United States Office of Water EPA 822-B-01-014

Environmental Protection 4304 December 2001

Agency

Ambient Water Quality

Criteria Recommendations

Information Supporting the Development 

of State and Tribal Nutrient Criteria

Rivers and Streams in 

Nutrient Ecoregion V
EPA-822-B-01-014

AMBIENT WATER QUALITY CRITERIA RECOMMENDATIONS

INFORMATION SUPPORTING THE DEVELOPMENT OF STATE AND TRIBAL

NUTRIENT CRITERIA

FOR

RIVERS AND STREAMS IN NUTRIENT ECOREGION V

South Central Cultivated Great Plains

including all or parts of the States of:

Montana, North Dakota, South Dakota, Nebraska, Wyoming,

Colorado, Kansas, Oklahoma, Texas, and New Mexico,

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, DC

DECEMBER 2001
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FOREWORD

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

Ecoregion V. 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 the Clean

Water Act (CWA). Under section 303(c) of the CWA, States and authorized Tribes have the

primary responsibility for adopting water quality standards as part of State or Tribal law or

regulation. Federal regulations require State and Tribal standards to 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 in creating their own water quality standards. 

The term “water quality criteria” is used in two sections of the CWA, section 304(a)(1) and

section 303(c)(2). The term has a different impact in each section. On the one hand, 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. On the other hand, in section 303, ambient water quality criteria are developed by

States and Tribes as part of their water quality standards, to 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

numerically or as quantified translations of narrative criteria within State or Tribal water quality

standards, quantified criteria are critical for assessing attainment of designated uses and

measuring progress toward meeting CWA goals.

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 that as many as half of

the Nation’s surface waters surveyed 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 14 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 has published and will continue to publish technical

guidance manuals that describe a process for assessing nutrient conditions in the four waterbody

types listed above. 

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

criteria and procedures to help establish quantified 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 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.
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States and authorized Tribes have several options in adopting these criteria. EPA

recommends the following approaches, in order of preference:

1. Wherever possible, develop nutrient criteria that fully reflect local conditions and protect

specific designated uses through 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.

EPA developed the nutrient criteria recommendations in this document with the intent that

they serve as a starting point for States and Tribes to develop more refined criteria, as

appropriate, to reflect local conditions. The values presented in this document generally

represent nutrient levels that protect against the adverse effects of nutrient overenrichment. They

are based on the information that was available to the Agency at the time of this publication. 

EPA expects States and Tribes may have additional information and data that may be utilized in

the refinement of these criteria. EPA offers to work with States and authorized Tribes to

establish the necessary quantitative endpoints to reduce the excess nutrient inputs into our

nation's waters and to prevent any further impairments.

 

Geoffrey H. Grubbs, Director

Office of Science and Technology
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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 decisionmakers retain the discretion to adopt

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

scientifically defensible. Even though this document contains EPA’s scientific

recommendations regarding ambient concentrations of nutrients that will 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.
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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 the end of 2000. In addition, the Agency formed Regional Technical Assistance Groups

(RTAGs), which include State and Tribal representatives working to develop more refined and

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

This document presents EPA’s current recommended criteria for total phosphorus (TP), total

nitrogen (TN), chlorophyll a, and turbidity for rivers and streams in Nutrient Ecoregion V, which

were derived using the procedures described in the Rivers and Streams Nutrient Criteria

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

EPA’s ecoregional nutrient criteria address cultural eutrophication—the adverse effects of

excess human-caused nutrient inputs. The criteria are empirically derived to represent surface

waters that are minimally impacted by human activities and protective of aquatic life and

recreational uses. The information contained in this document represents 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 that included, to the

extent they were readily available, the following critical elements: 

C Historical and recent nutrient data in Nutrient Ecoregion V. Data sets from Legacy

STORET, NASQAN, NAWQA, EPA Region 7 - Central Plains Center for BioAssessment

(CPCB), EPA Region 7 - CPCB 2, EPA Region 7 - REMAP, EPA Region 8 - Montana and

Wyoming, EPA Region 8 - South Dakota, and EPA Region 8 - North Dakota were used to

assess nutrient conditions from 1990 to 2000.

C Reference sites/reference conditions in Nutrient Ecoregion V. Reference conditions

presented are based on 25th percentiles of all nutrient data, including a comparison of

reference conditions for the aggregate Ecoregion versus the subecoregions. States and

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

geographic scales and to compare them to EPA’s reference conditions.

C Models employed for prediction or validation. EPA did not identify any specific models

to develop nutrient criteria. States and Tribes are encouraged to identify and apply

appropriate models to support nutrient criteria development. 

C 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.

C Downstream effects of criteria. EPA encourages the RTAG to assess the potential effects

of the proposed criteria on downstream water quality and uses.
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In addition, EPA followed specific QA/QC procedures during data collection and analysis. 

All data were reviewed for duplications. All data were 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: North

Dakota, South Dakota, Montana, Wyoming, Colorado, Kansas, Oklahoma, and Texas. Nebraska

indicated that standard or EPA-approved methods were used for some specific nutrient

parameters.

The following tables contain a summary of aggregate and level III Ecoregion values for

TN, TP, water column chlorophyll a, and turbidity.

BASED ON 25th PERCENTILES ONLY

Nutrient Parameters Aggregate Nutrient Ecoregion V 

Reference Conditions

Total phosphorus (μg/L) 67

Total nitrogen (mg/L) (reported) 0.88

Chlorophyll a (μg/L) (Fluorometric method) 3

Turbidity (FTU) 7.83

For subecoregions 25, 27, 32, and 42, the ranges of nutrient parameter reference conditions are

as follows:

BASED ON 25th PERCENTILE ONLY

Nutrient Parameters Range of Level III Subecoregions

Reference Conditions

Total phosphorus (μg/L) 41 - 90*

Total nitrogen (mg/L) 0.84 - 1.07

Chlorophyll a (μg/L) (Fluorometric method) 2.51 - 3.2

Turbidity (FTU) 3 - 9.01

* This value appears inordinately high and may either be a statistical anomaly or reflect a unique condition. In any case, further

regional investigation is indicated to determine the sources, i.e., measurement error, notational error, statistical anomaly,

naturally enriched conditions, or cultural impacts.
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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; telephone (513) 489-8190 or toll free (800) 490-

9198. Please refer to EPA document number EPA-822-B-01-014 .
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ACKNOWLEDGMENTS

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

reviewers: EPA Regions 6, 7, and 8; the States of North Dakota, South Dakota, Montana,

Wyoming, Nebraska, Colorado, Kansas, Oklahoma, New Mexico, 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 Office of Science and Technology. EPA also acknowledges the external

peer review efforts of Nina Caraco, Institute of Ecosystem Studies; Amy Parker, University of

Georgia; Jan Stevenson, University of Michigan.
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TABLE OF CONTENTS

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Disclaimer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Notice of Document Availability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Acknowledgments .............................................................x

List of Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii

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

2.0 Best Use of This Information ................................................6

3.0 Area Covered by This Document ..............................................8

3.1 Description of Aggregate Ecoregion V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.2 Geographical Boundaries of Aggregate Ecoregion V .........................9

3.3 Level III Ecoregions Within Aggregate Ecoregion V . . . . . . . . . . . . . . . . . . . . . . . . 11

3.4 Suggested Ecoregional Subdivisions or Adjustments . . . . . . . . . . . . . . . . . . . . . . . . 13

4.0 Data Review for Rivers and Streams in Aggregate Ecoregion V . . . . . . . . . . . . . . . . . . . . 13

4.1 Data Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.2 Historical Data from Aggregate Ecoregion V (TP, TN, chl a, turbidity) . . . . . . . . . . 13

4.3 QA/QC of Data Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.4 Data for All Rivers and Streams Within Aggregate Ecoregion V . . . . . . . . . . . . . . . 14

4.5 Statistical Analysis of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

4.6 Classification of River/Stream Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.7 Summary of Data Reduction Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5.0 Reference Sites and Conditions in Aggregate Ecoregion V . . . . . . . . . . . . . . . . . . . . . . . . 26

6.0 Models Used to Predict or Verify Response Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 27

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

Aggregate Ecoregion V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7.1 Example Worksheet for Developing Aggregate Ecoregion and 

Subecoregion Nutrient Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7.2 Setting Seasonal Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7.3 When Data/Reference Conditions Are Lacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.4 Site-Specific Criteria Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

8.0 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

9.0 Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

A. Descriptive Statistics Data Tables for Aggregate Ecoregion . . . . . . . . . . . . . . . . . . A-1

B. Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate 

Ecoregion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

C. Quality Control/Quality Assurance Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1
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LIST OF TABLES AND FIGURES

Tables

Table 1 River and stream records for Aggregate Ecoregion V—South Central

Cultivated Great Plains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

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

Table 3a-d Reference conditions for Ecoregion V streams . . . . . . . . . . . . . . . . . . . . . . . . . 18

Table 4 Suggested boundaries for trophic classification of streams from cumulative

frequency distributions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Table 5 Nutrient (:g/L) and algal biomass criteria limits recommended to prevent

nuisance conditions and water quality degradation in streams based either on

nutrient-chlorophyll a relationships or preventing risks to stream impairment as

indicated. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figures

Figure 1a Fourteen Nutrient Ecoregions as Delineated by Omernik (2000) .............4

Figure 1b Level III Ecoregions of the United States ...............................5

Figure 2 Aggregate Ecoregion V . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 3 Aggregate Ecoregion V with level III Ecoregions shown . . . . . . . . . . . . . . . . . 12

Figure 4 Sampling locations within each level III Ecoregion . . . . . . . . . . . . . . . . . . . . . . 15

Figure 5a Illustration of data reduction process for stream data . . . . . . . . . . . . . . . . . . . . . 24

Figure 5b Illustration of reference condition calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
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1.0 INTRODUCTION

Background

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

amounts nutrients cause eutrophication or hypereutrophication, which results in overgrowth of

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

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

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

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

kills, overabundance of macrophytes, likely increased sedimentation, 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 after siltation 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 (CWA) establishes that, wherever

possible, water quality must provide for the protection and propagation of fish, shellfish, and

wildlife, and recreation in and on the water and/or protecting the physical, chemical, and

biological integrity of those waters. In adopting water quality standards, States and Tribes

designate uses for their waters in consideration of these CWA goals, and establish water quality

criteria that contain sufficient parameters to protect that integrity and 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 them how best to deal with the

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

values for phosphorus (P) or nitrogen (N) applicable to all waterbodies and regions of the

country. Rather, they 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 was

published in fall 2001, and the draft wetlands technical guidance manual will be published by
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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

States and Tribes to develop more refined and 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 [chl a] and some measure of turbidity). Other indicators such as dissolved

oxygen, macrophyte or benthic algal growth or speciation, and other fauna and flora changes are

also useful. However, the first four variables 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, or

natural resources management—especially water resource management, chemistry, and ecology. 

The RTAG evaluates and recommends appropriate classification techniques, usually physical,

for criteria determination 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 10-25

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

resource.

The third factor is the existing reference condition, a selection of reference sites chosen to

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

these sites are combined and a value is selected to represent the reference condition, the best

attainable, most natural condition of the resource base at this time.

The RTAG comprehensively evaluates these three elements to propose a candidate criterion

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

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

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

The final element of the process is 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.
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Although States and authorized Tribes do 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 is a balanced

incorporation of all five elements.

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

content and different precipitation regimes, the application of the criterion development process

should reflect this regional variation. Therefore, an ecoregional approach was chosen. Initially,

the continental United States was divided into 14 separate Ecoregions of similar geographical

characteristics and similar nutrient condition (Figure 1a). 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 from

adjacent areas in a holistic sense. Geographic characteristics such as soils, vegetation, climate,

geology, and land cover are relatively similar within each Ecoregion (Omernik, 2000). 

The nutrient Ecoregions are aggregates of EPA’s hierarchical level III Ecoregions (see

Figure 1b for map of 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 because of 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 and

the more refined scales (level III Ecoregions and waterbody classes), where data were available

to make such assessments, are presented for comparison and completeness of analysis. 

Comparison 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 data from sites that represent the least impacted

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 their basic approaches to 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 use 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 uses

of existing resources and are holistic indicators of the water quality necessary to protect uses.

States and authorized Tribes can develop and apply nutrient 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

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
4

Figure 1a. Fourteen nutrient Ecoregions as delineated by Omernik (2000). Ecoregions were based on ecosystem type, and nutrient conditions.
5

Figure 1b. Level III Ecoregions of the United States.
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through designing and conducting a common sampling program. The traditional biological

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

nutrient assessment. To investigate the effectiveness of this tandem approach, EPA has initiated

pilot projects in both freshwater and marine environments to pursue the relationship between

nutrient overenrichment and apparent declines in diversity 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 and ultimately controlling discharges or releases of pollutants. The recommendations

also provide guidance to EPA when it determines that it is necessary to promulgate Federal

water quality standards under section 303(c). 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 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 efforts where possible. States and Tribes can

address nutrient overenrichment through establishment of numerical criteria or use of 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 will establish procedures to

quantitatively translate these statements for both assessment and source control purposes. 

Ecoregional nutrient criteria are developed to represent 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 judgment, and evaluation of

downstream effects. EPA has used elements of this process to produce the information

contained in this document. The 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.
7

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. EPA has also published methods for modifying 304(a) criteria, such as the water

effect ratio, on a site-specific basis where conditions warrant modification to achieve the

intended level of protection. For nutrients, however, EPA expects that it will usually be

necessary for States and authorized Tribes to be more precise in identifying the nutrient levels

that protect aquatic life and recreational uses. This can be achieved through criteria modified to

reflect a smaller geographic scale than an Ecoregion, such as a subecoregion, the State or Tribe

level, or a specific class of waterbodies. Criteria can be refined by grouping data or performing

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

consideration of other elements such as published literature or models.

EPA expects that the values presented in this document generally represent nutrient levels

that protect against the adverse effects of cultural 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 uses that need to be protected. For

example, more sensitive uses may require more stringent criteria to ensure adequate protection. 

On the other hand, overly stringent levels of protection against cultural eutrophication may

actually fall below 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 using historical data and expert judgment and current reference conditions. 

These elements of the 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 to develop more refined criteria according to

the methods described in EPA’s technical guidance manuals for specific waterbody types.

To assist in further refinement of nutrient criteria, EPA has established 10 RTAGs (experts

from EPA Regional Offices and States/Tribes). In 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.

In using the information and recommendations in this document and elsewhere 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 protect uses before impairment occurs and to maintain

downstream uses. Early response variables are necessary to warn of possible impairment

and to integrate the effects of variable and potentially unmeasured nutrient loads.
8

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 (how long) and frequency (how often) of

occurrence in addition to magnitude (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 or biweekly measurements) is considered appropriate. 

However, these central tendency measures should apply each season or each year, except

under the most extraordinary conditions (e.g., a 100-year flood).

3.0 AREA COVERED BY THIS DOCUMENT

This chapter provides a general description of the aggregate Ecoregion and its geographical

boundaries. Descriptions of the level III subecoregions contained within the aggregate

Ecoregion are also provided.

3.1 Description of Aggregate Ecoregion V

The nearly level, rolling, and irregular plains of Ecoregion V are mostly semiarid and

originally supported mostly grassland. A large part of the area is now cropland and includes the

major winter wheat growing area of the United States. The annual freeze-free growing season

ranges from 120 days in the northwest to over 240 days in the southeast. Mean annual

precipitation is typically erratic and generally decreases from about 28 inches in most eastern

areas to about 15 inches in the west. Most of the precipitation occurs during the summer and

amounts are usually enough to support dryland farming and rangeland. Intermittent and

ephemeral streams are common in drier, western portions and/or where irrigation has lowered

the water table.

Ecoregion V is in the transition zone between short and tall grass prairies. Purely tall grass

is limited to wetter, easternmost areas whereas short grass is exclusively found in the drier,

western part; in between, the potential natural vegetation is a mixture of tall and short grass

species. Riparian woodland is usually restricted to wetter eastern areas. Scattered ponderosa

pine is found on some ridgetops and bluffs especially in Nebraska. In southwestern Oklahoma

and central Texas, shortgrass prairie originally grew with scattered, low shrubs and deciduous

trees. The region’s characteristic mix of short and tall grass prairie is distinct.

Parent geology (including salt formations) and soils help create the alkalinity, dissolved

solid, sulfate, sodium, chloride, and suspended sediment concentrations of streams in Ecoregion

V. High sulfate concentrations in stream water occur over broad areas; they are primarily the

product of soil leaching and the dissolution of gypsum beds, although agricultural compounds

such as ammonium sulfate and gypsum also can contribute sulfate to rivers (USGS, 1993).

The landforms, soils, and climate of Ecoregion V are favorable to agriculture. Today, more

than half of Ecoregion V is dryland farmed, about a third is rangeland, and most of the remainder

is used for irrigated farming. Ecoregion V is dominated by dryland winter wheat, grain
9

sorghum, and alfalfa farming. Irrigated agriculture occurs in areas with sufficient available

ground water and along some reaches of perennial rivers. The number of acres under irrigation

have increased rapidly in Ecoregion V and produce silage corn, winter wheat, soybeans, grain

sorghum, sugar beets, and other livestock feed and forage crops. The use of commercial

fertilizer on cropland increased between 1969 and 1992. Cattle feed lots are found throughout

most of the southern and central parts of the South Central Cultivated Great Plains (V); their

density is higher than elsewhere in the United States and the number of cattle fattened at feedlots

has increased between 1969 and 1992. Cattle graze much of the agriculturally marginal land and

ground water is generally adequate to meet the needs of livestock; rangeland is not uncommon. 

Overall, the land use mosaic of the South Central Cultivated Great Plains (V) is distinct from

that of the surrounding regions; winter wheat and feedlots are far more common than in adjacent

ecoregions. 

Agricultural runoff has affected regional water quality. Upward trends in nitrite plus nitrate

levels in rivers have mirrored increasing nitrogen fertilizer use (U.S. Geological Survey, 1993). 

In the Platte River of central Nebraska between 1993 and 1995, dissolved nitrate concentrations

were highest near cropland and pasture that have had intensive applications of chemical

fertilizers. Stream sedimentation from agricultural activity has occurred and has negatively

impacted aquatic habitat although no-till cropping practices and other conservation efforts have

locally reduced field erosion. Runoff from feedlots is a significant regional water quality

problem; nondisinfected runoff from livestock confinement areas have significantly elevated

fecal coliform bacteria and nitrite plus nitrate concentrations in rivers (USGS, 1993).

Much of the region’s irrigation water is obtained from wells or perennial streams. In many

areas, ground water withdrawal rates have greatly exceeded recharge rates and have caused the

water table to gradually decline, pumping costs to increase, and both springflow and streamflow

to diminish. Perennial streams are uncommon and can fluctuate widely in flow from year to year

due to the erratic rainfall that characterizes the region. In addition, irrigation return flows have

increased the concentrations of sodium, sulfate, chloride, and dissolved solids in base flows. 

Irrigation return flows have the greatest impact on river quality during droughts when discharge

is dominated by tailwater from irrigated fields. Locally, brines associated with petroleum

production have increased the alkalinity, dissolved solid, sulfate, sodium, chloride, and

suspended sediment concentrations of streams (USGS, 1993).

Some urban areas in Ecoregion V especially in Texas and Colorado have been growing

rapidly and, resultantly, a great deal of agricultural land has been recently converted to urban and

industrial uses. Discharges from municipalities and industries have caused elevated

concentrations of nitrate and phosphorus in streams. Such increased nutrient loading has caused

a corresponding increase in the eutrophication rates of some downstream lakes and reservoirs

(USGS, 1993). 

3.2 Geographical Boundaries of Aggregate Ecoregion V

Ecoregion V is a fragmented region composed of four separate segments in the central

portion of the United States where cultivated Great Plains prevail (Figure 2). The northern most 
10

Figure 2. Aggregate Ecoregion V.
11

segment begins along the northern border of Montana and goes southeast into the states of North

Dakota, South Dakota, and Nebraska. 

The second and largest segment is located in the south central portion of the country. It

begins in small section of southwestern South Dakota and continues south into Texas. It

encompasses the southeastern portion Wyoming, the eastern border of Colorado, and a large

portion of Nebraska, Kansas, and Oklahoma. From north central Texas, the segment runs west

into eastern New Mexico. 

The last two segments are thin strips that run almost parallel from northeast to southeast

Texas. The western segment is over double the size of the eastern strip.

3.3 Level III Subecoregions Within Aggregate Ecoregion V

There are four level III subecoregions contained within Aggregate Ecoregion V (Figure 3). 

The following are brief descriptions provided by Omernik (1999) of the climate, vegetative

cover, topography, and other ecological information pertaining to these subecoregions.

25. Western High Plains

Higher and drier than the Central Great Plains to the east, and in contrast to the irregular,

mostly grassland or grazing land of the Northwestern Great Plains to the north, much of the

Western High Plains comprises smooth to slightly irregular plains having a high percentage of

cropland. Grama-buffalo grass is the potential natural vegetation in this region as compared to

mostly wheatgrass-needlegrass to the north, Trans-Pecos shrub savanna to the south, and taller

grasses to the east. The northern boundary of this ecological region is also the approximate

northern limit of winter wheat and sorghum and the southern limit of spring wheat crop

production.

27. Central Great Plains

The Central Great Plains are slightly lower, receive more precipitation, and are somewhat

more irregular than the Western High Plains to the west. Once a grassland, with scattered low

trees and shrubs in the south, much of this ecological region is now cropland, the eastern

boundary of the region marking the eastern limits of the major winter wheat growing area of the

United States.

32. Texas Blackland Prairies

The Texas Blackland Prairies is a disjunct ecological region distinguished from

surrounding regions by its fine textured clayey soils and predominantly prairie potential natural

vegetation. This region now contains a higher percent of cropland than adjacent regions,

although much of the land has been recently converted to urban and industrial uses.
12

Figure 3. Aggregate Ecoregion V with level III Ecoregions shown.
13

42. Northwestern Glaciated Plains

The Northwestern Glaciated Plains Ecoregion is a transitional region between the generally more

level, moister, more agricultural Northern Glaciated Plains to the east and the generally more

irregular, dryer, Northwestern Great Plains to the west and southwest. The western and

southwestern boundary roughly coincides with the limits of continental glaciation. This

Ecoregion has a moderately high concentration of semi-permanent and seasonal wetlands,

locally referred to as Prairie Potholes, that dot the landscape.

3.4 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. See the paper

by Dale Robertson (USGS, 2001b) for an alternative approach to ecoregions entitled “An

Alternative Regarding the Scheme for Defining Nutrient Criteria for Rivers and Streams.”

4.0 DATA REVIEW FOR RIVERS AND STREAMS IN AGGREGATE ECOREGION V

This 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). EPA considers these parameters 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 enrichment for most 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). 

4.1 Data Sources

Data sets from Legacy STORET, NASQAN, NAWQA, EPA Region 7 - Central Plains

Center for BioAssessment (CPCB), EPA Region 7 - CPCB 2, EPA Region 7 - REMAP, EPA

Region 8 - Montana and Wyoming, EPA Region 8 - South Dakota, and EPA Region 8 - North

Dakota were used to assess nutrient conditions from 1990 to 2000. 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 V (TP, TN, chl a, and turbidity)

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

years to assess the relative stability of the systems. 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 variations over the

past 10 years (e.g., what do seasonal variations indicate?).
14

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, stormwater

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

States within Ecoregion V were contacted regarding the quality of their data and

information on the methods used to sample and analyze their waters. The following States

indicated standard methods or approved EPA methods were used: North Dakota, South Dakota,

Montana, Wyoming, Colorado, Kansas, Oklahoma, and Texas. Nebraska indicated that standard

or EPA-approved methods were used for some specific nutrient parameters. New Mexico did

not provide information prior to the publication of this document. 

4.4 Data for All Rivers and Streams Within Aggregate Ecoregion V 

Figure 4 shows the location of the sampling stations within each subecoregion. Table 1

presents all data records for all parameters for Aggregate Ecoregion V 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. The 75th percentile is preferred by EPA because 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 to attempt to approximate the preferred

approach. 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 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], the

letter from Tennessee Department of Environment and Conservation to Geoffrey Grubbs

[TNDEC, 2000], the unpublished paper titled “Estimating the Natural Background

Concentrations of Nutrients in Streams and Rivers of the Conterminous United States” [USGS,

2001], and the letter from Matthew Liebman, U.S. EPA Region 1 Nutrient Criteria Coordinator

to Geoffrey Grubbs [U.S. EPA, 2000c]). 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).

Tables 2 and 3a-d present potential reference conditions for both the aggregate Ecoregion

and the subecoregions using both methods. However, the reference stream column is left blank 
15

Figure 4. Sampling locations within each level III Ecoregion.
16

Table 1. River and stream records* for Aggregate Ecoregion V—South Central Cultivated

Great Plains

Aggregate

Ecoregion V

Sub ecoR

25

Sub ecoR

27

Sub ecoR

32

Sub ecoR

42

# of named streams 556 123 266 109 58

# of stream stations 984 236 425 210 113

Key nutrient parameters (listed below)

- # of records for turbidity 

(all methods) 5,725 714 4,108 656 247

- # of records for chlorophyll a

(all methods) 1,517 237 532 722 26

- # of records for total Kjeldhal

nitrogen (TKN) 7,817 2,402 2,639 2,233 543

- # of records for nitrite +

nitrate (NO2+NO3) 6,830 1,542 3,638 1,274 376

- # of records for total nitrogen

(TN) 987 219 562 49 157

- # of records for total

phosphorus (TP) 12,325 3,221 6,025 2,381 698

Total # of records for key 

nutrient parameters 35,201 8,335 17,504 7,315 2,047

*The number of rivers and streams presented in this table is based on the number of rivers and streams for which nutrient data

were provided in the National Nutrient database. This does not imply that this is the total of rivers and streams within the

Ecoregion. States and Tribes should determine the representativeness of the tabular data by comparing this information with any

additional material they may have.

Definitions: (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.
17

Table 2. Reference conditions for Aggregate Ecoregion V 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) 332 0.00 5.54 0.45

NO2+NO3-N (mg/L) 350 0.00 9.64 0.26

TN (mg/L) - calculated 0.71

TN (mg/L) - reported 94 0.23 9.85 0.88

TP (μg/L) 489 0.00 2232 68

Turbidity (NTU) 105 2 492 16

Turbidity (FTU) 179 1.13 131.50 7.83

Turbidity (JCU) 41 1.75 138.50 8.70

Chlorophyll a (μg/L) - F 42 0.4 51 3

Chlorophyll a (μg/L) - S 110 0.2 79.1 0.4

Chlorophyll a (μg/L) - T — — — —

Periphyton Chl a (mg/m2

) — — ——

* 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.

† 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 10 μg/L, summer 15 μg/L, fall 12 μg/L, and winter 5 μg/L, the median value of all

seasons’ P25 will be 11μg/L. 

‡ As determined by the Regional Technical Assistance Groups (RTAGs).

Abbreviations: P25, 25th percentile of all data; P75, 75th percentile of all data; 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; —, not applicable.

Definitions: (1) Number of Streams refers to the largest number of streams and rivers for which data existed for a given season

within an aggregate nutrient Ecoregion. (2) 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. (3) 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 fewer than 3 seasons were used to derive

the median, the entry is flagged (z). (4) 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 fewer than 4 streams/season in order to

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

statistical program automatically used the minimum value within the fewer-than-4 population. If fewer than 4 streams were used

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

Note: For seasonal values, refer to Appendix A, “Descriptive Statistics Data Tables for Aggregate Ecoregion.”
18

Table 3a. Reference conditions for Ecoregion V streams

subecoregion 25

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) 73 0.00 5.28 0.54

NO2+NO3-N (mg/L) 61 0.00 5.89 0.72

TN (mg/L) - calculated 1.26

TN (mg/L) - reported 24 0.49 9.36 1.07

TP (μg/L) 103 0 1,988 60

Turbidity (NTU) 24 2 492 12.60

Turbidity (FTU) 16 2.75 57.50 4.36

Turbidity (JCU) — — — —

Chlorophyll a (μg/L) - F 20 1 51 3

Chlorophyll a (μg/L) - S 12 0.2 26.1 5.1

Chlorophyll a (μg/L) - T — — — —

Periphyton Chl a (mg/m2) — — ——

Table 3b. Reference conditions for Ecoregion V streams

subecoregion 27

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) 139 0.05 4.41 0.52

NO2+NO3-N (mg/L) 201 0.01 9.48 0.19

TN (mg/L) - calculated 0.71

TN (mg/L) - reported 54 0.26 3.74 0.84

TP (μg/L) 246 3 1,958 90

Turbidity (NTU) 68 3 179 22.13

Turbidity (FTU) 133 1.88 119.75 9.01

Turbidity (JCU) 33 2.53 137.25 10

Chlorophyll a (μg/L) - F 16 0.7 38 2.5

Chlorophyll a (μg/L) - S 32 0.2 49.4 1.3

Chlorophyll a (μg/L) - T — — — —

Periphyton Chl a (mg/m2

) — — ——
19

Table 3c. Reference conditions for Ecoregion V streams

subecoregion 32

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) 89 0.09 2.59 0.38

NO2+NO3-N (mg/L) 52 0.01 8.75 0.39

TN (mg/L) - calculated 0.77

TN (mg/L) - reported 3 0.85 1.90 0.85 (zz)

TP (μg/L) 94 2 1,998 45

Turbidity (NTU) — — — —

Turbidity (FTU) 25 1.95 121.75 6.23

Turbidity (JCU) — — — —

Chlorophyll a (μg/L) - F — — — —

Chlorophyll a (μg/L) - S 66 0.2 32.1 0.2

Chlorophyll a (μg/L) - T — — — —

Periphyton Chl a (mg/m2)— — — —
20

Table 3d. Reference conditions for Ecoregion V streams

subecoregion 42

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) 36 0.24 3.14 0.55

NO2+NO3-N (mg/L) 38 0.01 3.36 0.06

TN (mg/L) - calculated 0.61

TN (mg/L) - reported 13 0.55 2.96 0.96

TP (μg/L) 50 6 1,070 41

Turbidity (NTU) 13 2.10 142 30

Turbidity (FTU) 7 2.43 75.88 3

Turbidity (JCU) 8 (z) 0.25 140 4.50

Chlorophyll a (μg/L) - F 7 3.2 7.9 3.2

Chlorophyll a (μg/L) - S — — — —

Chlorophyll a (μg/L) - T — — — —

Periphyton Chl a (mg/m2) — — ——

* 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.

† 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 10 μg/L, summer 15 μg/L, fall 12 μg/L, and winter 5 μg/L, the median value of all

seasons’ P25 will be 11μg/L. 

‡ As determined by the Regional Technical Assistance Groups (RTAGs).

Abbreviations: P25, 25th percentile of all data; P75, 75th percentile of all data; 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; —, not applicable.

Definitions: (1) Number of Streams 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). (2) 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. (3) 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 fewer than 3 seasons were used to

derive the median, the entry is flagged (z). (4). 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 fewer than 4 streams/season in order to

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

statistical program automatically used the minimum value within the fewer-than-4 population. If fewer than 4 streams were used

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

Note: For seasonal and yearly values, refer to Appendix B, “Descriptive Statistics Data Tables for Level III Subecoregions

Within Aggregate Ecoregion.”
21

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

information on reference streams. Tables 3a-d present potential reference conditions for rivers

and streams in the level III subecoregions within the aggregate Ecoregion. Note that the

footnotes for Table 2 apply to Tables 3a-d. Appendixes A and B provide a complete

presentation of all descriptive statistics for both the aggregate Ecoregion and the level III

subecoregions. 

Tables 4 and 5 are presented for comparison purposes. They allow the reader to determine

where, in the trophic state, the recommended reference conditions fall within traditionally

viewed trophic boundaries.

4.6 Classification of River/Stream Type

Assessing the data by stream type should 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 V for which data existed. For example, if one stream had 300 observations for

phosphorus over the decade or 1 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 (Figures 5a, 5b).

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 cannot be determined, use

the 25th percentile for the aggregate Ecoregion or consider the lowest 25th percentile from

a subecoregion (level III) within the aggregate nutrient Ecoregion. Without data, one may

assume that the subecoregion in question is 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 are added, resulting in a calculated TN value. The number of samples (N)

for calculated TN is not filled in because 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.
22

Table 4. Suggested boundaries for trophic classification of streams from cumulative

frequency distributions. The boundary between oligotrophic and mesotrophic systems

represents the lowest third of the distribution and the boundary between mesotrophic and

eutrophic marks the top third of the distribution.

Variable (units)

Oligotrophicmesotrophic 

boundary

Mesotrophic-eutrophic 

boundary

Sample size

(N)

mean benthic chlorophyll (mg m-2)

a 20 70 286

maximum benthic chlorophyll (mg m-2)

a 60 200 176

sestonic chlorophyll 

(:g L-1)

b 10 30 292

TN (:g L-1)

a,c 700 1,500 1,070

TP (:g L-1)

a,b,c 25 75 1,366

Note: This table is provided to allow the reader to make comparisons between the ecoregional criteria provided in this document

and traditional nutrient and biological endpoints.

a

Data from Dodds et al. (1998); bdata from Van Nieuwenhuyse and Jones (1996); cdata from Omernik (1977).
23

Table 5. Nutrient (μg/L) and algal biomass criteria limits recommended to prevent

nuisance conditions and water quality degradation in streams based either on nutrientchlorophyll a relationships or preventing risks to stream impairment as indicated.

Periphyton Maximum in mg/m2

TN TP DIN SRP Chlorophyll a Impairment Risk Source

100-200 nuisance growth Welch et al. 1988, 1989

275-650 38-90 100-200 nuisance growth Dodds et al. 1997 

 1,500 75 200 eutrophy Dodds et al. 1998

 300 20 150 nuisance growth Clark Fork River Tri-State

 20 Cladophora

nuisance growth

Chetelat et al. 1999

 10-20 Cladophora

nuisance growth

Stevenson unpubl. data

 430 60 eutrophy UK Environ. Agency 1988

 100a 10a 200 nuisance growth Biggs 2000

 25 3 100 reduced invertebrate

diversity

Nordin 1985

15 100 nuisance growth Quinn 1991

1,000 10b ~100 eutrophy Sosiak pers. comm.

Plankton Mean in μg/L

TN TP DIN SRP Chlorophyll a Impairment Risk Source

 300c 42 8 eutrophy Van Nieuwenhuyse and

Jones 1996

70 15 chlorophyll action level OAR 2000

 250c 35 8 eutrophy OECD 1992 (for lakes)

a

30-day biomass accrual time.

b

Total dissolved P.

c

Based on Redfield ratio of 7.2N:1P (Smith et al. 1997).
Figure 5a. Illustration of data reduction process for stream data.

24
Figure 5b. Illustration of reference condition calculation.

25
26

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 observations are preferred over all other

methods. However, when no data exist for fluorometric and spectrophotometric methods,

trichromatic values may be used. Data from the various techniques are not interchangeable.

5. Periphyton: Where periphyton data exist, record them separately. For periphytondominated streams, a measure of periphyton chlorophyll is a more appropriate response

variable than planktonic chlorophyll a. See Table 4, page 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 because this is the only

variable for which the value of the parameter increases with greater clarity (for lakes and

reservoirs only).

7. Turbidity units: 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 because 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. 

According to EPA statistical analyses, 5% or fewer of the reported observations are “below

detection.” Because of this low incidence, these data were retained and factored into the

statistical analysis as reported according to the protocols described in Appendix C, “Quality

Control/Quality Assurance Rules.” 

5.0 REFERENCE SITES AND CONDITIONS IN AGGREGATE ECOREGION V

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

to be the most attainable conditions. This chapter 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-d in Section 4.0.
27

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

V. 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. There are three scenarios under which models may be used to derive criteria or

support criteria development:

• Models for predicting correlations between causal and response variables

• Models used to verify reference conditions based on percentiles

• Regression models used to predict reference conditions in impacted areas

Appendix C of the Rivers and Streams Technical Guidance Manual (U.S. EPA, 2000b) and

Chapter 9 of the Lakes and Reservoirs Technical Guidance Manual (U.S. EPA, 2000a) should be

consulted for further details.

7.0 FRAMEWORK FOR REFINING RECOMMENDED NUTRIENT CRITERIA FOR

RIVERS AND STREAMS IN AGGREGATE ECOREGION V

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 EPA’s 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 worksheet (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-d and other literature and information readily available to the EPA Headquarters nutrient

team to develop nutrient water quality recommendations for this Ecoregion.

7.1 Example Worksheet for Developing Aggregate Ecoregion and Subecoregion Nutrient

Criteria

Literature sources: 

 

 

 

 

 
28

Historical data and trends: 

 

 

 

 

Reference condition: 

 

 

 

 

 

Models: 

 

 

 

 

 

RTAG expert review and consensus: 

 

 

 

 

 

Downstream effects: 

 

 

 

 

 

7.2 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 reflect 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 that reflect

each particular season or given season or a given year when there is significant variability
29

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 require increased

monitoring within each season to assess compliance. If a case can be made that one season is

more appropriate than another season, or more appropriate than the annual median, criteria

should be season specific. For example, in most parts of the country, spring and summer are the

most common growth periods, so criteria for chlorophyll a and Secchi may be set for spring and

summer only. However, caution should be used when developing criteria for TN and TP

because the peak loading of these nutrients may take place in seasons other than summer, such as

winter and spring. For these reasons, EPA developed annual criteria and provided additional

seasonal information in appendices.

7.3 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 conditions developed for the Cascades); (2) use the 25th

percentiles 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.

7.4 Site-Specific Criteria Development 

Criteria may be refined in a number of ways. The best way 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). See paper by Dale Robertson (USGS, 2001b), an

alternative approach to ecoregions entitled “An Alternative Regarding the Scheme for

Defining Nutrient Criteria for Rivers and Streams.”

• 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.

Omernik JM. 1999. Primary Distinguishing Characteristics of Level III Ecoregions of the

Continental United States. Draft.
30

Omernik JM. 2000. Draft Aggregations of Level III Ecoregions for the National Nutrient

Strategy. [http://www.epa.gov/ost/standards/ecomap.htm]

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.

U.S. EPA. 2000c. Memorandum from Matthew Liebman to Geoffrey Grubbs, December 15,

2000, regarding comments on draft ambient water quality recommendations for development of

numeric nutrient criteria.

USGS (U.S. Geological Survey). 1993. National Water Summary 1990-1991. Water Supply

Paper 2400. U.S. Government Printing Office, Washington, D.C. 589 pages.

USGS (U.S. Geological Survey). 2001a. Unpublished paper titled: “Estimating the Natural

Background Concentrations of Nutrients in Streams and Rivers of the Conterminous United

States.” 34 pages.

USGS. 2001b. An Alternative Regarding the Scheme for Defining Nutrient Criteria for Rivers

and Streams. Dale M. Robertson, David A. Saad, and Ann Wieben. Water Resources

Investigations Report 01-4073.

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
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1999 to 2000 Chloro_A_Fluor_cor_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 42 5.33 .70000 19.00 4.50 0.69 85 1.00 1.60 3.90 7.85  SPRING 21 8.64 .03000 50.89 12.53 2.73 145 0.28 3.04 4.84 6.70  SUMMER 41 21.92 .37000 67.80 21.38 3.34 98 1.55 5.85 14.85 36.20  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1999 to 2000 Chloro_A_Pheo_cor_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 21 3.19 .50000 7.60 2.19 0.48 69 0.60 1.60 2.70 3.40  SPRING 21 4.11 .05000 19.78 5.05 1.10 123 0.19 1.70 2.44 3.48  SUMMER 21 9.89 1.9000 41.40 9.19 2.01 93 2.90 4.65 6.80 12.35  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 1996 Chloro_A_Phyto_Spec_A_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 78 4.60 .25000 42.20 7.31 0.83 159 0.25 0.25 1.42 5.90  SPRING 93 6.93 .25000 116.00 13.46 1.40 194 0.25 0.50 2.86 9.10  SUMMER 110 11.58 .25000 128.00 18.83 1.80 163 0.25 1.02 3.95 14.18  WINTER 75 3.38 .25000 21.90 4.33 0.50 128 0.25 0.38 2.00 4.00  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 2000 DIP_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 62 165.54 5.0000 1875.00 306.42 38.92 185 5.00 20.00 43.75 175.00 7 SPRING 42 185.80 5.0000 1375.00 289.45 44.66 156 5.00 12.50 67.50 175.00 7 SUMMER 61 153.78 5.0000 1660.00 318.48 40.78 207 5.00 13.35 39.19 110.00 1 WINTER 43 208.36 5.0000 2100.00 390.45 59.54 187 5.00 13.75 77.50 170.00 9 Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1998 to 1998 Dissolved_Oxygen_percent_sat season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  SUMMER 1 138.03 138.03 138.03 . . . 138.03 138.03 138.03 138.03 13 Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 2000 Dissolved_Oxygen_mg_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 328 8.67 .40000 13.70 1.95 0.11 22 4.75 7.80 8.83 10.00  SPRING 379 8.98 .70000 14.00 1.64 0.08 18 6.43 8.10 9.05 10.00  SUMMER 446 7.43 .70000 12.50 1.58 0.07 21 4.90 6.48 7.60 8.33  WINTER 316 11.24 5.6000 16.09 1.38 0.08 12 8.90 10.30 11.41 12.20  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 2000 Nitrite_Nitrate_NO2_NO3_mg_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 289 1.33 .00250 10.00 1.70 0.10 127 0.02 0.28 0.76 1.68  SPRING 278 1.10 .00000 8.22 1.29 0.08 117 0.02 0.24 0.65 1.39  SUMMER 350 0.97 .00000 10.50 1.35 0.07 140 0.01 0.13 0.56 1.19  WINTER 260 1.57 .00000 9.28 1.63 0.10 104 0.03 0.45 0.99 1.92  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 2000 Nitrogen_Tot_Kjeldhal_mg_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 235 0.82 .00000 5.37 0.71 0.05 87 0.14 0.40 0.65 0.95  SPRING 267 0.89 .00000 5.70 0.69 0.04 78 0.20 0.50 0.71 1.06  SUMMER 332 1.02 .00000 5.10 0.73 0.04 72 0.27 0.56 0.82 1.26  WINTER 237 0.75 .00000 6.75 0.73 0.05 98 0.15 0.37 0.56 0.80  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1999 to 2000 Organic_P_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 42 32.54 1.5100 99.08 27.12 4.18 83 3.17 12.39 20.97 49.31  SPRING 21 67.56 1.8400 177.15 53.56 11.69 79 2.15 17.35 69.94 104.97 1 SUMMER 41 93.42 4.3300 348.11 79.09 12.35 85 23.13 46.81 65.55 128.74 2 Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 1992 Phosph_Ortho_Tot_as_P_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 25 155.20 5.0000 2200.00 431.20 86.24 278 5.00 20.00 35.00 135.00 2 SPRING 23 166.79 5.0000 2050.00 419.60 87.49 252 10.00 21.25 65.00 120.00 4 SUMMER 25 146.20 8.7500 1400.00 279.08 55.82 191 12.50 27.50 40.00 192.50 3 WINTER 24 205.78 5.0000 2900.00 581.87 118.77 283 5.00 9.38 51.25 150.00 3 Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 2000 Total_Nitrogen_mg_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 68 2.06 .20000 9.50 1.78 0.22 87 0.40 0.95 1.41 2.83  SPRING 54 1.85 .16000 9.23 1.55 0.21 84 0.34 1.00 1.34 2.20  SUMMER 94 1.64 .26000 10.20 1.43 0.15 88 0.45 0.79 1.30 2.04  WINTER 52 1.83 .25000 12.00 1.79 0.25 98 0.44 0.81 1.41 2.15  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 2000 Total_Phosphorus_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 380 280.02 .00000 2075.00 345.56 17.73 123 20.00 65.00 150.00 340.00 1 SPRING 403 276.81 2.5000 2115.00 337.56 16.81 122 20.00 70.00 160.84 340.00 9 SUMMER 489 319.26 .00000 2350.00 371.78 16.81 116 20.00 80.00 190.00 415.00 1 WINTER 334 253.14 .00000 2950.00 390.19 21.35 154 10.00 40.00 110.00 260.00 1 Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 1998 Turbidity_FTU season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 165 21.14 1.9500 160.00 22.54 1.75 107 2.60 6.08 14.00 27.00  SPRING 167 24.95 1.0000 136.00 22.31 1.73 89 3.78 9.58 20.00 30.50  SUMMER 179 33.74 1.2500 127.00 27.16 2.03 80 3.00 10.50 27.43 50.50  WINTER 155 15.30 1.0000 123.50 21.21 1.70 139 2.00 4.80 9.05 13.65  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 1993 Turbidity_JCU season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 15 29.25 .50000 137.00 38.81 10.02 133 0.50 3.65 17.00 32.55 1 SPRING 23 50.44 3.0000 163.00 47.63 9.93 94 5.90 10.00 25.00 92.55 1 SUMMER 41 39.56 .25000 140.00 42.03 6.56 106 2.25 7.40 22.50 54.00 1 WINTER 32 19.18 4.3500 69.00 15.03 2.66 78 5.05 10.00 15.00 24.63  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 2000 Turbidity_NTU season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 78 35.30 1.0000 230.00 40.07 4.54 113 3.00 11.00 24.68 43.60 1 SPRING 37 74.47 2.0000 941.00 152.60 25.09 205 3.00 16.00 42.00 72.00 1 SUMMER 105 60.67 2.0000 492.00 68.13 6.65 112 3.00 19.40 49.00 74.20 1 Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Decade and Season from 1990 to 2000 pH_S_U season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 64 8.14 5.3200 8.82 0.44 0.06 5 7.70 8.00 8.24 8.30  SPRING 43 8.18 6.8100 9.70 0.45 0.07 5 7.57 7.90 8.20 8.41  SUMMER 70 8.44 7.4500 9.59 0.54 0.06 6 7.65 8.00 8.38 8.78  WINTER 17 7.99 7.1600 8.55 0.36 0.09 5 7.16 7.80 8.00 8.13  Data were not always available for all years.
APPENDIX B

Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1999 to 2000 Chloro_A_Fluor_cor_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 25 FALL 19 5.00 1.0000 19.00 5.54 1.27 111 1.00 1.55 1.90 7.20 19 25 SPRING 10 9.81 1.1700 50.89 14.9 4.70 151 1.17 3.04 4.56 9.68 50 25 SUMMER 20 12.55 .37000 67.80 19.6 4.38 156 0.37 3.08 5.85 11.3 67 27 FALL 16 6.09 .70000 11.50 4.06 1.02 67 0.70 1.75 7.03 9.50 11 27 SPRING 8 8.97 .28000 37.98 12.2 4.32 136 0.28 2.51 5.26 8.97 38 27 SUMMER 14 29.21 8.8000 58.20 17.2 4.60 59 8.80 15.6 25.4 44.4 58 42 FALL 7 4.47 3.2000 7.90 1.62 0.61 36 3.20 3.20 3.90 4.60 7. 42 SPRING 3 3.86 .03000 6.70 3.44 1.99 89 0.03 0.03 4.84 6.70 6. 42 SUMMER 7 34.13 8.1000 62.69 24.5 9.27 72 8.10 8.10 22.3 62.7 62 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1999 to 2000 Chloro_A_Pheo_cor_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 25 FALL 10 2.43 .50000 6.80 1.86 0.59 76 0.50 1.20 2.10 3.40 6. 25 SPRING 10 4.44 1.2300 19.78 5.58 1.77 126 1.23 1.77 2.71 3.21 19 25 SUMMER 10 5.66 1.9000 13.00 3.28 1.04 58 1.90 2.92 5.23 6.98 13 27 FALL 8 4.33 .70000 7.60 2.61 0.92 60 0.70 2.30 3.95 6.90 7. 27 SPRING 8 4.45 .19000 15.90 5.46 1.93 123 0.19 0.85 2.04 6.87 15 27 SUMMER 8 15.51 4.1000 41.40 12.8 4.51 82 4.10 6.00 11.4 21.9 41 42 FALL 3 2.67 2.3000 3.20 0.47 0.27 18 2.30 2.30 2.50 3.20 3. 42 SPRING 3 2.14 .05000 3.48 1.83 1.06 86 0.05 0.05 2.88 3.48 3. 42 SUMMER 3 9.02 6.2000 12.35 3.11 1.79 34 6.20 6.20 8.51 12.4 12 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1996 Chloro_A_Phyto_Spec_A_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 25 FALL 5 6.76 .25000 13.27 5.15 2.30 76 0.25 4.74 5.00 10.5 13 25 SPRING 8 12.38 1.5250 30.70 8.54 3.02 69 1.53 8.44 10.1 14.9 30 25 SUMMER 12 19.35 .25000 44.10 16.1 4.64 83 0.25 5.43 13.8 34.5 44 25 WINTER 5 5.37 .25000 21.50 9.06 4.05 169 0.25 0.88 1.63 2.60 21 27 FALL 22 7.16 .25000 27.60 8.58 1.83 120 0.25 0.50 4.07 9.20 24 27 SPRING 27 12.12 .25000 116.00 22.6 4.35 187 0.25 2.00 4.81 15.8 38 27 SUMMER 32 16.52 .25000 71.20 19.6 3.47 119 0.25 1.89 7.37 26.9 64 27 WINTER 25 4.14 .25000 21.90 5.03 1.01 121 0.25 0.64 3.20 4.15 13 32 FALL 51 3.29 .25000 42.20 6.65 0.93 202 0.25 0.25 0.50 3.28 10 32 SPRING 58 3.77 .25000 22.08 4.84 0.64 129 0.25 0.25 1.33 5.80 15 32 SUMMER 66 7.78 .25000 128.00 18.1 2.23 233 0.25 0.50 2.06 6.36 37 32 WINTER 45 2.73 .25000 14.60 3.01 0.45 110 0.25 0.25 1.91 3.72 8. Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 2000 DIP_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 25 FALL 19 239.64 10.000 1875.00 446 102 186 10.0 23.8 32.5 268 18 25 SPRING 10 361.88 12.500 1375.00 426 135 118 12.5 30.0 220 615 13 25 SUMMER 20 160.61 5.8800 1150.00 268 59.9 167 9.62 23.7 47.7 195 8 25 WINTER 10 564.63 6.2500 2100.00 669 211 118 6.25 42.5 275 938 21 27 FALL 26 133.56 5.0000 840.00 184 36.0 138 5.73 20.0 60.4 175 3 27 SPRING 18 121.88 5.0000 875.00 198 46.7 162 5.00 12.5 75.0 145 8 27 SUMMER 24 104.96 5.0000 1100.00 219 44.7 208 5.00 12.5 57.5 103 2 27 WINTER 18 101.39 5.0000 432.50 103 24.2 101 5.00 7.50 91.3 145 4 32 FALL 6 151.67 10.000 640.00 243 99.0 160 10.0 30.0 55.0 120 6 32 SPRING 6 147.92 7.5000 765.00 303 124 205 7.50 10.0 25.0 55.0 7 32 SUMMER 6 193.33 6.2500 1062.50 426 174 220 6.25 6.25 13.8 57.5 10 32 WINTER 6 177.71 7.5000 780.00 300 123 169 7.50 13.8 63.8 138 7 42 FALL 11 120.73 5.0000 992.50 291 87.7 241 5.00 5.00 26.8 78.7 9 42 SPRING 8 137.97 5.0000 553.00 194 68.7 141 5.00 13.8 44.4 215 5 42 SUMMER 11 226.28 5.0000 1660.00 509 153 225 5.00 7.50 15.9 100 16 42 WINTER 9 46.89 5.0000 208.00 65.9 22.0 140 5.00 11.0 16.3 61.0 2 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1998 to 1998 Dissolved_Oxygen_percent_sat subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 SUMMER 1 138.03 138.03 138.03 . . . 138 138 138 138 1 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 2000 Dissolved_Oxygen_mg_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 FALL 52 9.30 3.3000 13.20 1.66 0.23 18 5.30 8.73 9.50 10.1 1 25 SPRING 78 9.35 .70000 12.60 1.75 0.20 19 6.70 8.70 9.33 10.3 1 25 SUMMER 82 7.74 .70000 11.80 1.71 0.19 22 3.45 7.50 7.91 8.45 1 25 WINTER 54 11.08 5.6000 12.83 1.28 0.17 12 9.40 10.5 11.3 12.1 1 27 FALL 199 8.75 .40000 13.70 2.01 0.14 23 4.30 7.80 9.05 10.1 1 27 SPRING 189 9.04 .80000 14.00 1.63 0.12 18 6.50 8.25 9.15 10.0 1 27 SUMMER 241 7.36 2.0000 12.50 1.53 0.10 21 5.10 6.40 7.25 8.23 1 27 WINTER 174 11.74 8.1000 14.20 1.16 0.09 10 9.30 11.2 11.8 12.5 1 32 FALL 67 7.68 1.4000 10.60 1.60 0.20 21 4.20 7.10 8.10 8.70 9 32 SPRING 89 8.27 4.1000 11.00 1.15 0.12 14 6.00 7.78 8.40 9.00 1 32 SUMMER 85 7.01 3.6000 11.05 1.40 0.15 20 4.80 6.00 7.00 7.90 9 32 WINTER 79 10.23 8.0000 13.10 1.15 0.13 11 8.20 9.30 10.2 11.0 1 42 FALL 10 10.44 7.6000 11.85 1.26 0.40 12 7.60 10.1 10.8 11.3 1 42 SPRING 23 10.07 5.9500 13.05 1.91 0.40 19 6.70 8.08 10.5 11.2 1 42 SUMMER 38 8.13 3.8750 12.10 1.69 0.27 21 4.70 7.60 8.26 9.10 1 42 WINTER 9 11.32 6.6000 16.09 2.48 0.83 22 6.60 10.7 10.9 12.1 1 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 2000 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 FALL 54 2.09 .01000 5.65 1.66 0.23 79 0.06 0.81 1.69 3.33 4 25 SPRING 49 2.04 .00000 6.13 1.72 0.25 84 0.00 0.63 1.73 3.15 5 25 SUMMER 61 1.30 .00000 4.98 1.27 0.16 98 0.00 0.37 0.96 1.75 3 25 WINTER 35 2.98 .00000 6.80 2.00 0.34 67 0.01 1.38 2.62 4.70 6 27 FALL 166 0.98 .00500 10.00 1.28 0.10 131 0.03 0.21 0.62 1.20 2 27 SPRING 157 0.79 .00500 3.79 0.76 0.06 96 0.03 0.17 0.58 1.16 2 27 SUMMER 201 0.83 .00000 10.50 1.17 0.08 141 0.01 0.13 0.52 1.04 2 27 WINTER 161 1.29 .00500 8.95 1.25 0.10 97 0.04 0.44 0.92 1.76 3 32 FALL 50 1.80 .00250 9.40 2.55 0.36 142 0.02 0.30 0.93 1.82 8 32 SPRING 51 1.50 .01000 8.22 1.70 0.24 113 0.17 0.48 0.99 1.93 4 32 SUMMER 50 1.10 .00250 6.60 1.40 0.20 128 0.02 0.21 0.60 1.28 5 32 WINTER 52 1.72 .02500 9.28 1.98 0.27 115 0.19 0.52 0.82 1.87 6 42 FALL 19 1.07 .01000 4.61 1.38 0.32 130 0.01 0.15 0.60 1.75 4 42 SPRING 21 0.31 .01000 2.10 0.46 0.10 150 0.01 0.06 0.16 0.40 0 42 SUMMER 38 0.96 .00000 8.44 2.06 0.33 214 0.00 0.02 0.10 0.71 6 42 WINTER 12 0.48 .01000 1.24 0.50 0.15 105 0.01 0.07 0.18 0.97 1 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 2000 Nitrogen_Tot_Kjeldhal_mg_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 FALL 59 1.07 .00000 4.85 0.92 0.12 86 0.01 0.53 0.80 1.50 2 25 SPRING 69 1.15 .00000 5.70 1.01 0.12 87 0.24 0.60 0.80 1.48 3 25 SUMMER 73 0.96 .00000 3.60 0.76 0.09 79 0.00 0.55 0.75 1.10 3 25 WINTER 56 1.19 .00000 6.75 1.20 0.16 101 0.13 0.45 0.72 1.73 3 27 FALL 96 0.78 .05000 5.37 0.69 0.07 88 0.14 0.44 0.65 0.90 1 27 SPRING 88 0.90 .05000 3.72 0.57 0.06 64 0.19 0.60 0.80 1.00 1 27 SUMMER 139 1.10 .05000 5.10 0.68 0.06 61 0.33 0.68 0.90 1.42 2 27 WINTER 90 0.63 .07500 1.81 0.30 0.03 47 0.26 0.43 0.60 0.77 1 32 FALL 65 0.62 .12000 2.35 0.38 0.05 60 0.23 0.35 0.59 0.77 1 32 SPRING 89 0.66 .05000 2.38 0.38 0.04 57 0.23 0.40 0.60 0.78 1 32 SUMMER 84 0.76 .14250 2.80 0.54 0.06 71 0.25 0.40 0.60 0.89 2 32 WINTER 80 0.58 .05000 3.78 0.54 0.06 94 0.09 0.30 0.43 0.70 1 42 FALL 15 0.95 .20000 3.40 0.83 0.21 87 0.20 0.50 0.70 1.00 3 42 SPRING 21 1.02 .10000 2.88 0.62 0.14 61 0.20 0.60 1.10 1.40 1 42 SUMMER 36 1.46 .28000 4.00 1.01 0.17 69 0.30 0.88 1.10 1.78 4 42 WINTER 11 0.70 .34000 1.50 0.34 0.10 49 0.34 0.50 0.63 0.75 1 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1999 to 2000 Organic_P_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 25 FALL 19 17.34 1.5100 87.01 19.6 4.51 113 1.51 6.24 12.4 21.0 87 25 SPRING 10 38.64 1.8400 154.83 53.9 17.0 140 1.84 8.61 14.8 40.1 1 25 SUMMER 20 103.22 4.3300 348.11 105 23.6 102 4.33 29.3 65.2 157 3 27 FALL 16 51.05 13.710 99.08 24.9 6.23 49 13.7 37.9 45.0 65.0 99 27 SPRING 8 91.13 31.850 177.15 44.0 15.6 48 31.9 61.9 88.1 110 1 27 SUMMER 14 73.14 38.590 149.17 36.5 9.75 50 38.6 51.0 57.2 96.3 1 42 FALL 7 31.50 4.1000 59.50 25.9 9.79 82 4.10 4.10 18.5 59.5 59 42 SPRING 3 101.14 76.890 130.27 27.0 15.6 27 76.9 76.9 96.3 130 1 42 SUMMER 7 105.99 46.810 177.75 46.9 17.7 44 46.8 46.8 107 129 1 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1992 Phosph_Ortho_Tot_as_P_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 25 FALL 4 576.88 5.0000 2200.00 1082 541 188 5.00 17.5 51.3 1136 22 25 SPRING 4 547.50 12.500 2050.00 1002 501 183 12.5 27.5 63.8 1068 20 25 SUMMER 4 406.25 35.000 1400.00 664 332 163 35.0 42.5 95.0 770 14 25 WINTER 3 1098.33 45.000 2900.00 1568 905 143 45.0 45.0 350 2900 29 27 FALL 13 88.08 5.0000 230.00 80.2 22.2 91 5.00 20.0 70.0 140 2 27 SPRING 11 114.43 5.0000 400.00 113 34.2 99 5.00 21.3 82.5 175 4 27 SUMMER 13 132.02 8.7500 330.00 120 33.2 91 8.75 27.5 70.0 235 3 27 WINTER 13 89.33 5.0000 280.00 93.1 25.8 104 5.00 8.75 57.5 130 2 32 FALL 3 75.00 20.000 135.00 57.7 33.3 77 20.0 20.0 70.0 135 1 32 SPRING 3 55.00 15.000 85.00 36.1 20.8 66 15.0 15.0 65.0 85.0 85 32 SUMMER 3 55.83 12.500 125.00 60.5 35.0 108 12.5 12.5 30.0 125 1 32 WINTER 3 106.67 20.000 170.00 77.7 44.8 73 20.0 20.0 130 170 1 42 FALL 5 40.50 5.0000 120.00 46.1 20.6 114 5.00 12.5 30.0 35.0 1 42 SPRING 5 44.50 10.000 120.00 43.5 19.5 98 10.0 25.0 27.5 40.0 1 42 SUMMER 5 29.25 17.500 45.00 11.5 5.15 39 17.5 18.8 30.0 35.0 45 42 WINTER 5 32.50 5.0000 120.00 49.2 22.0 152 5.00 7.50 10.0 20.0 1 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 2000 Total_Nitrogen_mg_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 25 FALL 23 3.01 .40000 9.50 2.59 0.54 86 0.40 1.06 2.60 4.27 7. 25 SPRING 14 2.95 .16000 9.23 2.56 0.68 87 0.16 0.67 2.94 4.35 9. 25 SUMMER 24 2.25 .58000 7.45 1.71 0.35 76 0.58 1.07 1.42 3.59 4. 25 WINTER 4 6.09 3.1000 12.00 4.01 2.00 66 3.10 3.83 4.63 8.35 12 27 FALL 30 1.60 .20000 3.00 0.89 0.16 55 0.30 0.90 1.47 2.71 2. 27 SPRING 28 1.50 .30000 2.89 0.70 0.13 47 0.34 1.01 1.45 1.93 2. 27 SUMMER 54 1.45 .26000 10.20 1.41 0.19 97 0.34 0.72 1.13 1.83 2. 27 WINTER 40 1.51 .25000 4.47 0.92 0.15 61 0.44 0.79 1.38 2.00 3. 32 FALL 2 1.60 1.6000 1.60 0.00 0.00 0 1.60 1.60 1.60 1.60 1. 32 SPRING 3 1.08 .78500 1.25 0.26 0.15 24 0.79 0.79 1.20 1.25 1. 32 SUMMER 3 1.18 .50000 2.20 0.90 0.52 76 0.50 0.50 0.84 2.20 2. 32 WINTER 3 1.56 .91000 2.60 0.91 0.53 59 0.91 0.91 1.16 2.60 2. 42 FALL 13 1.49 .50000 3.97 0.98 0.27 66 0.50 0.95 1.17 1.95 3. 42 SPRING 9 1.45 .70000 2.98 0.73 0.24 50 0.70 1.11 1.23 1.40 2. 42 SUMMER 13 1.38 .60000 2.95 0.64 0.18 46 0.60 0.98 1.37 1.40 2. 42 WINTER 5 1.20 .42500 1.85 0.63 0.28 53 0.43 0.75 1.15 1.80 1. Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 2000 Total_Phosphorus_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 FALL 84 264.00 .00000 2075.00 374 40.8 142 20.0 44.0 118 290  25 SPRING 89 341.04 9.0000 1900.00 395 41.9 116 28.5 70.0 185 490  25 SUMMER 103 255.37 .00000 1640.00 284 28.0 111 20.0 89.7 165 350  25 WINTER 61 433.09 .00000 2950.00 583 74.6 135 10.0 50.0 170 600 1 27 FALL 199 275.07 10.000 1800.00 300 21.2 109 30.0 90.0 168 375  27 SPRING 190 267.40 2.5000 2115.00 308 22.4 115 20.0 90.0 194 325  27 SUMMER 246 365.09 .00000 2350.00 380 24.2 104 50.0 115 259 445 1 27 WINTER 177 194.86 3.7500 1640.00 264 19.9 136 15.0 50.0 118 206  32 FALL 71 357.83 10.000 1600.00 441 52.3 123 16.3 50.0 115 510 1 32 SPRING 94 250.36 2.5000 1880.00 357 36.8 142 20.0 50.0 113 270 1 32 SUMMER 90 280.19 2.5000 2115.00 435 45.9 155 20.0 40.0 75.0 305 1 32 WINTER 82 269.75 2.5000 2170.00 429 47.4 159 10.0 30.0 70.0 295 1 42 FALL 26 157.22 2.5000 1080.00 235 46.1 149 8.13 40.0 81.5 138  42 SPRING 30 228.74 20.000 1060.50 247 45.0 108 20.0 41.5 165 300  42 SUMMER 50 295.76 4.0000 1780.00 346 48.9 117 20.0 55.5 180 380  42 WINTER 14 108.50 8.7500 420.00 127 33.9 117 8.75 16.0 57.5 165  Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1998 Turbidity_FTU subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 FALL 16 13.65 2.5000 63.00 17.0 4.25 125 2.50 3.33 6.56 14.7 6 25 SPRING 16 13.82 3.0000 36.25 10.7 2.66 77 3.00 6.80 9.65 20.3 3 25 SUMMER 16 25.25 3.0000 94.93 30.0 7.50 119 3.00 5.38 8.88 41.8 9 25 WINTER 16 11.21 2.0000 52.00 13.0 3.24 116 2.00 3.35 7.60 11.8 5 27 FALL 122 20.74 2.5000 160.00 21.1 1.91 102 3.45 7.00 14.9 25.8 5 27 SPRING 119 23.82 3.0000 112.50 17.5 1.61 74 5.00 11.0 20.4 29.0 6 27 SUMMER 133 37.75 1.2500 127.00 26.3 2.28 70 5.00 17.8 34.0 52.1 8 27 WINTER 110 11.25 1.0000 100.50 12.8 1.22 113 2.15 4.80 8.78 11.9 2 32 FALL 20 29.75 1.9500 95.00 30.6 6.84 103 2.23 3.95 14.3 55.6 8 32 SPRING 25 37.55 1.0000 136.00 38.4 7.68 102 1.70 10.8 25.1 59.0  32 SUMMER 23 18.96 2.0000 120.00 26.6 5.54 140 2.10 3.00 10.6 26.0 6 32 WINTER 23 35.84 1.9500 123.50 36.8 7.67 103 2.20 8.50 19.5 69.0  42 FALL 7 20.67 2.0000 82.00 28.5 10.8 138 2.00 2.50 12.5 27.5 8 42 SPRING 7 24.58 2.5500 69.75 23.1 8.74 94 2.55 3.00 20.8 33.0 6 42 SUMMER 7 25.61 2.3000 51.00 18.6 7.01 72 2.30 3.00 24.5 44.0 5 42 WINTER 6 21.80 2.9000 99.00 38.0 15.5 174 2.90 4.75 5.59 13.0 9 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1993 Turbidity_JCU subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 27 FALL 15 29.25 .50000 137.00 38.8 10.0 133 0.50 3.65 17.0 32.6 1 27 SPRING 23 50.44 3.0000 163.00 47.6 9.93 94 5.90 10.0 25.0 92.6 1 27 SUMMER 33 42.63 2.0500 137.50 41.0 7.14 96 2.25 14.5 29.0 63.0 1 27 WINTER 32 19.18 4.3500 69.00 15.0 2.66 78 5.05 10.0 15.0 24.6 52 42 SUMMER 8 26.91 .25000 140.00 46.6 16.5 173 0.25 4.50 8.20 24.8 1 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 2000 Turbidity_NTU subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 25 FALL 22 29.82 1.0000 72.50 21.9 4.68 74 1.00 12.6 28.0 47.0 66 25 SPRING 14 88.54 2.0000 941.00 246 65.8 278 2.00 5.60 19.0 42.0 9 25 SUMMER 24 90.61 2.0000 492.00 117 23.9 129 2.00 26.1 54.8 77.8 3 27 FALL 48 35.61 3.0000 230.00 47.2 6.81 133 7.00 10.0 20.4 42.8 1 27 SPRING 20 61.54 3.0000 179.00 44.7 9.99 73 5.90 36.6 49.4 84.1 1 27 SUMMER 68 50.39 2.0000 157.00 35.9 4.36 71 5.50 22.1 46.2 73.3 1 42 FALL 8 48.51 2.1000 104.00 31.0 11.0 64 2.10 30.0 43.0 68.0 1 42 SPRING 3 95.00 45.000 142.00 48.6 28.0 51 45.0 45.0 98.0 142 1 42 SUMMER 13 59.17 2.0000 192.50 66.4 18.4 112 2.00 8.00 15.5 120 1 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 2000 pH_S_U subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 25 FALL 27 8.19 7.7000 8.39 0.16 0.03 2 7.99 8.05 8.25 8.30 8. 25 SPRING 17 8.36 7.9000 9.70 0.44 0.11 5 7.90 8.05 8.30 8.53 9. 25 SUMMER 28 8.48 7.8000 9.59 0.55 0.10 6 7.84 8.04 8.31 8.89 9. 25 WINTER 7 8.13 7.8000 8.40 0.21 0.08 3 7.80 8.00 8.10 8.40 8. 27 FALL 21 8.15 7.7700 8.55 0.25 0.05 3 7.77 7.94 8.20 8.36 8. 27 SPRING 13 8.16 7.8000 8.50 0.24 0.07 3 7.80 8.00 8.16 8.35 8. 27 SUMMER 19 8.35 7.5400 9.35 0.48 0.11 6 7.54 7.95 8.38 8.63 9. 27 WINTER 5 8.15 7.6750 8.55 0.36 0.16 4 7.68 7.93 8.13 8.45 8. 32 FALL 3 7.75 7.5500 7.90 0.18 0.10 2 7.55 7.55 7.80 7.90 7. 32 SPRING 3 7.70 7.5000 7.80 0.17 0.10 2 7.50 7.50 7.80 7.80 7. 32 SUMMER 3 7.63 7.4500 7.80 0.18 0.10 2 7.45 7.45 7.65 7.80 7. 32 WINTER 3 7.85 7.7000 7.95 0.13 0.08 2 7.70 7.70 7.90 7.95 7. 42 FALL 13 8.10 5.3200 8.82 0.91 0.25 11 5.32 8.14 8.30 8.43 8. 42 SPRING 10 8.03 6.8100 8.66 0.58 0.18 7 6.81 7.74 8.16 8.50 8. 42 SUMMER 20 8.58 7.5500 9.30 0.53 0.12 6 7.64 8.26 8.64 8.88 9. 42 WINTER 2 7.33 7.1600 7.50 0.24 0.17 3 7.16 7.16 7.33 7.50 7. Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1999 to 2000 Chloro_A_Fluor_cor_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1999 FALL 19 5.00 1.0000 19.00 5.54 1.27 111 1.00 1.55 1.90 7.20 19 25 1999 SUMMER 20 12.55 .37000 67.80 19.59 4.38 156 0.37 3.08 5.85 11.28 67 25 2000 SPRING 10 9.81 1.1700 50.89 14.86 4.70 151 1.17 3.04 4.56 9.68 50 27 1999 FALL 16 6.09 .70000 11.50 4.06 1.02 67 0.70 1.75 7.03 9.50 11 27 1999 SUMMER 14 29.21 8.8000 58.20 17.21 4.60 59 8.80 15.60 25.35 44.40 58 27 2000 SPRING 8 8.97 .28000 37.98 12.22 4.32 136 0.28 2.51 5.26 8.97 37 42 1999 FALL 7 4.47 3.2000 7.90 1.62 0.61 36 3.20 3.20 3.90 4.60 7 42 1999 SUMMER 7 34.13 8.1000 62.69 24.51 9.27 72 8.10 8.10 22.35 62.69 62 42 2000 SPRING 3 3.86 .03000 6.70 3.44 1.99 89 0.03 0.03 4.84 6.70 6
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1999 to 2000 Chloro_A_Pheo_cor_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1999 FALL 10 2.43 .50000 6.80 1.86 0.59 76 0.50 1.20 2.10 3.40 6 25 1999 SUMMER 10 5.66 1.9000 13.00 3.28 1.04 58 1.90 2.92 5.23 6.98 13 25 2000 SPRING 10 4.44 1.2300 19.78 5.58 1.77 126 1.23 1.77 2.71 3.21 19 27 1999 FALL 8 4.33 .70000 7.60 2.61 0.92 60 0.70 2.30 3.95 6.90 7 27 1999 SUMMER 8 15.51 4.1000 41.40 12.76 4.51 82 4.10 6.00 11.40 21.90 41 27 2000 SPRING 8 4.45 .19000 15.90 5.46 1.93 123 0.19 0.85 2.04 6.87 15 42 1999 FALL 3 2.67 2.3000 3.20 0.47 0.27 18 2.30 2.30 2.50 3.20 3 42 1999 SUMMER 3 9.02 6.2000 12.35 3.11 1.79 34 6.20 6.20 8.51 12.35 12 42 2000 SPRING 3 2.14 .05000 3.48 1.83 1.06 86 0.05 0.05 2.88 3.48 3
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1996 Chloro_A_Phyto_Spec_A_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 3 11.77 .25000 22.00 10.93 6.31 93 0.25 0.25 13.05 22.00 22 25 1990 SPRING 5 20.95 .25000 55.50 22.35 9.99 107 0.25 8.20 10.10 30.70 55 25 1990 SUMMER 9 24.07 3.3500 69.30 21.33 7.11 89 3.35 9.00 15.65 29.40 69 25 1990 WINTER 3 13.54 1.3250 29.90 14.73 8.50 109 1.33 1.33 9.40 29.90 29 25 1991 FALL 3 5.03 2.1000 8.00 2.95 1.70 59 2.10 2.10 5.00 8.00 8 25 1991 SPRING 4 55.66 2.8000 157.00 71.08 35.54 128 2.80 6.40 31.41 104.91 157 25 1991 SUMMER 5 23.13 2.9250 58.70 24.78 11.08 107 2.93 5.00 9.50 39.50 58 25 1991 WINTER 2 18.69 .87500 36.50 25.19 17.81 135 0.88 0.88 18.69 36.50 36 25 1992 FALL 3 26.23 3.6000 49.90 23.17 13.38 88 3.60 3.60 25.20 49.90 49 25 1992 SPRING 2 20.00 5.7000 34.30 20.22 14.30 101 5.70 5.70 20.00 34.30 34 25 1992 SUMMER 4 33.89 3.8000 79.00 35.47 17.73 105 3.80 5.60 26.38 62.18 79 25 1992 WINTER 3 9.98 .25000 27.10 14.87 8.59 149 0.25 0.25 2.60 27.10 27 25 1993 FALL 3 9.13 .25000 19.76 9.87 5.70 108 0.25 0.25 7.37 19.76 19 25 1993 SPRING 2 11.73 .25000 23.20 16.23 11.48 138 0.25 0.25 11.73 23.20 23 25 1993 SUMMER 2 14.23 5.8600 22.60 11.84 8.37 83 5.86 5.86 14.23 22.60 22 25 1993 WINTER 3 1.17 .25000 3.00 1.59 0.92 136 0.25 0.25 0.25 3.00 3 25 1994 FALL 4 7.54 .25000 22.87 10.68 5.34 142 0.25 0.25 3.51 14.82 22 25 1994 SPRING 3 4.80 .25000 13.90 7.88 4.55 164 0.25 0.25 0.25 13.90 13 25 1994 SUMMER 3 7.57 .25000 22.20 12.67 7.32 167 0.25 0.25 0.25 22.20 22 25 1994 WINTER 1 6.39 6.3900 6.39 . . . 6.39 6.39 6.39 6.39 6 25 1995 FALL 2 4.60 .25000 8.95 6.15 4.35 134 0.25 0.25 4.60 8.95 8 25 1995 SPRING 3 8.72 7.7400 9.73 0.99 0.57 11 7.74 7.74 8.68 9.73 9 25 1995 SUMMER 4 30.72 .25000 96.70 45.59 22.80 148 0.25 0.25 12.96 61.19 96 25 1995 WINTER 4 6.17 .25000 21.50 10.25 5.12 166 0.25 0.57 1.47 11.78 21 25 1996 SPRING 3 24.82 5.7700 59.95 30.46 17.59 123 5.77 5.77 8.73 59.95 59 25 1996 SUMMER 4 9.65 .25000 24.30 11.67 5.83 121 0.25 0.25 7.03 19.05 24 25 1996 WINTER 4 0.25 .25000 0.25 0.00 0.00 0 0.25 0.25 0.25 0.25 0 27 1990 FALL 5 10.33 .50000 27.60 10.93 4.89 106 0.50 2.63 7.00 13.90 27 27 1990 SPRING 6 25.85 1.6000 120.00 46.64 19.04 180 1.60 3.75 4.51 20.70 120 27 1990 SUMMER 12 17.67 .25000 71.20 19.55 5.64 111 0.25 5.25 13.25 24.53 71 27 1990 WINTER 11 12.70 .25000 87.30 25.10 7.57 198 0.25 1.90 4.00 10.60 87 27 1991 FALL 3 1.67 .50000 4.00 2.02 1.17 121 0.50 0.50 0.50 4.00 4
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1996 Chloro_A_Phyto_Spec_A_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1991 SPRING 9 9.53 .50000 25.25 9.12 3.04 96 0.50 2.00 5.60 15.80 25 27 1991 SUMMER 12 14.44 .25000 48.60 15.70 4.53 109 0.25 0.73 10.85 24.70 48 27 1991 WINTER 3 3.08 .50000 5.75 2.63 1.52 85 0.50 0.50 3.00 5.75 5 27 1992 FALL 4 27.86 .25000 42.40 18.89 9.45 68 0.25 16.13 34.40 39.60 42 27 1992 SPRING 7 5.18 .50000 10.20 3.85 1.46 74 0.50 0.50 4.80 9.50 10 27 1992 SUMMER 23 19.05 .25000 93.60 24.67 5.14 130 0.50 3.00 10.60 22.00 67 27 1992 WINTER 3 1.25 .25000 3.00 1.52 0.88 122 0.25 0.25 0.50 3.00 3 27 1993 FALL 8 5.75 .25000 18.70 7.32 2.59 127 0.25 0.38 2.81 10.36 18 27 1993 SPRING 10 8.33 .25000 25.60 9.00 2.85 108 0.25 2.00 5.08 18.00 25 27 1993 SUMMER 17 26.51 .25000 152.00 38.87 9.43 147 0.25 3.65 10.80 27.75 152 27 1993 WINTER 7 6.28 .25000 25.00 8.97 3.39 143 0.25 0.25 3.44 10.40 25 27 1994 FALL 16 2.89 .25000 18.00 5.07 1.27 176 0.25 0.25 0.25 2.72 18 27 1994 SPRING 19 14.52 .25000 132.00 33.13 7.60 228 0.25 0.25 2.20 12.81 132 27 1994 SUMMER 10 10.66 .25000 52.50 15.82 5.00 148 0.25 0.25 6.18 12.00 52 27 1994 WINTER 11 2.54 .25000 7.84 2.74 0.83 108 0.25 0.25 0.50 4.74 7 27 1995 FALL 18 9.44 .25000 39.88 10.07 2.37 107 0.25 1.14 7.57 12.60 39 27 1995 SPRING 17 8.32 .25000 41.60 13.85 3.36 166 0.25 0.25 0.25 10.00 41 27 1995 SUMMER 17 4.27 .25000 26.70 7.60 1.84 178 0.25 0.25 0.25 6.60 26 27 1995 WINTER 13 1.61 .25000 6.14 1.95 0.54 121 0.25 0.25 0.25 3.20 6 27 1996 SPRING 17 19.60 .25000 116.00 29.72 7.21 152 0.25 2.76 7.04 21.90 116 27 1996 SUMMER 17 33.47 .25000 143.00 40.63 9.85 121 0.25 4.41 20.30 37.35 143 27 1996 WINTER 18 5.33 .25000 21.90 5.76 1.36 108 0.25 1.15 4.12 7.93 21 32 1990 FALL 12 1.28 .25000 3.80 1.28 0.37 100 0.25 0.25 0.63 2.20 3 32 1990 SPRING 15 4.55 .25000 22.90 6.05 1.56 133 0.25 0.50 2.08 7.00 22 32 1990 SUMMER 32 5.20 .25000 30.20 6.98 1.23 134 0.25 0.50 2.93 6.40 23 32 1990 WINTER 13 6.53 .25000 25.10 7.37 2.05 113 0.25 1.00 4.00 8.70 25 32 1991 FALL 12 2.58 .25000 8.60 2.77 0.80 107 0.25 0.25 1.85 4.00 8 32 1991 SPRING 29 6.45 .25000 38.95 8.44 1.57 131 0.25 0.50 3.90 8.40 18 32 1991 SUMMER 36 6.69 .25000 45.00 11.50 1.92 172 0.25 0.31 2.05 6.15 40 32 1991 WINTER 11 4.14 .25000 20.90 6.34 1.91 153 0.25 0.25 2.00 4.90 20 32 1992 FALL 12 3.70 .25000 20.10 6.69 1.93 181 0.25 0.25 0.25 3.75 20 32 1992 SPRING 19 4.20 .25000 14.40 4.10 0.94 98 0.25 0.25 3.80 7.10 14
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1996 Chloro_A_Phyto_Spec_A_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  32 1992 SUMMER 34 8.38 .25000 43.00 10.40 1.78 124 0.25 0.25 4.54 11.70 28 32 1992 WINTER 10 3.31 .25000 9.85 3.02 0.95 91 0.25 1.38 2.48 5.30 9 32 1993 FALL 21 5.89 .25000 42.20 11.24 2.45 191 0.25 0.25 0.25 5.01 32 32 1993 SPRING 23 2.75 .25000 12.10 3.66 0.76 133 0.25 0.25 0.50 5.61 10 32 1993 SUMMER 25 6.29 .25000 63.90 13.52 2.70 215 0.25 0.25 1.31 6.36 24 32 1993 WINTER 14 3.18 .25000 13.10 3.61 0.97 114 0.25 0.25 2.16 3.48 13 32 1994 FALL 23 1.58 .25000 7.78 2.61 0.54 165 0.25 0.25 0.25 1.91 7 32 1994 SPRING 26 4.09 .25000 29.20 7.37 1.44 180 0.25 0.25 0.25 3.27 20 32 1994 SUMMER 25 3.54 .25000 19.20 4.95 0.99 140 0.25 0.25 0.25 5.72 15 32 1994 WINTER 14 1.40 .25000 7.44 2.03 0.54 145 0.25 0.25 0.25 1.50 7 32 1995 FALL 22 3.35 .25000 11.60 3.27 0.70 98 0.25 0.25 2.79 5.90 7 32 1995 SPRING 23 2.04 .25000 15.60 4.04 0.84 198 0.25 0.25 0.25 2.40 13 32 1995 SUMMER 26 2.71 .25000 21.10 5.19 1.02 192 0.25 0.25 0.25 2.39 13 32 1995 WINTER 23 2.23 .25000 11.20 3.10 0.65 139 0.25 0.25 0.25 3.56 8 32 1996 FALL 4 18.61 .25000 73.70 36.73 18.36 197 0.25 0.25 0.25 36.98 73 32 1996 SPRING 21 3.62 .25000 11.40 4.44 0.97 123 0.25 0.25 1.15 8.50 11 32 1996 SUMMER 21 16.25 .25000 128.00 28.96 6.32 178 0.25 1.78 6.66 22.10 52 32 1996 WINTER 21 3.27 .25000 14.90 4.83 1.05 148 0.25 0.25 0.72 3.72 14
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 DIP_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 4 540.00 15.000 2100.00 1040.0 520.00 193 15.00 17.50 22.50 1062.5 210 25 1990 SPRING 4 493.75 25.000 1450.00 670.76 335.38 136 25.00 27.50 250.00 960.00 145 25 1990 SUMMER 4 500.63 7.5000 1950.00 966.28 483.14 193 7.50 13.75 22.50 987.50 195 25 1990 WINTER 3 1385.83 7.5000 4100.00 2350.6 1357.1 170 7.50 7.50 50.00 4100.0 410 25 1991 FALL 4 578.75 10.000 2200.00 1081.2 540.59 187 10.00 20.00 52.50 1137.5 220 25 1991 SPRING 4 718.75 15.000 2750.00 1354.5 677.23 188 15.00 22.50 55.00 1415.0 275 25 1991 SUMMER 4 304.38 7.5000 935.00 430.17 215.08 141 7.50 31.25 137.50 577.50 935 25 1991 WINTER 1 45.00 45.000 45.00 . . . 45.00 45.00 45.00 45.00 45 25 1992 FALL 3 813.33 20.000 2400.00 1374.1 793.33 169 20.00 20.00 20.00 2400.0 240 25 1992 SPRING 4 333.13 17.500 1200.00 578.52 289.26 174 17.50 26.25 57.50 640.00 120 25 1992 SUMMER 4 481.25 7.5000 1850.00 912.75 456.37 190 7.50 10.00 33.75 952.50 185 25 1992 WINTER 3 1035.00 25.000 2750.00 1493.0 862.01 144 25.00 25.00 330.00 2750.0 275 25 1993 FALL 9 424.78 15.000 1650.00 520.83 173.61 123 15.00 25.00 280.00 455.00 165 25 1993 SPRING 10 513.75 5.0000 2100.00 636.61 201.31 124 5.00 190.00 237.50 850.00 210 25 1993 SUMMER 10 303.00 10.000 1000.00 297.38 94.04 98 10.00 80.00 252.50 340.00 100 25 1993 WINTER 9 600.56 5.0000 2100.00 665.76 221.92 111 5.00 160.00 325.00 825.00 210 25 1994 FALL 9 439.44 5.0000 1650.00 536.46 178.82 122 5.00 30.00 255.00 515.00 165 25 1994 SPRING 10 326.75 12.500 1150.00 364.94 115.40 112 12.50 40.00 210.00 600.00 115 25 1994 SUMMER 10 296.25 5.0000 1300.00 387.33 122.49 131 5.00 25.00 195.00 325.00 130 25 1994 WINTER 8 690.00 25.000 1850.00 631.64 223.32 92 25.00 187.50 535.00 1100.0 185 25 1995 FALL 4 510.00 220.00 1000.00 349.40 174.70 69 220.00 262.50 410.00 757.50 100 25 1995 SPRING 8 473.75 5.0000 1300.00 418.71 148.04 88 5.00 175.00 395.00 672.50 130 25 1995 SUMMER 9 85.83 20.000 145.00 48.64 16.21 57 20.00 30.00 95.00 130.00 145 25 1995 WINTER 8 658.75 15.000 1850.00 652.85 230.82 99 15.00 122.50 492.50 1087.5 185 25 1996 WINTER 1 1000.00 1000.0 1000.00 . . . 1000.0 1000.0 1000.0 1000.0 100 25 1999 FALL 9 48.79 18.230 191.05 54.52 18.17 112 18.23 23.78 30.37 43.42 191 25 1999 SUMMER 10 37.60 5.8800 85.72 23.95 7.57 64 5.88 18.67 34.78 51.78 85 27 1990 FALL 13 96.15 5.0000 455.00 128.84 35.73 134 5.00 7.50 30.00 155.00 455 27 1990 SPRING 13 71.15 5.0000 255.00 74.15 20.56 104 5.00 17.50 40.00 110.00 255 27 1990 SUMMER 13 55.58 5.0000 270.00 73.96 20.51 133 5.00 5.00 27.50 75.00 270 27 1990 WINTER 12 66.88 5.0000 175.00 62.57 18.06 94 5.00 6.25 40.00 120.00 175 27 1991 FALL 13 95.77 5.0000 520.00 140.07 38.85 146 5.00 20.00 45.00 90.00 520
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 DIP_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1991 SPRING 11 85.45 5.0000 380.00 109.94 33.15 129 5.00 7.50 45.00 140.00 380 27 1991 SUMMER 13 124.42 5.0000 585.00 168.45 46.72 135 5.00 7.50 25.00 210.00 585 27 1991 WINTER 13 87.88 5.0000 330.00 103.27 28.64 118 5.00 5.00 45.00 125.00 330 27 1992 FALL 12 66.04 5.0000 185.00 66.28 19.13 100 5.00 8.75 45.00 110.00 185 27 1992 SPRING 11 151.36 5.0000 815.00 231.82 69.90 153 5.00 7.50 90.00 190.00 815 27 1992 SUMMER 14 67.32 5.0000 205.00 66.61 17.80 99 5.00 5.00 55.00 100.00 205 27 1992 WINTER 13 71.92 5.0000 175.00 66.88 18.55 93 5.00 5.00 70.00 110.00 175 27 1993 FALL 16 120.94 5.0000 580.00 143.88 35.97 119 5.00 22.50 67.50 180.00 580 27 1993 SPRING 16 189.69 5.0000 1500.00 359.43 89.86 189 5.00 23.75 92.50 190.00 150 27 1993 SUMMER 18 166.00 5.0000 1200.00 274.91 64.80 166 5.00 10.00 105.00 230.00 120 27 1993 WINTER 15 157.33 5.0000 985.00 252.85 65.29 161 5.00 7.50 95.00 150.00 985 27 1994 FALL 9 233.06 5.0000 1100.00 352.18 117.39 151 5.00 25.00 65.00 230.00 110 27 1994 SPRING 14 118.04 5.0000 875.00 224.82 60.09 190 5.00 17.50 42.50 130.00 875 27 1994 SUMMER 14 120.00 5.0000 1000.00 258.97 69.21 216 5.00 12.50 23.75 110.00 100 27 1994 WINTER 12 113.33 5.0000 440.00 120.18 34.69 106 5.00 18.75 102.50 150.00 440 27 1995 FALL 1 30.00 30.000 30.00 . . . 30.00 30.00 30.00 30.00 30 27 1995 SPRING 6 93.75 5.0000 315.00 118.64 48.43 127 5.00 12.50 45.00 140.00 315 27 1995 SUMMER 7 55.79 5.0000 190.00 63.41 23.97 114 5.00 5.00 40.00 60.50 190 27 1995 WINTER 5 64.00 7.5000 170.00 65.45 29.27 102 7.50 12.50 60.00 70.00 170 27 1999 FALL 8 161.25 5.7300 395.64 171.79 60.74 107 5.73 34.51 60.39 349.44 395 27 1999 SUMMER 6 45.89 8.3600 127.89 42.20 17.23 92 8.36 20.69 37.94 42.53 127 32 1990 SPRING 3 21.67 5.0000 30.00 14.43 8.33 67 5.00 5.00 30.00 30.00 30 32 1990 SUMMER 3 39.17 7.5000 80.00 37.11 21.42 95 7.50 7.50 30.00 80.00 80 32 1990 WINTER 3 143.33 20.000 300.00 142.95 82.53 100 20.00 20.00 110.00 300.00 300 32 1991 FALL 3 76.67 30.000 120.00 45.09 26.03 59 30.00 30.00 80.00 120.00 120 32 1991 SPRING 3 54.17 7.5000 100.00 46.26 26.71 85 7.50 7.50 55.00 100.00 100 32 1991 SUMMER 3 81.67 7.5000 230.00 128.46 74.17 157 7.50 7.50 7.50 230.00 230 32 1991 WINTER 3 113.33 25.000 175.00 78.48 45.31 69 25.00 25.00 140.00 175.00 175 32 1992 SPRING 3 47.50 12.500 85.00 36.31 20.97 76 12.50 12.50 45.00 85.00 85 32 1992 SUMMER 3 15.00 5.0000 35.00 17.32 10.00 115 5.00 5.00 5.00 35.00 35 32 1992 WINTER 3 120.00 15.000 210.00 98.36 56.79 82 15.00 15.00 135.00 210.00 210 32 1993 FALL 3 236.67 25.000 640.00 349.44 201.75 148 25.00 25.00 45.00 640.00 640
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 DIP_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 32 1993 SPRING 6 161.67 5.0000 905.00 364.20 148.68 225 5.00 10.00 15.00 20.00 905. 32 1993 SUMMER 6 165.00 5.0000 925.00 372.67 152.14 226 5.00 5.00 5.00 45.00 925. 32 1993 WINTER 6 158.75 5.0000 860.00 343.92 140.41 217 5.00 5.00 18.75 45.00 860. 32 1994 FALL 3 66.67 10.000 155.00 77.51 44.75 116 10.00 10.00 35.00 155.00 155. 32 1994 SPRING 4 215.63 5.0000 760.00 365.06 182.53 169 5.00 6.25 48.75 425.00 760. 32 1994 SUMMER 4 342.50 20.000 1300.00 638.34 319.17 186 20.00 22.50 25.00 662.50 1300 32 1994 WINTER 4 138.75 20.000 470.00 221.00 110.50 159 20.00 22.50 32.50 255.00 470. 32 1995 FALL 2 510.00 5.0000 1015.00 714.18 505.00 140 5.00 5.00 510.00 1015.0 1015 32 1995 SPRING 3 80.00 10.000 210.00 112.69 65.06 141 10.00 10.00 20.00 210.00 210. 32 1995 SUMMER 3 404.17 5.0000 1200.00 689.21 397.92 171 5.00 5.00 7.50 1200.0 1200 32 1995 WINTER 3 242.50 5.0000 700.00 396.30 228.81 163 5.00 5.00 22.50 700.00 700. 32 1996 SPRING 2 387.50 5.0000 770.00 540.94 382.50 140 5.00 5.00 387.50 770.00 770. 32 1996 SUMMER 2 431.25 7.5000 855.00 599.27 423.75 139 7.50 7.50 431.25 855.00 855. 32 1996 WINTER 2 902.50 5.0000 1800.00 1269.3 897.50 141 5.00 5.00 902.50 1800.0 1800 42 1990 FALL 4 16.25 5.0000 50.00 22.50 11.25 138 5.00 5.00 5.00 27.50 50. 42 1990 SPRING 6 44.08 5.0000 132.00 49.94 20.39 113 5.00 5.00 26.25 70.00 132. 42 1990 SUMMER 6 110.92 5.0000 618.00 248.45 101.43 224 5.00 5.00 11.25 15.00 618. 42 1990 WINTER 4 11.88 5.0000 30.00 12.14 6.07 102 5.00 5.00 6.25 18.75 30. 42 1991 FALL 6 19.58 5.0000 70.00 25.90 10.58 132 5.00 5.00 6.25 25.00 70. 42 1991 SPRING 5 21.50 5.0000 60.00 21.98 9.83 102 5.00 12.50 12.50 17.50 60. 42 1991 SUMMER 5 15.00 5.0000 25.00 8.48 3.79 57 5.00 7.50 17.50 20.00 25. 42 1991 WINTER 3 5.00 5.0000 5.00 0.00 0.00 0 5.00 5.00 5.00 5.00 5. 42 1992 FALL 4 26.25 5.0000 70.00 29.62 14.81 113 5.00 8.75 15.00 43.75 70. 42 1992 SPRING 4 12.50 5.0000 35.00 15.00 7.50 120 5.00 5.00 5.00 20.00 35. 42 1992 SUMMER 5 10.50 5.0000 20.00 6.71 3.00 64 5.00 5.00 7.50 15.00 20. 42 1992 WINTER 4 29.38 5.0000 80.00 34.30 17.15 117 5.00 8.75 16.25 50.00 80. 42 1993 FALL 5 20.00 5.0000 80.00 33.54 15.00 168 5.00 5.00 5.00 5.00 80. 42 1993 SPRING 5 28.50 5.0000 90.00 34.76 15.54 122 5.00 12.50 17.50 17.50 90. 42 1993 SUMMER 5 15.50 7.5000 35.00 11.24 5.02 72 7.50 10.00 10.00 15.00 35. 42 1993 WINTER 3 24.17 5.0000 47.50 21.55 12.44 89 5.00 5.00 20.00 47.50 47. 42 1994 FALL 3 8.33 5.0000 12.50 3.82 2.20 46 5.00 5.00 7.50 12.50 12. 42 1994 SPRING 5 39.50 7.5000 60.00 22.46 10.04 57 7.50 27.50 42.50 60.00 60.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 DIP_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1994 SUMMER 5 11.00 5.0000 25.00 8.94 4.00 81 5.00 5.00 5.00 15.00 25. 42 1995 SPRING 2 168.75 40.000 297.50 182.08 128.75 108 40.00 40.00 168.75 297.50 297. 42 1995 SUMMER 1 12.50 12.500 12.50 . . . 12.50 12.50 12.50 12.50 12. 42 1999 FALL 5 244.85 26.800 992.50 418.82 187.30 171 26.80 36.05 78.74 90.16 992. 42 1999 SUMMER 5 363.72 10.800 1660.00 725.53 324.47 199 10.80 15.88 31.66 100.28 1660 42 1999 WINTER 4 75.50 11.000 208.00 90.90 45.45 120 11.00 16.50 41.50 134.50 208. 42 2000 SPRING 1 553.00 553.00 553.00 . . . 553.00 553.00 553.00 553.00 553.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1998 to 1998 Dissolved_Oxygen_percent_sat subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1998 SUMMER 1 138.03 138.03 138.03 . . . 138.03 138.03 138.03 138.03 138.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 32 9.37 3.3000 13.10 1.78 0.32 19 7.00 8.45 9.35 10.50 12 25 1990 SPRING 36 9.20 3.8000 12.20 1.42 0.24 15 6.80 8.50 9.23 10.10 11 25 1990 SUMMER 40 7.95 .70000 12.40 2.20 0.35 28 2.58 7.38 8.10 9.35 10 25 1990 WINTER 30 10.84 8.2000 13.60 1.23 0.22 11 9.15 10.15 10.63 11.40 13 25 1991 FALL 31 9.76 5.0500 12.75 1.52 0.27 16 7.85 8.80 9.85 10.65 12 25 1991 SPRING 31 10.24 8.2000 13.20 1.24 0.22 12 8.60 9.40 10.10 11.00 12 25 1991 SUMMER 31 7.55 4.3000 10.70 1.19 0.21 16 6.10 7.10 7.50 7.85 10 25 1991 WINTER 26 11.19 8.2500 13.25 1.04 0.20 9 9.60 10.70 11.30 11.65 13 25 1992 FALL 24 9.51 5.3500 12.40 1.51 0.31 16 6.80 8.98 9.70 10.25 12 25 1992 SPRING 27 9.70 6.1000 12.35 1.32 0.25 14 7.90 8.90 9.60 10.50 12 25 1992 SUMMER 28 7.68 3.0000 10.20 1.54 0.29 20 3.80 7.25 7.98 8.35 9 25 1992 WINTER 28 11.47 9.1000 14.40 1.18 0.22 10 9.80 10.58 11.55 12.00 14 25 1993 FALL 32 10.09 4.4000 13.90 1.81 0.32 18 7.30 9.05 10.13 11.38 13 25 1993 SPRING 37 9.28 7.0000 11.50 1.17 0.19 13 7.60 8.20 9.10 10.10 11 25 1993 SUMMER 35 7.87 5.9500 10.60 0.84 0.14 11 6.40 7.40 7.80 8.30 10 25 1993 WINTER 28 11.90 8.8000 13.90 1.28 0.24 11 9.70 11.35 12.15 12.90 13 25 1994 FALL 31 8.74 4.3000 13.00 1.67 0.30 19 6.00 7.80 8.40 9.95 11 25 1994 SPRING 53 9.67 .70000 13.40 1.94 0.27 20 7.50 8.80 9.50 10.55 12 25 1994 SUMMER 37 7.65 1.3500 11.80 1.79 0.29 23 3.20 7.30 7.80 8.20 10 25 1994 WINTER 26 10.99 4.4000 13.50 1.97 0.39 18 6.40 10.10 11.53 11.95 13 25 1995 FALL 23 8.65 5.3000 12.70 1.49 0.31 17 6.60 8.00 8.50 9.60 10 25 1995 SPRING 26 9.56 6.1000 11.70 1.27 0.25 13 6.40 9.10 9.70 10.30 11 25 1995 SUMMER 28 7.53 2.8000 9.70 1.11 0.21 15 6.10 7.40 7.65 8.00 8 25 1995 WINTER 36 10.62 5.6000 13.70 1.91 0.32 18 7.10 9.95 10.98 11.90 13 25 1996 FALL 21 9.27 3.4000 12.60 2.02 0.44 22 6.95 8.40 9.75 10.90 11 25 1996 SPRING 17 9.40 6.7000 11.90 1.14 0.28 12 6.70 9.00 9.50 9.95 11 25 1996 SUMMER 19 7.19 4.4500 8.50 1.15 0.26 16 4.45 6.80 7.35 8.20 8 25 1996 WINTER 18 11.31 8.5000 13.20 1.26 0.30 11 8.50 10.60 11.28 12.40 13 25 1997 FALL 16 10.06 7.8000 13.30 1.27 0.32 13 7.80 9.33 9.90 10.50 13 25 1997 SPRING 16 10.17 1.4000 12.80 2.71 0.68 27 1.40 9.38 10.15 12.15 12 25 1997 SUMMER 14 8.70 6.4000 12.50 1.55 0.41 18 6.40 7.80 8.63 9.10 12 25 1997 WINTER 17 11.74 9.7000 14.30 1.39 0.34 12 9.70 10.90 11.10 12.80 14
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1998 WINTER 8 9.15 5.2000 12.80 2.23 0.79 24 5.20 8.20 9.00 10.40 12 25 1999 FALL 4 9.53 9.2000 9.86 0.38 0.19 4 9.20 9.20 9.53 9.86 9 25 1999 SUMMER 20 8.45 6.8000 10.70 1.19 0.27 14 6.80 7.66 8.39 8.74 10 25 2000 SPRING 10 8.52 4.3300 11.20 1.93 0.61 23 4.33 8.00 9.02 9.26 11 25 2000 SUMMER 10 8.79 6.4000 12.40 1.82 0.58 21 6.40 7.70 8.95 9.40 12 27 1990 FALL 85 9.07 1.9500 14.30 2.32 0.25 26 5.50 7.65 9.20 10.65 12 27 1990 SPRING 99 8.89 3.6000 13.40 1.82 0.18 20 5.70 7.70 9.10 10.15 11 27 1990 SUMMER 115 7.19 1.3000 13.90 2.18 0.20 30 4.30 5.65 7.00 8.25 11 27 1990 WINTER 62 11.40 8.1000 14.60 1.57 0.20 14 8.90 10.40 11.30 12.45 13 27 1991 FALL 89 8.79 .02500 14.30 2.61 0.28 30 2.70 8.20 9.40 10.30 11 27 1991 SPRING 98 8.61 .80000 14.20 2.16 0.22 25 4.30 7.40 8.78 9.90 11 27 1991 SUMMER 126 7.80 .70000 14.00 2.50 0.22 32 3.80 6.50 7.85 9.00 12 27 1991 WINTER 117 11.74 7.7000 14.70 1.34 0.12 11 9.15 11.00 11.95 12.50 13 27 1992 FALL 98 9.19 4.7000 13.25 1.75 0.18 19 5.80 8.30 9.10 10.30 12 27 1992 SPRING 104 9.26 3.6000 14.60 2.02 0.20 22 5.80 8.10 9.30 10.40 12 27 1992 SUMMER 132 6.96 .40000 13.90 2.13 0.19 31 3.55 5.73 7.15 8.28 10 27 1992 WINTER 102 11.66 6.9000 14.60 1.54 0.15 13 8.80 11.00 11.75 12.60 14 27 1993 FALL 90 9.21 2.3000 13.80 1.88 0.20 20 5.90 8.30 9.13 10.30 12 27 1993 SPRING 103 9.26 5.2500 12.20 1.28 0.13 14 7.30 8.75 9.20 10.00 11 27 1993 SUMMER 115 7.03 1.3000 10.55 1.38 0.13 20 4.60 6.40 7.05 7.70 9 27 1993 WINTER 99 11.07 5.3000 14.40 2.15 0.22 19 5.60 10.40 11.50 12.40 14 27 1994 FALL 99 8.40 .02500 13.70 2.46 0.25 29 4.00 6.90 8.85 10.00 11 27 1994 SPRING 95 9.02 3.3000 14.50 1.85 0.19 21 5.00 8.20 9.25 10.10 11 27 1994 SUMMER 119 7.20 1.2500 12.90 1.96 0.18 27 3.45 5.90 7.20 8.40 10 27 1994 WINTER 70 12.20 7.6000 14.40 1.48 0.18 12 9.00 11.90 12.70 13.00 13 27 1995 FALL 96 8.91 .80000 14.60 2.38 0.24 27 3.80 7.80 9.23 10.38 12 27 1995 SPRING 96 9.24 6.0000 13.30 1.51 0.15 16 6.75 8.30 9.10 9.90 12 27 1995 SUMMER 94 7.15 1.0000 11.90 1.41 0.15 20 5.00 6.45 7.03 8.05 9 27 1995 WINTER 78 11.55 5.0000 14.30 1.88 0.21 16 7.65 10.80 11.80 13.00 13 27 1996 FALL 88 9.32 2.6000 13.70 1.75 0.19 19 6.70 8.28 9.63 10.50 11 27 1996 SPRING 82 9.06 3.0000 14.00 2.24 0.25 25 5.60 7.40 9.25 10.70 12 27 1996 SUMMER 94 6.85 1.0000 13.90 2.07 0.21 30 2.60 5.80 6.83 7.80 10
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1996 WINTER 46 11.86 7.4000 14.50 1.57 0.23 13 9.30 10.90 12.30 13.00 14 27 1997 FALL 68 8.85 .60000 13.85 2.52 0.31 28 4.20 7.33 9.30 10.75 12 27 1997 SPRING 74 10.56 3.5000 14.70 1.73 0.20 16 8.20 9.60 10.50 11.50 13 27 1997 SUMMER 71 7.38 3.8000 12.00 1.74 0.21 24 4.55 6.30 7.25 8.30 10 27 1997 WINTER 76 12.11 8.3500 14.10 1.15 0.13 10 9.60 11.58 12.23 13.00 13 27 1999 FALL 10 9.09 5.3300 10.63 2.10 0.66 23 5.33 8.80 10.18 10.52 10 27 1999 SUMMER 14 9.53 7.6000 14.31 2.29 0.61 24 7.60 7.74 8.93 10.20 14 27 2000 SPRING 8 7.20 1.8400 9.00 2.68 0.95 37 1.84 6.01 8.53 8.84 9 27 2000 SUMMER 8 6.97 4.3000 9.50 1.57 0.56 23 4.30 6.20 6.73 8.05 9 32 1990 FALL 26 6.76 3.1000 9.20 1.42 0.28 21 4.20 6.05 6.80 7.70 9 32 1990 SPRING 35 8.24 3.4000 11.00 1.54 0.26 19 5.40 7.40 8.25 9.30 10 32 1990 SUMMER 47 7.36 2.1000 11.65 2.07 0.30 28 4.50 6.00 7.00 8.90 10 32 1990 WINTER 30 9.32 5.2000 12.80 1.80 0.33 19 5.20 8.30 9.43 10.35 12 32 1991 FALL 29 8.17 5.6000 10.20 1.29 0.24 16 5.90 7.30 8.40 9.10 10 32 1991 SPRING 46 8.49 6.1000 11.00 1.25 0.18 15 6.80 7.50 8.35 9.50 10 32 1991 SUMMER 50 7.19 4.4000 9.20 1.19 0.17 17 5.20 6.40 7.23 8.00 9 32 1991 WINTER 31 9.86 7.3000 12.70 1.21 0.22 12 7.80 9.10 9.60 10.50 12 32 1992 FALL 28 7.14 3.1000 9.40 1.57 0.30 22 3.10 6.60 7.45 7.95 9 32 1992 SPRING 38 8.36 5.7000 11.65 1.01 0.16 12 6.50 7.75 8.45 8.80 9 32 1992 SUMMER 49 7.33 4.4000 10.05 1.28 0.18 17 5.00 6.60 7.20 8.15 9 32 1992 WINTER 37 10.14 7.7000 13.00 1.24 0.20 12 8.10 9.15 10.20 11.10 12 32 1993 FALL 28 8.25 3.7000 10.60 1.64 0.31 20 5.80 7.25 8.40 9.40 10 32 1993 SPRING 33 8.75 6.1000 12.80 1.49 0.26 17 7.00 7.90 8.55 9.20 12 32 1993 SUMMER 34 7.33 5.6000 9.70 1.10 0.19 15 5.90 6.40 7.30 8.20 9 32 1993 WINTER 27 10.45 8.8500 13.10 1.05 0.20 10 9.00 9.70 10.20 10.80 12 32 1994 FALL 31 8.15 4.6000 10.90 1.38 0.25 17 5.10 7.30 8.30 9.00 10 32 1994 SPRING 43 7.92 4.1000 11.80 1.43 0.22 18 5.90 7.40 7.90 8.50 10 32 1994 SUMMER 34 6.88 3.6000 12.70 1.88 0.32 27 4.70 5.70 6.40 7.80 11 32 1994 WINTER 39 10.32 6.6000 14.70 1.57 0.25 15 7.90 9.30 10.30 11.00 13 32 1995 FALL 26 7.44 3.5000 9.80 1.71 0.34 23 4.00 7.00 7.90 8.60 9 32 1995 SPRING 37 8.78 6.9000 11.70 1.06 0.17 12 7.00 8.25 8.90 9.30 10 32 1995 SUMMER 37 6.87 3.5000 11.05 1.74 0.29 25 4.10 6.00 6.70 7.90 10
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  32 1995 WINTER 35 9.94 7.3000 13.70 1.37 0.23 14 7.30 9.00 10.05 10.80 12 32 1996 FALL 6 5.12 1.4000 7.90 2.48 1.01 48 1.40 3.80 5.00 7.60 7 32 1996 SPRING 22 7.55 4.1000 11.10 1.80 0.38 24 4.20 6.00 7.85 8.60 10 32 1996 SUMMER 25 6.79 3.5000 12.00 2.07 0.41 30 3.70 5.40 6.20 8.20 9 32 1996 WINTER 21 10.03 4.7000 13.70 2.00 0.44 20 6.80 9.20 9.80 11.40 12 32 1997 SPRING 4 8.00 7.4000 8.40 0.45 0.23 6 7.40 7.65 8.10 8.35 8 32 1997 WINTER 9 9.73 8.5500 11.10 0.96 0.32 10 8.55 8.95 9.75 10.40 11 42 1990 FALL 6 10.20 6.1000 11.80 2.13 0.87 21 6.10 9.75 11.05 11.45 11 42 1990 SPRING 11 10.93 6.8000 14.20 2.17 0.65 20 6.80 10.30 11.10 12.80 14 42 1990 SUMMER 20 8.34 3.8750 14.00 1.79 0.40 21 5.39 7.80 8.30 8.90 11 42 1990 WINTER 7 10.89 7.6000 12.50 1.65 0.63 15 7.60 10.30 11.40 12.00 12 42 1991 FALL 7 10.36 9.2500 11.25 0.64 0.24 6 9.25 9.90 10.50 10.70 11 42 1991 SPRING 9 9.74 5.2000 12.50 2.22 0.74 23 5.20 8.60 9.90 11.10 12 42 1991 SUMMER 11 7.39 5.3000 8.90 1.06 0.32 14 5.30 6.65 7.50 8.40 8 42 1991 WINTER 5 11.04 9.4000 13.00 1.47 0.66 13 9.40 9.80 11.20 11.80 13 42 1992 FALL 6 11.15 10.000 12.65 0.98 0.40 9 10.00 10.55 10.85 12.00 12 42 1992 SPRING 8 11.13 9.5000 12.10 0.90 0.32 8 9.50 10.60 11.15 11.95 12 42 1992 SUMMER 7 9.02 8.0000 10.20 0.85 0.32 9 8.00 8.50 8.80 10.20 10 42 1992 WINTER 6 13.05 10.900 16.09 1.74 0.71 13 10.90 12.20 12.85 13.40 16 42 1993 FALL 9 10.98 9.2000 13.00 1.13 0.38 10 9.20 10.40 10.60 11.60 13 42 1993 SPRING 15 10.79 5.9500 14.40 2.13 0.55 20 5.95 10.05 10.80 12.00 14 42 1993 SUMMER 12 7.83 5.6000 9.65 1.38 0.40 18 5.60 6.85 7.90 9.15 9 42 1993 WINTER 7 11.22 8.6000 13.80 1.73 0.65 15 8.60 10.10 11.05 12.55 13 42 1994 FALL 4 11.11 9.2000 12.75 1.78 0.89 16 9.20 9.60 11.25 12.63 12 42 1994 SPRING 9 9.88 3.4000 11.65 2.53 0.84 26 3.40 9.90 10.60 11.00 11 42 1994 SUMMER 12 8.68 5.7000 11.10 1.70 0.49 20 5.70 7.70 8.15 10.50 11 42 1994 WINTER 2 10.50 9.4000 11.60 1.56 1.10 15 9.40 9.40 10.50 11.60 11 42 1995 FALL 3 12.33 10.600 14.20 1.80 1.04 15 10.60 10.60 12.20 14.20 14 42 1995 SPRING 7 10.79 8.4000 12.80 1.66 0.63 15 8.40 9.30 10.50 12.60 12 42 1995 SUMMER 4 7.08 3.4000 9.60 2.62 1.31 37 3.40 5.45 7.65 8.70 9 42 1995 WINTER 2 12.30 10.900 13.70 1.98 1.40 16 10.90 10.90 12.30 13.70 13 42 1996 FALL 3 11.57 10.100 13.00 1.45 0.84 13 10.10 10.10 11.60 13.00 13
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1996 SPRING 5 9.94 8.3000 11.00 1.02 0.46 10 8.30 9.80 10.10 10.50 11. 42 1996 SUMMER 6 7.93 4.7000 11.10 2.59 1.06 33 4.70 5.60 8.00 10.20 11. 42 1996 WINTER 2 8.05 6.6000 9.50 2.05 1.45 25 6.60 6.60 8.05 9.50 9. 42 1997 FALL 1 10.20 10.200 10.20 . . . 10.20 10.20 10.20 10.20 10. 42 1997 SPRING 1 9.00 9.0000 9.00 . . . 9.00 9.00 9.00 9.00 9. 42 1997 SUMMER 1 9.50 9.5000 9.50 . . . 9.50 9.50 9.50 9.50 9. 42 1997 WINTER 2 6.70 .40000 13.00 8.91 6.30 133 0.40 0.40 6.70 13.00 13. 42 1998 SPRING 1 11.20 11.200 11.20 . . . 11.20 11.20 11.20 11.20 11. 42 1998 WINTER 1 10.50 10.500 10.50 . . . 10.50 10.50 10.50 10.50 10. 42 1999 FALL 1 7.60 7.6000 7.60 . . . 7.60 7.60 7.60 7.60 7. 42 1999 SUMMER 8 8.98 4.9000 10.79 1.87 0.66 21 4.90 8.48 9.37 10.22 10. 42 2000 SPRING 4 9.07 7.0100 11.17 1.87 0.94 21 7.01 7.55 9.04 10.59 11. 42 2000 SUMMER 3 9.80 7.2000 13.40 3.22 1.86 33 7.20 7.20 8.80 13.40 13.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 32 2.25 .00000 5.80 1.58 0.28 70 0.00 1.10 2.07 3.20 5 25 1990 SPRING 26 1.96 .10000 4.80 1.38 0.27 71 0.19 1.15 1.61 2.35 4 25 1990 SUMMER 30 1.31 .00000 4.95 1.33 0.24 101 0.00 0.37 1.04 1.55 4 25 1990 WINTER 26 2.72 .75000 6.65 1.60 0.31 59 0.77 1.45 2.13 3.80 6 25 1991 FALL 31 2.37 .00000 5.90 1.71 0.31 72 0.08 1.12 2.40 3.40 5 25 1991 SPRING 31 2.25 .00000 6.15 1.75 0.31 78 0.01 0.50 2.07 3.50 5 25 1991 SUMMER 29 1.18 .00000 4.40 1.04 0.19 88 0.00 0.35 1.14 1.65 3 25 1991 WINTER 25 2.86 .58500 6.45 1.82 0.36 64 0.88 1.40 2.16 4.70 6 25 1992 FALL 23 2.77 .00000 6.30 2.06 0.43 74 0.06 0.95 2.35 5.10 5 25 1992 SPRING 29 2.11 .00000 6.10 1.55 0.29 74 0.00 1.05 2.00 2.80 5 25 1992 SUMMER 30 1.46 .00000 5.00 1.29 0.24 89 0.00 0.45 1.12 2.50 4 25 1992 WINTER 29 3.05 .00000 7.10 2.07 0.39 68 0.22 1.58 2.40 4.80 6 25 1993 FALL 18 3.01 .00000 6.60 2.08 0.49 69 0.00 1.22 3.25 4.60 6 25 1993 SPRING 22 2.45 .30000 5.30 1.65 0.35 67 0.34 0.96 2.13 3.80 5 25 1993 SUMMER 19 2.00 .00000 5.10 1.59 0.37 80 0.00 0.86 1.60 3.10 5 25 1993 WINTER 20 3.33 .00000 7.00 2.24 0.50 67 0.08 1.60 3.03 5.20 6 25 1994 FALL 20 3.13 .06000 6.75 2.11 0.47 67 0.31 1.30 3.23 4.90 6 25 1994 SPRING 22 2.51 .00000 6.00 1.77 0.38 71 0.24 0.90 2.58 3.90 5 25 1994 SUMMER 21 2.44 .00000 6.40 2.06 0.45 84 0.00 1.15 1.49 4.05 6 25 1994 WINTER 15 3.47 .00000 6.90 2.49 0.64 72 0.00 1.32 4.20 5.65 6 25 1995 FALL 11 2.89 .00000 6.10 2.25 0.68 78 0.00 0.10 3.90 4.60 6 25 1995 SPRING 13 3.16 .05000 6.50 1.92 0.53 61 0.05 2.15 3.30 4.10 6 25 1995 SUMMER 14 0.95 .00000 2.80 0.79 0.21 83 0.00 0.60 0.79 1.21 2 25 1995 WINTER 12 4.23 .00250 9.40 2.78 0.80 66 0.00 2.88 4.25 5.83 9 25 1996 FALL 9 3.58 1.1000 5.50 1.42 0.47 40 1.10 2.75 3.75 4.50 5 25 1996 SPRING 11 4.22 .02000 8.76 2.83 0.85 67 0.02 1.80 4.30 7.00 8 25 1996 SUMMER 10 3.30 .08000 8.54 2.63 0.83 80 0.08 1.30 2.70 5.60 8 25 1996 WINTER 10 4.47 .02000 8.44 2.68 0.85 60 0.02 2.70 4.55 6.75 8 25 1997 FALL 9 3.03 .60000 5.20 1.48 0.49 49 0.60 1.90 3.00 4.10 5 25 1997 SPRING 8 3.67 .70000 7.00 2.18 0.77 59 0.70 2.33 3.00 5.50 7 25 1997 SUMMER 8 1.43 .00000 3.00 0.92 0.33 65 0.00 0.85 1.43 1.93 3 25 1997 WINTER 8 4.63 1.7000 7.10 1.77 0.63 38 1.70 3.50 4.60 6.00 7
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1998 WINTER 9 4.04 1.7000 6.85 1.84 0.61 45 1.70 3.10 3.70 4.90 6 25 1999 FALL 19 1.71 .01000 4.88 1.62 0.37 95 0.01 0.34 0.87 2.63 4 25 1999 SUMMER 20 1.34 .00000 3.78 1.38 0.31 103 0.00 0.34 0.81 2.86 3 25 2000 SPRING 10 1.85 .00000 5.66 2.06 0.65 111 0.00 0.28 0.83 2.85 5 27 1990 FALL 81 0.95 .00375 10.00 1.62 0.18 171 0.01 0.04 0.38 1.01 3 27 1990 SPRING 82 0.75 .00250 3.00 0.67 0.07 89 0.03 0.21 0.58 1.17 1 27 1990 SUMMER 102 0.63 .00500 7.00 1.02 0.10 162 0.01 0.13 0.20 0.80 2 27 1990 WINTER 54 1.15 .00500 6.60 1.18 0.16 102 0.03 0.50 0.82 1.50 2 27 1991 FALL 84 0.79 .00500 10.60 1.39 0.15 177 0.01 0.03 0.37 0.87 2 27 1991 SPRING 86 0.59 .00500 3.10 0.69 0.07 117 0.01 0.04 0.40 0.85 2 27 1991 SUMMER 118 0.58 .00500 7.10 0.99 0.09 170 0.01 0.08 0.16 0.71 2 27 1991 WINTER 118 1.09 .00500 6.98 1.27 0.12 117 0.01 0.13 0.71 1.41 3 27 1992 FALL 90 0.87 .00500 4.85 0.85 0.09 98 0.01 0.16 0.67 1.38 2 27 1992 SPRING 98 0.67 .00500 3.20 0.76 0.08 113 0.01 0.13 0.48 0.79 2 27 1992 SUMMER 123 0.65 .00500 4.65 0.69 0.06 105 0.01 0.13 0.50 1.00 1 27 1992 WINTER 109 1.22 .00500 5.10 1.18 0.11 97 0.02 0.24 0.88 1.89 3 27 1993 FALL 73 1.36 .03000 5.62 1.05 0.12 77 0.16 0.65 1.05 1.87 3 27 1993 SPRING 85 0.91 .02000 2.08 0.54 0.06 60 0.03 0.53 0.89 1.33 1 27 1993 SUMMER 79 0.95 .03000 3.07 0.65 0.07 69 0.09 0.47 0.84 1.21 2 27 1993 WINTER 93 1.30 .08300 3.15 0.71 0.07 55 0.14 0.78 1.30 1.90 2 27 1994 FALL 80 1.17 .00250 7.42 1.49 0.17 127 0.01 0.29 0.64 1.28 3 27 1994 SPRING 72 1.10 .02500 4.96 0.92 0.11 84 0.08 0.51 0.93 1.45 2 27 1994 SUMMER 99 1.05 .00000 7.54 1.30 0.13 124 0.00 0.23 0.70 1.26 3 27 1994 WINTER 61 2.04 .10000 8.95 1.56 0.20 76 0.34 0.99 1.71 2.68 4 27 1995 FALL 22 0.58 .01000 1.51 0.50 0.11 85 0.01 0.18 0.40 1.01 1 27 1995 SPRING 21 1.09 .01000 8.04 1.76 0.38 162 0.02 0.18 0.55 1.21 3 27 1995 SUMMER 23 1.19 .00250 10.50 2.59 0.54 218 0.00 0.03 0.35 0.78 7 27 1995 WINTER 16 1.11 .05000 7.30 1.87 0.47 167 0.05 0.21 0.41 1.16 7 27 1996 SPRING 15 0.85 .02000 3.09 1.09 0.28 128 0.02 0.06 0.26 1.56 3 27 1996 SUMMER 12 0.44 .00250 2.63 0.77 0.22 176 0.00 0.02 0.12 0.49 2 27 1996 WINTER 12 1.73 .01000 5.45 1.72 0.50 99 0.01 0.32 1.17 2.79 5 27 1997 FALL 5 0.16 .07000 0.41 0.14 0.06 93 0.07 0.07 0.11 0.12 0
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1997 SPRING 5 0.32 .01000 1.31 0.55 0.25 172 0.01 0.03 0.13 0.13 1 27 1997 SUMMER 5 0.15 .04000 0.29 0.11 0.05 70 0.04 0.05 0.17 0.20 0 27 1999 FALL 16 1.37 .22000 2.75 0.99 0.25 72 0.22 0.51 1.02 2.47 2 27 1999 SUMMER 14 1.60 .41000 3.43 0.86 0.23 54 0.41 0.87 1.63 1.85 3 27 2000 SPRING 8 1.08 .15000 2.67 1.00 0.35 93 0.15 0.22 0.70 1.99 2 32 1990 FALL 22 2.38 .02000 10.00 3.00 0.64 126 0.03 0.30 0.83 5.20 8 32 1990 SPRING 25 1.26 .02500 8.80 1.77 0.35 141 0.10 0.40 0.70 1.35 3 32 1990 SUMMER 26 1.32 .02500 9.90 2.50 0.49 190 0.03 0.10 0.40 1.10 8 32 1990 WINTER 24 2.37 .02500 6.50 2.10 0.43 88 0.15 0.65 1.73 3.90 6 32 1991 FALL 20 1.93 .13000 9.70 2.75 0.61 143 0.16 0.57 0.94 1.78 9 32 1991 SPRING 28 1.77 .01000 8.10 2.21 0.42 125 0.24 0.53 0.75 1.72 6 32 1991 SUMMER 26 1.43 .01000 9.00 2.39 0.47 167 0.01 0.06 0.48 1.40 8 32 1991 WINTER 26 2.69 .02000 10.00 2.89 0.57 108 0.50 0.63 1.20 4.20 8 32 1992 FALL 17 2.30 .01000 9.80 3.05 0.74 132 0.01 0.09 1.30 3.20 9 32 1992 SPRING 27 1.43 .13000 5.80 1.27 0.25 89 0.23 0.54 1.10 2.00 3 32 1992 SUMMER 26 1.71 .01000 6.60 1.82 0.36 106 0.06 0.34 0.91 2.30 5 32 1992 WINTER 30 1.43 .20000 5.60 1.50 0.27 105 0.27 0.53 0.83 1.55 5 32 1993 SPRING 3 0.84 .47500 1.20 0.36 0.21 43 0.48 0.48 0.83 1.20 1 32 1993 SUMMER 3 0.85 .20000 2.00 1.00 0.58 118 0.20 0.20 0.34 2.00 2 32 1993 WINTER 3 0.91 .53000 1.50 0.52 0.30 56 0.53 0.53 0.71 1.50 1 32 1994 FALL 15 0.86 .13000 2.43 0.64 0.17 74 0.13 0.29 0.93 1.27 2 32 1994 SPRING 1 0.81 .81000 0.81 . . . 0.81 0.81 0.81 0.81 0 32 1994 SUMMER 1 0.07 .07300 0.07 . . . 0.07 0.07 0.07 0.07 0 32 1994 WINTER 5 1.79 .16000 4.79 1.88 0.84 105 0.16 0.69 0.86 2.44 4 32 1995 FALL 22 2.13 .00250 9.29 2.58 0.55 121 0.02 0.36 1.23 2.63 6 32 1995 SPRING 23 1.68 .17000 8.22 1.80 0.38 107 0.38 0.43 1.28 1.99 4 32 1995 SUMMER 26 1.05 .00250 5.02 1.03 0.20 99 0.00 0.28 0.89 1.41 2 32 1995 WINTER 22 1.54 .00250 9.28 2.21 0.47 143 0.04 0.34 0.86 1.66 5 32 1996 FALL 4 0.59 .00250 1.82 0.85 0.42 145 0.00 0.03 0.26 1.14 1 32 1996 WINTER 7 2.70 .13000 8.09 2.52 0.95 93 0.13 1.54 2.05 2.62 8 42 1990 FALL 6 0.35 .02500 1.05 0.44 0.18 126 0.03 0.04 0.12 0.75 1 42 1990 SPRING 6 0.25 .00900 0.86 0.32 0.13 132 0.01 0.03 0.12 0.35 0
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  42 1990 SUMMER 13 0.07 .00250 0.50 0.14 0.04 204 0.00 0.00 0.02 0.09 0 42 1990 WINTER 6 0.32 .02500 1.06 0.45 0.18 141 0.03 0.04 0.04 0.70 1 42 1991 FALL 7 0.25 .01000 0.90 0.37 0.14 151 0.01 0.02 0.02 0.67 0 42 1991 SPRING 9 0.19 .01000 0.70 0.26 0.09 137 0.01 0.02 0.02 0.40 0 42 1991 SUMMER 10 0.11 .00250 0.60 0.20 0.06 174 0.00 0.01 0.02 0.10 0 42 1991 WINTER 6 0.66 .01000 1.54 0.66 0.27 101 0.01 0.03 0.54 1.30 1 42 1992 FALL 8 1.41 .01000 4.61 2.02 0.71 143 0.01 0.02 0.50 2.81 4 42 1992 SPRING 10 0.27 .01000 0.79 0.30 0.10 113 0.01 0.03 0.17 0.63 0 42 1992 SUMMER 9 0.16 .01000 0.94 0.30 0.10 187 0.01 0.02 0.08 0.12 0 42 1992 WINTER 8 0.50 .01000 1.12 0.54 0.19 109 0.01 0.02 0.31 1.11 1 42 1993 FALL 4 0.52 .06900 1.40 0.62 0.31 119 0.07 0.08 0.31 0.96 1 42 1993 SPRING 6 0.29 .01000 0.81 0.32 0.13 109 0.01 0.02 0.20 0.52 0 42 1993 SUMMER 4 0.20 .02500 0.57 0.25 0.13 126 0.03 0.06 0.10 0.34 0 42 1993 WINTER 5 0.75 .08100 1.27 0.49 0.22 66 0.08 0.45 0.80 1.15 1 42 1994 FALL 4 0.32 .10000 0.43 0.15 0.08 48 0.10 0.21 0.37 0.42 0 42 1994 SPRING 6 0.43 .02500 1.10 0.39 0.16 89 0.03 0.19 0.33 0.64 1 42 1994 SUMMER 8 3.59 .02500 8.44 3.39 1.20 94 0.03 0.29 2.97 6.88 8 42 1994 WINTER 1 0.80 .80000 0.80 . . . 0.80 0.80 0.80 0.80 0 42 1995 FALL 1 0.50 .50000 0.50 . . . 0.50 0.50 0.50 0.50 0 42 1995 SPRING 4 0.34 .20000 0.48 0.12 0.06 36 0.20 0.25 0.35 0.44 0 42 1995 SUMMER 8 0.18 .01000 0.72 0.27 0.10 155 0.01 0.01 0.04 0.30 0 42 1995 WINTER 2 0.98 .60000 1.35 0.53 0.38 54 0.60 0.60 0.98 1.35 1 42 1996 FALL 1 0.40 .40000 0.40 . . . 0.40 0.40 0.40 0.40 0 42 1996 SPRING 3 0.17 .06000 0.25 0.10 0.06 58 0.06 0.06 0.20 0.25 0 42 1996 SUMMER 1 0.03 .02500 0.03 . . . 0.03 0.03 0.03 0.03 0 42 1996 WINTER 1 1.00 1.0000 1.00 . . . 1.00 1.00 1.00 1.00 1 42 1997 FALL 1 0.50 .50000 0.50 . . . 0.50 0.50 0.50 0.50 0 42 1997 SPRING 1 0.10 .10000 0.10 . . . 0.10 0.10 0.10 0.10 0 42 1997 SUMMER 1 0.10 .10000 0.10 . . . 0.10 0.10 0.10 0.10 0 42 1997 WINTER 1 0.90 .90000 0.90 . . . 0.90 0.90 0.90 0.90 0 42 1998 SPRING 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0 42 1998 SUMMER 1 0.10 .10000 0.10 . . . 0.10 0.10 0.10 0.10 0
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1998 WINTER 1 0.80 .80000 0.80 . . . 0.80 0.80 0.80 0.80 0. 42 1999 FALL 8 1.05 .49000 2.00 0.66 0.23 63 0.49 0.55 0.66 1.75 2. 42 1999 SUMMER 8 0.72 .00000 1.67 0.64 0.23 88 0.00 0.28 0.59 1.19 1. 42 1999 WINTER 4 0.28 .10000 0.70 0.29 0.14 104 0.10 0.10 0.15 0.45 0. 42 2000 SPRING 4 0.75 .10000 2.10 0.91 0.46 122 0.10 0.24 0.40 1.27 2.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 32 1.14 .00000 9.00 1.76 0.31 155 0.00 0.18 0.51 1.50 4 25 1990 SPRING 30 1.14 .00000 6.50 1.33 0.24 117 0.00 0.53 0.73 1.15 3 25 1990 SUMMER 35 1.09 .00000 8.40 1.54 0.26 141 0.00 0.40 0.70 1.20 4 25 1990 WINTER 28 2.46 .00000 28.00 5.21 0.99 212 0.00 0.30 0.87 3.23 4 25 1991 FALL 32 1.36 .00000 6.20 1.38 0.24 101 0.00 0.60 0.85 1.78 4 25 1991 SPRING 33 1.41 .00000 6.20 1.41 0.24 100 0.00 0.50 0.95 2.10 5 25 1991 SUMMER 32 0.96 .00000 2.50 0.75 0.13 78 0.00 0.45 0.78 1.45 2 25 1991 WINTER 24 1.43 .00000 5.15 1.44 0.29 101 0.00 0.30 0.85 2.60 4 25 1992 FALL 23 1.04 .00000 5.60 1.33 0.28 129 0.00 0.30 0.60 1.30 4 25 1992 SPRING 30 1.16 .00000 4.50 1.18 0.22 101 0.00 0.50 0.65 1.50 4 25 1992 SUMMER 31 1.02 .00000 3.80 1.02 0.18 100 0.00 0.50 0.73 1.30 3 25 1992 WINTER 24 1.63 .00000 8.90 2.01 0.41 124 0.00 0.48 0.95 1.90 5 25 1993 FALL 37 1.15 .00000 4.10 1.00 0.16 87 0.00 0.60 0.90 1.40 4 25 1993 SPRING 39 1.24 .00000 6.45 1.10 0.18 89 0.13 0.69 0.90 1.70 2 25 1993 SUMMER 38 1.00 .00000 3.60 0.95 0.15 95 0.00 0.40 0.70 1.07 3 25 1993 WINTER 32 1.34 .00000 6.75 1.56 0.28 116 0.13 0.40 0.69 1.70 5 25 1994 FALL 32 1.13 .00000 3.90 1.03 0.18 91 0.05 0.40 0.67 1.59 3 25 1994 SPRING 54 1.18 .00000 5.30 1.04 0.14 89 0.24 0.60 0.88 1.35 4 25 1994 SUMMER 45 1.17 .00000 4.30 0.91 0.14 77 0.29 0.60 1.00 1.35 3 25 1994 WINTER 29 1.41 .00000 5.50 1.41 0.26 100 0.30 0.50 0.80 2.00 5 25 1995 FALL 26 1.08 .05000 2.40 0.66 0.13 61 0.30 0.50 1.03 1.50 2 25 1995 SPRING 30 1.43 .20000 5.20 1.36 0.25 95 0.40 0.65 0.90 1.65 5 25 1995 SUMMER 35 0.89 .00000 5.20 0.87 0.15 98 0.00 0.40 0.80 1.10 1 25 1995 WINTER 32 1.67 .17000 6.20 1.51 0.27 90 0.20 0.50 0.90 2.45 5 25 1996 FALL 14 1.36 .00000 4.50 1.21 0.32 89 0.00 0.70 1.13 1.60 4 25 1996 SPRING 15 1.20 .02500 3.05 0.92 0.24 77 0.03 0.39 0.97 1.80 3 25 1996 SUMMER 17 1.12 .40000 2.10 0.50 0.12 45 0.40 0.80 1.10 1.30 2 25 1996 WINTER 18 1.57 .10000 5.20 1.44 0.34 92 0.10 0.68 1.07 2.25 5 25 1997 FALL 14 1.20 .00000 4.80 1.24 0.33 103 0.00 0.45 0.78 1.80 4 25 1997 SPRING 13 1.20 .00000 3.50 1.08 0.30 90 0.00 0.50 0.70 2.00 3 25 1997 SUMMER 13 0.70 .00000 1.10 0.28 0.08 40 0.00 0.65 0.75 0.80 1 25 1997 WINTER 13 1.61 .60000 3.70 0.82 0.23 51 0.60 1.10 1.50 2.00 3
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1998 WINTER 13 1.27 .40000 2.55 0.76 0.21 60 0.40 0.70 0.80 2.00 2 27 1990 FALL 33 0.77 .07500 2.30 0.49 0.09 63 0.13 0.48 0.71 0.90 1 27 1990 SPRING 32 1.09 .07500 5.40 1.00 0.18 92 0.45 0.60 0.86 1.10 3 27 1990 SUMMER 60 0.85 .11000 6.30 0.99 0.13 116 0.11 0.22 0.58 1.05 2 27 1990 WINTER 55 0.74 .12500 2.00 0.38 0.05 51 0.21 0.51 0.70 0.85 1 27 1991 FALL 40 0.80 .05000 4.30 0.89 0.14 112 0.06 0.42 0.59 0.81 3 27 1991 SPRING 32 1.15 .31250 4.80 0.80 0.14 69 0.51 0.74 0.95 1.38 2 27 1991 SUMMER 66 1.13 .05000 3.00 0.65 0.08 57 0.40 0.70 0.88 1.41 2 27 1991 WINTER 66 0.75 .05000 3.30 0.53 0.07 71 0.20 0.48 0.58 0.85 1 27 1992 FALL 37 0.80 .05000 5.37 0.92 0.15 115 0.05 0.40 0.60 0.90 2 27 1992 SPRING 47 0.75 .05000 2.80 0.54 0.08 72 0.08 0.45 0.67 0.90 1 27 1992 SUMMER 69 1.25 .07500 5.11 1.09 0.13 87 0.40 0.69 0.90 1.23 4 27 1992 WINTER 57 0.57 .02500 1.40 0.27 0.04 48 0.20 0.35 0.60 0.70 1 27 1993 FALL 33 0.61 .20000 1.51 0.30 0.05 49 0.28 0.40 0.60 0.70 1 27 1993 SPRING 37 1.14 .07500 4.65 0.92 0.15 80 0.15 0.60 0.80 1.37 2 27 1993 SUMMER 50 1.10 .15000 2.90 0.64 0.09 58 0.30 0.70 0.99 1.23 2 27 1993 WINTER 52 0.65 .11500 2.19 0.41 0.06 63 0.20 0.38 0.60 0.70 1 27 1994 FALL 35 0.90 .07500 6.90 1.10 0.19 121 0.10 0.46 0.85 1.00 1 27 1994 SPRING 47 0.89 .08000 2.15 0.44 0.06 49 0.23 0.60 0.80 1.10 1 27 1994 SUMMER 62 1.18 .20000 3.03 0.65 0.08 55 0.40 0.72 1.02 1.50 2 27 1994 WINTER 28 0.57 .07500 1.17 0.31 0.06 53 0.10 0.36 0.55 0.90 1 27 1995 FALL 28 0.65 .05000 1.74 0.41 0.08 63 0.15 0.36 0.50 0.85 1 27 1995 SPRING 25 0.74 .12000 1.93 0.45 0.09 60 0.27 0.39 0.62 1.00 1 27 1995 SUMMER 26 0.75 .19000 1.36 0.31 0.06 41 0.20 0.60 0.79 0.95 1 27 1995 WINTER 19 0.46 .05000 0.96 0.27 0.06 59 0.05 0.21 0.50 0.70 0 27 1996 FALL 15 0.59 .12500 1.55 0.37 0.09 62 0.13 0.40 0.50 0.70 1 27 1996 SPRING 18 0.91 .24000 3.26 0.69 0.16 76 0.24 0.38 0.82 1.12 3 27 1996 SUMMER 31 1.05 .16000 3.45 0.77 0.14 74 0.21 0.55 0.89 1.13 2 27 1996 WINTER 19 0.57 .05000 1.37 0.32 0.07 56 0.05 0.34 0.52 0.79 1 27 1997 FALL 5 1.05 .40000 2.20 0.68 0.30 65 0.40 0.80 0.90 0.95 2 27 1997 SPRING 9 0.95 .22500 1.65 0.53 0.18 56 0.23 0.40 1.10 1.40 1 27 1997 SUMMER 5 1.68 1.2000 2.20 0.37 0.17 22 1.20 1.50 1.70 1.80 2
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1997 WINTER 4 0.38 .17500 0.80 0.28 0.14 74 0.18 0.23 0.28 0.54 0 32 1990 FALL 23 0.95 .30000 2.35 0.48 0.10 51 0.50 0.60 0.90 1.10 1 32 1990 SPRING 27 0.85 .20000 2.90 0.55 0.11 65 0.40 0.50 0.70 0.95 1 32 1990 SUMMER 27 0.62 .12500 1.50 0.35 0.07 56 0.20 0.40 0.60 0.80 1 32 1990 WINTER 25 0.96 .05000 2.70 0.64 0.13 66 0.20 0.50 0.90 1.35 2 32 1991 FALL 24 0.66 .05000 2.40 0.47 0.10 72 0.20 0.35 0.56 0.88 1 32 1991 SPRING 36 0.90 .05000 3.80 0.67 0.11 74 0.18 0.50 0.80 1.15 2 32 1991 SUMMER 35 0.89 .30000 2.80 0.51 0.09 57 0.30 0.60 0.80 1.00 2 32 1991 WINTER 29 0.98 .30000 5.40 1.03 0.19 105 0.30 0.45 0.70 1.00 3 32 1992 FALL 22 0.74 .05000 2.50 0.52 0.11 70 0.30 0.40 0.55 1.00 1 32 1992 SPRING 31 0.61 .16000 1.75 0.30 0.05 50 0.18 0.45 0.50 0.70 1 32 1992 SUMMER 30 0.71 .02500 2.20 0.56 0.10 79 0.05 0.30 0.63 0.90 2 32 1992 WINTER 34 0.54 .05000 1.20 0.30 0.05 55 0.05 0.40 0.50 0.60 1 32 1993 FALL 28 0.49 .12500 1.18 0.27 0.05 56 0.15 0.30 0.44 0.62 1 32 1993 SPRING 35 0.44 .05000 1.62 0.31 0.05 72 0.05 0.25 0.35 0.56 0 32 1993 SUMMER 33 0.57 .09000 1.45 0.33 0.06 58 0.13 0.33 0.50 0.80 1 32 1993 WINTER 29 0.45 .05000 1.61 0.33 0.06 73 0.05 0.30 0.42 0.60 0 32 1994 FALL 35 0.60 .12000 2.60 0.48 0.08 79 0.13 0.30 0.50 0.70 1 32 1994 SPRING 48 0.74 .19000 2.38 0.50 0.07 68 0.20 0.40 0.60 0.95 1 32 1994 SUMMER 34 0.66 .20000 1.90 0.37 0.06 56 0.22 0.47 0.57 0.86 1 32 1994 WINTER 39 0.60 .05000 3.78 0.62 0.10 102 0.05 0.30 0.40 0.77 1 32 1995 FALL 28 0.61 .13000 3.00 0.56 0.11 92 0.15 0.30 0.42 0.66 1 32 1995 SPRING 40 0.79 .16000 4.72 0.83 0.13 105 0.23 0.38 0.54 0.74 2 32 1995 SUMMER 39 0.59 .05000 2.76 0.47 0.08 80 0.18 0.30 0.46 0.65 1 32 1995 WINTER 37 0.44 .05000 1.30 0.31 0.05 70 0.12 0.22 0.40 0.58 1 32 1996 FALL 7 0.67 .05000 1.87 0.61 0.23 91 0.05 0.30 0.45 0.85 1 32 1996 SPRING 30 0.84 .05000 2.20 0.56 0.10 67 0.21 0.36 0.70 1.15 1 32 1996 SUMMER 28 0.78 .22000 2.11 0.49 0.09 62 0.27 0.40 0.70 0.93 2 32 1996 WINTER 27 0.65 .11000 1.89 0.48 0.09 75 0.13 0.23 0.55 0.82 1 32 1997 SPRING 6 1.10 .05000 3.60 1.32 0.54 120 0.05 0.30 0.58 1.50 3 32 1997 WINTER 6 0.18 .05000 0.45 0.19 0.08 111 0.05 0.05 0.05 0.40 0 42 1990 FALL 6 0.62 .20000 1.25 0.34 0.14 56 0.20 0.50 0.58 0.60 1
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  42 1990 SPRING 8 0.68 .07500 1.27 0.40 0.14 59 0.08 0.40 0.70 0.95 1 42 1990 SUMMER 19 1.33 .20000 4.00 1.03 0.24 78 0.20 0.70 1.00 1.55 4 42 1990 WINTER 6 0.55 .30000 0.90 0.20 0.08 36 0.30 0.45 0.53 0.57 0 42 1991 FALL 7 0.64 .15000 1.30 0.41 0.16 65 0.15 0.20 0.55 0.90 1 42 1991 SPRING 7 0.57 .30000 0.82 0.20 0.07 35 0.30 0.40 0.50 0.80 0 42 1991 SUMMER 11 0.94 .10000 1.90 0.46 0.14 49 0.10 0.70 1.00 1.10 1 42 1991 WINTER 5 0.58 .07500 0.85 0.30 0.13 51 0.08 0.60 0.69 0.70 0 42 1992 FALL 8 0.68 .30000 1.00 0.25 0.09 38 0.30 0.50 0.65 0.90 1 42 1992 SPRING 6 0.53 .15000 1.30 0.49 0.20 92 0.15 0.20 0.28 0.99 1 42 1992 SUMMER 7 0.79 .20000 1.15 0.37 0.14 46 0.20 0.40 0.90 1.11 1 42 1992 WINTER 5 0.51 .30000 0.73 0.17 0.07 33 0.30 0.40 0.50 0.60 0 42 1993 FALL 6 0.45 .07500 0.60 0.21 0.08 46 0.08 0.40 0.50 0.60 0 42 1993 SPRING 12 0.97 .20000 2.40 0.62 0.18 64 0.20 0.51 0.80 1.43 2 42 1993 SUMMER 9 0.93 .30000 1.70 0.54 0.18 58 0.30 0.60 0.75 1.30 1 42 1993 WINTER 5 1.00 .30000 2.18 0.72 0.32 72 0.30 0.70 0.70 1.10 2 42 1994 FALL 7 0.54 .20000 1.20 0.34 0.13 62 0.20 0.30 0.40 0.70 1 42 1994 SPRING 7 0.84 .20000 1.70 0.50 0.19 60 0.20 0.40 0.85 1.20 1 42 1994 SUMMER 13 0.82 .28000 2.17 0.58 0.16 71 0.28 0.30 0.70 1.20 2 42 1994 WINTER 1 0.80 .80000 0.80 . . . 0.80 0.80 0.80 0.80 0 42 1995 FALL 5 1.04 .30000 3.40 1.32 0.59 127 0.30 0.40 0.50 0.60 3 42 1995 SPRING 8 0.97 .10000 1.54 0.49 0.17 51 0.10 0.63 1.10 1.35 1 42 1995 SUMMER 12 1.53 .30000 4.50 1.27 0.37 83 0.30 0.93 1.08 1.40 4 42 1995 WINTER 2 1.00 .50000 1.50 0.71 0.50 71 0.50 0.50 1.00 1.50 1 42 1996 FALL 2 1.05 .50000 1.60 0.78 0.55 74 0.50 0.50 1.05 1.60 1 42 1996 SPRING 5 0.84 .40000 1.10 0.32 0.14 38 0.40 0.60 1.00 1.10 1 42 1996 SUMMER 6 1.64 .80000 2.85 0.71 0.29 43 0.80 1.15 1.58 1.90 2 42 1996 WINTER 1 1.50 1.5000 1.50 . . . 1.50 1.50 1.50 1.50 1 42 1997 SPRING 1 0.30 .30000 0.30 . . . 0.30 0.30 0.30 0.30 0 42 1997 SUMMER 1 0.60 .60000 0.60 . . . 0.60 0.60 0.60 0.60 0 42 1997 WINTER 1 4.05 4.0500 4.05 . . . 4.05 4.05 4.05 4.05 4 42 1999 FALL 1 1.97 1.9700 1.97 . . . 1.97 1.97 1.97 1.97 1 42 1999 SUMMER 1 2.84 2.8350 2.84 . . . 2.84 2.84 2.84 2.84 2
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1999 WINTER 4 0.66 .34000 1.14 0.35 0.17 53 0.34 0.42 0.57 0.89 1. 42 2000 SPRING 1 2.88 2.8800 2.88 . . . 2.88 2.88 2.88 2.88 2.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1999 to 2000 Organic_P_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1999 FALL 19 17.34 1.5100 87.01 19.64 4.51 113 1.51 6.24 12.39 20.97 87 25 1999 SUMMER 20 103.22 4.3300 348.11 105.37 23.56 102 4.33 29.29 65.20 156.62 348 25 2000 SPRING 10 38.64 1.8400 154.83 53.90 17.05 140 1.84 8.61 14.84 40.11 154 27 1999 FALL 16 51.05 13.710 99.08 24.91 6.23 49 13.71 37.88 44.97 64.96 99 27 1999 SUMMER 14 73.14 38.590 149.17 36.48 9.75 50 38.59 50.98 57.20 96.32 149 27 2000 SPRING 8 91.13 31.850 177.15 44.03 15.57 48 31.85 61.88 88.14 110.00 177 42 1999 FALL 7 31.50 4.1000 59.50 25.90 9.79 82 4.10 4.10 18.49 59.50 59 42 1999 SUMMER 7 105.99 46.810 177.75 46.89 17.72 44 46.81 46.81 106.54 128.74 177 42 2000 SPRING 3 101.14 76.890 130.27 27.02 15.60 27 76.89 76.89 96.26 130.27 130
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1992 Phosph_Ortho_Tot_as_P_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 4 526.25 5.0000 2000.00 982.76 491.38 187 5.00 22.50 50.00 1030.0 200 25 1991 FALL 4 580.00 5.0000 2200.00 1080.5 540.26 186 5.00 17.50 57.50 1142.5 220 25 1991 SPRING 4 735.00 20.000 2800.00 1377.0 688.51 187 20.00 25.00 60.00 1445.0 280 25 1991 SUMMER 3 426.67 30.000 1000.00 508.56 293.62 119 30.00 30.00 250.00 1000.0 100 25 1991 WINTER 1 40.00 40.000 40.00 . . . 40.00 40.00 40.00 40.00 40 25 1992 FALL 3 816.67 20.000 2400.00 1371.2 791.67 168 20.00 20.00 30.00 2400.0 240 25 1992 SPRING 4 360.00 5.0000 1300.00 627.44 313.72 174 5.00 30.00 67.50 690.00 130 25 1992 SUMMER 4 480.00 30.000 1800.00 880.04 440.02 183 30.00 35.00 45.00 925.00 180 25 1992 WINTER 3 1100.00 50.000 2900.00 1566.0 904.16 142 50.00 50.00 350.00 2900.0 290 27 1990 FALL 13 109.23 5.0000 430.00 123.57 34.27 113 5.00 20.00 30.00 190.00 430 27 1990 WINTER 2 160.00 120.00 200.00 56.57 40.00 35 120.00 120.00 160.00 200.00 200 27 1991 FALL 13 101.92 5.0000 450.00 126.43 35.07 124 5.00 20.00 70.00 140.00 450 27 1991 SPRING 10 132.00 5.0000 400.00 112.95 35.72 86 5.00 70.00 97.50 190.00 400 27 1991 SUMMER 13 165.96 12.500 590.00 180.96 50.19 109 12.50 25.00 50.00 280.00 590 27 1991 WINTER 13 97.50 5.0000 400.00 119.25 33.07 122 5.00 12.50 30.00 140.00 400 27 1992 FALL 12 80.83 5.0000 180.00 71.66 20.69 89 5.00 7.50 70.00 160.00 180 27 1992 SPRING 9 86.94 10.000 190.00 63.61 21.20 73 10.00 60.00 70.00 115.00 190 27 1992 SUMMER 13 98.08 5.0000 320.00 100.20 27.79 102 5.00 30.00 70.00 110.00 320 27 1992 WINTER 13 85.00 5.0000 250.00 83.24 23.09 98 5.00 5.00 85.00 130.00 250 32 1990 WINTER 3 136.67 10.000 290.00 141.89 81.92 104 10.00 10.00 110.00 290.00 290 32 1991 FALL 3 75.00 20.000 135.00 57.66 33.29 77 20.00 20.00 70.00 135.00 135 32 1991 SPRING 3 63.33 20.000 110.00 45.09 26.03 71 20.00 20.00 60.00 110.00 110 32 1991 SUMMER 3 81.67 5.0000 220.00 120.03 69.30 147 5.00 5.00 20.00 220.00 220 32 1991 WINTER 3 103.33 20.000 170.00 76.38 44.10 74 20.00 20.00 120.00 170.00 170 32 1992 SPRING 3 46.67 10.000 70.00 32.15 18.56 69 10.00 10.00 60.00 70.00 70 32 1992 SUMMER 3 30.00 20.000 40.00 10.00 5.77 33 20.00 20.00 30.00 40.00 40 32 1992 WINTER 3 126.67 25.000 225.00 100.04 57.76 79 25.00 25.00 130.00 225.00 225 42 1990 FALL 4 38.75 5.0000 120.00 54.52 27.26 141 5.00 7.50 15.00 70.00 120 42 1990 WINTER 4 12.50 5.0000 30.00 11.90 5.95 95 5.00 5.00 7.50 20.00 30 42 1991 FALL 5 41.50 5.0000 120.00 45.88 20.52 111 5.00 12.50 35.00 35.00 120 42 1991 SPRING 5 47.50 7.5000 150.00 59.74 26.72 126 7.50 10.00 20.00 50.00 150 42 1991 SUMMER 5 28.00 20.000 30.00 4.47 2.00 16 20.00 30.00 30.00 30.00 30
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1992 Phosph_Ortho_Tot_as_P_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1991 WINTER 3 5.83 5.0000 7.50 1.44 0.83 25 5.00 5.00 5.00 7.50 7. 42 1992 FALL 4 36.25 5.0000 90.00 37.28 18.64 103 5.00 12.50 25.00 60.00 90. 42 1992 SPRING 4 49.38 30.000 90.00 28.31 14.16 57 30.00 30.00 38.75 68.75 90. 42 1992 SUMMER 5 30.50 5.0000 60.00 21.10 9.43 69 5.00 17.50 30.00 40.00 60. 42 1992 WINTER 4 41.88 7.5000 120.00 53.05 26.52 127 7.50 8.75 20.00 75.00 120.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Total_Nitrogen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 4 5.16 2.6000 12.00 4.57 2.29 89 2.60 2.63 3.03 7.70 12 25 1990 SPRING 4 5.43 3.4000 8.35 2.19 1.10 40 3.40 3.78 4.98 7.08 8 25 1990 SUMMER 4 5.08 1.2000 11.00 4.34 2.17 85 1.20 1.90 4.05 8.25 11 25 1990 WINTER 3 12.67 3.4000 30.00 15.02 8.67 119 3.40 3.40 4.60 30.00 30 25 1991 FALL 4 4.98 2.4500 10.00 3.41 1.70 68 2.45 3.03 3.73 6.93 10 25 1991 SPRING 4 5.65 3.3000 11.00 3.59 1.80 64 3.30 3.60 4.15 7.70 11 25 1991 SUMMER 4 3.08 2.6000 4.10 0.71 0.35 23 2.60 2.60 2.80 3.55 4 25 1991 WINTER 1 4.20 4.2000 4.20 . . . 4.20 4.20 4.20 4.20 4 25 1992 FALL 3 5.80 2.3000 11.00 4.59 2.65 79 2.30 2.30 4.10 11.00 11 25 1992 SPRING 4 3.96 2.5000 5.95 1.46 0.73 37 2.50 2.95 3.70 4.98 5 25 1992 SUMMER 4 3.68 1.6000 7.40 2.61 1.30 71 1.60 1.90 2.85 5.45 7 25 1992 WINTER 3 8.15 4.7000 14.00 5.09 2.94 62 4.70 4.70 5.75 14.00 14 25 1993 FALL 3 4.82 3.2000 7.90 2.67 1.54 55 3.20 3.20 3.35 7.90 7 25 1993 SPRING 4 5.11 2.5000 10.70 3.81 1.90 75 2.50 2.70 3.63 7.53 10 25 1993 SUMMER 4 3.65 1.6000 7.50 2.69 1.35 74 1.60 1.80 2.75 5.50 7 25 1993 WINTER 3 6.33 2.8000 11.50 4.57 2.64 72 2.80 2.80 4.70 11.50 11 25 1994 FALL 3 5.07 2.9000 9.00 3.41 1.97 67 2.90 2.90 3.30 9.00 9 25 1994 SPRING 4 5.03 3.5000 8.80 2.52 1.26 50 3.50 3.70 3.90 6.35 8 25 1994 SUMMER 4 3.88 1.1000 8.70 3.32 1.66 86 1.10 1.90 2.85 5.85 8 25 1994 WINTER 2 8.25 4.5000 12.00 5.30 3.75 64 4.50 4.50 8.25 12.00 12 25 1995 FALL 1 6.10 6.1000 6.10 . . . 6.10 6.10 6.10 6.10 6 25 1995 SPRING 2 6.73 3.8000 9.65 4.14 2.93 62 3.80 3.80 6.73 9.65 9 25 1995 SUMMER 2 1.95 1.7000 2.20 0.35 0.25 18 1.70 1.70 1.95 2.20 2 25 1995 WINTER 2 7.25 3.5000 11.00 5.30 3.75 73 3.50 3.50 7.25 11.00 11 25 1999 FALL 19 2.64 .40000 7.34 2.38 0.55 90 0.40 0.73 1.25 4.27 7 25 1999 SUMMER 20 1.95 .58000 4.66 1.41 0.32 72 0.58 1.02 1.30 3.59 4 25 2000 SPRING 10 2.05 .16000 5.67 1.96 0.62 96 0.16 0.57 1.14 3.21 5 27 1990 FALL 12 1.58 .30000 3.60 0.97 0.28 61 0.30 0.88 1.25 2.13 3 27 1990 SPRING 12 1.82 .65000 5.40 1.22 0.35 67 0.65 1.10 1.70 1.93 5 27 1990 SUMMER 38 0.89 .11000 8.40 1.54 0.25 173 0.11 0.11 0.35 0.90 4 27 1990 WINTER 38 1.60 .21000 4.56 1.00 0.16 62 0.30 0.91 1.36 2.10 4 27 1991 FALL 11 1.93 .40000 7.30 1.93 0.58 100 0.40 0.60 1.50 2.00 7
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Total_Nitrogen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1991 SPRING 10 1.66 .85000 2.40 0.59 0.19 36 0.85 1.09 1.63 2.20 2 27 1991 SUMMER 39 1.52 .42500 5.70 1.24 0.20 82 0.47 0.79 0.89 2.15 4 27 1991 WINTER 36 1.22 .31000 3.18 0.78 0.13 64 0.43 0.58 0.81 1.77 2 27 1992 FALL 12 1.45 .20000 3.30 0.94 0.27 65 0.20 0.67 1.35 2.00 3 27 1992 SPRING 15 1.15 .34000 1.82 0.42 0.11 37 0.34 0.83 1.10 1.47 1 27 1992 SUMMER 35 1.21 .34000 3.49 0.68 0.11 56 0.34 0.73 1.01 1.71 2 27 1992 WINTER 32 1.43 .22000 4.68 0.92 0.16 64 0.26 0.86 1.29 1.75 2 27 1993 FALL 11 1.42 .20000 3.70 1.09 0.33 76 0.20 0.60 1.10 2.50 3 27 1993 SPRING 10 1.92 .80000 3.20 0.73 0.23 38 0.80 1.33 1.88 2.20 3 27 1993 SUMMER 13 1.60 .20000 3.70 1.05 0.29 65 0.20 0.90 1.45 1.90 3 27 1993 WINTER 27 1.64 .20000 3.71 0.88 0.17 54 0.34 0.92 1.66 2.26 2 27 1994 FALL 2 2.30 1.6000 3.00 0.99 0.70 43 1.60 1.60 2.30 3.00 3 27 1994 SPRING 8 1.48 .20000 2.60 0.86 0.30 58 0.20 0.85 1.45 2.23 2 27 1994 SUMMER 8 1.29 .20000 3.20 0.87 0.31 68 0.20 0.89 1.15 1.40 3 27 1994 WINTER 4 1.76 .60000 3.50 1.28 0.64 72 0.60 0.83 1.48 2.70 3 27 1995 SPRING 2 0.54 .30000 0.78 0.34 0.24 62 0.30 0.30 0.54 0.78 0 27 1995 SUMMER 3 0.82 .26000 1.50 0.63 0.36 76 0.26 0.26 0.71 1.50 1 27 1995 WINTER 2 1.95 1.8000 2.10 0.21 0.15 11 1.80 1.80 1.95 2.10 2 27 1999 FALL 16 1.85 .73000 2.99 0.85 0.21 46 0.73 1.21 1.51 2.81 2 27 1999 SUMMER 14 2.58 1.0100 10.20 2.30 0.62 89 1.01 1.48 2.16 2.71 10 27 2000 SPRING 8 1.78 .60000 2.89 0.86 0.30 48 0.60 1.09 1.75 2.53 2 32 1990 SPRING 3 0.90 .50000 1.20 0.36 0.21 40 0.50 0.50 1.00 1.20 1 32 1990 SUMMER 3 0.82 .50000 1.40 0.51 0.29 62 0.50 0.50 0.55 1.40 1 32 1990 WINTER 3 1.39 .45500 2.90 1.32 0.76 96 0.46 0.46 0.80 2.90 2 32 1991 FALL 2 1.60 1.6000 1.60 0.00 0.00 0 1.60 1.60 1.60 1.60 1 32 1991 SPRING 3 1.07 .72000 1.30 0.31 0.18 29 0.72 0.72 1.20 1.30 1 32 1991 SUMMER 3 1.35 .44000 2.80 1.27 0.73 94 0.44 0.44 0.80 2.80 2 32 1991 WINTER 3 2.20 1.5000 3.60 1.21 0.70 55 1.50 1.50 1.50 3.60 3 32 1992 SPRING 3 3.28 .85000 6.50 2.91 1.68 88 0.85 0.85 2.50 6.50 6 32 1992 SUMMER 3 1.25 .75000 2.10 0.74 0.43 59 0.75 0.75 0.90 2.10 2 32 1992 WINTER 3 1.85 .91000 2.90 1.00 0.58 54 0.91 0.91 1.75 2.90 2 32 1993 SPRING 3 1.13 .88500 1.40 0.26 0.15 23 0.89 0.89 1.10 1.40 1
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Total_Nitrogen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 32 1993 SUMMER 3 1.21 .50000 2.30 0.96 0.55 79 0.50 0.50 0.84 2.30 2. 32 1993 WINTER 2 1.73 1.1600 2.30 0.81 0.57 47 1.16 1.16 1.73 2.30 2. 32 1994 SPRING 1 1.80 1.8000 1.80 . . . 1.80 1.80 1.80 1.80 1. 32 1994 SUMMER 1 0.57 .57000 0.57 . . . 0.57 0.57 0.57 0.57 0. 32 1994 WINTER 1 0.56 .56000 0.56 . . . 0.56 0.56 0.56 0.56 0. 42 1990 FALL 4 1.04 .50000 1.80 0.61 0.30 59 0.50 0.55 0.93 1.53 1. 42 1990 SPRING 4 0.96 .60000 1.35 0.33 0.17 34 0.60 0.70 0.95 1.23 1. 42 1990 SUMMER 5 1.03 .30000 1.45 0.45 0.20 44 0.30 0.90 1.20 1.30 1. 42 1990 WINTER 4 0.94 .45000 1.20 0.35 0.18 38 0.45 0.68 1.05 1.20 1. 42 1991 FALL 5 0.97 .50000 2.20 0.70 0.31 72 0.50 0.55 0.71 0.90 2. 42 1991 SPRING 5 0.81 .50000 1.40 0.37 0.16 45 0.50 0.50 0.80 0.87 1. 42 1991 SUMMER 5 0.84 .51000 1.10 0.24 0.11 28 0.51 0.70 0.90 1.00 1. 42 1991 WINTER 2 0.90 .70000 1.10 0.28 0.20 31 0.70 0.70 0.90 1.10 1. 42 1992 FALL 4 1.07 .60000 1.90 0.62 0.31 58 0.60 0.60 0.90 1.55 1. 42 1992 SPRING 4 0.89 .30000 1.50 0.49 0.25 56 0.30 0.56 0.87 1.22 1. 42 1992 SUMMER 5 1.01 .75000 1.20 0.18 0.08 18 0.75 0.90 1.10 1.10 1. 42 1992 WINTER 4 0.83 .40000 1.80 0.66 0.33 79 0.40 0.45 0.55 1.20 1. 42 1993 FALL 4 0.87 .40000 2.00 0.76 0.38 88 0.40 0.44 0.54 1.30 2. 42 1993 SPRING 5 1.56 .70000 2.70 0.80 0.36 51 0.70 0.90 1.70 1.80 2. 42 1993 SUMMER 5 0.85 .60000 1.40 0.32 0.14 38 0.60 0.65 0.75 0.85 1. 42 1993 WINTER 3 1.36 .38000 2.50 1.07 0.62 79 0.38 0.38 1.20 2.50 2. 42 1994 FALL 3 0.74 .40000 1.20 0.41 0.24 56 0.40 0.40 0.61 1.20 1. 42 1994 SPRING 5 1.44 .95000 1.95 0.36 0.16 25 0.95 1.36 1.45 1.50 1. 42 1994 SUMMER 5 0.84 .30000 1.50 0.43 0.19 52 0.30 0.70 0.78 0.90 1. 42 1995 SPRING 1 0.70 .70000 0.70 . . . 0.70 0.70 0.70 0.70 0. 42 1995 SUMMER 1 0.95 .95000 0.95 . . . 0.95 0.95 0.95 0.95 0. 42 1999 FALL 8 1.82 .95000 3.97 1.07 0.38 59 0.95 1.17 1.17 2.48 3. 42 1999 SUMMER 8 1.70 1.0400 2.95 0.61 0.22 36 1.04 1.37 1.40 2.04 2. 42 2000 SPRING 4 1.91 1.1400 2.98 0.89 0.44 46 1.14 1.19 1.77 2.64 2.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 41 351.62 .00000 2350.00 532.28 83.13 151 10.00 30.00 100.00 470.00 145 25 1990 SPRING 44 437.05 5.0000 2300.00 545.01 82.16 125 25.00 55.00 182.50 695.00 170 25 1990 SUMMER 53 372.03 .00000 2300.00 501.11 68.83 135 10.00 70.00 170.00 510.00 164 25 1990 WINTER 32 584.42 .00000 4700.00 936.71 165.59 160 9.00 40.00 140.00 800.00 180 25 1991 FALL 40 489.81 2.5000 2400.00 655.48 103.64 134 10.00 60.00 242.50 820.00 225 25 1991 SPRING 40 509.48 5.0000 3000.00 676.36 106.94 133 14.50 60.00 197.50 815.00 202 25 1991 SUMMER 42 299.29 .00000 1200.00 291.35 44.96 97 10.00 105.00 195.00 460.00 102 25 1991 WINTER 32 462.19 .00000 2000.00 563.69 99.65 122 5.00 40.00 180.00 705.00 170 25 1992 FALL 30 479.21 16.250 2500.00 559.43 102.14 117 20.00 70.00 260.00 790.00 135 25 1992 SPRING 35 402.82 2.5000 1500.00 431.11 72.87 107 10.00 100.00 210.00 610.00 150 25 1992 SUMMER 36 375.00 2.5000 1950.00 426.39 71.07 114 2.50 145.00 240.00 475.00 170 25 1992 WINTER 33 610.68 .00000 3600.00 760.17 132.33 124 10.00 90.00 400.00 865.00 205 25 1993 FALL 46 352.25 .00000 2000.00 462.13 68.14 131 10.00 75.00 190.00 370.00 170 25 1993 SPRING 44 471.56 2.5000 2550.00 533.05 80.36 113 30.00 105.00 287.50 677.50 150 25 1993 SUMMER 44 283.64 2.5000 1350.00 281.98 42.51 99 20.00 80.00 210.00 365.00 660 25 1993 WINTER 37 567.64 5.0000 2950.00 622.16 102.28 110 10.00 80.00 320.00 895.00 170 25 1994 FALL 36 384.48 6.2500 1700.00 492.45 82.08 128 20.00 40.00 177.50 522.50 160 25 1994 SPRING 59 361.50 2.5000 1700.00 388.20 50.54 107 30.00 85.00 165.00 625.00 145 25 1994 SUMMER 48 379.51 .00000 1400.00 372.24 53.73 98 20.00 110.00 270.00 465.00 127 25 1994 WINTER 32 597.38 10.000 2000.00 583.48 103.15 98 10.00 100.00 370.00 1075.6 190 25 1995 FALL 33 296.82 2.5000 1250.00 307.78 53.58 104 2.50 100.00 170.00 400.00 110 25 1995 SPRING 35 433.57 10.000 1700.00 440.42 74.44 102 10.00 50.00 280.00 770.00 150 25 1995 SUMMER 41 206.31 10.000 740.00 172.17 26.89 83 30.00 75.00 180.00 310.00 530 25 1995 WINTER 37 510.98 2.5000 2100.00 626.63 103.02 123 10.00 60.00 180.00 930.00 210 25 1996 FALL 22 307.05 10.000 1700.00 386.71 82.45 126 10.00 80.00 140.00 440.00 785 25 1996 SPRING 22 378.52 2.5000 1900.00 497.47 106.06 131 20.00 65.00 100.00 560.00 121 25 1996 SUMMER 24 292.19 2.5000 1100.00 294.98 60.21 101 20.00 90.00 202.50 410.00 106 25 1996 WINTER 22 442.73 2.5000 1950.00 532.64 113.56 120 2.50 35.00 137.50 790.00 120 25 1997 FALL 21 315.71 25.000 1400.00 310.15 67.68 98 30.00 135.00 180.00 460.00 600 25 1997 SPRING 21 310.24 20.000 1100.00 350.09 76.40 113 35.00 50.00 110.00 590.00 930 25 1997 SUMMER 20 214.00 40.000 510.00 126.07 28.19 59 45.00 137.50 190.00 282.50 485 25 1997 WINTER 20 339.50 10.000 1500.00 425.17 95.07 125 15.00 40.00 90.00 720.00 121
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1998 WINTER 14 351.07 110.00 915.00 276.46 73.89 79 110.00 160.00 207.50 490.00 915 25 1999 FALL 19 67.40 30.890 226.12 62.82 14.41 93 30.89 38.14 39.59 65.26 226 25 1999 SUMMER 20 138.99 39.890 399.89 108.61 24.29 78 43.14 64.23 100.40 162.50 399 25 2000 SPRING 10 82.70 28.495 232.58 70.00 22.14 85 28.50 34.63 55.96 91.42 232 27 1990 FALL 84 339.11 10.000 2310.00 477.82 52.13 141 20.00 80.00 172.50 305.00 161 27 1990 SPRING 93 351.57 30.000 2235.00 388.81 40.32 111 40.00 115.00 220.00 455.00 886 27 1990 SUMMER 118 351.40 20.000 1360.00 323.89 29.82 92 50.00 110.00 260.00 430.00 118 27 1990 WINTER 66 279.55 30.000 2070.00 378.28 46.56 135 35.00 80.00 167.50 270.00 102 27 1991 FALL 84 292.54 3.7500 2180.00 378.16 41.26 129 10.00 70.00 157.50 375.00 110 27 1991 SPRING 92 340.76 10.000 1970.00 415.29 43.30 122 50.00 110.00 200.00 360.00 155 27 1991 SUMMER 125 360.27 1.5000 2140.00 380.16 34.00 106 20.00 90.00 270.00 480.00 108 27 1991 WINTER 120 230.38 1.5000 2070.00 347.92 31.76 151 4.88 30.00 100.00 245.00 109 27 1992 FALL 99 266.00 2.5000 1775.00 305.67 30.72 115 10.00 75.00 170.00 315.00 900 27 1992 SPRING 107 283.21 2.5000 1620.00 323.35 31.26 114 10.00 70.00 190.00 330.00 104 27 1992 SUMMER 143 502.67 1.5000 2350.00 556.64 46.55 111 20.00 90.00 240.00 760.00 161 27 1992 WINTER 109 204.02 3.7500 2110.00 289.46 27.73 142 10.00 55.00 120.00 240.00 635 27 1993 FALL 96 231.09 10.000 1310.00 247.02 25.21 107 10.00 80.00 170.00 282.50 730 27 1993 SPRING 107 285.64 3.7500 1700.00 301.31 29.13 105 10.00 100.00 200.00 390.00 740 27 1993 SUMMER 119 397.92 10.000 2390.00 392.63 35.99 99 50.00 140.00 330.00 485.00 125 27 1993 WINTER 109 197.84 10.000 1350.00 215.28 20.62 109 10.00 70.00 125.00 220.00 545 27 1994 FALL 101 279.86 2.5000 1450.00 313.59 31.20 112 20.00 75.00 175.00 320.00 109 27 1994 SPRING 111 310.43 2.5000 1995.00 339.13 32.19 109 30.00 100.00 210.00 345.00 120 27 1994 SUMMER 130 443.04 .00000 2300.00 427.48 37.49 96 55.00 160.00 295.00 600.00 131 27 1994 WINTER 80 170.44 10.000 1640.00 229.12 25.62 134 10.00 47.50 132.50 187.50 475 27 1995 FALL 94 199.60 2.5000 1100.00 197.26 20.35 99 20.00 80.00 150.00 230.00 650 27 1995 SPRING 96 271.73 2.5000 1620.00 248.98 25.41 92 20.00 80.00 217.50 382.50 705 27 1995 SUMMER 99 330.57 2.5000 1365.00 283.08 28.45 86 30.00 120.00 270.00 435.00 890 27 1995 WINTER 82 164.10 2.5000 1460.00 237.05 26.18 144 2.50 30.00 85.00 200.00 560 27 1996 FALL 82 303.72 2.5000 1650.00 260.01 28.71 86 55.00 145.00 220.00 405.00 800 27 1996 SPRING 83 301.45 10.000 2420.00 375.27 41.19 124 20.00 105.00 210.00 345.00 840 27 1996 SUMMER 94 391.22 20.000 1550.00 305.74 31.54 78 50.00 160.00 325.00 570.00 930 27 1996 WINTER 48 137.92 2.5000 680.00 165.09 23.83 120 2.50 25.00 72.50 190.00 520
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1997 FALL 70 402.64 30.000 1950.00 336.25 40.19 84 50.00 180.00 322.50 515.00 114 27 1997 SPRING 75 217.83 2.5000 2100.00 267.48 30.89 123 20.00 90.00 150.00 260.00 580 27 1997 SUMMER 73 401.51 95.000 1500.00 250.41 29.31 62 110.00 250.00 335.00 470.00 860 27 1997 WINTER 75 170.43 2.5000 1555.00 194.68 22.48 114 11.25 60.00 125.00 215.00 380 27 1999 FALL 16 212.30 63.460 492.98 181.42 45.36 85 63.46 68.23 96.05 406.71 492 27 1999 SUMMER 14 155.13 77.890 359.84 82.65 22.09 53 77.89 88.37 130.53 224.21 359 27 2000 SPRING 8 296.87 100.44 917.40 298.82 105.65 101 100.44 124.10 157.78 396.70 917 32 1990 FALL 23 401.85 2.5000 1825.00 580.66 121.08 144 20.00 50.00 135.00 370.00 180 32 1990 SPRING 35 303.64 2.5000 1670.00 367.35 62.09 121 20.00 90.00 160.00 305.00 114 32 1990 SUMMER 46 299.46 2.5000 2380.00 475.92 70.17 159 10.00 40.00 107.50 240.00 126 32 1990 WINTER 29 506.29 2.5000 2310.00 695.44 129.14 137 2.50 70.00 200.00 730.00 230 32 1991 FALL 27 349.17 2.5000 1900.00 433.79 83.48 124 10.00 80.00 210.00 440.00 122 32 1991 SPRING 51 346.69 20.000 2100.00 512.25 71.73 148 20.00 50.00 130.00 355.00 173 32 1991 SUMMER 51 341.32 2.5000 2270.00 545.24 76.35 160 20.00 40.00 120.00 480.00 183 32 1991 WINTER 30 324.25 2.5000 2060.00 463.54 84.63 143 30.00 70.00 145.00 260.00 130 32 1992 FALL 25 490.00 20.000 4470.00 920.31 184.06 188 25.00 50.00 140.00 510.00 150 32 1992 SPRING 41 233.54 10.000 1155.00 296.48 46.30 127 10.00 60.00 110.00 250.00 920 32 1992 SUMMER 50 357.35 2.5000 2310.00 534.24 75.55 150 5.00 30.00 95.00 450.00 142 32 1992 WINTER 39 212.53 2.5000 970.00 206.40 33.05 97 20.00 70.00 130.00 280.00 640 32 1993 FALL 28 476.25 20.000 2080.00 553.04 104.52 116 20.00 45.00 240.00 742.50 178 32 1993 SPRING 35 243.71 10.000 1410.00 348.81 58.96 143 10.00 30.00 70.00 340.00 965 32 1993 SUMMER 34 349.04 10.000 1700.00 483.20 82.87 138 15.00 30.00 95.00 490.00 149 32 1993 WINTER 28 247.23 2.5000 1120.00 302.74 57.21 122 10.00 20.00 90.00 405.00 970 32 1994 FALL 31 299.19 10.000 1700.00 433.50 77.86 145 20.00 45.00 100.00 330.00 130 32 1994 SPRING 48 305.83 2.5000 1540.00 406.88 58.73 133 10.00 40.00 110.00 340.00 114 32 1994 SUMMER 34 289.41 20.000 1650.00 471.47 80.86 163 20.00 40.00 80.00 230.00 165 32 1994 WINTER 40 299.31 2.5000 2400.00 508.63 80.42 170 20.00 30.00 50.00 375.00 142 32 1995 FALL 28 389.29 10.000 1320.00 504.14 95.27 130 20.00 30.00 90.00 730.00 129 32 1995 SPRING 39 193.14 2.5000 1470.00 270.62 43.33 140 20.00 40.00 115.00 220.00 730 32 1995 SUMMER 38 208.62 2.5000 1300.00 344.47 55.88 165 5.00 30.00 52.50 190.00 130 32 1995 WINTER 37 236.05 2.5000 1680.00 394.54 64.86 167 2.50 20.00 50.00 150.00 105 32 1996 FALL 7 114.64 2.5000 440.00 146.63 55.42 128 2.50 50.00 70.00 100.00 440
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  32 1996 SPRING 29 453.88 2.5000 2330.00 563.35 104.61 124 10.00 45.00 200.00 700.00 188 32 1996 SUMMER 28 363.57 2.5000 1850.00 454.79 85.95 125 2.50 40.00 135.00 565.00 102 32 1996 WINTER 26 566.20 10.000 2250.00 767.89 150.60 136 16.25 55.00 105.00 790.00 217 32 1997 SPRING 6 221.25 2.5000 570.00 211.29 86.26 95 2.50 90.00 145.00 375.00 570 32 1997 WINTER 6 21.46 2.5000 55.00 24.68 10.07 115 2.50 2.50 9.38 50.00 55 42 1990 FALL 8 62.03 3.7500 190.00 62.78 22.20 101 3.75 16.25 40.00 95.00 190 42 1990 SPRING 13 123.04 20.000 409.50 108.55 30.11 88 20.00 40.00 90.00 160.00 409 42 1990 SUMMER 22 230.91 10.000 970.00 313.54 66.85 136 20.00 40.00 100.00 190.00 930 42 1990 WINTER 9 66.67 7.5000 165.00 59.12 19.71 89 7.50 20.00 50.00 105.00 165 42 1991 FALL 8 108.13 20.000 560.00 183.94 65.03 170 20.00 26.25 41.25 75.00 560 42 1991 SPRING 10 111.75 2.5000 270.00 84.62 26.76 76 2.50 50.00 87.50 180.00 270 42 1991 SUMMER 13 156.54 20.000 640.00 163.83 45.44 105 20.00 50.00 100.00 190.00 640 42 1991 WINTER 6 53.13 3.7500 150.00 53.49 21.84 101 3.75 10.00 42.50 70.00 150 42 1992 FALL 9 77.92 10.000 300.00 93.71 31.24 120 10.00 16.25 50.00 90.00 300 42 1992 SPRING 12 102.60 2.5000 390.00 130.00 37.53 127 2.50 15.00 25.00 165.00 390 42 1992 SUMMER 10 105.38 3.7500 290.00 103.35 32.68 98 3.75 30.00 65.00 220.00 290 42 1992 WINTER 6 76.67 10.000 330.00 125.01 51.03 163 10.00 10.00 30.00 50.00 330 42 1993 FALL 9 178.19 3.7500 630.00 220.56 73.52 124 3.75 45.00 70.00 240.00 630 42 1993 SPRING 16 251.22 22.000 880.00 272.86 68.21 109 22.00 38.00 107.50 410.00 880 42 1993 SUMMER 14 331.46 10.000 1270.00 412.02 110.12 124 10.00 80.00 130.00 380.00 127 42 1993 WINTER 7 214.46 3.7500 830.00 311.53 117.75 145 3.75 30.00 67.50 450.00 830 42 1994 FALL 8 56.75 2.5000 169.00 59.47 21.03 105 2.50 3.75 47.50 90.00 169 42 1994 SPRING 9 201.67 20.000 750.00 226.81 75.60 112 20.00 35.00 155.00 210.00 750 42 1994 SUMMER 15 254.53 20.000 713.00 242.38 62.58 95 20.00 40.00 140.00 370.00 713 42 1994 WINTER 2 45.00 10.000 80.00 49.50 35.00 110 10.00 10.00 45.00 80.00 80 42 1995 FALL 6 158.17 2.5000 373.50 168.13 68.64 106 2.50 40.00 81.50 370.00 373 42 1995 SPRING 10 312.70 20.000 1060.50 318.57 100.74 102 20.00 90.00 240.00 410.00 106 42 1995 SUMMER 15 217.57 4.0000 730.00 265.16 68.46 122 4.00 38.00 77.00 520.00 730 42 1995 WINTER 4 121.00 10.000 420.00 199.78 99.89 165 10.00 12.00 27.00 230.00 420 42 1996 FALL 5 65.00 2.5000 210.00 90.95 40.67 140 2.50 2.50 10.00 100.00 210 42 1996 SPRING 8 120.44 35.000 180.00 55.38 19.58 46 35.00 70.00 134.25 170.00 180 42 1996 SUMMER 9 300.56 30.000 735.00 280.48 93.49 93 30.00 60.00 290.00 485.00 735
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1996 WINTER 2 177.50 60.000 295.00 166.17 117.50 94 60.00 60.00 177.50 295.00 295. 42 1997 FALL 1 170.00 170.00 170.00 . . . 170.00 170.00 170.00 170.00 170. 42 1997 SPRING 4 180.00 30.000 390.00 156.42 78.21 87 30.00 65.00 150.00 295.00 390. 42 1997 SUMMER 2 295.00 140.00 450.00 219.20 155.00 74 140.00 140.00 295.00 450.00 450. 42 1997 WINTER 4 347.50 30.000 845.00 370.15 185.07 107 30.00 67.50 257.50 627.50 845. 42 1998 SPRING 1 140.00 140.00 140.00 . . . 140.00 140.00 140.00 140.00 140. 42 1998 WINTER 1 50.00 50.000 50.00 . . . 50.00 50.00 50.00 50.00 50. 42 1999 FALL 8 215.99 45.290 1080.00 350.88 124.05 162 45.29 68.83 94.26 138.24 1080 42 1999 SUMMER 8 352.91 78.470 1780.00 578.96 204.69 164 78.47 109.01 166.59 206.82 1780 42 1999 WINTER 4 117.50 16.000 296.00 122.98 61.49 105 16.00 42.00 79.00 193.00 296. 42 2000 SPRING 4 327.77 160.84 737.00 274.24 137.12 84 160.84 172.93 206.62 482.62 737.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 Turbidity_FTU subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 12 20.64 2.0000 63.00 21.36 6.17 103 2.00 4.75 11.15 36.80 63 25 1990 SPRING 15 21.50 2.6000 99.00 25.07 6.47 117 2.60 4.00 9.50 32.50 99 25 1990 SUMMER 15 22.89 1.0000 96.35 29.80 7.69 130 1.00 2.30 11.20 22.00 96 25 1990 WINTER 4 35.79 4.5000 97.00 42.04 21.02 117 4.50 8.65 20.83 62.93 97 25 1991 FALL 15 18.15 3.0000 101.00 29.89 7.72 165 3.00 4.10 5.00 9.00 101 25 1991 SPRING 15 17.14 2.0000 50.10 15.45 3.99 90 2.00 4.50 11.20 25.00 50 25 1991 SUMMER 14 21.47 5.0000 73.50 18.47 4.94 86 5.00 9.00 16.10 23.00 73 25 1991 WINTER 13 13.13 2.0000 38.00 11.55 3.20 88 2.00 4.00 9.95 19.00 38 25 1992 FALL 14 11.01 1.0000 63.00 16.09 4.30 146 1.00 3.00 4.63 15.50 63 25 1992 SPRING 15 19.03 1.1250 69.00 17.85 4.61 94 1.13 7.50 14.00 26.50 69 25 1992 SUMMER 14 20.19 2.0000 107.50 27.58 7.37 137 2.00 4.00 11.98 20.00 107 25 1992 WINTER 9 12.78 3.0000 25.70 7.36 2.45 58 3.00 7.00 11.20 17.00 25 25 1993 FALL 14 11.78 1.0000 38.00 12.77 3.41 108 1.00 2.00 5.50 23.00 38 25 1993 SPRING 14 15.79 3.0000 38.00 11.27 3.01 71 3.00 8.00 11.53 25.00 38 25 1993 SUMMER 15 20.97 1.0000 95.00 29.06 7.50 139 1.00 3.00 6.00 34.00 95 25 1993 WINTER 10 10.42 .25000 37.50 12.17 3.85 117 0.25 1.00 7.10 12.20 37 25 1994 FALL 13 20.51 1.2000 131.00 39.66 11.00 193 1.20 2.00 4.00 9.00 131 25 1994 SPRING 15 14.77 3.0000 42.00 12.87 3.32 87 3.00 5.00 9.50 26.50 42 25 1994 SUMMER 14 27.43 .60000 131.00 42.99 11.49 157 0.60 4.00 6.20 17.00 131 25 1994 WINTER 11 5.82 1.0000 25.00 6.73 2.03 116 1.00 2.80 3.30 7.70 25 25 1995 FALL 12 12.59 2.0000 61.50 17.49 5.05 139 2.00 2.50 5.33 14.15 61 25 1995 SPRING 13 18.29 2.0000 94.00 25.81 7.16 141 2.00 3.00 6.00 32.00 94 25 1995 SUMMER 13 15.12 2.0000 76.00 20.59 5.71 136 2.00 4.00 6.50 12.00 76 25 1995 WINTER 8 5.23 .60000 11.00 4.26 1.51 81 0.60 1.45 4.15 9.50 11 25 1996 FALL 12 16.79 3.0000 103.00 29.36 8.48 175 3.00 3.75 5.00 11.00 103 25 1996 SPRING 12 8.14 1.0000 19.50 6.04 1.74 74 1.00 4.53 6.95 9.98 19 25 1996 SUMMER 13 32.92 1.0000 139.50 46.56 12.91 141 1.00 4.00 7.00 55.00 139 25 1996 WINTER 11 10.65 1.0000 70.00 20.31 6.12 191 1.00 1.00 3.50 13.70 70 25 1997 FALL 12 28.53 6.5000 81.00 23.74 6.85 83 6.50 9.05 18.00 45.50 81 25 1997 SPRING 13 16.72 2.6000 60.00 16.88 4.68 101 2.60 6.00 8.50 28.50 60 25 1997 SUMMER 11 25.36 6.0000 70.00 19.94 6.01 79 6.00 11.00 21.50 27.50 70 25 1997 WINTER 13 11.42 2.0000 52.00 14.33 3.97 125 2.00 4.50 7.00 9.00 52
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 Turbidity_FTU subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1998 WINTER 6 8.17 2.0000 31.00 11.29 4.61 138 2.00 2.00 4.00 6.00 31 27 1990 FALL 64 21.06 1.7000 150.00 22.80 2.85 108 2.50 5.00 15.68 28.78 57 27 1990 SPRING 68 35.41 2.4000 122.00 25.77 3.12 73 5.00 14.55 29.63 50.75 84 27 1990 SUMMER 49 40.83 2.0000 184.00 42.58 6.08 104 3.20 12.80 27.00 53.60 124 27 1990 WINTER 19 23.50 2.2000 150.00 34.37 7.88 146 2.20 5.50 15.00 21.50 150 27 1991 FALL 69 15.47 1.1500 104.25 16.12 1.94 104 2.00 6.00 11.50 17.00 42 27 1991 SPRING 69 28.21 2.2000 92.45 21.10 2.54 75 4.00 11.00 22.00 40.55 71 27 1991 SUMMER 75 34.61 1.0000 100.00 24.47 2.83 71 5.00 13.80 30.40 50.20 89 27 1991 WINTER 74 12.00 1.8000 48.10 10.07 1.17 84 2.75 5.00 9.38 13.30 37 27 1992 FALL 70 17.94 2.5500 84.50 15.38 1.84 86 3.50 6.40 14.38 23.60 47 27 1992 SPRING 73 23.87 2.8000 175.00 24.74 2.90 104 4.25 9.00 17.75 27.55 67 27 1992 SUMMER 52 46.47 3.1000 177.00 37.02 5.13 80 3.60 19.30 39.25 68.63 113 27 1992 WINTER 73 15.03 2.0000 59.00 13.44 1.57 89 2.80 5.90 10.00 19.50 47 27 1993 FALL 76 25.51 1.0000 163.00 30.67 3.52 120 1.40 7.50 15.50 31.50 102 27 1993 SPRING 78 42.63 5.3000 121.00 32.80 3.71 77 6.90 19.40 30.50 62.00 119 27 1993 SUMMER 88 49.24 1.1000 160.00 35.26 3.76 72 3.50 22.20 41.75 74.75 115 27 1993 WINTER 67 23.43 1.3000 165.00 27.26 3.33 116 2.30 7.50 16.00 28.00 82 27 1994 FALL 70 19.68 1.0000 84.00 18.18 2.17 92 2.50 7.00 14.75 25.50 58 27 1994 SPRING 71 25.80 .80000 77.50 17.26 2.05 67 3.00 12.65 22.30 35.25 59 27 1994 SUMMER 71 45.78 .50000 185.00 40.00 4.75 87 1.50 14.00 34.00 70.50 137 27 1994 WINTER 59 8.53 1.0000 40.00 7.98 1.04 94 1.60 3.10 5.10 11.20 27 27 1995 FALL 71 12.52 .80000 109.00 15.30 1.82 122 2.00 4.50 8.90 14.00 32 27 1995 SPRING 75 27.88 1.4500 112.00 30.23 3.49 108 2.00 5.00 17.50 42.00 101 27 1995 SUMMER 78 29.92 .90000 146.00 30.97 3.51 104 3.30 10.00 18.75 37.50 96 27 1995 WINTER 68 5.14 .70000 43.00 5.53 0.67 108 1.50 2.47 3.50 6.05 10 27 1996 FALL 64 34.66 2.0000 174.00 36.32 4.54 105 3.50 9.50 21.25 45.75 86 27 1996 SPRING 66 22.14 3.0000 115.00 21.14 2.60 95 3.85 7.90 16.25 27.00 60 27 1996 SUMMER 59 62.39 2.5000 190.00 47.08 6.13 75 6.00 28.00 51.00 86.00 170 27 1996 WINTER 31 5.64 .70000 34.50 6.22 1.12 110 1.20 2.60 3.75 6.00 15 27 1997 FALL 62 35.50 2.4000 185.00 44.48 5.65 125 3.80 8.90 15.00 39.00 150 27 1997 SPRING 69 19.20 2.0000 100.00 19.36 2.33 101 3.10 7.30 13.50 21.50 63 27 1997 SUMMER 69 53.88 6.2500 142.00 30.04 3.62 56 10.25 35.00 52.00 71.50 112
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 Turbidity_FTU subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1997 WINTER 71 16.13 1.0000 142.00 22.85 2.71 142 1.50 4.00 8.50 20.00 46 32 1990 FALL 12 33.95 3.5000 125.00 36.99 10.68 109 3.50 7.20 20.50 45.00 125 32 1990 SPRING 19 44.33 1.4000 140.00 42.09 9.66 95 1.40 4.50 46.50 70.00 140 32 1990 SUMMER 20 17.84 .60000 120.00 27.90 6.24 156 0.90 3.25 8.90 18.15 91 32 1990 WINTER 13 26.98 1.9000 150.00 43.73 12.13 162 1.90 3.80 14.00 17.50 150 32 1991 FALL 15 29.42 2.4000 95.00 35.00 9.04 119 2.40 3.60 7.40 59.50 95 32 1991 SPRING 17 38.80 2.0000 155.00 39.39 9.55 102 2.00 13.00 28.00 52.00 155 32 1991 SUMMER 17 27.72 2.0000 100.00 29.66 7.19 107 2.00 4.30 15.00 33.00 100 32 1991 WINTER 16 39.95 2.0000 130.00 42.40 10.60 106 2.00 8.70 20.75 64.00 130 32 1992 FALL 10 17.45 1.2000 84.00 25.34 8.01 145 1.20 2.40 8.00 20.00 84 32 1992 SPRING 20 38.75 1.0000 160.00 42.94 9.60 111 2.35 7.85 26.75 51.00 133 32 1992 SUMMER 18 19.83 .90000 67.00 20.79 4.90 105 0.90 6.05 11.28 28.50 67 32 1992 WINTER 21 53.34 5.2000 150.00 44.61 9.74 84 8.50 16.00 37.00 68.15 142 32 1993 FALL 2 3.90 1.5000 6.30 3.39 2.40 87 1.50 1.50 3.90 6.30 6 32 1993 SPRING 8 18.89 1.0000 72.00 23.68 8.37 125 1.00 1.80 12.25 25.00 72 32 1993 SUMMER 6 10.83 1.2000 26.00 11.91 4.86 110 1.20 1.80 5.00 26.00 26 32 1993 WINTER 10 30.13 1.5000 150.00 47.28 14.95 157 1.50 4.10 11.10 29.50 150 32 1994 FALL 3 42.87 .90000 120.00 66.89 38.62 156 0.90 0.90 7.70 120.00 120 32 1994 SPRING 2 95.35 .70000 190.00 133.86 94.65 140 0.70 0.70 95.35 190.00 190 32 1994 SUMMER 4 2.58 1.8000 3.40 0.75 0.38 29 1.80 1.95 2.55 3.20 3 32 1994 WINTER 3 39.13 1.9000 110.00 61.40 35.45 157 1.90 1.90 5.50 110.00 110 32 1995 FALL 2 3.48 2.8000 4.15 0.95 0.68 27 2.80 2.80 3.48 4.15 4 32 1995 SPRING 4 59.96 3.0500 136.00 65.62 32.81 109 3.05 5.18 50.40 114.75 136 32 1995 SUMMER 3 5.17 4.0000 5.80 1.01 0.58 20 4.00 4.00 5.70 5.80 5 32 1995 WINTER 2 2.25 2.2000 2.30 0.07 0.05 3 2.20 2.20 2.25 2.30 2 32 1996 SPRING 1 1.00 1.0000 1.00 . . . 1.00 1.00 1.00 1.00 1 32 1996 WINTER 1 98.00 98.000 98.00 . . . 98.00 98.00 98.00 98.00 98 32 1997 SPRING 1 5.10 5.1000 5.10 . . . 5.10 5.10 5.10 5.10 5 32 1997 WINTER 2 1.05 .30000 1.80 1.06 0.75 101 0.30 0.30 1.05 1.80 1 42 1990 FALL 6 20.26 2.0000 87.00 33.00 13.47 163 2.00 3.90 7.33 14.00 87 42 1990 SPRING 7 24.37 2.6000 65.00 24.12 9.12 99 2.60 4.00 16.00 51.00 65 42 1990 SUMMER 7 22.04 3.0000 44.00 16.13 6.10 73 3.00 4.80 24.50 40.00 44
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 Turbidity_FTU subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1990 WINTER 5 5.65 1.5000 10.00 3.44 1.54 61 1.50 3.75 4.75 8.25 10. 42 1991 FALL 7 23.45 2.0000 100.00 34.90 13.19 149 2.00 5.00 9.90 29.00 100. 42 1991 SPRING 7 35.86 2.0000 140.00 47.89 18.10 134 2.00 2.55 20.00 37.50 140. 42 1991 SUMMER 6 33.38 2.3000 90.00 33.84 13.81 101 2.30 4.00 24.00 56.00 90. 42 1991 WINTER 4 4.88 3.3000 6.20 1.49 0.75 31 3.30 3.60 5.00 6.15 6. 42 1992 FALL 6 20.42 .25000 77.00 29.01 11.84 142 0.25 3.50 9.38 23.00 77. 42 1992 SPRING 4 9.63 2.0000 20.75 8.95 4.48 93 2.00 2.38 7.88 16.88 20. 42 1992 SUMMER 6 32.05 2.0000 73.00 27.77 11.34 87 2.00 2.30 32.00 51.00 73. 42 1992 WINTER 5 27.05 2.4000 99.00 40.55 18.13 150 2.40 6.30 11.55 16.00 99. 42 1993 FALL 6 23.58 .80000 48.00 20.65 8.43 88 0.80 1.70 26.00 39.00 48. 42 1993 SPRING 6 32.96 .25000 77.00 30.18 12.32 92 0.25 1.50 32.50 54.00 77. 42 1993 SUMMER 6 37.79 2.2500 88.00 33.70 13.76 89 2.25 3.00 35.00 63.50 88. 42 1993 WINTER 4 3.38 2.1500 6.55 2.12 1.06 63 2.15 2.23 2.40 4.53 6. 42 1994 FALL 4 13.63 2.5000 26.00 12.62 6.31 93 2.50 2.75 13.00 24.50 26. 42 1994 SPRING 6 39.33 .75000 81.50 37.14 15.16 94 0.75 3.00 38.63 73.50 81. 42 1994 SUMMER 7 20.34 1.1500 68.00 22.89 8.65 113 1.15 3.00 18.00 23.50 68. 42 1994 WINTER 1 4.40 4.4000 4.40 . . . 4.40 4.40 4.40 4.40 4. 42 1995 FALL 3 9.40 1.2000 22.00 11.08 6.39 118 1.20 1.20 5.00 22.00 22. 42 1995 SPRING 2 14.55 7.1000 22.00 10.54 7.45 72 7.10 7.10 14.55 22.00 22. 42 1995 SUMMER 3 15.05 3.0000 38.00 19.88 11.48 132 3.00 3.00 4.15 38.00 38. 42 1995 WINTER 1 4.90 4.9000 4.90 . . . 4.90 4.90 4.90 4.90 4. 42 1996 FALL 1 2.00 2.0000 2.00 . . . 2.00 2.00 2.00 2.00 2. 42 1996 SPRING 3 12.40 1.2000 33.00 17.86 10.31 144 1.20 1.20 3.00 33.00 33. 42 1996 SUMMER 2 2.70 2.4000 3.00 0.42 0.30 16 2.40 2.40 2.70 3.00 3. 42 1997 SPRING 1 5.00 5.0000 5.00 . . . 5.00 5.00 5.00 5.00 5. 42 1997 SUMMER 1 3.00 3.0000 3.00 . . . 3.00 3.00 3.00 3.00 3.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1993 Turbidity_JCU subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1990 FALL 7 13.51 2.8000 31.75 10.72 4.05 79 2.80 2.80 14.00 22.00 31 27 1990 SPRING 13 44.28 4.0000 98.00 33.14 9.19 75 4.00 14.00 44.00 74.00 98 27 1990 SUMMER 28 58.95 2.0000 210.00 60.11 11.36 102 2.00 12.50 25.75 100.25 185 27 1990 WINTER 30 33.37 4.4000 170.00 32.86 6.00 98 5.90 13.00 24.50 46.00 74 27 1991 FALL 9 49.17 .50000 173.00 63.05 21.02 128 0.50 10.00 17.00 59.00 173 27 1991 SPRING 13 89.08 2.5000 300.00 90.09 24.99 101 2.50 16.00 92.00 120.00 300 27 1991 SUMMER 33 36.24 2.0000 220.00 45.96 8.00 127 2.00 6.95 20.50 47.00 126 27 1991 WINTER 32 11.09 1.5000 45.00 9.36 1.65 84 1.80 4.75 8.00 14.25 27 27 1992 FALL 7 14.62 1.1000 32.55 14.07 5.32 96 1.10 1.20 11.30 31.00 32 27 1992 SPRING 12 31.38 3.0000 165.00 48.58 14.02 155 3.00 5.95 13.00 24.25 165 27 1992 SUMMER 26 43.82 1.5000 274.00 68.35 13.41 156 2.00 4.35 16.70 39.00 227 27 1992 WINTER 22 22.40 3.0000 80.00 22.89 4.88 102 3.00 8.00 11.75 35.00 65 27 1993 WINTER 18 50.29 4.7000 229.00 54.84 12.93 109 4.70 12.60 34.80 67.70 229 42 1990 SUMMER 7 29.69 .25000 140.00 49.64 18.76 167 0.25 3.00 9.00 26.00 140 42 1991 SUMMER 1 7.40 7.4000 7.40 . . . 7.40 7.40 7.40 7.40 7
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Turbidity_NTU subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1990 FALL 2 10.20 7.8000 12.60 3.39 2.40 33 7.80 7.80 10.20 12.60 12 25 1990 SPRING 2 4.30 3.0000 5.60 1.84 1.30 43 3.00 3.00 4.30 5.60 5 25 1990 SUMMER 1 2.00 2.0000 2.00 . . . 2.00 2.00 2.00 2.00 2 25 1993 FALL 1 4.00 4.0000 4.00 . . . 4.00 4.00 4.00 4.00 4 25 1994 FALL 1 15.00 15.000 15.00 . . . 15.00 15.00 15.00 15.00 15 25 1994 SPRING 2 5.00 2.0000 8.00 4.24 3.00 85 2.00 2.00 5.00 8.00 8 25 1994 SUMMER 4 11.50 2.0000 21.00 8.96 4.48 78 2.00 4.00 11.50 19.00 21 25 1996 FALL 1 4.80 4.8000 4.80 . . . 4.80 4.80 4.80 4.80 4 25 1997 FALL 1 12.30 12.300 12.30 . . . 12.30 12.30 12.30 12.30 12 25 1999 FALL 19 34.53 1.0000 72.50 23.88 5.48 69 1.00 17.00 35.00 53.00 72 25 1999 SUMMER 20 108.35 18.000 343.00 101.98 22.80 94 22.25 50.00 65.00 116.00 343 25 2000 SPRING 10 122.10 4.0000 941.00 288.46 91.22 236 4.00 16.00 30.00 53.00 941 25 2000 SUMMER 10 107.25 7.0000 735.00 221.97 70.19 207 7.00 15.00 41.25 70.00 735 27 1990 FALL 10 21.92 7.0000 43.60 12.61 3.99 58 7.00 10.00 22.58 29.40 43 27 1990 SPRING 10 52.53 3.0000 123.60 41.78 13.21 80 3.00 13.20 47.00 90.70 123 27 1990 SUMMER 19 46.47 6.0000 190.00 40.84 9.37 88 6.00 25.00 33.00 65.00 190 27 1991 SUMMER 2 22.00 19.000 25.00 4.24 3.00 19 19.00 19.00 22.00 25.00 25 27 1992 FALL 1 42.00 42.000 42.00 . . . 42.00 42.00 42.00 42.00 42 27 1992 SUMMER 1 84.00 84.000 84.00 . . . 84.00 84.00 84.00 84.00 84 27 1993 SUMMER 2 16.50 10.000 23.00 9.19 6.50 56 10.00 10.00 16.50 23.00 23 27 1994 FALL 8 29.50 8.0000 78.00 23.46 8.29 80 8.00 10.50 25.00 39.50 78 27 1994 SUMMER 25 53.24 2.0000 157.00 40.14 8.03 75 3.00 26.00 49.00 74.00 118 27 1995 FALL 6 56.17 12.000 137.00 42.73 17.44 76 12.00 34.00 49.00 56.00 137 27 1995 SPRING 2 67.60 66.200 69.00 1.98 1.40 3 66.20 66.20 67.60 69.00 69 27 1995 SUMMER 2 86.50 68.500 104.50 25.46 18.00 29 68.50 68.50 86.50 104.50 104 27 1996 FALL 11 16.65 6.8000 53.00 14.60 4.40 88 6.80 7.80 8.90 22.70 53 27 1996 SPRING 2 13.40 1.4000 25.40 16.97 12.00 127 1.40 1.40 13.40 25.40 25 27 1996 SUMMER 11 28.34 5.5000 76.65 22.12 6.67 78 5.50 12.90 19.85 38.95 76 27 1999 FALL 16 49.19 3.0000 230.00 72.10 18.03 147 3.00 15.00 19.50 45.75 230 27 1999 SUMMER 14 60.25 12.000 144.00 44.03 11.77 73 12.00 23.00 57.25 76.00 144 27 2000 SPRING 8 78.06 38.000 179.00 51.09 18.06 65 38.00 43.00 60.75 100.00 179 27 2000 SUMMER 8 113.00 7.0000 226.00 68.02 24.05 60 7.00 72.50 104.50 158.50 226
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 Turbidity_NTU subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1991 SUMMER 1 10.70 10.700 10.70 . . . 10.70 10.70 10.70 10.70 10. 42 1992 FALL 1 2.10 2.1000 2.10 . . . 2.10 2.10 2.10 2.10 2. 42 1994 SUMMER 5 29.00 2.0000 120.00 50.94 22.78 176 2.00 6.00 8.00 9.00 120. 42 1999 FALL 7 55.14 30.000 104.00 26.70 10.09 48 30.00 30.00 43.00 68.00 104. 42 1999 SUMMER 7 73.71 6.0000 150.00 60.27 22.78 82 6.00 6.00 50.00 127.00 150. 42 2000 SPRING 3 95.00 45.000 142.00 48.57 28.04 51 45.00 45.00 98.00 142.00 142. 42 2000 SUMMER 3 126.00 25.000 258.00 119.55 69.02 95 25.00 25.00 95.00 258.00 258.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 pH_S_U subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  25 1993 FALL 8 8.17 7.9000 8.35 0.16 0.06 2 7.90 8.03 8.23 8.30 8 25 1993 SPRING 7 8.13 8.0000 8.40 0.14 0.05 2 8.00 8.00 8.10 8.20 8 25 1993 SUMMER 7 8.11 7.8000 8.35 0.17 0.07 2 7.80 8.00 8.10 8.20 8 25 1993 WINTER 7 8.11 7.9000 8.50 0.24 0.09 3 7.90 7.90 8.00 8.40 8 25 1994 FALL 7 8.06 7.5000 8.25 0.27 0.10 3 7.50 8.00 8.20 8.25 8 25 1994 SPRING 7 8.23 7.9000 8.40 0.18 0.07 2 7.90 8.10 8.30 8.35 8 25 1994 SUMMER 8 8.08 7.8000 8.40 0.18 0.06 2 7.80 7.98 8.08 8.15 8 25 1994 WINTER 7 8.21 7.8000 8.40 0.22 0.08 3 7.80 8.10 8.20 8.40 8 25 1995 FALL 4 8.00 7.7000 8.30 0.26 0.13 3 7.70 7.80 8.00 8.20 8 25 1995 SPRING 7 8.08 7.9000 8.30 0.16 0.06 2 7.90 7.90 8.05 8.20 8 25 1995 SUMMER 7 7.91 7.6000 8.10 0.17 0.06 2 7.60 7.80 7.90 8.05 8 25 1995 WINTER 7 8.08 7.7500 8.40 0.21 0.08 3 7.75 7.95 8.10 8.25 8 25 1996 FALL 1 8.10 8.1000 8.10 . . . 8.10 8.10 8.10 8.10 8 25 1996 WINTER 1 7.95 7.9500 7.95 . . . 7.95 7.95 7.95 7.95 7 25 1997 FALL 1 8.30 8.3000 8.30 . . . 8.30 8.30 8.30 8.30 8 25 1999 FALL 19 8.21 7.9900 8.39 0.14 0.03 2 7.99 8.10 8.25 8.30 8 25 1999 SUMMER 20 8.26 7.8300 8.71 0.32 0.07 4 7.84 7.90 8.26 8.58 8 25 2000 SPRING 10 8.53 7.9000 9.70 0.50 0.16 6 7.90 8.28 8.52 8.64 9 25 2000 SUMMER 10 9.80 8.2200 10.60 0.90 0.28 9 8.22 8.80 10.25 10.40 10 27 1992 SPRING 2 7.75 7.5000 8.00 0.35 0.25 5 7.50 7.50 7.75 8.00 8 27 1992 SUMMER 1 7.90 7.9000 7.90 . . . 7.90 7.90 7.90 7.90 7 27 1993 FALL 5 8.21 7.8000 8.50 0.26 0.12 3 7.80 8.15 8.30 8.30 8 27 1993 SPRING 5 8.08 7.7000 8.40 0.31 0.14 4 7.70 7.80 8.20 8.30 8 27 1993 SUMMER 5 8.21 7.8000 8.55 0.34 0.15 4 7.80 7.90 8.30 8.50 8 27 1993 WINTER 5 8.34 7.8000 8.90 0.42 0.19 5 7.80 8.10 8.40 8.50 8 27 1994 FALL 5 8.35 8.1000 8.80 0.29 0.13 3 8.10 8.10 8.30 8.45 8 27 1994 SPRING 5 8.37 8.0000 8.80 0.29 0.13 3 8.00 8.25 8.35 8.45 8 27 1994 SUMMER 5 8.39 7.9500 8.80 0.41 0.18 5 7.95 8.00 8.40 8.80 8 27 1994 WINTER 5 7.95 7.2500 8.40 0.44 0.20 6 7.25 7.85 8.05 8.20 8 27 1995 FALL 1 8.00 8.0000 8.00 . . . 8.00 8.00 8.00 8.00 8 27 1995 SPRING 3 8.33 8.2000 8.40 0.12 0.07 1 8.20 8.20 8.40 8.40 8 27 1995 SUMMER 3 8.57 8.3500 8.80 0.23 0.13 3 8.35 8.35 8.55 8.80 8
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 pH_S_U subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  27 1995 WINTER 1 8.45 8.4500 8.45 . . . 8.45 8.45 8.45 8.45 8 27 1999 FALL 16 8.11 7.7700 8.46 0.25 0.06 3 7.77 7.87 8.14 8.33 8 27 1999 SUMMER 14 8.08 7.1900 8.63 0.41 0.11 5 7.19 7.71 8.23 8.31 8 27 2000 SPRING 8 8.15 7.8100 8.50 0.24 0.09 3 7.81 7.94 8.16 8.34 8 27 2000 SUMMER 8 9.03 8.1100 10.20 0.81 0.29 9 8.11 8.41 8.71 9.83 10 32 1991 FALL 1 7.90 7.9000 7.90 . . . 7.90 7.90 7.90 7.90 7 32 1991 WINTER 2 7.95 7.7000 8.20 0.35 0.25 4 7.70 7.70 7.95 8.20 8 32 1992 FALL 2 7.40 7.2000 7.60 0.28 0.20 4 7.20 7.20 7.40 7.60 7 32 1992 SPRING 2 7.85 7.7000 8.00 0.21 0.15 3 7.70 7.70 7.85 8.00 8 32 1992 SUMMER 2 7.80 7.5000 8.10 0.42 0.30 5 7.50 7.50 7.80 8.10 8 32 1992 WINTER 2 7.90 7.7000 8.10 0.28 0.20 4 7.70 7.70 7.90 8.10 8 32 1993 FALL 3 7.80 7.7000 7.90 0.10 0.06 1 7.70 7.70 7.80 7.90 7 32 1993 SPRING 3 7.83 7.5000 8.00 0.29 0.17 4 7.50 7.50 8.00 8.00 8 32 1993 SUMMER 3 7.73 7.7000 7.80 0.06 0.03 1 7.70 7.70 7.70 7.80 7 32 1993 WINTER 3 7.63 7.5000 7.70 0.12 0.07 2 7.50 7.50 7.70 7.70 7 32 1994 FALL 3 7.77 7.6000 7.90 0.15 0.09 2 7.60 7.60 7.80 7.90 7 32 1994 SPRING 3 7.70 7.5000 7.80 0.17 0.10 2 7.50 7.50 7.80 7.80 7 32 1994 SUMMER 3 7.45 7.2500 7.60 0.18 0.10 2 7.25 7.25 7.50 7.60 7 32 1994 WINTER 3 7.83 7.7500 7.90 0.08 0.04 1 7.75 7.75 7.85 7.90 7 32 1995 FALL 2 7.50 7.5000 7.50 0.00 0.00 0 7.50 7.50 7.50 7.50 7 32 1995 SPRING 3 7.73 7.7000 7.80 0.06 0.03 1 7.70 7.70 7.70 7.80 7 32 1995 SUMMER 3 7.62 7.4000 7.80 0.20 0.12 3 7.40 7.40 7.65 7.80 7 32 1995 WINTER 3 7.92 7.7000 8.05 0.19 0.11 2 7.70 7.70 8.00 8.05 8 32 1996 SPRING 2 7.38 7.3000 7.45 0.11 0.08 1 7.30 7.30 7.38 7.45 7 32 1996 SUMMER 2 7.43 7.4000 7.45 0.04 0.02 0 7.40 7.40 7.43 7.45 7 32 1996 WINTER 2 7.60 7.3500 7.85 0.35 0.25 5 7.35 7.35 7.60 7.85 7 42 1990 FALL 2 5.20 2.8000 7.60 3.39 2.40 65 2.80 2.80 5.20 7.60 7 42 1990 SPRING 1 7.79 7.7900 7.79 . . . 7.79 7.79 7.79 7.79 7 42 1990 SUMMER 7 8.38 7.5500 8.88 0.43 0.16 5 7.55 8.26 8.37 8.75 8 42 1990 WINTER 1 7.50 7.5000 7.50 . . . 7.50 7.50 7.50 7.50 7 42 1991 FALL 1 7.80 7.8000 7.80 . . . 7.80 7.80 7.80 7.80 7 42 1991 SPRING 1 7.70 7.7000 7.70 . . . 7.70 7.70 7.70 7.70 7
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: V  Rivers and Streams Descriptive Statistics by Subecoregion, Year and Season from 1990 to 2000 pH_S_U subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 42 1991 SUMMER 4 8.45 7.9000 8.77 0.38 0.19 5 7.90 8.19 8.57 8.71 8. 42 1992 FALL 1 7.80 7.8000 7.80 . . . 7.80 7.80 7.80 7.80 7. 42 1992 SUMMER 1 7.60 7.6000 7.60 . . . 7.60 7.60 7.60 7.60 7. 42 1992 WINTER 1 7.16 7.1600 7.16 . . . 7.16 7.16 7.16 7.16 7. 42 1993 FALL 1 7.40 7.4000 7.40 . . . 7.40 7.40 7.40 7.40 7. 42 1993 SPRING 3 7.92 7.5700 8.39 0.43 0.25 5 7.57 7.57 7.79 8.39 8. 42 1994 FALL 2 8.07 7.8400 8.30 0.33 0.23 4 7.84 7.84 8.07 8.30 8. 42 1994 SPRING 1 7.90 7.9000 7.90 . . . 7.90 7.90 7.90 7.90 7. 42 1994 SUMMER 1 9.30 9.3000 9.30 . . . 9.30 9.30 9.30 9.30 9. 42 1995 FALL 3 8.27 7.6100 8.80 0.61 0.35 7 7.61 7.61 8.40 8.80 8. 42 1995 SPRING 2 7.37 6.8100 7.92 0.78 0.55 11 6.81 6.81 7.37 7.92 7. 42 1995 SUMMER 6 8.75 7.9000 9.30 0.52 0.21 6 7.90 8.50 8.80 9.20 9. 42 1997 SPRING 1 7.45 7.4500 7.45 . . . 7.45 7.45 7.45 7.45 7. 42 1998 SUMMER 1 8.78 8.7800 8.78 . . . 8.78 8.78 8.78 8.78 8. 42 1999 FALL 8 8.37 7.9800 8.82 0.31 0.11 4 7.98 8.14 8.30 8.63 8. 42 1999 SUMMER 8 8.26 7.7200 8.56 0.25 0.09 3 7.72 8.17 8.35 8.37 8. 42 2000 SPRING 4 8.53 8.4100 8.66 0.10 0.05 1 8.41 8.46 8.53 8.61 8. 42 2000 SUMMER 3 10.03 9.8000 10.20 0.21 0.12 2 9.80 9.80 10.10 10.20 10.
APPENDIX C

Quality Control/Quality Assurance Rules

Appendix C—Quality Control/Quality Assurance Rules

Continued Support for the Compilation and

Analysis of National Nutrient Data

9 Nutrient Ecoregion/Waterbody Type Summary

Chapters

Prepared for:

Steve Potts

Environmental Protection Agency

OW/OST/HECD

Prepared by:

INDUS Corporation

1953 Gallows Road

Vienna, Virginia 22182

Contract Number:68-C-99-226

Task Number:07

Subtask Number:4

August 27, 2001

9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-iii

CONTENTS

1.0 BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

1.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

1.2 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

2.0 QA/QC PROCEDURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

2.1 National Data Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-3

2.2 State Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-3

2.3 Laboratory Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-4

2.4 Waterbody Name and Class Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-4

2.5 Ecoregion Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-5

3.0 STATISTICAL ANALYSIS REPORTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-5

3.1 Data Source Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-6

3.2 Remark Code Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-6

3.3 Median of Each Waterbody . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-7

3.4 Descriptive Statistic Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-7

3.5 Regression Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-7

4.0 TIME PERIOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-8

5.0 DATA SOURCES AND PARAMETERS FOR THE AGGREGATE NUTRIENT

ECOREGIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-8

5.1 Lakes and Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-9

5.1.1 Aggregate Nutrient Ecoregion 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-9

5.1.2 Aggregate Nutrient Ecoregion 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-9

5.1.3 Aggregate Nutrient Ecoregion 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-10

5.1.4 Aggregate Nutrient Ecoregion 14 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-10

5.2 Rivers and Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-11

5.2.1 Aggregate Nutrient Ecoregion 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-11

5.2.2 Aggregate Nutrient Ecoregion 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-12

5.2.3 Aggregate Nutrient Ecoregion 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-13

5.2.4 Aggregate Nutrient Ecoregion 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-13

5.2.5 Aggregate Nutrient Ecoregion 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-14

APPENDIX A Process Used to QA/QA the Legacy STORET Nutrient Data Set . . . . . . C-16

APPENDIX B Process for Adding Aggregate Nutrient Ecoregions and Level III 

Ecoregions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-22

APPENDIX C Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-23

9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-1

1.0 BACKGROUND

The Nutrient Criteria Program initiated the development of a national Nutrient Criteria Database

application that is used to store and analyze nutrient data. The ultimate use of these data is to

derive ecoregion specific nutrient criteria. EPA converted STOrage and RETrieval (STORET)

legacy data, National Stream Quality Accounting Network (NASQAN) data, National WaterQuality Assessment (NAWQA) data, and other relevant nutrient data from universities and

States/Tribes into the database. The data imported into the Nutrient Criteria Database are used

to develop national nutrient criteria recommendations. 

1.1 Purpose

The purpose of this deliverable is to provide EPA with information regarding the database used

to create the statistical reports which will be used to derive ecoregion-specific nutrient criteria

for Level III ecoregions. There are fourteen aggregate nutrient ecoregions. Each aggregate

nutrient ecoregion is divided into smaller ecoregions (subecoregions) referred to as Level III

ecoregions. EPA will determine criteria for the waterbody types and Level III ecoregions within

the following aggregate nutrient ecoregions:

• Lakes and Reservoirs

- Aggregate Nutrient ecoregions: 3, 4, 5, and 14

• Rivers and Streams 

- Aggregate Nutrient ecoregions: 1, 4, 5, 8, and 10

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 Document: 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.

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
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-2 Appendix C—Quality Control/Quality Assurance Rules

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

• EPA Region 1

• EPA Region 2 - Lake Champlain Monitoring Project

• EPA Region 2 - NYSDEC Finger Lakes Monitoring Program

• EPA Region 2 - NY Citizens Lake Assessment Program

• EPA Region 2 - Lake Classification and Inventory Survey

• EPA Region 2 - NYCDEP (1990-1998)

• EPA Region 2 - NYCDEP (Storm Event data)

• EPA Region 2 - New Jersey Nutrient Data ( Tidal Waters)

• EPA Region 5

• EPA Region 3 

• EPA Region 3 - Nitrite Data

• EPA Region 3 - Choptank River files

• EPA Region 4 - Tennessee Valley Authority

• EPA Region 7 - Central Plains Center for BioAssessment (CPCB) 

• EPA Region 7 - REMAP

• EPA Region 2 - Delaware River Basin Commission (1990-1998)

• EPA Region 3 - PA Lake Data

• EPA Region 3 - University of Delaware

• EPA Region 10 

• University of Auburn

• EPA Region 8 - MT and WY

• EPA Region 9

• Suffolk County

• NYCDEC

• NY Lakes Morphometry

• EPA Region 8 - South Dakota

• EPA Region 8 - Colorado Reservoir

• EPA Region 4

• EPA Region 10 - Lake Data

• EPA Region 7 - Central Plains Center for BioAssessment (CPCB) 2

• EPA Region 8 - North Dakota

• EPA Region 8 - Eagle River

• EPA Region 8 - Utah

• Florida
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-3

As part of the conversion process, INDUS performed a number of Quality Assurance/Quality

Control (QA/QC) steps to ensure that the data were properly converted into the Nutrient Criteria

Database. Sections 2.1 and 2.2 explain the steps performed by INDUS to convert the data.

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. However, if there was not enough information

provided to determine duplicates such as sampling date, there was no way for INDUS to locate

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. 
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-4 Appendix C—Quality Control/Quality Assurance Rules

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

copy of each e-mail correspondence with the states to ensure that a record of the decision was

maintained. 

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. In other cases, the methods are unknown. 

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 were 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

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.
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-5

2.5 Ecoregion Data

Aggregate nutrient ecoregions and Level III ecoregions were added to the database using the

station latitude and longitude coordinates, the county centroid, or HUC (Hydrological Unit

Code) centroid. If a station was lacking latitude and longitude coordinates and 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 were 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/HUC listed in the station

table. The county information was assumed to be correct; therefore, the county centroid was

used.

The HUC centroid was used to determine the ecoregions under the following circumstances:

• The latitude and longitude coordinates and county were missing, but the HUC information

was available.

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, state, county, 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,

state, county, decade and season.

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.
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-6 Appendix C—Quality Control/Quality Assurance Rules

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 to 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 waterbody 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 waterbody 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 aggregate nutrient ecoregion for all seasons 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. 

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.
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-7

• 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

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. Secchi data were used

in the lake and reservoir models, and Turbidity data were used in the river and stream models. 
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-8 Appendix C—Quality Control/Quality Assurance Rules

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. 

4.0 TIME PERIOD

Data collected from January 1990 to December 2000 were used in the statistical analysis reports. 

To capture seasonal differences, the data were classified as follows:

• Aggregate nutrient ecoregions: 6, 7, and 8

S Spring: April to May 

S Summer: June to August 

S Fall: September to October

S Winter: November to March

• Aggregate nutrient ecoregions: 1, 2, 3, 4, 5, 9, 10, 11, 12, 13, and 14

S Spring: March to May

S Summer: June to August 

S Fall: September to November

S Winter: December to February 

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, data for the following parameters were grouped together and

reported under Phosphorous, Dissolved Inorganic (DIP):

Phosphorus, Dissolved Inorganic (DIP) 

Phosphorus, Dissolved (DP) 

Phosphorus, Dissolved Reactive (DRP)

Orthophosphate, dissolved, mg/L as P 

Orthophosphate (OPO4_PO4)
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-9

5.1 Lakes and Reservoirs

5.1.1 Aggregate Nutrient Ecoregion 3

Data Sources:

Legacy STORET

EPA Region 10

EPA Region 8 - Colorado Reservoir

Parameters:

Chlorophyll A, Fluorometric, corrected (ug/L)

Chlorophyll A, Phytoplankton, spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, uncorrected (ug/L)

Dissolved Inorganic Phosphorus (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldhal (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

pH

Level III ecoregions:

6, 10, 12, 13, 18, 20, 22, 24, 80, 81

5.1.2 Aggregate Nutrient Ecoregion 4

Data Sources:

Legacy STORET

EPA Region 8 - MT and WY

EPA Region 8 - South Dakota

EPA Region 8 - North Dakota

Parameters:

Chlorophyll A, Phytoplankton, spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, uncorrected (ug/L)

Dissolved Inorganic Phosphorus (DIP) (ug/L)

Dissolved Oxygen (DO) (% Saturated)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-10 Appendix C—Quality Control/Quality Assurance Rules

Nitrogen, Total Kjeldhal (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

pH

Level III ecoregions:

26, 28, 30, 31, 43, 44

5.1.3 Aggregate Nutrient Ecoregion 5

Data sources:

Legacy STORET

EPA Region 8 - MT and WY

EPA Region 8 - South Dakota

EPA Region 8 - North Dakota

Parameters:

Chlorophyll A, Phytoplankton, spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, uncorrected (ug/L)

Dissolved Inorganic Phosphorus (DIP) (ug/L)

Dissolved Oxygen (DO) (% Saturated)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldhal (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

pH

Level III ecoregions:

25, 27, 32, 42

5.1.4 Aggregate Nutrient Ecoregion 14

Data sources:

Legacy STORET

Region 2 - NY Citizens Lake Assessment Program

Region 2 - NYCDEP (1990-1998)

EPA Region 1
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-11

Parameters:

CHLB (ug/L)

CHLC (ug/L)

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)

Dissolved Inorganic Phosphorus (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldhal (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

SECCHI (m)

pH

Level III ecoregions:

59, 63, 84

5.2 Rivers and Streams

5.2.1 Aggregate Nutrient Ecoregion 1

Data sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 10

Parameters:

Chlorophyll A, Fluorometric, corrected (ug/L)

Chlorophyll A, Periphyton, spectrophotometric, uncorrected (mg/sqm)

Chlorophyll A, Phytoplankton, spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, uncorrected (ug/L)

Dissolved Inorganic Phosphorus (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldhal (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Phosphorus, orthophosphate, total, as P(ug/L)

Turbidity (FTU)
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-12 Appendix C—Quality Control/Quality Assurance Rules

Turbidity (NTU)

Turbidity (JCU)

pH

Level III ecoregions:

3, 7

5.2.2 Aggregate Nutrient Ecoregion 4

Data sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 7 - Central Plains Center for BioAssessment (CPCB)

EPA Region 7 - Central Plains Center for BioAssessment (CPCB) 2

EPA Region 7 - REMAP

EPA Region 8 - MT and WY

EPA Region 8 - South Dakota

EPA Region 8 - North Dakota

Parameters:

Chlorophyll A, Fluorometric, corrected (ug/L)

Chlorophyll A, Pheophytin, corrected (ug/L)

Chlorophyll A, Phytoplankton, spectrophotometric Acid (ug/L)

Dissolved Inorganic Phosphorus (DIP) (ug/L)

Dissolved Oxygen (DO) (% Saturated)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldhal (TKN) (mg/L)

Organic_P (ug/L)

Phosphorus, Total (TP) (ug/L)

Phosphorus, orthophosphate, total, as P(ug/L)

Turbidity (FTU)

Turbidity (NTU)

Turbidity (JCU)

pH

Level III ecoregions:

26, 28, 30, 31, 43, 44
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-13

5.2.3 Aggregate Nutrient Ecoregion 5

Data sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 7 - Central Plains Center for BioAssessment (CPCB)

EPA Region 7 - Central Plains Center for BioAssessment (CPCB) 2

EPA Region 7 - REMAP

EPA Region 8 - MT and WY

EPA Region 8 - South Dakota

EPA Region 8 - North Dakota

Parameters:

Chlorophyll A, Fluorometric, corrected (ug/L)

Chlorophyll A, Pheophytin, corrected (ug/L)

Chlorophyll A, Phytoplankton, spectrophotometric Acid (ug/L)

Dissolved Inorganic Phosphorus (DIP) (ug/L)

Dissolved Oxygen (DO) (% Saturated)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldhal (TKN) (mg/L)

Organic_P (ug/L)

Phosphorus, Total (TP) (ug/L)

Phosphorus, orthophosphate, total, as P (ug/L)

Turbidity (FTU)

Turbidity (NTU)

Turbidity (JCU)

pH

Level III ecoregions:

25, 27, 32, 42

5.2.4 Aggregate Nutrient Ecoregion 8 

Data sources:

Legacy STORET

NASQAN

NAWQA

EPA Region 2 - NYCDEP (1990-1998)

EPA Region 1
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-14 Appendix C—Quality Control/Quality Assurance Rules

EPA Region 3

EPA Region 5

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)

Dissolved Inorganic Phosphorus (DIP) (ug/L)

Dissolved Oxygen (DO) (% Saturated)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)

Nitrogen, Total Kjeldhal (TKN) (mg/L)

Phosphorus, Total (TP) (ug/L)

Phosphorus, orthophosphate, total, as P (ug/L)

Turbidity (FTU)

Turbidity (NTU)

pH

Level III ecoregions:

49, 50, 58, 62, 82

5.2.5 Aggregate Nutrient Ecoregion 10

Data sources:

Legacy STORET

NASQAN

EPA Region 7 - Central Plains Center for BioAssessment (CPCB)

EPA Region 7 - Central Plains Center for BioAssessment (CPCB) 2

EPA Region 7 - REMAP

Parameters:

Chlorophyll A, Fluorometric, corrected (ug/L)

Chlorophyll A, Pheophytin, corrected (ug/L)

Chlorophyll A, Phytoplankton, chromotographic- fluorometric (ug/L)

Chlorophyll A, Phytoplankton, spectrophotometric Acid (ug/L)

Chlorophyll A, Trichromatic, uncorrected (ug/L)

Chlorophyll B, Phytoplankton, chromotographic- fluorometric (ug/L)

Dissolved Inorganic Phosphorus (DIP) (ug/L)

Dissolved Oxygen (DO) (mg/L)

Nitrite and Nitrate, (NO2+NO3) (mg/L)

Nitrogen, Total (TN) (mg/L)
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-15

Nitrogen, Total Kjeldhal (TKN) (mg/L)

Organic_P (ug/L)

Phosphorus, Total (TP) (ug/L)

Phosphorus, orthophosphate, total, as P(ug/L)

Turbidity (FTU)

Turbidity (NTU)

Turbidity (JCU)

pH

Level III ecoregions:

34, 73
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-16 Appendix C—Quality Control/Quality Assurance Rules

APPENDIX A. Process Used to QA/QC the Legacy STORET Nutrient Data Set

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:

C 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.

• Data were retrieved that were designated as either ‘grab’ samples and ‘composite’ samples

(mean result only).
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Appendix C—Quality Control/Quality Assurance Rules C-17

• 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

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
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

TABLE 2: STORET REMARK CODE RULES

C-18 Appendix C—Quality Control/Quality Assurance Rules

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.

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
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-19

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 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
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-20 Appendix C—Quality Control/Quality Assurance Rules

• 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 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
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-21

nutrient data set contains the following:

41,174 station records

919,895 sample records
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

C-22 Appendix C—Quality Control/Quality Assurance Rules

APPENDIX B. Process for Adding Aggregate Nutrient Ecoregions 

and Level III Ecoregions

The flag_id tracks the type of changes that were made to the data. There are a total of eight flags

that are used to describe the changes made to the data. The flags are defined as follows:

1—The latitude and longitude coordinates match the county that was provided. If the HUC was

null, it was updated based on the latitude and longitude coordinates. The ecoregions were

determined by using the latitude and longitude coordinates.

2—The county and HUC are available, but the latitude and/or longitude coordinates are missing. 

Therefore, the centroid of the intersection of the county and HUC was used to determine the

ecoregions and the latitude and longitude coordinates. If the HUC and county did not intersect, 

the county centroid was used to determine the ecoregions and the latitude and longitude

coordinates.

3—The county is available, but the HUC and the latitude and/or longitude coordinates are

missing. Therefore, the county centroid was used to determine the ecoregions, HUC, and the

latitude and longitude coordinates.

4—The HUC is available, but the county is not and the latitude and/or longitude coordinates are

missing. Therefore, the HUC centroid was used to determine the ecoregions, county, and the

latitude and longitude coordinates.

5—The county is missing, but the latitude and longitude coordinates are available. Note: A

county is considered missing if it is invalid. In other words, if the county entered did not exist in

the state, it was considered null. Therefore, the latitude and longitude coordinates were used to

determine the ecoregions, county, and HUC (if it was missing).

6—The latitude and longitude coordinates did not match the county that was provided, but they

did match the HUC. Therefore, the county centroid was used to determine ecoregion values. 

7—The latitude and longitude coordinates did not match the county or the HUC that was

provided (including null HUCs). Therefore, the county centroid was used to determine

ecoregion values.

8—The latitude and longitude coordinates were missing, but the ecoregions were provided by

the state.

The ecoregions provided by the states were used as the ecoregion values.
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001

Appendix C—Quality Control/Quality Assurance Rules C-23

APPENDIX C. Glossary

Coefficient of Variation - A measure of variability. The standard deviation divided by the mean

multiplied by 100. 

Maximum - The highest value.

Mean – A measure of central tendency. The arithmetic average.

Median – A measure of central tendency. The value which cuts the distribution in half, such that

half of the values are above the median, and half of the values are below the median. Also called

the 50th percentile or middle value.

Minimum - The lowest value.

Standard Deviation – A measure of variability. 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 - A measure of variability. The standard deviation divided by the square root of

the sample size.

5th % - the 5th percentile

25th % - the 25th percentile, the first quartile.

75th % - the 75th percentile, the third quartile.

95th % - the 95th percentile