8

 40 SPRING 90 9.34 4.25 13.80 1.38 0.15 15 7.20 8.75 9.43 10.1 11.5

 40 SUMMER 115 6.74 .200 13.10 1.83 0.17 27 3.30 5.88 6.70 7.85 9.37

 40 WINTER 75 11.8 6.30 13.80 1.33 0.15 11 9.21 11.4 12.0 12.7 13.5

 45 FALL 344 8.24 1.70 10.95 1.02 0.06 12 6.40 7.90 8.30 8.80 9.70

 45 SPRING 367 8.93 5.60 12.00 1.01 0.05 11 7.20 8.30 8.93 9.50 10.7

 45 SUMMER 371 7.28 1.50 12.00 1.03 0.05 14 5.40 6.90 7.43 7.85 8.50

 45 WINTER 264 10.7 8.80 14.10 0.83 0.05 8 9.50 10.2 10.6 11.2 12.1

 64 FALL 115 10.2 6.50 13.85 1.26 0.12 12 8.00 9.40 10.3 10.9 12.2

 64 SPRING 91 10.5 3.30 12.90 1.58 0.17 15 7.30 10.0 10.8 11.6 12.4

 64 SUMMER 167 8.63 6.05 13.20 1.13 0.09 13 6.80 7.98 8.60 9.10 10.9

 64 WINTER 69 12.4 9.13 14.10 1.07 0.13 9 10.3 11.9 12.8 13.1 13.7

 65 FALL 352 7.08 .400 11.60 1.79 0.10 25 3.25 6.24 7.55 8.30 9.30

 65 SPRING 371 7.73 1.80 11.90 1.64 0.09 21 4.70 6.83 7.90 8.80 10.1

 65 SUMMER 402 6.20 .450 10.63 1.66 0.08 27 2.80 5.65 6.55 7.25 8.10

 Aggregate Nutrient Ecoregion: IX 18

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter DO_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 330 9.57 4.10 13.20 1.51 0.08 16 6.90 8.60 9.80 10.6 11.8

 71 FALL 93 8.04 .000 12.50 2.09 0.22 26 4.00 7.45 8.20 9.20 11.0

 71 SPRING 79 9.49 4.70 12.40 1.22 0.14 13 7.70 8.75 9.50 10.1 11.6

 71 SUMMER 95 7.36 2.50 10.10 1.46 0.15 20 4.70 6.40 7.60 8.50 9.45

 71 WINTER 78 11.0 7.68 14.60 1.28 0.15 12 8.80 10.2 10.9 11.8 13.0

 72 FALL 84 7.55 2.33 11.80 2.04 0.22 27 4.00 6.30 7.63 8.95 11.0

 72 SPRING 83 9.43 7.30 12.40 1.04 0.11 11 8.05 8.80 9.20 10.1 11.3

 72 SUMMER 84 6.26 .000 8.85 1.52 0.17 24 3.60 5.38 6.40 7.30 8.40

 72 WINTER 80 11.5 7.00 13.80 0.99 0.11 9 10.3 11.1 11.6 12.1 13.0

 74 FALL 52 7.71 1.60 11.90 1.78 0.25 23 3.90 6.80 8.25 8.70 9.88

 74 SPRING 52 8.55 5.85 12.15 1.31 0.18 15 6.60 7.55 8.55 9.39 10.5

 74 SUMMER 54 6.93 2.35 13.50 1.74 0.24 25 3.35 6.15 7.20 7.70 9.30

 74 WINTER 49 10.2 5.75 12.40 1.38 0.20 14 7.20 9.50 10.4 11.1 12.3

 Aggregate Nutrient Ecoregion: IX 19

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter NO2_NO3_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 74 0.57 .010 5.40 1.08 0.13 189 0.01 0.05 0.13 0.48 3.36

 29 SPRING 65 0.37 .010 3.75 0.60 0.07 164 0.03 0.09 0.15 0.39 1.41

 29 SUMMER 67 0.33 .000 6.20 0.79 0.10 235 0.01 0.07 0.13 0.35 0.92

 29 WINTER 78 0.46 .025 4.00 0.66 0.07 143 0.05 0.12 0.21 0.49 1.70

 33 FALL 24 2.31 .010 8.32 2.99 0.61 130 0.02 0.09 0.91 4.38 8.27

 33 SPRING 22 1.33 .093 5.43 1.67 0.36 125 0.11 0.21 0.68 1.67 5.35

 33 SUMMER 21 1.60 .010 6.84 2.30 0.50 144 0.02 0.11 0.35 2.04 6.60
 33 WINTER 25 2.13 .070 8.45 2.51 0.50 118 0.10 0.16 0.77 3.42 6.51

 35 FALL 142 0.56 .005 9.08 1.43 0.12 254 0.01 0.04 0.11 0.26 3.70

 35 SPRING 134 0.37 .005 4.45 0.72 0.06 195 0.03 0.09 0.15 0.32 1.51

 35 SUMMER 140 0.43 .005 6.15 0.92 0.08 212 0.01 0.06 0.14 0.29 2.65

 35 WINTER 143 0.33 .005 6.34 0.72 0.06 220 0.02 0.07 0.14 0.25 1.19

 37 FALL 35 0.57 .003 7.16 1.38 0.23 243 0.01 0.03 0.07 0.34 4.25

 37 SPRING 30 0.41 .025 4.92 0.89 0.16 215 0.05 0.10 0.17 0.32 1.25

 37 SUMMER 37 0.48 .005 6.84 1.27 0.21 265 0.01 0.05 0.13 0.23 4.05

 37 WINTER 32 0.52 .093 6.12 1.05 0.19 205 0.10 0.15 0.27 0.45 1.28

 40 FALL 125 0.82 .000 7.84 1.42 0.13 172 0.00 0.11 0.34 0.76 4.20

 40 SPRING 111 1.03 .005 9.80 1.59 0.15 153 0.05 0.26 0.51 1.01 4.92

 40 SUMMER 137 1.03 .000 9.03 1.72 0.15 167 0.00 0.20 0.50 0.83 5.63

 40 WINTER 78 1.25 .025 9.38 1.71 0.19 137 0.13 0.40 0.67 1.24 6.32

 45 FALL 315 0.73 .003 8.85 1.26 0.07 173 0.03 0.12 0.33 0.71 3.26

 45 SPRING 332 0.64 .000 9.30 1.03 0.06 162 0.04 0.19 0.37 0.64 2.23

 45 SUMMER 327 0.73 .003 7.00 1.14 0.06 157 0.01 0.17 0.37 0.75 3.11

 45 WINTER 241 0.70 .020 8.78 1.03 0.07 148 0.06 0.21 0.38 0.73 2.40

 64 FALL 62 2.24 .330 9.02 1.77 0.22 79 0.52 0.98 1.73 3.00 5.80

 64 SPRING 61 2.20 .110 7.70 1.76 0.23 80 0.55 0.96 1.63 2.70 6.24

 64 SUMMER 77 2.05 .120 6.27 1.47 0.17 72 0.23 1.01 1.69 2.80 5.57

 64 WINTER 53 2.74 .660 9.76 1.97 0.27 72 0.80 1.57 2.16 3.10 8.28

 65 FALL 439 0.45 .000 5.95 0.76 0.04 168 0.01 0.07 0.20 0.44 1.88

 65 SPRING 496 0.39 .000 5.46 0.57 0.03 147 0.01 0.10 0.20 0.43 1.50

 65 SUMMER 518 0.41 .000 4.70 0.62 0.03 152 0.01 0.09 0.21 0.45 1.66

 Aggregate Nutrient Ecoregion: IX 20

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter NO2_NO3_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 433 0.44 .000 4.10 0.60 0.03 138 0.01 0.10 0.23 0.51 1.57

 71 FALL 107 0.99 .003 10.00 1.50 0.14 151 0.03 0.20 0.44 1.35 2.72

 71 SPRING 94 1.05 .025 5.41 1.06 0.11 101 0.13 0.40 0.60 1.17 3.38

 71 SUMMER 109 0.98 .012 4.72 1.01 0.10 103 0.06 0.29 0.62 1.20 2.95

 71 WINTER 91 1.36 .003 5.34 1.19 0.13 88 0.11 0.49 1.04 1.72 4.20

 72 FALL 151 0.97 .000 5.70 1.24 0.10 127 0.01 0.14 0.44 1.40 3.75

 72 SPRING 124 1.53 .023 8.45 1.81 0.16 118 0.07 0.29 0.86 1.90 5.50

 72 SUMMER 173 1.13 .003 8.80 1.61 0.12 142 0.02 0.14 0.46 1.45 4.45

 72 WINTER 151 1.58 .003 9.00 1.84 0.15 116 0.05 0.39 0.83 2.13 5.98

 74 FALL 53 0.28 .005 1.05 0.23 0.03 81 0.04 0.14 0.21 0.33 0.69

 74 SPRING 60 0.52 .020 3.30 0.67 0.09 129 0.03 0.14 0.27 0.63 2.11

 74 SUMMER 65 0.48 .024 6.00 1.00 0.12 210 0.03 0.09 0.18 0.49 1.20

 74 WINTER 53 0.43 .033 1.73 0.41 0.06 95 0.08 0.15 0.27 0.55 1.55
 Aggregate Nutrient Ecoregion: IX 21

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Org_P_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 1 37.6 37.6 37.64 . . . 37.6 37.6 37.6 37.6 37.6

 29 SPRING 0 . . . . . . . . . . .

 29 SUMMER 1 36.5 36.5 36.48 . . . 36.5 36.5 36.5 36.5 36.5

 29 WINTER 0 . . . . . . . . . . .

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 0 . . . . . . . . . . .

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 0 . . . . . . . . . . .

 35 WINTER 0 . . . . . . . . . . .

 37 FALL 0 . . . . . . . . . . .

 37 SPRING 0 . . . . . . . . . . .

 37 SUMMER 0 . . . . . . . . . . .

 37 WINTER 0 . . . . . . . . . . .

 40 FALL 11 73.3 22.5 188.30 52.1 15.7 71 22.5 37.6 58.6 84.1 188

 40 SPRING 0 . . . . . . . . . . .

 40 SUMMER 12 53.7 23.1 115.44 25.3 7.30 47 23.1 36.4 49.8 64.3 115

 40 WINTER 0 . . . . . . . . . . .

 45 FALL 0 . . . . . . . . . . .

 45 SPRING 0 . . . . . . . . . . .

 45 SUMMER 0 . . . . . . . . . . .

 45 WINTER 0 . . . . . . . . . . .

 64 FALL 0 . . . . . . . . . . .

 64 SPRING 0 . . . . . . . . . . .

 64 SUMMER 0 . . . . . . . . . . .

 64 WINTER 0 . . . . . . . . . . .

 65 FALL 0 . . . . . . . . . . .

 65 SPRING 0 . . . . . . . . . . .

 65 SUMMER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 22

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Org_P_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 0 . . . . . . . . . . .

 71 FALL 0 . . . . . . . . . . .

 71 SPRING 0 . . . . . . . . . . .

 71 SUMMER 0 . . . . . . . . . . .

 71 WINTER 0 . . . . . . . . . . .
 72 FALL 3 70.6 34.6 138.53 58.9 34.0 83 34.6 34.6 38.7 139 139

 72 SPRING 0 . . . . . . . . . . .

 72 SUMMER 2 52.0 6.77 97.22 64.0 45.2 123 6.77 6.77 52.0 97.2 97.2

 72 WINTER 0 . . . . . . . . . . .

 74 FALL 0 . . . . . . . . . . .

 74 SPRING 0 . . . . . . . . . . .

 74 SUMMER 0 . . . . . . . . . . .

 74 WINTER 0 . . . . . . . . . . .

 Aggregate Nutrient Ecoregion: IX 23

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Orthophosphate_T_as_P_ug_L_Med

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 5 45.0 20.0 60.00 15.8 7.07 35 20.0 40.0 50.0 55.0 60.0

 29 SPRING 5 46.5 22.5 70.00 22.3 9.99 48 22.5 30.0 40.0 70.0 70.0

 29 SUMMER 5 54.3 25.0 97.50 26.9 12.0 50 25.0 43.8 47.5 57.5 97.5

 29 WINTER 4 90.9 31.3 225.00 91.0 45.5 100 31.3 34.4 53.8 148 225

 33 FALL 3 920 60.0 1600.00 786 454 85 60.0 60.0 1100 1600 1600

 33 SPRING 3 733 70.0 1095.00 575 332 78 70.0 70.0 1033 1095 1095

 33 SUMMER 3 822 103 1307.50 635 367 77 103 103 1055 1308 1308

 33 WINTER 3 522 70.0 815.00 397 229 76 70.0 70.0 680 815 815

 35 FALL 10 265 5.00 1600.00 525 166 198 5.00 12.5 40.0 95.0 1600

 35 SPRING 13 92.8 12.5 550.00 149 41.4 161 12.5 26.3 35.0 60.0 550

 35 SUMMER 13 153 10.0 897.50 295 81.9 193 10.0 20.0 32.5 70.0 898

 35 WINTER 13 50.4 12.5 130.00 36.4 10.1 72 12.5 30.0 37.5 70.0 130

 37 FALL 3 90.0 30.0 200.00 95.4 55.1 106 30.0 30.0 40.0 200 200

 37 SPRING 3 64.2 27.5 125.00 53.1 30.6 83 27.5 27.5 40.0 125 125

 37 SUMMER 3 95.8 47.5 185.00 77.3 44.6 81 47.5 47.5 55.0 185 185

 37 WINTER 3 102 30.0 225.00 107 61.9 106 30.0 30.0 50.0 225 225

 40 FALL 11 87.7 30.0 130.00 33.6 10.1 38 30.0 50.0 95.0 118 130

 40 SPRING 11 85.9 12.5 210.00 58.6 17.7 68 12.5 37.5 65.0 130 210

 40 SUMMER 11 88.5 20.0 150.00 39.8 12.0 45 20.0 55.0 90.0 120 150

 40 WINTER 11 104 30.0 240.00 68.9 20.8 66 30.0 40.0 95.0 170 240

 45 FALL 8 63.8 5.00 255.00 82.8 29.3 130 5.00 10.0 40.0 75.0 255

 45 SPRING 8 36.3 5.00 112.50 36.4 12.9 100 5.00 12.5 23.1 50.6 113

 45 SUMMER 7 74.3 7.50 240.00 82.8 31.3 111 7.50 15.0 31.3 110 240

 45 WINTER 8 38.0 5.00 115.00 38.4 13.6 101 5.00 9.38 22.5 60.0 115

 64 FALL 6 257 20.0 595.00 219 89.3 85 20.0 40.0 250 385 595

 64 SPRING 6 160 25.0 452.50 165 67.2 103 25.0 25.0 110 238 453

 64 SUMMER 6 128 5.00 285.00 113 46.0 88 5.00 21.5 118 220 285

 64 WINTER 6 96.3 20.0 180.00 65.8 26.9 68 20.0 27.5 95.0 160 180

 65 FALL 34 32.6 5.00 150.00 41.1 7.05 126 5.00 5.00 20.0 30.0 150

 65 SPRING 34 27.8 5.00 120.00 28.9 4.95 104 5.00 7.50 18.1 40.0 105

 65 SUMMER 34 36.0 5.00 310.00 57.4 9.85 160 5.00 10.0 16.9 29.5 120
 Aggregate Nutrient Ecoregion: IX 24

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Orthophosphate_T_as_P_ug_L_Med

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 34 29.5 5.00 155.00 31.4 5.39 107 5.00 7.50 15.6 35.0 90.0

 71 FALL 10 90.0 5.00 270.00 84.1 26.6 93 5.00 20.0 80.0 120 270

 71 SPRING 10 74.9 5.00 282.50 86.8 27.4 116 5.00 20.0 36.3 133 283

 71 SUMMER 10 114 5.00 575.00 169 53.6 149 5.00 17.5 77.5 95.0 575

 71 WINTER 9 111 21.3 260.00 83.4 27.8 75 21.3 50.0 90.0 130 260

 72 FALL 7 92.9 15.0 175.00 58.7 22.2 63 15.0 30.0 120 130 175

 72 SPRING 7 72.5 10.0 182.50 54.7 20.7 75 10.0 37.5 60.0 87.5 183

 72 SUMMER 8 117 20.0 255.00 69.4 24.5 60 20.0 77.5 110 141 255

 72 WINTER 7 103 20.0 157.50 50.1 18.9 49 20.0 50.0 120 140 158

 74 FALL 3 48.3 5.00 75.00 37.9 21.9 78 5.00 5.00 65.0 75.0 75.0

 74 SPRING 3 105 80.0 125.00 22.9 13.2 22 80.0 80.0 110 125 125

 74 SUMMER 3 53.3 10.0 100.00 45.1 26.0 85 10.0 10.0 50.0 100 100

 74 WINTER 3 66.7 17.5 102.50 44.0 25.4 66 17.5 17.5 80.0 103 103

 Aggregate Nutrient Ecoregion: IX 25

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter TKN_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 83 0.60 .050 1.75 0.33 0.04 54 0.17 0.40 0.55 0.79 1.20

 29 SPRING 83 0.65 .125 1.84 0.34 0.04 52 0.25 0.40 0.60 0.73 1.35

 29 SUMMER 83 0.64 .050 2.75 0.41 0.05 64 0.21 0.40 0.56 0.78 1.45

 29 WINTER 93 0.58 .050 2.28 0.33 0.03 58 0.19 0.38 0.56 0.65 1.16

 33 FALL 29 0.91 .240 5.40 0.91 0.17 100 0.35 0.57 0.71 0.97 1.60

 33 SPRING 33 0.83 .390 1.63 0.25 0.04 30 0.46 0.70 0.80 0.93 1.33

 33 SUMMER 30 0.83 .330 1.88 0.37 0.07 45 0.36 0.50 0.81 0.99 1.58

 33 WINTER 32 0.77 .200 3.08 0.50 0.09 65 0.29 0.52 0.62 1.00 1.30

 35 FALL 125 0.67 .010 2.61 0.40 0.04 59 0.23 0.43 0.60 0.80 1.45

 35 SPRING 110 0.71 .050 2.63 0.45 0.04 63 0.05 0.45 0.63 0.84 1.59

 35 SUMMER 124 0.78 .050 3.80 0.54 0.05 69 0.20 0.51 0.70 0.88 1.80

 35 WINTER 137 0.68 .050 4.65 0.60 0.05 89 0.20 0.40 0.55 0.74 1.38

 37 FALL 20 0.80 .200 1.80 0.47 0.10 58 0.22 0.50 0.67 1.19 1.68

 37 SPRING 19 0.98 .345 2.83 0.68 0.15 69 0.35 0.60 0.70 1.20 2.83

 37 SUMMER 24 0.82 .240 1.66 0.35 0.07 42 0.49 0.56 0.72 1.08 1.50

 37 WINTER 26 0.82 .220 3.60 0.84 0.16 102 0.22 0.43 0.55 0.78 3.37

 40 FALL 79 1.17 .175 5.00 0.95 0.11 81 0.45 0.60 0.90 1.27 4.55

 40 SPRING 76 1.08 .315 4.02 0.68 0.08 63 0.33 0.65 0.96 1.28 1.98

 40 SUMMER 81 1.11 .193 3.10 0.56 0.06 51 0.50 0.70 1.00 1.35 2.25

 40 WINTER 49 0.87 .125 4.33 0.73 0.10 84 0.30 0.50 0.60 0.89 2.30

 45 FALL 301 0.47 .025 3.20 0.42 0.02 90 0.10 0.24 0.31 0.56 1.23

 45 SPRING 328 0.45 .025 3.95 0.48 0.03 108 0.10 0.23 0.33 0.50 1.10

 45 SUMMER 338 0.49 .025 3.00 0.40 0.02 81 0.09 0.29 0.40 0.59 1.22

 45 WINTER 279 0.40 .025 1.84 0.28 0.02 69 0.10 0.23 0.35 0.50 1.04
 64 FALL 98 0.59 .050 3.01 0.51 0.05 87 0.10 0.30 0.43 0.80 1.85

 64 SPRING 98 0.60 .050 2.68 0.52 0.05 87 0.05 0.31 0.46 0.65 1.60

 64 SUMMER 125 0.59 .050 3.88 0.57 0.05 96 0.05 0.30 0.50 0.65 1.20

 64 WINTER 78 0.55 .100 1.90 0.38 0.04 69 0.15 0.30 0.42 0.70 1.50

 65 FALL 453 0.50 .000 4.10 0.38 0.02 75 0.10 0.30 0.42 0.60 1.10

 65 SPRING 515 0.49 .000 3.93 0.34 0.02 70 0.13 0.30 0.42 0.60 1.00

 65 SUMMER 554 0.58 .000 4.30 0.41 0.02 71 0.17 0.34 0.49 0.74 1.28

 Aggregate Nutrient Ecoregion: IX 26

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter TKN_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 492 0.45 .000 4.18 0.34 0.02 76 0.12 0.28 0.40 0.55 0.94

 71 FALL 72 0.71 .050 3.60 0.68 0.08 97 0.10 0.29 0.46 0.90 1.82

 71 SPRING 56 0.45 .035 1.58 0.31 0.04 68 0.05 0.27 0.40 0.54 1.00

 71 SUMMER 65 0.56 .110 2.47 0.41 0.05 73 0.15 0.30 0.46 0.75 1.20

 71 WINTER 48 0.47 .050 1.62 0.30 0.04 63 0.09 0.28 0.44 0.61 0.90

 72 FALL 120 0.93 .025 4.80 0.75 0.07 81 0.28 0.53 0.79 0.99 2.70

 72 SPRING 104 0.97 .025 4.80 0.75 0.07 77 0.30 0.60 0.80 1.07 2.30

 72 SUMMER 154 0.85 .025 3.84 0.45 0.04 53 0.30 0.55 0.84 1.04 1.44

 72 WINTER 134 0.68 .025 2.40 0.41 0.04 60 0.03 0.39 0.65 0.90 1.40

 74 FALL 24 0.72 .195 1.65 0.41 0.08 57 0.25 0.38 0.70 0.96 1.40

 74 SPRING 30 1.07 .110 5.00 1.30 0.24 122 0.16 0.35 0.58 1.25 4.85

 74 SUMMER 31 0.88 .093 4.10 0.76 0.14 87 0.26 0.40 0.67 1.05 2.30

 74 WINTER 29 0.67 .163 1.60 0.40 0.07 59 0.17 0.32 0.55 0.88 1.34

 Aggregate Nutrient Ecoregion: IX 27

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter TN_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 13 1.29 .450 2.80 0.81 0.22 63 0.45 0.80 1.00 1.17 2.80

 29 SPRING 14 1.26 .330 4.30 1.04 0.28 83 0.33 0.56 1.13 1.45 4.30

 29 SUMMER 20 0.80 .250 1.45 0.36 0.08 45 0.30 0.51 0.77 1.04 1.42

 29 WINTER 21 1.24 .520 3.66 0.70 0.15 56 0.59 0.88 0.95 1.50 2.00

 33 FALL 3 4.73 .600 7.70 3.69 2.13 78 0.60 0.60 5.90 7.70 7.70

 33 SPRING 3 2.60 1.10 4.30 1.61 0.93 62 1.10 1.10 2.40 4.30 4.30

 33 SUMMER 3 3.53 1.04 5.30 2.22 1.28 63 1.04 1.04 4.25 5.30 5.30

 33 WINTER 3 3.94 .830 6.08 2.75 1.59 70 0.83 0.83 4.90 6.08 6.08

 35 FALL 10 1.34 .300 4.90 1.71 0.54 128 0.30 0.35 0.68 0.81 4.90

 35 SPRING 12 0.75 .400 1.60 0.38 0.11 51 0.40 0.51 0.55 1.03 1.60

 35 SUMMER 19 1.49 .270 11.00 2.59 0.59 174 0.27 0.37 0.62 0.87 11.0

 35 WINTER 18 0.69 .360 2.58 0.52 0.12 76 0.36 0.41 0.52 0.67 2.58

 37 FALL 3 1.10 .600 1.90 0.70 0.40 64 0.60 0.60 0.80 1.90 1.90

 37 SPRING 3 1.06 .760 1.60 0.47 0.27 44 0.76 0.76 0.82 1.60 1.60

 37 SUMMER 8 0.94 .500 1.40 0.27 0.09 29 0.50 0.85 0.87 1.08 1.40

 37 WINTER 8 1.02 .450 2.15 0.57 0.20 56 0.45 0.61 0.84 1.33 2.15
 40 FALL 30 1.29 .180 5.10 1.04 0.19 81 0.25 0.72 0.98 1.45 3.83

 40 SPRING 19 1.93 .340 7.90 1.83 0.42 95 0.34 0.67 1.48 2.43 7.90

 40 SUMMER 31 1.38 .220 7.25 1.34 0.24 97 0.33 0.70 0.94 1.70 3.66

 40 WINTER 19 1.54 .490 5.20 1.23 0.28 80 0.49 0.75 1.06 1.95 5.20

 45 FALL 18 1.00 .200 2.98 0.68 0.16 69 0.20 0.56 0.70 1.30 2.98

 45 SPRING 17 0.95 .300 1.80 0.38 0.09 41 0.30 0.70 0.89 1.23 1.80

 45 SUMMER 18 0.93 .200 2.45 0.60 0.14 64 0.20 0.48 0.86 1.41 2.45

 45 WINTER 16 1.03 .275 2.69 0.61 0.15 60 0.28 0.67 0.84 1.29 2.69

 64 FALL 37 4.08 .567 12.50 3.30 0.54 81 0.63 1.65 3.12 4.02 11.0

 64 SPRING 38 4.07 .547 11.00 2.50 0.41 61 0.65 2.10 3.63 5.25 10.0

 64 SUMMER 76 4.84 .552 12.30 2.92 0.34 60 1.44 2.49 4.16 7.08 10.7

 64 WINTER 30 4.48 1.85 13.00 3.04 0.55 68 1.88 2.35 3.60 4.57 12.0

 65 FALL 64 1.00 .290 3.10 0.59 0.07 59 0.40 0.57 0.75 1.34 2.20

 65 SPRING 65 1.06 .360 2.94 0.56 0.07 53 0.51 0.66 0.90 1.30 2.08

 65 SUMMER 65 1.03 .385 2.75 0.54 0.07 52 0.46 0.65 0.83 1.36 2.06

 Aggregate Nutrient Ecoregion: IX 28

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter TN_mg_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 65 1.10 .300 2.94 0.67 0.08 61 0.40 0.59 0.85 1.63 2.30

 71 FALL 10 1.35 .370 3.60 1.14 0.36 84 0.37 0.51 0.97 1.65 3.60

 71 SPRING 10 1.61 .550 4.65 1.43 0.45 89 0.55 0.72 0.94 1.70 4.65

 71 SUMMER 10 1.73 .740 4.05 1.12 0.36 65 0.74 0.88 1.35 2.00 4.05

 71 WINTER 9 2.28 .700 5.40 1.53 0.51 67 0.70 1.35 2.00 2.30 5.40

 72 FALL 22 2.86 .230 6.30 1.73 0.37 61 0.46 1.32 2.86 4.26 5.03

 72 SPRING 20 3.86 .943 7.88 2.29 0.51 59 1.09 1.81 3.72 5.62 7.76

 72 SUMMER 21 2.74 .280 6.18 1.58 0.34 58 0.61 1.52 2.35 3.73 4.98

 72 WINTER 19 4.10 .660 8.20 2.32 0.53 57 0.66 2.40 4.06 6.16 8.20

 74 FALL 3 0.96 .570 1.20 0.34 0.20 35 0.57 0.57 1.10 1.20 1.20

 74 SPRING 3 1.22 .935 1.45 0.26 0.15 21 0.94 0.94 1.28 1.45 1.45

 74 SUMMER 3 0.81 .630 0.95 0.16 0.09 20 0.63 0.63 0.84 0.95 0.95

 74 WINTER 3 0.99 .555 1.30 0.39 0.22 39 0.56 0.56 1.10 1.30 1.30

 Aggregate Nutrient Ecoregion: IX 29

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter TP_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 85 163 2.50 1500.00 265 28.7 163 20.0 40.0 75.0 155 445

 29 SPRING 84 131 2.50 1235.00 188 20.5 143 16.3 35.0 70.0 135 475

 29 SUMMER 90 106 2.50 690.00 125 13.2 118 10.0 30.0 50.0 140 385

 29 WINTER 100 141 2.50 1430.00 201 20.1 142 8.13 43.8 87.5 170 380

 33 FALL 29 486 40.0 2120.00 572 106 118 50.0 90.0 265 495 1800

 33 SPRING 35 420 50.0 2360.00 493 83.3 117 50.0 140 218 480 1630

 33 SUMMER 28 381 50.0 1640.00 420 79.4 110 50.0 110 213 450 1230

 33 WINTER 31 352 20.0 1210.00 351 63.1 100 40.0 90.0 200 660 1100
 35 FALL 158 173 2.50 2420.00 316 25.1 183 10.0 50.0 75.0 140 778

 35 SPRING 153 151 2.50 2090.00 258 20.9 171 10.0 50.0 72.5 150 510

 35 SUMMER 164 159 2.50 1510.00 247 19.3 155 10.0 50.0 80.0 147 700

 35 WINTER 160 143 2.50 1710.00 251 19.8 175 18.8 45.0 70.0 130 450

 37 FALL 34 176 5.00 1345.00 278 47.8 158 11.3 45.0 70.0 150 925

 37 SPRING 31 188 5.00 1440.00 345 62.1 184 5.00 37.5 70.0 120 1215

 37 SUMMER 39 229 17.5 1592.50 389 62.3 170 20.0 50.0 90.0 170 1515

 37 WINTER 33 167 5.00 1380.00 316 55.0 189 5.00 40.0 60.0 100 1045

 40 FALL 139 242 10.0 1880.00 299 25.3 124 41.2 95.0 150 240 930

 40 SPRING 126 261 10.0 2140.00 377 33.6 144 40.0 90.0 135 255 1040

 40 SUMMER 146 242 20.0 2040.00 284 23.5 117 49.3 100 156 260 940

 40 WINTER 96 195 2.50 2140.00 320 32.7 164 10.0 43.8 87.5 198 975

 45 FALL 395 130 .000 1650.00 221 11.1 170 10.0 30.0 56.3 115 565

 45 SPRING 425 104 .000 1187.50 159 7.72 153 10.0 35.0 50.0 95.0 415

 45 SUMMER 436 145 .000 2400.00 266 12.7 184 9.00 30.0 60.0 124 625

 45 WINTER 322 93.0 .000 1200.00 137 7.64 147 6.25 30.0 51.3 100 310

 64 FALL 110 182 2.50 1335.00 243 23.1 134 10.0 40.0 85.0 220 793

 64 SPRING 108 144 .000 1755.00 233 22.4 162 20.0 42.5 70.0 130 590

 64 SUMMER 181 150 2.50 1760.00 237 17.6 157 10.0 40.0 70.0 150 510

 64 WINTER 86 114 .000 550.00 124 13.4 108 10.0 40.0 70.0 130 450

 65 FALL 532 82.0 .000 1770.00 139 6.01 169 0.00 20.0 50.0 95.0 255

 65 SPRING 603 72.8 .000 990.00 96.6 3.94 133 0.00 25.0 50.0 90.0 185

 65 SUMMER 650 95.8 .000 1700.00 132 5.18 138 0.00 30.0 60.0 120 270

 Aggregate Nutrient Ecoregion: IX 30

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter TP_ug_L_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 543 79.7 .000 2400.00 163 6.98 204 0.00 20.0 45.0 80.0 215

 71 FALL 115 145 2.50 1900.00 250 23.3 173 4.50 30.0 75.0 140 435

 71 SPRING 98 80.9 2.50 625.00 112 11.3 138 2.50 20.0 40.0 90.0 325

 71 SUMMER 117 142 2.50 1150.00 203 18.8 143 2.50 30.0 60.0 163 615

 71 WINTER 94 124 2.50 1410.00 216 22.2 174 5.00 30.0 60.0 97.5 475

 72 FALL 156 275 2.50 1800.00 306 24.5 111 20.0 110 190 279 948

 72 SPRING 136 231 10.0 2300.00 373 32.0 162 30.0 86.3 138 241 740

 72 SUMMER 183 203 .000 1400.00 199 14.7 98 25.0 80.0 163 240 530

 72 WINTER 160 174 .000 920.00 164 12.9 94 20.0 70.0 140 214 500

 74 FALL 58 243 2.50 1125.00 279 36.7 115 25.0 50.0 110 370 970

 74 SPRING 65 219 10.0 2170.00 338 42.0 154 25.0 70.0 123 205 760

 74 SUMMER 70 212 .000 1200.00 228 27.3 107 20.0 80.0 140 250 660

 74 WINTER 60 195 2.50 840.00 170 22.0 87 13.1 81.3 134 291 530
 Aggregate Nutrient Ecoregion: IX 31

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Turb_FTU_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 53 23.0 2.10 95.00 25.1 3.45 109 2.90 5.95 11.8 29.0 89.5

 29 SPRING 46 22.9 .900 96.00 22.2 3.27 97 3.10 7.10 13.0 32.5 66.0

 29 SUMMER 46 26.1 .900 81.00 22.7 3.34 87 4.68 10.6 15.5 42.5 73.8

 29 WINTER 52 30.1 .800 117.00 26.9 3.73 89 3.50 11.5 20.4 44.5 99.0

 33 FALL 6 27.8 1.10 87.00 31.8 13.0 114 1.10 7.10 19.3 33.0 87.0

 33 SPRING 8 42.2 1.00 64.00 23.6 8.36 56 1.00 21.9 55.0 59.3 64.0

 33 SUMMER 7 44.4 8.50 110.00 39.1 14.8 88 8.50 11.8 29.7 81.8 110

 33 WINTER 7 43.9 7.50 93.50 36.0 13.6 82 7.50 10.0 24.0 79.0 93.5

 35 FALL 47 14.5 2.20 55.00 11.8 1.72 81 2.60 6.00 10.1 19.9 40.0

 35 SPRING 57 18.3 1.80 75.00 12.9 1.71 71 3.50 9.00 15.3 25.0 47.0

 35 SUMMER 42 14.8 1.30 77.00 15.2 2.34 103 2.95 6.00 8.69 21.5 47.0

 35 WINTER 57 18.7 2.55 63.75 13.2 1.75 71 2.70 7.88 19.0 25.0 45.5

 37 FALL 6 24.7 3.60 57.50 19.8 8.08 80 3.60 8.00 23.0 33.0 57.5

 37 SPRING 17 24.8 5.50 57.00 15.6 3.79 63 5.50 15.0 20.0 32.0 57.0

 37 SUMMER 7 28.8 12.0 50.00 15.1 5.70 52 12.0 17.5 22.5 49.4 50.0

 37 WINTER 17 22.2 4.80 48.00 15.9 3.86 72 4.80 12.0 15.0 32.0 48.0

 40 FALL 71 19.2 3.90 67.00 12.4 1.48 65 7.00 11.0 16.8 22.5 40.8

 40 SPRING 73 30.3 3.00 123.00 25.9 3.03 86 7.30 13.5 20.7 38.7 92.0

 40 SUMMER 78 31.5 1.40 74.50 17.2 1.94 55 8.00 19.0 27.3 41.5 67.0

 40 WINTER 70 13.6 1.00 72.75 13.6 1.63 100 2.00 5.10 8.30 17.3 38.0

 45 FALL 342 9.87 1.00 110.00 8.05 0.44 81 2.95 5.93 8.50 12.0 19.5

 45 SPRING 357 13.1 1.00 106.00 8.98 0.48 68 2.95 7.65 12.0 16.0 25.5

 45 SUMMER 356 13.1 1.25 102.50 9.64 0.51 74 2.65 7.33 11.8 16.0 27.0

 45 WINTER 271 15.9 1.40 136.00 12.0 0.73 76 3.63 8.68 14.0 20.0 32.5

 64 FALL 46 2.78 .450 8.75 1.90 0.28 68 0.70 1.20 2.25 3.80 6.40

 64 SPRING 28 5.22 1.00 11.10 2.69 0.51 52 1.13 3.30 5.10 7.05 10.1

 64 SUMMER 30 7.01 .800 16.75 4.16 0.76 59 1.00 4.05 6.08 9.40 16.5

 64 WINTER 29 5.81 .400 15.08 3.65 0.68 63 1.00 3.00 5.25 7.30 15.0

 65 FALL 358 6.86 .000 41.03 5.46 0.29 80 1.80 3.40 5.30 8.50 17.0

 65 SPRING 418 9.61 .650 54.00 7.57 0.37 79 2.00 4.60 7.50 11.9 24.0

 65 SUMMER 426 11.5 1.10 156.00 14.9 0.72 130 2.20 4.85 7.88 12.0 28.8

 Aggregate Nutrient Ecoregion: IX 32

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Turb_FTU_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 350 10.4 .300 123.50 12.6 0.67 122 1.85 4.08 6.75 11.0 31.4

 71 FALL 20 9.18 1.45 18.40 5.17 1.16 56 1.55 5.09 8.45 13.3 18.2

 71 SPRING 21 13.4 1.80 41.00 10.5 2.30 78 2.40 6.40 10.1 17.0 31.0

 71 SUMMER 22 15.3 1.95 47.15 10.8 2.31 71 2.25 8.20 13.7 19.4 34.5

 71 WINTER 13 19.7 1.80 70.00 18.1 5.03 92 1.80 8.50 14.9 25.2 70.0

 72 FALL 96 17.2 1.00 180.00 24.3 2.48 141 2.70 7.36 12.0 20.3 32.0
 72 SPRING 77 15.8 2.80 61.50 11.5 1.31 73 4.60 9.00 13.0 17.8 48.0

 72 SUMMER 118 13.5 1.00 160.00 16.6 1.53 123 2.70 5.10 9.45 16.9 35.0

 72 WINTER 112 10.8 1.30 93.50 10.8 1.02 100 2.60 5.16 7.68 12.8 30.0

 74 FALL 14 19.9 1.00 120.00 31.5 8.42 158 1.00 3.00 6.50 26.5 120

 74 SPRING 11 29.9 4.00 64.00 18.2 5.49 61 4.00 22.3 28.3 34.0 64.0

 74 SUMMER 11 24.6 2.50 62.50 23.0 6.92 93 2.50 7.00 9.50 49.0 62.5

 74 WINTER 13 44.3 14.8 92.75 26.5 7.35 60 14.8 20.0 42.5 62.5 92.8

 Aggregate Nutrient Ecoregion: IX 33

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Turb_JCU_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 11 50.2 2.00 171.00 51.0 15.4 102 2.00 3.80 35.0 79.5 171

 29 SPRING 11 39.0 2.00 158.00 45.8 13.8 117 2.00 11.0 25.0 46.0 158

 29 SUMMER 17 47.1 2.35 173.00 59.1 14.3 125 2.35 7.25 21.0 46.5 173

 29 WINTER 15 32.3 2.00 79.10 23.4 6.04 72 2.00 13.0 31.3 44.0 79.1

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 0 . . . . . . . . . . .

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 5 56.2 3.50 140.50 57.4 25.7 102 3.50 22.0 25.0 90.0 141

 35 SPRING 0 . . . . . . . . . . .

 35 SUMMER 8 46.4 2.00 127.00 48.7 17.2 105 2.00 5.00 25.9 90.0 127

 35 WINTER 7 31.8 4.00 72.00 24.0 9.06 75 4.00 13.0 21.5 48.0 72.0

 37 FALL 5 20.2 2.00 62.00 23.9 10.7 118 2.00 10.0 12.8 14.0 62.0

 37 SPRING 3 62.3 19.0 115.00 48.7 28.1 78 19.0 19.0 53.0 115 115

 37 SUMMER 7 31.9 1.00 61.00 20.3 7.66 64 1.00 16.5 27.0 47.0 61.0

 37 WINTER 5 16.0 2.00 26.00 9.35 4.18 58 2.00 14.0 15.0 23.0 26.0

 40 FALL 14 35.5 4.90 134.50 32.8 8.77 93 4.90 16.5 26.5 35.5 135

 40 SPRING 13 37.6 .700 130.50 37.9 10.5 101 0.70 10.0 31.0 42.0 131

 40 SUMMER 19 26.3 4.90 100.00 22.9 5.25 87 4.90 10.0 20.0 36.5 100

 40 WINTER 11 20.4 7.00 57.00 13.4 4.04 66 7.00 11.0 17.5 23.0 57.0

 45 FALL 11 8.04 1.70 30.00 8.03 2.42 100 1.70 3.05 5.70 11.0 30.0

 45 SPRING 11 12.8 2.10 29.00 7.01 2.11 55 2.10 9.60 12.1 17.0 29.0

 45 SUMMER 10 11.8 1.10 23.10 8.52 2.69 72 1.10 2.10 12.3 20.5 23.1

 45 WINTER 12 11.6 3.60 19.50 4.87 1.40 42 3.60 8.85 10.5 15.4 19.5

 64 FALL 1 3.73 3.73 3.73 . . . 3.73 3.73 3.73 3.73 3.73

 64 SPRING 1 6.50 6.50 6.50 . . . 6.50 6.50 6.50 6.50 6.50

 64 SUMMER 2 4.30 4.10 4.50 0.28 0.20 7 4.10 4.10 4.30 4.50 4.50

 64 WINTER 2 5.53 4.70 6.35 1.17 0.83 21 4.70 4.70 5.53 6.35 6.35

 65 FALL 17 16.5 2.30 80.00 18.8 4.55 114 2.30 7.50 11.1 18.0 80.0

 65 SPRING 21 10.5 1.75 29.30 6.63 1.45 63 2.15 5.60 11.0 13.0 20.0

 65 SUMMER 11 20.6 1.60 135.00 38.4 11.6 186 1.60 2.88 9.30 15.0 135
 Aggregate Nutrient Ecoregion: IX 34

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Turb_JCU_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 18 22.9 2.00 96.00 24.0 5.65 105 2.00 10.7 15.0 21.7 96.0

 71 FALL 18 2.42 .600 4.60 1.30 0.31 54 0.60 1.15 2.38 3.60 4.60

 71 SPRING 21 7.68 .900 88.80 18.8 4.11 245 1.15 1.55 2.95 4.18 14.9

 71 SUMMER 15 3.00 .725 16.00 3.81 0.98 127 0.73 1.05 1.70 3.35 16.0

 71 WINTER 17 4.74 1.10 15.50 4.10 0.99 86 1.10 1.50 3.10 6.40 15.5

 72 FALL 2 25.3 22.5 28.00 3.89 2.75 15 22.5 22.5 25.3 28.0 28.0

 72 SPRING 2 41.5 37.0 46.00 6.36 4.50 15 37.0 37.0 41.5 46.0 46.0

 72 SUMMER 3 59.5 43.5 84.00 21.5 12.4 36 43.5 43.5 51.0 84.0 84.0

 72 WINTER 2 15.0 13.0 17.00 2.83 2.00 19 13.0 13.0 15.0 17.0 17.0

 74 FALL 5 11.1 1.00 17.50 6.13 2.74 55 1.00 11.0 13.0 13.0 17.5

 74 SPRING 5 9.89 2.15 26.50 9.96 4.46 101 2.15 3.23 6.10 11.5 26.5

 74 SUMMER 5 5.90 1.40 12.50 4.19 1.87 71 1.40 4.10 4.50 7.00 12.5

 74 WINTER 3 17.3 15.0 19.00 2.08 1.20 12 15.0 15.0 18.0 19.0 19.0

 Aggregate Nutrient Ecoregion: IX 35

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Turb_NTU_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 29 FALL 5 13.0 2.43 48.50 19.9 8.89 153 2.43 3.95 4.55 5.53 48.5

 29 SPRING 4 3.23 1.70 4.00 1.04 0.52 32 1.70 2.60 3.60 3.85 4.00

 29 SUMMER 6 18.5 3.43 70.00 26.2 10.7 141 3.43 4.48 5.65 22.0 70.0

 29 WINTER 4 4.50 3.05 6.30 1.39 0.69 31 3.05 3.48 4.33 5.53 6.30

 33 FALL 0 . . . . . . . . . . .

 33 SPRING 0 . . . . . . . . . . .

 33 SUMMER 1 0.50 .500 0.50 . . . 0.50 0.50 0.50 0.50 0.50

 33 WINTER 0 . . . . . . . . . . .

 35 FALL 81 15.6 2.15 63.00 12.4 1.38 80 4.58 7.80 12.0 18.0 40.0

 35 SPRING 83 27.6 2.25 175.00 28.2 3.09 102 8.20 12.5 18.5 26.5 75.0

 35 SUMMER 82 16.5 3.55 58.50 10.1 1.12 61 4.65 8.80 15.3 22.3 36.1

 35 WINTER 72 22.4 3.48 150.00 25.5 3.00 114 6.25 10.2 14.3 24.1 53.5

 37 FALL 27 19.3 2.20 91.00 23.0 4.42 119 3.80 5.60 10.8 17.5 76.0

 37 SPRING 22 19.5 4.80 52.00 12.3 2.63 63 6.10 10.4 15.6 28.0 44.7

 37 SUMMER 23 25.3 2.15 150.00 35.5 7.41 140 4.10 5.75 11.5 26.5 86.7

 37 WINTER 21 15.9 4.10 50.25 10.4 2.28 66 6.50 8.15 13.5 19.5 29.5

 40 FALL 32 36.2 3.00 113.00 26.3 4.64 72 7.00 17.0 25.5 57.5 73.4

 40 SPRING 18 37.2 16.5 80.15 18.5 4.35 50 16.5 21.0 33.5 43.0 80.2

 40 SUMMER 53 41.5 4.65 212.00 37.3 5.13 90 5.80 14.0 32.0 52.7 104

 40 WINTER 6 31.0 11.0 55.00 19.6 8.01 63 11.0 14.0 25.5 55.0 55.0

 45 FALL 25 9.29 2.80 23.75 5.52 1.10 59 3.05 5.95 8.60 10.7 21.0

 45 SPRING 26 10.5 .900 28.50 7.07 1.39 67 1.20 5.48 9.25 14.2 23.0

 45 SUMMER 35 11.9 1.70 80.50 13.3 2.24 112 2.30 5.30 9.35 14.0 28.3

 45 WINTER 22 12.0 4.35 42.40 8.39 1.79 70 4.73 7.70 10.4 13.9 28.2
 64 FALL 20 4.75 .250 19.00 5.06 1.13 106 0.25 1.63 2.43 6.85 17.0

 64 SPRING 21 6.98 1.10 27.00 6.78 1.48 97 1.30 2.75 4.30 7.60 20.0

 64 SUMMER 33 6.42 1.40 16.90 4.07 0.71 63 1.80 3.05 5.10 10.0 13.2

 64 WINTER 15 7.25 1.00 32.75 7.77 2.01 107 1.00 2.90 5.18 8.50 32.8

 65 FALL 115 10.8 .250 71.68 11.0 1.03 102 1.25 4.10 7.10 14.1 27.0

 65 SPRING 152 17.8 .100 128.00 16.8 1.36 94 1.60 7.41 14.0 22.0 43.5

 65 SUMMER 173 17.3 .250 116.00 20.6 1.57 119 1.30 6.00 10.2 19.0 72.0

 Aggregate Nutrient Ecoregion: IX 36

 Rivers and Streams

 Descriptive Statistics by Decade and Season

 Parameter Turb_NTU_Median

 Eco_

 Level_

 III SEASON N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95

 65 WINTER 133 18.2 .250 84.00 16.5 1.43 91 1.30 6.40 14.0 25.0 50.3

 71 FALL 45 11.8 .250 82.75 13.9 2.07 117 2.00 4.60 7.55 14.5 35.3

 71 SPRING 34 20.0 3.00 72.75 17.8 3.05 89 3.95 9.00 12.1 25.5 63.0

 71 SUMMER 47 19.0 1.50 199.90 29.9 4.36 157 2.00 4.95 11.5 24.0 40.0

 71 WINTER 33 26.1 .250 125.53 28.7 5.00 110 5.35 9.50 18.5 26.1 108

 72 FALL 6 28.7 10.0 64.00 19.9 8.13 69 10.0 13.0 25.0 35.0 64.0

 72 SPRING 3 20.8 17.0 26.00 4.68 2.70 23 17.0 17.0 19.3 26.0 26.0

 72 SUMMER 5 23.7 .000 50.25 19.9 8.92 84 0.00 13.0 18.0 37.0 50.3

 72 WINTER 2 22.4 17.0 27.75 7.60 5.38 34 17.0 17.0 22.4 27.8 27.8

 74 FALL 10 23.4 7.60 39.25 11.2 3.53 48 7.60 14.3 22.5 35.0 39.3

 74 SPRING 16 30.7 4.00 90.00 22.3 5.57 73 4.00 17.0 23.5 38.3 90.0

 74 SUMMER 18 41.9 5.00 130.00 36.9 8.69 88 5.00 15.5 30.6 54.0 130

 74 WINTER 15 31.4 10.0 93.50 21.2 5.48 67 10.0 17.5 25.0 37.2 93.5
APPENDIX C

Quality Control/Quality Assurance Rules
Support for the Compilation and Analysis of National Nutrient Data

15 Nutrient Ecoregion/Waterbody Type Summary Chapters 

Prepared for:

Robert Cantilli

Environmental Protection Agency

OW/OST/HECD

Prepared by:

INDUS Corporation

1953 Gallows Road

Vienna, Virginia 22182

Contract Number: 68-C-99-226

Task Number: 04

Subtask Number: 4

August 8, 2000
ii

CONTENTS

1.0 BACKGROUND ........................................................ 1

1.1 Purpose .......................................................... 1

1.2 References ....................................................... 1

2.0 QA/QC PROCEDURES ................................................ 2

2.1 National Data Sets ............................................... 3

2.2 State Data ..................................................... 3

2.3 Laboratory Methods .............................................. 4

2.4 Waterbody Name ................................................ 4

2.5 Ecoregion Data ................................................. 5

3.0 STATISTICAL ANALYSIS REPORTS .................................... 5

3.1 Data Source Reports ............................................. 6

3.2 Remark Code Reports ............................................ 7

3.3 Median of Each Waterbody ........................................ 7

3.4 Descriptive Statistic Reports ........................................ 7

3.5 Regression Models ............................................... 8

4.0 TIME PERIOD ....................................................... 8

5.0 DATA SOURCES AND PARAMETERS FOR THE AGGREGATE NUTRIENT

ECOREGIONS ....................................................... 9

5.1 Lakes and Reservoirs ............................................ 9

5.1.1 Aggregate Nutrient Ecoregion 2 ............................... 9

5.1.2 Aggregate Nutrient Ecoregion 6 .............................. 10

5.1.3 Aggregate Nutrient Ecoregion 7 .............................. 10

5.1.4 Aggregate Nutrient Ecoregion 8 .............................. 11

5.1.5 Aggregate Nutrient Ecoregion 9 .............................. 12

5.1.6 Aggregate Nutrient Ecoregion 11 ............................. 12

5.1.7 Aggregate Nutrient Ecoregion 12 ............................. 13

5.1.8 Aggregate Nutrient Ecoregion 13 ............................. 13

5.2 Rivers and Streams .............................................. 14

5.2.1 Aggregate Nutrient Ecoregion 2 .............................. 14

5.2.2 Aggregate Nutrient Ecoregion 3 .............................. 15

5.2.3 Aggregate Nutrient Ecoregion 6 .............................. 16

5.2.4 Aggregate Nutrient Ecoregion 7 .............................. 16

5.2.5 Aggregate Nutrient Ecoregion 9 .............................. 17

5.2.6 Aggregate Nutrient Ecoregion 11 ............................. 18

5.2.7 Aggregate Nutrient Ecoregion 12 ............................. 19

5.2.8 Aggregate Nutrient Ecoregion 14 ............................. 20
iii

APPENDIX A Process Used to QA/QA the Legacy STORET Nutrient Data Set

APPENDIX B Process for Adding Aggregate Nutrient Ecoregions and Level III

Ecoregions

APPENDIX C Glossary
15 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 04 August 8, 2000

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1.0 BACKGROUND 

The Nutrient Criteria Program has initiated development of a national Nutrient Criteria Database

application that will be used to store and analyze nutrient data. The ultimate use of these data will

be to derive ecoregion- and waterbody-specific nutrient criteria ranges. EPA converted STOrage

and RETrieval (STORET) legacy data, National Stream Quality Accounting Network

(NASQAN) data, National Water-Quality Assessment (NAWQA) data, and other relevant

nutrient data from universities and States/Tribes into the database. The data imported into the

Nutrient Criteria Database will be used to develop national nutrient criteria ranges. 

1.1 Purpose

The purpose of this deliverable is to provide EPA with information regarding the data used to

create the statistical reports which will be used to derive ecoregion- and waterbody-specific

nutrient criteria ranges for Level III ecoregions. There are fourteen aggregate nutrient

ecoregions. Each aggregate nutrient ecoregion is divided into smaller ecoregions referred to as

Level III ecoregions. EPA will determine criteria ranges for the waterbody types and Level III

ecoregions within the following aggregate nutrient ecoregions:

• Lakes and Reservoirs

- Aggregate Nutrient ecoregions: 2, 6, 7, 8, 9, 11, 12, 13

• Rivers and Streams 

- Aggregate Nutrient ecoregions: 2, 3, 6, 7, 9, 11, 12, 14

1.2 References

This section lists documents that contain baselines, standards, guidelines, policies, and references

that apply to the data analysis. Listed editions were valid at the time of publication. All

documents are subject to revision, but these specific editions govern the concepts described in this

document. 

Nutrient Criteria Technical Guidance Manual: Lakes and Reservoirs (Draft). EPA, Office of

Water, EPA 822-D-99-001, April 1999.

Nutrient Criteria Technical Guidance Manual: Rivers and Streams (Draft). EPA, Office of

Water, EPA 822-D-99-003, September 1999.

Guidance for Data Quality Assessment: Practical Methods for Data Analysis. EPA, Office of

Research and Development, EPA QA/G-9, January 1998.
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2.0 QA/QC PROCEDURES

In order to develop nutrient criteria, EPA needed to obtain nutrient data from the states. EPA

requested nutrient data from the states and forwarded the data sets to INDUS via e-mail and/or

US mail. In addition, EPA tasked INDUS to convert data from three national data sets. EPA

provided INDUS with a Legacy STORET extraction to convert into the database. The United

States Geologic Survey (USGS) sent INDUS a CD-ROM with NASQAN data to convert. 

INDUS downloaded NAWQA files from the USGS Web site to convert the data. In total,

INDUS converted and imported the following national and state data sets into the Nutrient

Criteria Database:

• Legacy STORET

• NAWQA

• NASQAN

• Region 1

• Region 2 - Lake Champlain Monitoring Project

• Region 2 - NYSDEC Finger Lakes Monitoring Program

• Region 2 - NY Citizens Lake Assessment Program

• Region 2 - Lake Classification and Inventory Survey

• Region 2 - NYCDEP (1990-1998)

• Region 2 - NYCDEP (Storm Event data)

• Region 2 - New Jersey Nutrient Data ( Tidal Waters)

• Region 5

• Region 3 

• Region 3 - Nitrite Data

• Region 3 - Choptank River files

• Region 4 - Tennessee Valley Authority

• Region 7 - Central Plains Center for BioAssessment (CPCB)

• Region 7 - REMAP

• Region 2 - Delaware River Basin Commission (1990-1998)

• Region 3 - PA Lake Data

• Region 3 - University of Delaware

• Region 10 

• University of Auburn

As part of the conversion process, INDUS performed a number of Quality Assurance/Quality

Control (QA/QC) steps to ensure that the data was properly converted into the Nutrient Criteria

Database. Section 2 explains the steps performed by INDUS to convert the data.
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2.1 National Data Sets

INDUS converted three national data sets into the Nutrient Criteria Database: Legacy STORET

data, NASQAN data, and NAWQA data. A previous EPA contractor performed the extraction of

Legacy STORET data and documented the QA/QC procedures used on the data. This

documentation is included in Appendix A. INDUS performed minimal QA/QC on the Legacy

STORET data set because the previous contractor completed the steps outlined in Appendix A. 

INDUS and EPA also agreed to convert the NAWQA and NASQAN data sets with minimal

QA/QC on the assumption that the source agency, the USGS, QA/QC'd the data. 

For each of the three national data sets, INDUS ran queries to determine if 1) samples existed

without results and 2) if stations existed without samples. Per Task Order Project Officer

(TOPO) direction, these records were deleted from the system. For analysis purposes, EPA

determined that there was no need to keep station records with no samples and sample records

with no results. INDUS also confirmed that each data set contained no duplicate records. 

In addition, INDUS deleted all composite results from the Legacy STORET data. Per TOPO

direction, it was decided that composite sample results would not be used in the statistical

analysis.

2.2 State Data

Each state data set was delivered in a unique format. Many of the data sets were delivered to

INDUS without corresponding documentation. INDUS analyzed each state data set in order to

determine which parameters should be converted for analysis. INDUS obtained a master

parameter table from EPA and converted the parameters in the state data sets according to those

that were present in the EPA parameter table. INDUS converted all of the data elements in the

state data sets that mapped directly to the Nutrient Criteria Database; data elements that did not

map to the Nutrient Criteria Database were not converted. In some cases, state data elements

that did not directly map into the Oracle database were inserted into a comment field within the

database. Also, INDUS maintained an internal record of which state data elements were inserted

into the comment field. 

As part of the data clean-up efforts, INDUS determined whether or not there were any duplicate

records in the state data sets and deleted the duplicate records. INDUS checked the waterbody,

station, and sample entities for duplicate records. In addition, INDUS deleted station records

with no samples and sample records with no results. INDUS also deleted waterbody records that

were not associated with a station. In each case, INDUS maintained an internal record of how

many records were deleted. 

If INDUS encountered referential integrity errors, such as samples that referred to stations that

did not exist, or if INDUS was unsure of whether a record was a duplicate, INDUS contacted the

agency directly via e-mail or phone to resolve any issues that arose. INDUS saved an electronic
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copy of each e-mail correspondence with the states to ensure that a record of the decision was

maintained. INDUS also contacted each agency to determine which laboratory methods were

used for each parameter.

Finally, INDUS examined the remark codes of each result record in the state data sets. INDUS

mapped the remark codes to the STORET remark codes listed in Table 2 of Appendix A. If any

of the state result records were associated with remark codes marked as "Delete" in Table 2 of

Appendix A, the result records were not converted into the database.

2.3 Laboratory Methods 

Many of the state data sets did not contain laboratory method information. In addition, laboratory

method information was not available for the three national data sets. In order to determine

missing laboratory method information, EPA tasked another contractor to contact the data

owners to obtain the laboratory method. In some cases, the data owners responded and the

laboratory methods were added to the database. 

2.4 Waterbody Name and Class Information

A large percentage of the data did not have waterbody-specific information. The only waterbody

information contained in the three national data sets was the waterbody name, which was

embedded in the station 'location description' field. Most of the state data sets contained

waterbody name information; however, much of the data was duplicated throughout the data sets. 

Therefore, the waterbody information was cleaned manually. For the three national data sets, the

'location description' field was extracted from the station table and moved to a temporary table. 

The 'location description' field was sorted alphabetically. Unique waterbodies were grouped

together based on name similarity and whether or not the waterbodies fell within the same county,

state, and waterbody type. Finally, the 'location description' field was edited to include only

waterbody name information, not descriptive information. For example, 110 MILE CREEK AT

POMONA DAM OUTFLOW, KS PO-2 was edited to 110 MILE CREEK. Also, if 100 MILE

CREEK was listed ten times in New York, but in four different counties, four 100 MILE CREEK

waterbody records were created.

Similar steps were taken to eliminate duplicate waterbody records in the state data sets. If a

number of records had similar waterbody names and fell within the same state, county, and

waterbody type, the records were grouped to create a unique waterbody record.

Most of the waterbody data did not contain depth, surface area, and volume measurements. EPA

needed this information to classify waterbody types. EPA attempted to obtain waterbody class 
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information from the states. EPA sent waterbody files to the regional coordinators and requested

that certain class information be completed by each state. The state response was poor; therefore,

EPA was not able to perform statistical analysis for the waterbody types by class.

2.5 Ecoregion Data

Aggregate nutrient ecoregions and Level III ecoregions were added to the database using the

station latitude and longitude coordinates. If a station was lacking latitude and longitude

coordinates or county information, the data were not included in the statistical analysis. Appendix

B lists the steps taken to add the two ecoregion types (aggregate and Level III) to the Nutrient

Criteria Database. The ecoregion names were pulled from aggregate nutrient ecoregion and Level

III ecoregion Geographical Information System (GIS) coverages. In summary, the station latitude

and longitude coordinates were used to determine the ecoregion under the following

circumstances:

• The latitude and longitude coordinates fell within the county/state listed in the station

table.

• The county data was missing.

The county centroid was used to determine the ecoregions under the following circumstances:

• The latitude and longitude coordinates were missing, but the state/county information was

available.

• The latitude and longitude coordinates fell outside the county/state listed in the station

table. The county information was assumed to be correct; therefore, the county centroid

was used.

If the latitude and longitude coordinates fell outside the continental US county coverage file 

(i.e., the point fell in the ocean or Mexico/Canada), the nearest ecoregion was assigned to the

station.

3.0 STATISTICAL ANALYSIS REPORTS

Aggregate nutrient ecoregion tables were created by extracting all observations for a specific

aggregate nutrient ecoregion from the nutrient criteria database. Then, the data were reduced to

create tables containing only the yearly median values. To create these tables, the median value

for each waterbody was calculated using all observations for each waterbody by Level III

ecoregion, year, and season. Tables of decade median values were created from the yearly

median tables by calculating the median for each waterbody by Level III ecoregion by decade and

season.
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The Data Source and the Remark Code reports were created using all observations (all reported

values). All the other reports were created from either the yearly median tables or the decade

median tables. In other words, the descriptive statistics and regressions were run using the

median values for each waterbody and not the individual reported values.

Statistical analyses were performed under the assumption that this data set is a random sample. If

this assumption cannot be verified, the observations may or may not be valid. Values below the

1st and 99th percentile were removed from the Legacy STORET database prior to the creation of

the national database. Also, data were treated according the Legacy STORET remark codes in

Appendix A. 

The following contains a list of each report and the purpose for creating each report: 

• Data Source Created to provide a count of the amount of data and to identify the

source(s).

• Remark Codes Created to provide a description of the data. 

• Median of Each Waterbody by Year This was an intermediate step performed to obtain a

median value for each lake to be used in the yearly descriptive statistics reports and the

regression models. 

• Median of Each Waterbody by Decade This was an intermediate step performed to obtain

a median value for each lake to be used in the decade descriptive statistics.

• Descriptive Statistics Created to provide EPA with the desired statistics for setting criteria

levels.

• Regression Models Created to examine the relationships between biological and nutrient

variables. 

Note: Separate reports were created for each season.

3.1 Data Source Reports

Data source reports were presented in the following formats:

• The number and percentage of data from each data source were summarized in tables for

each aggregate nutrient ecoregion by season and waterbody type.

• The number and percentage of data from each data source were summarized in tables for

each Level III ecoregion by season and waterbody type.

The 'Frequency' represents the number of data values from a specific data source for each

parameter by data source. The 'Row Pct' represents the percentage of data from a specific data

source for each parameter. 
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3.2 Remark Code Reports

Remark code reports were presented in the following formats:

• The number and percentage of data associated with a particular remark code for each

parameter were summarized in tables by Level III ecoregion by decade and season.

• The number and percentage of data associated with a particular remark code for each

parameter were summarized in tables by Level III ecoregion by year and season.

The 'Frequency' represents the number of data values corresponding to the remark code in the

column. The 'Row Pct' represents the percentage of data that was associated with the remark

code in that row.

In the database, remark codes that were entered by the states were mapped to Legacy STORET

remark codes. Prior to the analysis, the data were treated according to these remark codes. For

example, if the remark code was 'K,' then the reported value was divided by two. Appendix A

contains a complete list of Legacy STORET remark codes.

Note: For the reports, a remark code of 'Z' indicates that no remark codes were recorded. It does

not correspond to Legacy STORET code 'Z.'

3.3 Median of Each Waterbody

To reduce the data and to ensure heavily sampled waterbodies or years were not over represented

in the analysis, median value tables (described above) were created. The yearly median tables and

decade median tables were delivered to the EPA in electronic format as csv (comma separated

value or comma delimited) files.

3.4 Descriptive Statistic Reports

The number of waterbodies, median, mean, minimum, maximum, 5th, 25th , 75th , 95th

percentiles, standard deviation, standard error, and coefficient of variation were calculated. The

tables (described above) containing the decade median values for each waterbody for each

parameter were used to create descriptive statistics reports for:

• Level III ecoregions by decade and season

• Aggregate nutrient ecoregions by decade and season

In addition, the tables containing the yearly median values for each waterbody for each parameter

were used to create descriptive statistics reports for:

• Level III ecoregions by year and season
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3.5 Regression Models

Simple linear regressions using the least squares method were performed to examine the

relationships between biological and nutrient variables in lakes and reservoirs, and rivers and

streams. Regressions were performed using the yearly median tables. Chlorophyll(s) in

micrograms per liter (ug/L), secchi in meters (m), dissolved oxygen in milligrams per liter (mg/L),

turbidity, and pH were the biological variables in these models. When there was little or no data

for chlorophyll, then pH or dissolved oxygen was substituted for chlorophyll. Secchi data were

used in the lake and reservoir models, and turbidity data were used in the river and stream models. 

The nutrient variables in these models include: total phosphorus in ug/L, total nitrogen in mg/L,

total kjeldahl nitrogen in mg/L, and nitrate and nitrite in mg/L. Regressions were also run for

total nitrogen and total phosphorus for ecoregions where both these variables were measured. 

Note: At the time of creation of this document only regressions for aggregate nutrient ecoregion 7

for lakes and reservoirs were delivered to the EPA. Regressions for the remaining aggregate

nutrient ecoregions will be delivered in August 2000.

4.0 TIME PERIOD

Data collected from January 1990 to December 1999 were used in the statistical analysis reports. 

To capture seasonal differences, the data were classified as follows:

• Aggregate nutrient ecoregions: 6, 7, and 8

 - Spring: April to May 

 - Summer: June to August 

 - Fall: September to October

 - Winter: November to March

• Aggregate nutrient ecoregions: 1, 2, 9, 10, 11, 12, and 13

 - Spring: March to May

 - Summer: June to August 

 - Fall: September to November

 - Winter: December to February 
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5.0 DATA SOURCES AND PARAMETERS FOR THE AGGREGATE NUTRIENT

ECOREGIONS

This section provides information for the nutrient aggregate ecoregions that were analyzed by

waterbody type. Each section lists the data sources for the aggregate nutrient ecoregion

including: 1) the data sources, 2) the parameters included in the analysis, and 3) the Level III

ecoregions within the aggregate nutrient ecoregions.

Note: For analysis purposes, the following parameters were combined to form Phosphorous,

Dissolved Inorganic (DIP):

Phosphorus, Dissolved Inorganic (DIP) 

Phosphorus, Dissolved (DP) 

Phosphorus, Dissolved Reactive (DRP)

Orthophosphate, dissolved, mg/L as P 

Orthophosphate (OPO4_PO4)

5.1 Lakes and Reservoirs

5.1.1 Aggregate Nutrient Ecoregion 2

Data Sources:

Legacy STORET

EPA Region 10

Parameter:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Phosphorus, Total Reactive (ug/L)

SECCHI (m)

pH
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Level III ecoregions:

1, 2, 4, 5, 9, 11, 15, 16, 17, 19, 21, 23, 41, 77, 78

5.1.2 Aggregate Nutrient Ecoregion 6

Data Sources:

Legacy STORET

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

46, 47, 48, 54, 55, 57

5.1.3 Aggregate Nutrient Ecoregion 7

Data Sources:

LCMPD

Legacy STORET

NYCDEP

EPA Region 1

Parameters:

Chlorophyll A, Fluorometric Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)
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Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

51, 52, 53, 56, 60, 61, 83

5.1.4 Aggregate Nutrient Ecoregion 8

Data Sources:

LCMPD

Legacy STORET

NYCDEP

NYCDEC

EPA Region 1

EPA Region 3

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B (ug/L)

Chlorophyll C (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

49, 50, 58, 62, 82
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5.1.5 Aggregate Nutrient Ecoregion 9

Data Sources:

Auburn University

Legacy STORET

EPA Region 4

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Pheophytin (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

29, 33, 35, 37, 40, 45, 64, 65, 71, 72, 74

5.1.6 Aggregate Nutrient Ecoregion 11

Data Sources:

Auburn University

Legacy STORET

NYSDEC

EPA Region 3

EPA Region 4

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Pheophytin (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)
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Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

36, 38, 39, 66, 67, 68, 69, 70

5.1.7 Aggregate Nutrient Ecoregion 12

Data Sources:

Legacy STORET

Parameters:

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

75

5.1.8 Aggregate Nutrient Ecoregion 13

Data Sources:

Legacy STORET
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Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

Level III ecoregions:

76

5.2 Rivers and Streams

5.2.1 Aggregate Nutrient Ecoregion 2

Data Sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 10

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Phosphorus, Total (TP) Reactive (ug/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)
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Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

1, 2, 4, 5, 8, 9, 11, 15, 16, 17, 19, 21, 23, 41, 77, 78

5.2.2 Aggregate Nutrient Ecoregion 3

Data Sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 10

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

6, 10, 12, 13, 14, 18, 20, 22, 24, 79, 80, 81
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5.2.3 Aggregate Nutrient Ecoregion 6

Data Sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 5

EPA Region 7

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Organic, Phosphorus (ug/L)

Phosphorus, Total (TP) (ug/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

46, 47, 48, 54, 55, 57

5.2.4 Aggregate Nutrient Ecoregion 7 

Data Sources:

LCMPD

Legacy STORET

NASQAN

NAWQA

NYCDEP
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Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Organic, Phosphorus (ug/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

51, 52, 53, 56, 60, 61, 83

5.2.5 Aggregate Nutrient Ecoregion 9

Data Sources:

Auburn University

Legacy STORET

NASQAN

NAWQA

EPA Region 3

EPA Region 5

EPA Region 7

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)
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Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll B, Phytoplankton, Spectrophotometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Organic, Phosphorus (ug/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

29, 33, 35, 37, 40, 45, 64, 65, 71, 72, 74

5.2.6 Aggregate Nutrient Ecoregion 11

Data Sources:

Auburn University

Legacy STORET

NASQAN

NAWQA

EPA Region 3

EPA Region 5

EPA Region 7

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Organic, Phosphorus (ug/L)
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Phosphorus, Orthophosphate, Total as P (ug/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

36, 38, 39, 66, 67, 68, 69, 70

5.2.7 Aggregate Nutrient Ecoregion 12

Data Sources:

Legacy STORET

NASQAN

NAWQA

Parameters:

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Chlorophyll B, Phytoplankton, Spectrophotometric (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (NTU)

Level III ecoregions:

75
15 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 04 August 8, 2000

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5.2.8 Aggregate Nutrient Ecoregion 14

Data Sources:

Legacy STORET

NASQAN

NAWQA

NYCDEP

EPA Region 1

EPA Region 3

Parameters:

Chlorophyll A, Fluorometric, Corrected (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric Acid (ug/L)

Chlorophyll A, Phytoplankton, Spectrophotometric, Uncorrected (ug/L)

Chlorophyll A, Trichromatic, Uncorrected (ug/L)

Phosphorous, Dissolved Inorganic (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Phosphorus, Orthophosphate, Total as P (ug/L)

Nitrogen, Total Kjeldahl (TKN) (mg/L)

Nitrogen, Total (TN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Turbidity (FTU)

Turbidity (JCU)

Turbidity (NTU)

Level III ecoregions:

59, 63, 84
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APPENDIX A

Process Used to QA/QA the Legacy STORET Nutrient Data Set
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1. STORET water quality parameters and Station and Sample data items were retrieved from

USEPA's mainframe computer. Table 1 lists all retrieved parameters and data items.

TABLE 1: PARAMETERS AND DATA ITEMS RETRIEVED FROM STORET

Parameters Retrieved

(STORET Parameter Code)

Station Data Items

Included

(STORET Item Name)

Sample Data Items Included

(STORET Item Name)

TN - mg/l (600)

TKN - mg/l (625)

Total Ammonia (NH3+NH4) - mg/l (610)

Total NO2+NO3 - mg/l (630)

Total Nitrite - mg/l (615)

Total Nitrate - mg/l (620)

Organic N - mg/L (605)

TP - mg/l (665)

Chlor a - ug/L (spectrophotometric method,

32211) 

Chlor a - ug/L (fluorometric method

corrected, 32209)

Chlor a - ug/L (trichromatic method

corrected, 32210)

Secchi Transp. - inches (77)

Secchi Transp. - meters (78)

+Turbidity JCUs (70)

+Turbidity FTUs (76)

+Turbidity NTUs field (82078)

+Turbidity NTUs lab (82079)

+DO - mg/L (300)

+Water Temperature (degrees C, 10/degrees

F, 11)

Station Type (TYPE)

Agency Code (AGENCY)

Station No. (STATION)

Latitude - std. decimal degrees

(LATSTD)

Longitude - std. decimal degrees 

(LONGSTD)

Station Location (LOCNAME)

County Name (CONAME)

State Name (STNAME)

Ecoregion Name - Level III

(ECONAME)

Ecoregion Code -Level III

(ECOREG)

Station Elevation (ELEV)

Hydrologic Unit Code

(CATUNIT)

RF1 Segment and Mile

(RCHMIL)

RF1ON/OFF tag (ONOFF)

Sample Date (DATE)

Sample Time (TIME)

Sample Depth (DEPTH)

Composite Sample Code 

(SAMPMETH)

+ If data record available at a station included data only for this or other such marked parameters, data record was deleted

from data set.

The following set of retrieval rules were applied to the retrieval process:

• Data were retrieved for waterbodies specified only as 'lake', 'stream', 'reservoir', or 'estuary'

under "Station Type" parameter. Any stations specified as 'well,' 'spring,' or 'outfall' were

eliminated from the retrieved data set.

• Data were retrieved for station types described as 'ambient' (e.g., no pipe or facility

discharge data) under the "Station Type" parameter.

• Data were retrieved that were designated as 'water' samples only. This includes 'bottom'

and 'vertically integrated' water samples.
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• Data were retrieved that were designated as either 'grab' samples and 'composite' samples

(mean result only).

• No limits were specified for sample depths.

• Data were retrieved for all fifty states, Puerto Rico, and the District of Columbia.

• The time period specified for data retrieval was January 1990 to September 1998.

• No data marked as "Retired Data" (i.e., data from a generally unknown source) were

retrieved.

• Data marked as "National Urban Runoff data" (i.e., data associated with sampling

conducted after storm events to assess nonpoint source pollutants) were included in the

retrieval. Such data are part of STORET's 'Archived' data. 

• Intensive survey data (i.e., data collected as part of specific studies) were retrieved.

2. Any values falling below the 1st percentile and any values falling above the 99th percentile

were transformed into 'missing' values (i.e., values were effectively removed from the data

set, but were not permanently eliminated).

3. Based on the STORET 'Remark Code' associated with each retrieved data point, the

following rules were applied (Table 2): 

TABLE 2: STORET REMARK CODE RULES

STORET Remark Code Keep or Delete Data Point

blank - Data not remarked. Keep

A - Value reported is the mean of two or more

determinations.

Keep

B - Results based upon colony counts outside the acceptable

ranges.

Delete

C - Calculated. Value stored was not measured directly, but

was calculated from other data available.

Keep

D - Field measurement. Keep
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E - Extra sample taken in compositing process. Delete

F - In the case of species, F indicates female sex. Delete

G - Value reported is the maximum of two or more

determinations.

Delete

H - Value based on field kit determination; results may not

be accurate.

Delete

I - The value reported is less than the practical

quantification limit and greater than or equal to the method

detection limit.

Keep, but used one-half the reported value as the new value.

J - Estimated. Value shown is not a result of analytical

measurement.

Delete

K - Off-scale low. Actual value not known, but known to be

less than value shown.

Keep, but used one-half the reported value as the new value.

L - Off-scale high. Actual value not known, but known to

be greater than value shown.

Keep

M - Presence of material verified, but not quantified. 

Indicates a positive detection, at a level too low to permit

accurate quantification.

Keep, but used one half the reported value as the new value.

N - Presumptive evidence of presence of material. Delete

O - Sample for, but analysis lost. Accompanying value is

not meaningful for analysis.

Delete

P - Too numerous to count. Delete

Q - Sample held beyond normal holding time. Delete

R - Significant rain in the past 48 hours. Delete

S - Laboratory test. Keep

T - Value reported is less than the criteria of detection. Keep, but replaced reported value with 0.
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U - Material was analyzed for, but not detected. Value

stored is the limit of detection for the process in use. 

Keep, but replaced reported value with 0.

V - Indicates the analyte was detected in both the sample

and associated method blank.

Delete

W - Value observed is less than the lowest value reportable

under remark "T."

Keep, but replaced reported value with 0.

X - Value is quasi vertically-integrated sample. No data point with this remark code in data set.

Y - Laboratory analysis from unpreserved sample. Data

may not be accurate.

Delete

Z - Too many colonies were present to count. Delete

If a parameter (excluding water temperature) value was less than or equal to zero and no remark code was present, the value

was transformed into a missing value.

Rationale - Parameter concentrations should never be zero without a proper explanation. A method detection limit should

at least be listed.

4. Station records were eliminated from the data set if any of the following descriptors were

present within the "Station Type" parameter:

< MONITR - Source monitoring site, which monitors a known problem or

to detect a specific problem.

< HAZARD - Site of hazardous or toxic wastes or substances.

< ANPOOL - Anchialine pool, underground pools with subsurface

connections to watertable and ocean.

< DOWN - Downstream (i.e., within a potentially polluted area) from a

facility which has a potential to pollute.

< IMPDMT - Impoundment. Includes waste pits, treatment lagoons, and

settling and evaporation ponds.

< STMSWR - Storm water sewer.

< LNDFL - Landfill.

< CMBMI - Combined municipal and industrial facilities.

< CMBSRC - Combined source (intake and outfall).

Rationale - these descriptors potentially indicate a station location that at which an

ambient water sample would not be obtained (i.e., such sampling locations are potentially 
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biased) or the sample location is not located within one of the designated water body types (i.e,

ANPOOL). 

5. Station records were eliminated from data set if the station location did not fall within any

established cataloging unit boundaries based on their latitude and longitude.

6. Using nutrient ecoregion GIS coverage provided by USEPA, all station locations with

latitude and longitude coordinates were tagged with a nutrient ecoregion identifier

(nutrient region identifiers are values 1 - 14) and the associated nutrient ecoregion name. 

Because no nutrient ecoregions exist for Alaska, Hawaii, and Puerto Rico, stations located

in these states were tagged with "dummy" nutrient ecoregion numbers (20 = Alaska, 21 =

Hawaii, 22 = Puerto Rico).

7. Using information provided by TVA, 59 station locations that were marked as 'stream'

locations under the "Station Type" parameter were changed to 'reservoir' locations. 

8. The nutrient data retrieved from STORET were assessed for the presence of duplicate

data records. The duplicate data identification process consisted of three steps: 1)

identification of records that matched exactly in terms of each variable retrieved; 2)

identification of records that matched exactly in terms of each variable retrieved except for

their station identification numbers; and 3) identification of records that matched exactly in

terms of each variable retrieved except for their collecting agency codes. The data

duplication assessment procedures were conducted using SAS programs. 

Prior to initiating the data duplication assessment process, the STORET nutrient data set

contained:

41,210 station records

924,420 sample records

• Identification of exactly matching records

All data records were sorted to identify those records that matched exactly. For

two records to match exactly, all variables retrieved had to be the same. For

example, they had to have the same water quality parameters, parameter results

and associated remark codes, and have the same station data item and sample data

item information. Exactly matching records were considered to be exact

duplicates, and one duplicate record of each identified matching set were

eliminated from the nutrient data set. A total of 924 sample records identified as

duplicates by this process were eliminated from the data set. 

• Identification of matching records with the exception of station identification

number

All data records were sorted to identify those records that matched exactly except

for their station identification number (i.e., they had the same water quality
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parameters, parameter results and associated remark codes, and the same station

and sample data item information with the exception of station identification

number). Although the station identification numbers were different, the latitude

and longitude for the stations were the same indicating a duplication of station data

due to the existence of two station identification numbers for the same station. For

each set of matching records, one of the station identification numbers was

randomly selected and its associated data were eliminated from the data set. A

total of 686 sample records were eliminated from the data set through this process. 

• Identification of matching records with the exception of collecting agency codes

All data records were sorted to identify those records that matched exactly except

for their collecting agency codes (i.e., they had the same water quality parameters,

parameter results and associated remark codes, and the same station and sample

data item information with the exception of agency code). The presence of two

matching data records each with a different agency code attached to it suggested

that one agency had utilized data collected by the other agency and had entered the

data into STORET without realizing that it already had been placed in STORET

by the other agency. No matching records with greater than two different agency

codes were identified. For determining which record to delete from the data set,

the following rules were developed: 

< If one of the matching records had a USGS agency code, the USGS

record was retained and the other record was deleted. 

< Higher level agency monitoring program data were retained. For

example, federal program data (indicated by a "1" at the beginning

of the STORET agency code) were retained against state (indicated

by a "2") and local (indicated by values higher than 2) program

data. 

< If two matching records had the same level agency code, the record

from the agency with the greater number of overall observations

(potentially indicating the data set as the source data set) was

retained.

A total of 2,915 sample records were eliminated through this process. 

As a result of the duplicate data identification process, a total of 4,525 sample records and

36 individual station records were removed from the STORET nutrient data set. The

resulting nutrient data set contains the following:

41,174 station records

919,895 sample records
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APPENDIX B

Process for Adding Aggregate Nutrient Ecoregions and Level III Ecoregions
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Steps for assigning Level III ecoregions and aggregate nutrient ecoregion codes and names to the

Nutrient Criteria Database (performed using ESRI's ARCView v 3.2 and its GeoProcessing

Wizard). This process is performed twice; once for the Level III ecoregions and once for the

aggregate nutrient ecoregions:

- Add the station .dbf data table, with latitude and longitude data, to project by 'Add

Event Theme'

- Convert to the shapefile format

- Create 'stcojoin' field, populate the 'stcojoin' field with the following formula:

'County.LCase+State.LCase'

- Add field 'stco_flag' to the station shapefile

- Spatially join the station data with the county shapefile (cntys_jned.shp)

- Select 'stcojoin' (station shapefile) field = 'stco_join2' (county shapefile) field 

- Calculate stco_flag = 0 for selected features

- Step through all blank stco_flag records, assign the appropriate stco_flags, see list

on the following page

- Select all stco_flags = 4 or 7, switch selection

- Calculate ctyfips (station) to cntyfips (county)

- Stop editing and save edits, remove all joins

- Add in 2 new fields 'x-coord1' and 'y-coord1' into station table

- Select all stco_flags = 1, 2, and 6

- Link county coverage with station coverage

- Populate 'x-coord1' and 'y-coord1' with 'x-coord' and 'y-coord' from county

coverage

- Select all stco_flags = 1, 2, and 6, export to new .dbf file

- Add new .dbf file as event theme

- Convert to shapefile format

- Add the following fields to both tables (original station and station126 shapefiles):

'eco_omer', 'name_omer', 'dis_aggr', 'code_aggr', 'name_aggr'

- Spatially join station126 and eco-omer coverage

- Populate the 'eco_omer' field with the 'eco' value

- Repeat the previous step using the nearest method (line coverage) to determine

ecoregion assignment for the line coverage, if some records are blank

- Spatially join the ecoregion line coverage to station coverage, link the LPoly#

(from the spatially joined table) to Poly# (of the ecoregion polygon coverage)

- Populate the Eco fields with the appropriate information.

- Follow the same steps to the Rpoly#

- Remove all table joins

- Link the useco-om table with station126 table and populate 'name-omer' field

- Spatially join station aggr coverage and populate the rest of the fields. Follow the

same procedures as outlined above

- Remove all joins

- Make sure the new Eco field added into the station126 shapefile are different than
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the ones in the original station shapefile

- Join station126 and station coverage by station-id

- Populate all the Eco fields in the original station coverage

- Remove all joins

- Save table

- Make sure that all ctyfips records are populated; the county shapefile may have to

be joined to populate the records, if the stco_flag = 4

- Create 2 new fields, 'NewCounty' and 'NewState'

- Populate these new fields with a spatial join to the county coverage

- Select by feature (ecoregion shapefile) all of the records in the station shapefile

- Switch selection (to get records outside of the ecoregion shapefile)

- If any of the selected records have stco_flag = 0 (they are outside the ecoregion

shapefile boundary), calculate them to stco_flag = 3

stco_flags (state/county flags in order of importance)

0 The state and county values from the data set matched the state and county values 

from the spatial join.

(Ecoregions were assigned based on the latitude/longitude coordinates.)

1 The state and county values from the data set did not match the state and county

values from the spatial join, but the point was inside the county coverage 

boundary.

(Ecoregions were assigned based on the county centroid.)

2 The state and county values from the data set did not match the state and county 

values from the spatial join because the point was outside the county coverage 

boundary; therefore, there was nothing to compare to the point (i.e., the point 

falls in the ocean/Canada/Mexico). This occurred for some coastal samples.

(Ecoregions were assigned based on the county centroid.)

3 The state and county values from the data set matched the state and county from

the spatial join, but the point was outside the ecoregion boundary.

(Ecoregions were assigned to the closest ecoregion to the point.)

(No ecoregions were assigned to AK, HI, PR, BC, and GU.)

4 Latitude/longitude coordinates were provided, but there was no county 

 information.

(Ecoregions were assigned based on the latitude/longitude coordinates.)

5 The state and county values from the data set did not match the state and county 

 values from the spatial join due to spelling or naming convention errors.

The matches were performed manually. 

(Ecoregions were assigned based on the latitude/longitude coordinates.)

6 No latitude/longitude coordinates were provided, only state and county

information was available.

(Ecoregions were assigned based on the county centroid.)

7 No latitude/longitude coordinates were provided, only state information was 

available; therefore, no matches were possible.

(Ecoregions were not assigned. Data is not included in the analysis.)
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APPENDIX C

Glossary

Coefficient of Variation- Equal to the standard deviation divided by the mean multiplied by 100.

Maximum- The highest value.

Mean- The arithmetic average.

Median- The 50th percentile or middle value. Half of the values are above the median, and half of

the values are below the median.

Minimum- The lowest value.

Standard Deviation- Equal to the square root of the variance with the variance defined as the sum

of the squared deviations divided by the sample size minus one.

Standard Error- Standard error of the mean is equal to the standard deviation divided by the

square root of the sample size.