United States Office of Water EPA 822-B-01-008

Environmental Protection 4304 December 2001

Agency

Ambient Water Quality

Criteria Recommendations

Information Supporting the Development 

of State and Tribal Nutrient Criteria

Lakes and Reservoirs in 

Nutrient Ecoregion III
EPA-822-B-01-008

AMBIENT WATER QUALITY CRITERIA RECOMMENDATIONS

INFORMATION SUPPORTING THE DEVELOPMENT OF STATE AND TRIBAL

NUTRIENT CRITERIA

FOR

LAKES AND RESERVOIRS IN NUTRIENT ECOREGION III

Xeric West

including all or parts of the States of:

Washington, Oregon, California, Nevada, Idaho, Wyoming, Montana, Utah, Colorado, 

New Mexico, Arizona, and Texas,

and the authorized Tribes within the Ecoregion

U.S. ENVIRONMENTAL PROTECTION AGENCY

OFFICE OF WATER

OFFICE OF SCIENCE AND TECHNOLOGY

HEALTH AND ECOLOGICAL CRITERIA DIVISION

WASHINGTON, DC

DECEMBER 2001
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FOREWORD

This document presents EPA’s nutrient criteria for Lakes and Reservoirs in Nutrient

Ecoregion III. 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., Secchi depth

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 lakes and reservoirs in Nutrient Ecoregion III

(Xeric West), which were derived using the procedures described in the Lakes and Reservoirs

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

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 III. Data sets from Legacy

STORET, EPA Region 8 and Colorado Reservoir, EPA Region 10 were used to assess

nutrient conditions from 1990 to 2000.

C Reference sites/reference conditions in Nutrient Ecoregion III. 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 lakes and reservoirs 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:

Washington, Oregon, Idaho, Wyoming, Montana, Utah, Colorado, Arizona, and Texas. 

California 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 Secchi.

BASED ON 25th PERCENTILES ONLY

Nutrient Parameters Aggregate Nutrient Ecoregion III

Reference Conditions

Total phosphorus (μg/L) 17

Total nitrogen (mg/L) (reported) 0.40

Chlorophyll a (μg/L) (fluorometric method) 3.4

Secchi (m) 2.7

For subecoregions 6, 10, 12, 13, 14, 18, 20, 22, 24, 79, 80, and 81, 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) 3-172*

Total nitrogen (mg/L) (calculated) 0.15-1.44

Chlorophyll a (μg/L) (fluorometric method) 0-24.6*

Secchi (m) 1.4-3.1

* 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-01-008.
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ACKNOWLEDGMENTS

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

reviewers: EPA Regions 6, 8, 9, and 10; the States of Washington, Oregon, California, Nevada,

Idaho, Wyoming, Montana, Utah, Colorado, New Mexico, Arizona, 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 Paul Garrison, Wisconsin Department of Natural Resources; John Reuter,

University of California, Davis; and Eugene Welch, University of Washington.
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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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

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 III—Xeric West ........................8

3.2 Geographical Boundaries of Aggregate Ecoregion III ........................8

3.3 Level III Subecoregions within Aggregate Ecoregion III ......................8

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

4.0 Data Review for Lakes and Reservoirs in Aggregate Ecoregion III . . . . . . . . . . . . . . . . . 13

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

4.2 Historical Data from Aggregate Ecoregion III (TP, TN, chl a, Secchi) . . . . . . . . . . . 14

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

4.4 Data for All Lakes and Reservoirs Within Aggregate Ecoregion III . . . . . . . . . . . . . 14

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

4.6 Classification of Lakes and Reservoirs Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

4.7 Summary of Data Reduction Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

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

6.0 Models Used to Predict or Verify Response Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.0 Framework for Refining Recommended Nutrient Criteria for Lakes and Reservoirs in

Aggregate Ecoregion III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.1 Example Worksheet for Developing Aggregate Ecoregion and 

Subecoregion Nutrient Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.2 Setting Seasonal Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

7.3 When Data/Reference Conditions Are Lacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.4 Site-Specific Criteria Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

8.0 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
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9.0 Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

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

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

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

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

Tables

Table 1 Lake and reservoir records for Aggregate Ecoregion III—Xeric West . . . . . . . . 16

Table 2 Reference conditions for Aggregate Ecoregion III lakes and reservoirs . . . . . . . 18

Table 3a-j Reference conditions for level III Ecoregion lakes and reservoirs . . . . . . . . . . . 19

Table 4 Changes in temperate lake attributes according to trophic state . . . . . . . . . . . . . 25

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 III ............................................9

Figure 3 Aggregate Ecoregion III with level III Ecoregions shown . . . . . . . . . . . . . . . . . 10

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

Figure 5a Illustration of data reduction process for lake data . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 5b Illustration of reference condition calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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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

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
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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 Secchi). 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 Secchi).

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.

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.
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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 a 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 largescale 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

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.
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Figure 1a. Fourteen nutrient Ecoregions as delineated by Omernik (2000). Ecoregions were based on ecosystem type, and nutrient conditions.
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Figure 1b. Level III Ecoregions of the United States.
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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, Secchi) variables represent a set of starting points for States

and Tribes to use in establishing their own criteria.

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
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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.

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).
8

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 III—Xeric West

The Xeric West is composed of unforested basins, alluvial fans, plateaus, buttes, and

scattered mountains. Region III is drier than surrounding regions, and naturally occurring water

is scarce in nearly all places. Its climate is subject to large year-to-year, seasonal, and diurnal

variations. Perennial streams are rare and those that occur typically originate outside the region

in the higher, wetter, more rugged Western Forested Mountains (II). Vegetation is often

desertic, with areas of woodland occurring only locally in wetter locations. Most of the area is

uncultivated and used for range. However, irrigated agriculture occurs where water is available

and soils are suitable. In parts of the region, groundwater overdraft has lowered the water table,

causing diminished spring flow/streamflow, saltwater intrusion (in coastal areas), and ground

subsidence. Rivers that are heavily used for irrigation have high concentrations of dissolved

solids, nitrite plus nitrate, and salinity that can increase downstream through irrigation return

flow and evaporation. Areas of high human population density occur along with associated

water quality problems including elevated levels of fecal coliform bacteria, nitrite plus nitrate,

phosphorus, sulfate, and dissolved solids.

3.2 Geographical Boundaries of Aggregate Ecoregion III

Ecoregion III encompasses the areas of the western United States where dry conditions

prevail (Figure 2). More specifically, the region includes central Washington, southeastern

Oregon, and the southern third of Idaho. The entire State of Nevada is included in this region, as 

well as the vast majority of Utah (excluding the central mountainous region that is part of

Ecoregion II). The region continues south to include the southeastern portion of California. The 

region also includes a U-shaped portion of California that starts up the central portion of the

Pacific coast and then turns back southward around the central part of California included in

Ecoregion I. From southern California, the region stretches east into Arizona, New Mexico, and

a small area of southwest Texas. All of Arizona and New Mexico are included in Ecoregion III,

with the exception of the mountainous areas that are part of Ecoregion II. In addition, extreme

western Colorado and central Wyoming are included in this Ecoregion.

3.3 Level III Subecoregions Within Aggregate Ecoregion III

There are 12 level III subecoregions contained within Aggregate Ecoregion III (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.

6. Southern and Central California Chaparral and Oak Woodlands

The primary distinguishing characteristic of this subecoregion is its Mediterranean climate

of hot, dry summers and cool, moist winters, and associated vegetative cover comprising mainly 
9

Figure 2. Aggregate Ecoregion III.
10

Figure 3. Aggregate Ecoregion III with level III Ecoregions shown.
11

chaparral and oak woodlands; grasslands occur in some lower elevations and patches of pine are

found at higher elevations. Most of the region consists of open low mountains or foothills, but

there are areas of irregular plains in the south and near the border of the adjacent Central

California Valley Ecoregion. Much of this region is grazed by domestic livestock; very little

land has been cultivated. 

10. Columbia Plateau

The Columbia Plateau is an arid sagebrush steppe and grassland surrounded on all sides by

moister, predominantly forested, mountainous ecological regions. This region is underlain by

lava rock up to 2 miles thick and is covered in some places by loess soils that have been

extensively cultivated for wheat, particularly in the eastern portions of the region where

precipitation amounts are greater. 

12. Snake River Basin

This portion of the xeric intermontane basin and range area of the western United States is

considerably lower and more gently sloping than the surrounding subecoregions. Mostly

because of the available water for irrigation, a large percentage of the alluvial valleys bordering

the Snake River is devoted to agriculture, with sugar beets, potatoes, and vegetables being the

principal crops. Cattle feedlots and dairy operations are also common in the river plain. Except

for the scattered barren lava fields, the remainder of the plains and low hills in the subecoregion

have a potential for natural vegetation in the form of sagebrush steppe and are now used for

cattle grazing.

13. Central Basin and Range

The Central Basin and Range subecoregion is characterized by a mosaic of xeric basins,

scattered low and high mountains, and salt flats. Compared with the Snake River Basin and

Northern Basin and Range regions to the north, the region is hotter and contains higher dense

mountains that have perennial streams and ponderosa pine forests at higher elevations. Also,

there is less grassland and more shrubland, and the soils are mostly Aridisols rather than dry

Mollisols. The region is not as hot as the Mojave and Sonoran Basin and Range subecoregions

and it has a greater percentage of grazed land.

14. Mojave Basin and Range

This subecoregion contains scattered mountains that are generally lower than those of the

Central Basin and Range. Potential natural vegetation in this region is predominantly creosote

bush, compared with the mostly saltbush-greasewood and Great Basin sagebrush of the

Ecoregion to the north, and creosote bush-bur sage with large patches of palo verde-cactus shrub

and saguaro cactus in the Sonoran Basin and Range to the south. Most of this region is federally

owned and there is relatively little grazing activity because of the lack of water and forage for

livestock. Heavy use of off-road vehicles and motorcycles in some areas has caused severe wind

and water erosion problems.
12

18. Wyoming Basin

This subecoregion is a broad intermontane basin dominated by arid grasslands and

shrublands interrupted by high hills and low mountains. Nearly surrounded by forest-covered

mountains, the region is somewhat drier than the Northwestern Great Plains to the northeast and

does not have the extensive cover of pinyon-juniper woodland found in the Colorado Plateaus to

the south. Much of the region is used for livestock grazing, although many areas lack sufficient

vegetation to support this activity. The region contains major producing natural gas and

petroleum fields.

20. Colorado Plateaus

Rugged tableland topography is typical of the Colorado Plateau subecoregion. Precipitous

side-walls mark abrupt changes in local relief, often from 300 to 600 meters. The region is more

elevated than the Wyoming Basin to the north and therefore contains a far greater extent of

pinyon-juniper woodlands. However, the region also has large low-lying areas containing

saltbrush-greasewood (typical of hotter, drier areas), which are generally not found in the higher

Arizona/New Mexico Plateau to the south, where grasslands are common.

22. Arizona/New Mexico Plateau

The Arizona/New Mexico Plateau represents a large transitional region between the

semiarid grasslands and low-relief tablelands of the Southwestern Tablelands subecoregion in

the east, the drier shrublands and woodland-covered higher relief tablelands of the Colorado

Plateau in the north, and the lower, hotter, less vegetated Mojave Basin and Range in the west

and Chihuahuan Deserts in the south. Higher, more forest-covered, mountainous subecoregions

border the region on the northeast and southwest. Local relief in the region varies from a few

meters on plains and mesa tops to well over 300 meters along tableland side slopes.

24. Chihuahuan Deserts

This desertic subecoregion extends from the Madrean Archipelago in southeastern Arizona

to the Edwards Plateau in south-central Texas. The region comprises broad basins and valleys

bordered by sloping alluvial fans and terraces. Isolated mesas and mountains are located in the

central and western parts of the region. Vegetative cover is predominantly arid grass and

shrubland, except on the higher mountains where oak-juniper woodlands occur. 

79. Madrean Archipelago

Also known as the Sky Islands in the United States, this is a region of basins and ranges

with medium to high local relief, typically 1,000 to 1,500 meters. Native vegetation in the

region is mostly grama-tobosa shrubsteppe in the basins and oak-juniper woodlands on the

ranges, except at higher elevations where ponderosa pine is predominant. The region has

ecological significance as both a barrier and a bridge between two major cordilleras of North

America, the Rocky Mountains and the Sierra Madre Occidental.
13

80. Northern Basin and Range

This subecoregion consists of arid tablelands, intermontane basins, dissected lava plains,

and widely scattered low mountains. The bulk of the region is covered by sagebrush steppe

vegetation. The subecoregion is drier and less suitable for agriculture than the Columbia

Plateau, is higher and cooler than the Snake River Basin to the east, and contains a lower density

of mountain ranges than the adjacent Central Basin and Range subecoregion to the south. Much

of the region is used as rangeland.

81. Sonoran Basin and Range

Similar to the Mojave Basin and Range to the north, this subecoregion contains scattered

low mountains and has large tracts of federally owned land, most of which is used for military

training. However, the Sonoran Basin and Range is slightly hotter than the Mojave and contains

large areas of palo verde-cactus shrub and giant saguaro cactus, whereas the potential natural

vegetation in the Mojave is largely creosote bush.

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 LAKES AND RESERVOIRS IN AGGREGATE

ECOREGION III

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 (Secchi 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 5 of the Lakes and Reservoirs Nutrient Criteria

Technical Guidance Manual [U.S. EPA, 2000a] for a complete discussion on choosing causal

and response variables). 

4.1 Data Sources

Data sets from Legacy STORET, EPA Region 10, and EPA Region 8-Colorado Reservoir

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.
14

4.2 Historical Data from Aggregate Ecoregion III (TP, TN, chl a, and Secchi)

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 trends over the past

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

4.3 QA/QC of Data Sources

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

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

analytical records, sampling errors or omissions, stations associated with outfalls, stormwater

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

States within Ecoregion III 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: Washington, Oregon, Idaho,

Wyoming, Montana, Utah, Colorado, Arizona, and Texas. California 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 Lakes and Reservoirs Within Aggregate Ecoregion III 

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

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

the Aggregate Ecoregion.

4.5 Statistical Analysis of Data

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

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

the upper 25th percentile (75th percentile) of a reference population of lakes. 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 lakes are not identified, the second method is to determine the lower

25th percentile of the population of all lakes 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, 
15

Figure 4. Sampling locations within each level III Ecoregion.
16Table 1. Lake and reservoir records* for Aggregate Ecoregion III — Xeric West

Aggregate

Ecoregion III

Sub

ecoR

6

Sub

ecoR

10

Sub

ecoR

12

Sub

ecoR

13

Sub

ecoR

18

Sub

ecoR

20

Sub

ecoR

22

Sub

ecoR

24

# of lakes 190 9 17 18 50 11 40 17 19 # of lake stations 378 35 33 27 96 22 93 32 30 Key nutrient parameters (listed below)- # of records forSecchi depth 1,699 22 267 50 603 100 486 42 114 - # of records forchlorophyll a(all methods)

1,674 23 194 50 637 66 505 65 104 

- # of records for totalKjeldhal nitrogen(TKN)

1,966 37 215 138 755 40 596 53 70 

- # of records for nitrite+ nitrate (NO2+NO3) 959 25 605 76 56 1 33 56 57 

- # of records for totalnitrogen (TN) 668 — 489 — 103 — — 43 33 - # of records for totalphosphorus (TP) 4,080 192 712 178 1,355 197 1,181 74 126 Total # of records forkey nutrient parameters 11,046 299 2,482 492 3,509 404 2,801 333 504 

Definitions: (1) # of records refers to the total count of observations for that parameter over the entire decade (1990-1999) for that particular aggregaare counts for all seasons over that decade. (2) # of lake stations refers to the total number of lake and reservoir stations within the aggregate or subedata were collected. Since lakes and reservoirs can cross ecoregional boundaries, it is important to note that only those portions of a lake or reservoir 

those stations) that exist within the Ecoregion are included within this table.

*The number of lakes presented in this table is based on the number of lakes and reservoirs for which nutrient data were provided in the National Nut

imply that this is the total of lakes within the Ecoregion. States and Tribes should determine the representativeness of the tabular data by comparing tadditional material they may have.
17

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-j present potential reference conditions for both the Aggregate Ecoregion

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

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

information on reference lakes. Tables 3a-j present potential reference conditions for lakes and

reservoirs in the level III subecoregions within the Aggregate Ecoregion. Note that the footnotes

for Table 2 apply to Tables 3a-j. Appendixes A and B provide a complete presentation of all

descriptive statistics for both the Aggregate Ecoregion and the level III subecoregions.

Table 4 is presented for comparison purposes. It allows the reader to determine where, in

the trophic state, the recommended reference conditions fall within traditionally viewed trophic

boundaries.

4.6 Classification of Lake/Reservoir Type

Assessing the data by lake 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 lakes before developing a

final criterion.

4.7 Summary of Data Reduction Methods

All descriptive statistics were calculated using the medians for each lake within Ecoregion

III for which data existed. For example, if one lake had 300 observations for phosphorus over

the decade or 1 year’s time, one median resulted. Each median from each lake 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. 
18

Table 2. Reference conditions for Aggregate Ecoregion III lakes and reservoirs

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 122 0.00 3.07 0.30

NO2+NO3-N (mg/L) 54 0.00 2.66 0.01

TN (mg/L) - calculated 0.31

TN (mg/L) - reported 26 0.17 2.37 0.40

TP (μg/L) 170 1 1,000 17

Secchi (m) 121 0.1 5.65 2.8

Chlorophyll a (μg/L) - F 28 2.9 16 3.5

Chlorophyll a (μg/L) - S 83 0.3 61.0 1.8

Chlorophyll a (μg/L) - T 20 (z) 0.9 42.1 1.4

* N = largest value reported for a decadal 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.

† 75th percentile for Secchi.

‡ 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 Lakes refers to the largest number of lakes and reservoirs 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 lake for the decade were reduced to one median for that lake. 

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 lakes/season. 

However, this table provides 25th percentiles that were derived with fewer than 4 lakes/season in order to retain all information

for all seasons. In calculating the 25th percentile for a season with fewer than 4 lake medians, the statistical program

automatically used the minimum value within the fewer-than-4 population. If fewer than 4 lakes 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.”
19

Table 3a. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 6

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 4 0.45 0.53 0.45

NO2+NO3-N (mg/L) 1 0.06 0.06 0.06 (zz)

TN (mg/L) - calculated 0.51

TN (mg/L) - reported — — — —

TP (μg/L) 7 55 309 1722

Secchi (meters) 2 0.9 1.9 1.9 (zz)

Chlorophyll a (μg/L) - F 1 24.6 24.6 24.6 (zz)

Chlorophyll a (μg/L) - S — — — —

Chlorophyll a (μg/L) - T — — — —

Table 3b. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 10

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 13 0.32 1.25 0.60

NO2+NO3-N (mg/L) 12 0.01 0.37 0.12

TN (mg/L) - calculated 0.72

TN (mg/L) - reported 3 0.36 0.39 0.36

TP (μg/L) 17 30 208 35

Secchi (meters) 7 1.3 2.4 2

Chlorophyll a (μg/L) - F 4 3.4 5.6 3.4

Chlorophyll a (μg/L) - S — — — —

Chlorophyll a (μg/L) - T 2 (z) 33.5 71 33.5 (zz)
20

Table 3c. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 12

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 9 — 0.54 —

NO2+NO3-N (mg/L) 2 1.44 2.07 1.44 (zz)

TN (mg/L) - calculated 1.44

TN (mg/L) - reported — — — —

TP (μg/L) 18 17 152 20

Secchi (meters) 15 (z) 0.5 4.6 2.2

Chlorophyll a (μg/L) - F 9 (z) 1.2 40.5 2.7

Chlorophyll a (μg/L) - S — — — —

Chlorophyll a (μg/L) - T 6 (z) 1.1 30.1 4.7

Table 3d. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 13

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 42 0.07 2.69 0.34

NO2+NO3-N (mg/L) 10 0.01 0.68 0.01

TN (mg/L) - calculated 0.35

TN (mg/L) - reported 7 0.50 2.37 0.51

TP (μg/L) 49 11 742 30

Secchi (meters) 36 0.1 4.9 2.3

Chlorophyll a (μg/L) - F 4 (z) 1.7 5.5 1.9

Chlorophyll a (μg/L) - S 32 1.8 46.2 3.5

Chlorophyll a (μg/L) - T — — — —
21

Table 3e. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 18

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 5 0.33 0.38 0.33

NO2+NO3-N (mg/L) 1 (z) 0.05 0.05 0.05 (zz)

TN (mg/L) - calculated 0.38

TN (mg/L) - reported — — — —

TP (μg/L) 11 10 100 10

Secchi (meters) 9 1.1 4.5 3

Chlorophyll a (μg/L) - F 2 (z) 4 5.30 4 (zz)

Chlorophyll a (μg/L) - S 5 0.8 7.4 1.4

Chlorophyll a (μg/L) - T — — — —

Table 3f. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 20

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 26 0.03 2.89 0.14

NO2+NO3-N (mg/L) 9 — 0.13 0.01

TN (mg/L) - calculated 0.15

TN (mg/L) - reported — — — —

TP (μg/L) 38 2 170 3

Secchi (meters) 33 1.9 4.61 3.2

Chlorophyll a (μg/L) - F 2 (z) 0.00 3 0.00 (zz)

Chlorophyll a (μg/L) - S 34 0.3 14.3 1.4

Chlorophyll a (μg/L) - T — — — —
22

Table 3g. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 22

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 12 0.10 1.35 0.21

NO2+NO3-N (mg/L) 11 0.02 0.24 0.02

TN (mg/L) - calculated 0.23

TN (mg/L) - reported 9 0.23 1.51 0.31

TP (μg/L) 15 2 135 15

Secchi (meters) 8 0.7 4 2.9

Chlorophyll a (μg/L) - F 1 (z) 2.5 2.5 2.50 (zz)

Chlorophyll a (μg/L) - S 5 1.1 4.4 2

Chlorophyll a (μg/L) - T 5 1.2 4.4 1.9

Table 3h. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 24

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 12 0.27 1.30 0.36

NO2+NO3-N (mg/L) 16 0.01 2.25 0.01

TN (mg/L) - calculated 0.37

TN (mg/L) - reported 11 0.45 1.30 0.57

TP (μg/L) 16 13 67 22

Secchi (meters) 10 0.4 2.9 1.5

Chlorophyll a (μg/L) - F — — — —

Chlorophyll a (μg/L) - S 9 0.6 30.3 3.3

Chlorophyll a (μg/L) - T 7 0.9 17.2 1.7
23

Table 3i. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 80

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 4 0.16 0.16 0.16

NO2+NO3-N (mg/L) 3 0.01 0.01 0.01 (zz)

TN (mg/L) - calculated 0.17

TN (mg/L) - reported — — — —

TP (μg/L) 7 86 90 86

Secchi (meters) 6 (z) 1.7 3.7 2.80

Chlorophyll a (μg/L) - F 5 (z) 4.4 5.2 4.4 

Chlorophyll a (μg/L) - S — — — —

Chlorophyll a (μg/L) - T 3 3.1 61.5 3.1 (zz)
24

Table 3j. Reference conditions for Ecoregion III lakes and reservoirs

subecoregion 81

Parameter No. of lakes

N*

Reported values 25th percentiles based on all

seasons data for the decade Reference lakes§

Min Max P25† all seasons‡ P75 all seasons

TKN (mg/L) 1 (z) 0.50 0.50 0.50 (zz)

NO2+NO3-N (mg/L) 1 (z) 0.02 0.02 0.02 (zz)

TN (mg/L) - calculated 0.52

TN (mg/L) - reported — — — —

TP (μg/L) 1 (z) 20 20 20 (zz)

Secchi (meters) 1 (z) 1.7 1.7 1.7 (zz)

Chlorophyll a (μg/L) - F — — — —

Chlorophyll a (μg/L) - S — — — —

Chlorophyll a (μg/L) - T — — — —

* N = largest value reported for a decadal 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.

† 75th percentile for Secchi.

‡ 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).

2 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.

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 Lakes refers to the number of lakes and reservoirs 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 lake for the decade were reduced to one median for

that lake. 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

lakes/season. However, this table provides 25th percentiles that were derived with fewer than 4 lakes/season in order to retain all

information for all seasons. In calculating the 25th percentile for a season with fewer than 4 lake medians, the statistical program

automatically used the minimum value within the fewer-than-4 population. If fewer than 4 lakes 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.”
25

Table 4. Changes in temperate lake attributes according to trophic state (adapted from

Carlson and Simpson, 1995)

TSI

Value

SD (m) TP

(μg/L)

Attributes Water Supply Recreation Fisheries

<30 >8 <6 Oligotrophy: Clear water,

oxygen throughout the year

in the hypolimnion

Salmonid

fisheries

dominate

30-40 8-4 6-12 Hypolimnia of shallower

lakes may become anoxic

Salmonid

fisheries in

deep lakes

40-50 4-2 12-24 Mesotrophy: Water

moderately clear but

increasing probability of

hypolimnetic anoxia during

summer

Iron and manganese

evident during the

summer. THM

precursors exceed 0.1

mg/L and turbidity >1

NTU

Hypolimnetic

anoxia results

in loss of

salmonids.

Walleye may

predominate

50-60 2-1 24-48 Eutrophy: Anoxic

hypolimnia, macrophyte

problems possible

Iron, manganese, taste,

and odor problems

worsen

Warm-water

fisheries only.

Bass may be

dominant

60-70 0.5-1 48-96 Blue-green algae dominate,

algal scums and

macrophyte problems

Weeds, algal

scums, and

low

transparency

discourage

swimming and 

boating

70-80 0.25-

0.5

96-192 Hypereutrophy (light

limited). Dense algae and

macrophytes

>80 <0.25 192-

384

Algal scums, few

macrophytes

Rough fish

dominate,

summer fish

kills possible

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.
26

Figure 5a. Illustration of data reduction process for lake data.
Figure 5b. Illustration of reference condition calculation.

27
28

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

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

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

from a particular method, it is recommended that the method with the most observations be

used. Fluorometric and spectrophotometric 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 III

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-l in Section 4.0.

• RTAG discussion and rationale for selection of reference sites and conditions in Ecoregion
29

III. 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

LAKES AND RESERVOIRS IN AGGREGATE ECOREGION III

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-l 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: 

 

 

 

 

Historical data and trends: 

 

 

 
30

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

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
31

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 Lakes and Reservoirs Nutrient Criteria

Technical Guidance Manual (U.S. EPA, 2000a). The Technical Guidance Manual presents

sections on each of the following factors to consider in setting criteria:

• Refinements to Ecoregions (Chapter 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 3)

• Setting seasonal criteria to reflect major seasonal climate differences and accounting for

significant or cyclical precipitation events (high-flow/low-flow conditions) (Chapter 7)

• Setting criteria for reservoirs only. (The technical guidance manual recommends that data

be separated for lakes and reservoirs and treated independently if possible because of

differing physical conditions that occur in lakes and reservoirs. In this document all data

from both reservoirs and lakes were considered together since STORET does not allow for

the differentiation of data except by waterbody name.)

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.

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.
32

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). 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: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1990 to 1999 Chloro_A_Fluor_cor_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 5 10.17 5.2500 24.65 8.17 3.65 80 5.25 5.85 7.15 7.93  SPRING 4 5.89 4.4000 8.18 1.61 0.81 27 4.40 4.86 5.49 6.91  SUMMER 28 8.66 .00000 40.50 11.71 2.21 135 0.70 2.08 3.60 7.65  WINTER 4 2.94 1.4500 4.50 1.27 0.63 43 1.45 2.03 2.90 3.85  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1990 to 1997 Chloro_A_Phyto_Spec_A_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 48 7.79 .25000 83.40 12.54 1.81 161 0.72 2.05 3.98 9.38  SPRING 57 5.73 .30000 38.69 7.69 1.02 134 0.44 1.90 2.80 5.75  SUMMER 83 9.28 .00000 155.80 19.73 2.17 213 0.85 1.80 3.10 7.40  WINTER 7 17.61 1.2000 29.90 11.79 4.46 67 1.20 5.60 17.00 29.90  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1990 to 1997 Chloro_A_Trich_unco_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 7 4.95 .40000 11.15 4.24 1.60 86 0.40 0.74 4.25 10.23  SPRING 11 8.62 .95000 42.08 13.76 4.15 160 0.95 1.42 2.76 4.69  SUMMER 20 16.29 .95000 71.00 19.46 4.35 119 1.01 3.02 9.79 17.61  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1991 to 1999 DIP_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 10 45.70 2.0000 138.00 49.03 15.50 107 2.00 4.50 27.50 83.50 1 SPRING 10 31.83 5.5000 110.00 31.10 9.84 98 5.50 7.50 23.00 43.00 1 SUMMER 10 44.85 .00000 140.00 62.75 19.84 140 0.00 4.00 5.50 127.00 1 WINTER 10 47.78 13.250 122.50 38.98 12.33 82 13.25 17.50 33.00 64.00 1 Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1990 to 1999 Dissolved_Oxygen_mg_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 66 7.60 .50000 14.70 2.20 0.27 29 4.35 6.70 7.69 8.70  SPRING 72 8.40 2.2000 13.00 1.89 0.22 23 4.90 7.43 8.08 9.63  SUMMER 115 7.09 1.0500 13.40 1.78 0.17 25 4.20 6.15 7.00 8.20  WINTER 24 9.89 2.3500 13.85 2.68 0.55 27 4.50 8.78 10.30 11.69  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1990 to 1999 Nitrite_Nitrate_NO2_NO3_mg_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 36 0.19 .00250 2.11 0.44 0.07 235 0.00 0.02 0.06 0.13  SPRING 41 0.49 .00150 3.68 0.88 0.14 181 0.01 0.01 0.07 0.56  SUMMER 54 0.19 .00000 3.20 0.54 0.07 279 0.00 0.01 0.03 0.11  WINTER 22 0.44 .01000 1.94 0.60 0.13 135 0.01 0.04 0.20 0.43  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1990 to 1999 Nitrogen_Tot_Kjeldhal_mg_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 63 0.62 .00000 2.96 0.50 0.06 81 0.11 0.29 0.50 0.90  SPRING 93 0.60 .00000 3.51 0.69 0.07 115 0.03 0.20 0.41 0.69  SUMMER 122 0.61 .00000 3.19 0.52 0.05 85 0.10 0.30 0.47 0.75  WINTER 31 0.69 .00000 2.48 0.62 0.11 90 0.05 0.34 0.51 0.90  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1990 to 1998 SECCHI_m season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 61 2.14 .17500 7.00 1.48 0.19 69 0.21 1.00 2.08 2.90  SPRING 65 1.74 .10000 4.30 1.25 0.15 72 0.15 0.70 1.60 2.84  SUMMER 121 2.03 .02500 7.80 1.42 0.13 70 0.23 1.00 1.80 2.70  WINTER 12 1.79 .50000 3.59 1.02 0.29 57 0.50 0.91 1.85 2.46  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1990 to 1998 Total_Nitrogen_mg_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 19 0.62 .18000 2.28 0.50 0.12 81 0.18 0.29 0.46 0.82  SPRING 26 1.12 .16500 4.33 1.06 0.21 95 0.23 0.50 0.56 1.63  SUMMER 24 0.85 .15500 2.42 0.64 0.13 76 0.22 0.36 0.69 1.00  WINTER 8 0.72 .36000 2.32 0.65 0.23 90 0.36 0.44 0.47 0.64  Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1990 to 1999 Total_Phosphorus_ug_L season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 91 93.61 .00000 755.00 138.26 14.49 148 2.50 15.00 35.50 120.00 4 SPRING 104 98.67 1.5000 1630.00 214.12 21.00 217 2.50 20.00 40.00 82.00 2 SUMMER 170 77.23 .00000 1200.00 138.39 10.61 179 2.50 11.25 30.00 75.00 2 WINTER 41 107.48 2.5000 800.00 151.81 23.71 141 6.25 30.00 60.00 115.00 2 Data were not always available for all years.
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion 

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Decade and Season from 1991 to 1999 pH_S_U season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  FALL 10 8.37 8.0000 9.05 0.32 0.10 4 8.00 8.17 8.30 8.40  SPRING 10 8.31 7.9400 8.70 0.23 0.07 3 7.94 8.13 8.26 8.50  SUMMER 33 8.19 6.3000 9.48 0.59 0.10 7 7.28 8.00 8.18 8.43  WINTER 10 8.18 8.0250 8.60 0.17 0.05 2 8.03 8.07 8.10 8.25  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: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1999 Chloro_A_Fluor_cor_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 FALL 1 24.65 24.650 24.65 . . . 24.7 24.7 24.7 24.7 24 6 SUMMER 1 32.00 32.000 32.00 . . . 32.0 32.0 32.0 32.0 32 6 WINTER 1 4.50 4.5000 4.50 . . . 4.50 4.50 4.50 4.50 4. 10 FALL 3 6.98 5.8500 7.93 1.05 0.61 15 5.85 5.85 7.15 7.93 7. 10 SPRING 3 6.38 5.3250 8.18 1.56 0.90 24 5.33 5.33 5.65 8.18 8. 10 SUMMER 4 1.93 .90000 2.58 0.72 0.36 37 0.90 1.48 2.13 2.39 2. 10 WINTER 3 2.42 1.4500 3.20 0.89 0.51 37 1.45 1.45 2.60 3.20 3. 12 SUMMER 9 17.31 1.2000 40.50 15.3 5.09 88 1.20 2.70 12.8 31.3 40 13 SUMMER 4 3.18 1.7000 5.50 1.71 0.86 54 1.70 1.90 2.75 4.45 5. 18 SUMMER 2 4.65 4.0000 5.30 0.92 0.65 20 4.00 4.00 4.65 5.30 5. 20 SUMMER 2 1.50 .00000 3.00 2.12 1.50 141 0.00 0.00 1.50 3.00 3. 22 SUMMER 1 2.50 2.5000 2.50 . . . 2.50 2.50 2.50 2.50 2. 80 FALL 1 5.25 5.2500 5.25 . . . 5.25 5.25 5.25 5.25 5. 80 SPRING 1 4.40 4.4000 4.40 . . . 4.40 4.40 4.40 4.40 4. 80 SUMMER 5 3.88 .70000 5.30 1.88 0.84 48 0.70 3.80 4.40 5.20 5.

 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1997 Chloro_A_Phyto_Spec_A_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 13 FALL 18 12.74 2.4000 83.40 18.4 4.34 144 2.40 4.55 7.73 13.1 83 13 SPRING 23 7.43 .80000 23.70 7.50 1.56 101 1.00 2.40 3.50 11.0 22 13 SUMMER 32 11.85 1.2500 62.50 15.1 2.67 127 1.65 2.39 5.15 13.9 45 13 WINTER 5 21.02 5.6000 29.90 11.3 5.03 54 5.60 12.5 27.2 29.9 29 18 FALL 2 6.13 2.4000 9.85 5.27 3.73 86 2.40 2.40 6.13 9.85 9. 18 SPRING 3 1.60 .30000 2.40 1.14 0.66 71 0.30 0.30 2.10 2.40 2. 18 SUMMER 5 3.38 .85000 7.40 2.64 1.18 78 0.85 1.40 2.80 4.45 7. 20 FALL 20 3.96 .40000 21.30 5.03 1.12 127 0.65 1.40 2.05 4.38 17 20 SPRING 18 2.70 .30000 7.30 1.60 0.38 60 0.30 1.80 2.30 3.13 7. 20 SUMMER 34 4.11 .00000 42.20 7.11 1.22 173 0.75 1.50 2.35 4.30 10 20 WINTER 1 1.20 1.2000 1.20 . . . 1.20 1.20 1.20 1.20 1. 22 FALL 4 2.64 .72000 4.36 1.53 0.76 58 0.72 1.53 2.74 3.76 4. 22 SPRING 4 2.41 1.2150 3.00 0.81 0.41 34 1.22 1.96 2.72 2.87 3. 22 SUMMER 5 5.56 1.1450 11.45 3.99 1.78 72 1.15 2.83 5.42 6.96 11 24 FALL 4 10.62 .25000 22.00 8.92 4.46 84 0.25 4.80 10.1 16.4 22 24 SPRING 9 10.31 .43750 38.69 13.7 4.58 133 0.44 1.21 3.78 14.4 38 24 SUMMER 7 29.52 .79000 155.80 56.1 21.2 190 0.79 1.75 15.3 15.4 1 24 WINTER 1 17.00 17.000 17.00 . . . 17.0 17.0 17.0 17.0 17

 Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1997 Chloro_A_Trich_unco_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 10 SUMMER 2 52.25 33.500 71.00 26.5 18.8 51 33.5 33.5 52.3 71.0 71 12 SUMMER 6 12.51 1.0600 30.10 10.1 4.14 81 1.06 4.70 12.0 15.3 30 22 FALL 5 2.65 .40000 4.44 1.94 0.87 73 0.40 0.74 3.43 4.25 4. 22 SPRING 4 2.40 1.2350 2.97 0.79 0.39 33 1.24 1.94 2.69 2.86 2. 22 SUMMER 5 5.22 1.3500 9.18 3.15 1.41 60 1.35 2.94 5.48 7.17 9. 24 FALL 2 10.69 10.230 11.15 0.65 0.46 6 10.2 10.2 10.7 11.2 11 24 SPRING 7 12.18 .95000 42.08 16.6 6.26 136 0.95 1.42 3.92 29.4 42 24 SUMMER 4 9.39 .95000 17.22 8.94 4.47 95 0.95 1.66 9.70 17.1 17 80 SUMMER 3 27.53 3.1000 61.50 30.3 17.5 110 3.10 3.10 18.0 61.5 61

Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1991 to 1999 DIP_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 10 FALL 8 40.88 2.0000 138.00 48.8 17.2 119 2.00 3.75 22.3 67.5 1 10 SPRING 8 23.53 5.5000 47.00 16.5 5.83 70 5.50 7.13 22.8 38.0 47 10 SUMMER 8 36.06 .00000 139.00 59.9 21.2 166 0.00 3.75 4.75 66.3 1 10 WINTER 8 42.22 13.250 101.75 31.5 11.1 75 13.3 16.4 33.0 62.0 1 12 FALL 2 65.00 20.000 110.00 63.6 45.0 98 20.0 20.0 65.0 110 1 12 SPRING 2 65.00 20.000 110.00 63.6 45.0 98 20.0 20.0 65.0 110 1 12 SUMMER 2 80.00 20.000 140.00 84.9 60.0 106 20.0 20.0 80.0 140 1 12 WINTER 2 70.00 17.500 122.50 74.2 52.5 106 17.5 17.5 70.0 123 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: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1999 Dissolved_Oxygen_mg_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 FALL 1 5.23 5.2250 5.23 . . . 5.23 5.23 5.23 5.23 5. 6 SPRING 3 9.17 7.3000 10.20 1.62 0.94 18 7.30 7.30 10.0 10.2 10 6 SUMMER 1 4.73 4.7250 4.73 . . . 4.73 4.73 4.73 4.73 4. 10 FALL 11 8.93 5.7500 10.90 1.42 0.43 16 5.75 8.53 9.05 9.90 10 10 SPRING 11 10.54 8.9000 11.73 1.00 0.30 9 8.90 9.90 10.6 11.4 11 10 SUMMER 14 8.15 3.4000 10.30 1.83 0.49 23 3.40 7.70 8.75 9.45 10 10 WINTER 10 11.86 10.000 13.85 1.07 0.34 9 10.0 11.4 11.7 12.5 13 12 FALL 2 7.65 6.7000 8.60 1.34 0.95 18 6.70 6.70 7.65 8.60 8. 12 SPRING 2 8.20 7.8000 8.60 0.57 0.40 7 7.80 7.80 8.20 8.60 8. 12 SUMMER 9 6.96 4.7000 8.40 1.27 0.42 18 4.70 6.73 7.00 8.10 8. 12 WINTER 2 8.78 8.3500 9.20 0.60 0.42 7 8.35 8.35 8.78 9.20 9. 13 FALL 19 7.53 5.5000 10.98 1.48 0.34 20 5.50 6.43 7.75 8.38 11 13 SPRING 29 8.19 4.9000 13.00 1.81 0.34 22 5.80 7.00 7.90 9.00 12 13 SUMMER 34 6.96 2.1000 9.13 1.35 0.23 19 4.20 6.35 6.95 7.83 8. 13 WINTER 6 7.43 2.3500 10.75 3.35 1.37 45 2.35 4.50 8.55 9.90 10 18 FALL 4 5.01 1.6500 7.20 2.52 1.26 50 1.65 3.08 5.59 6.94 7. 18 SPRING 1 8.35 8.3500 8.35 . . . 8.35 8.35 8.35 8.35 8. 18 SUMMER 9 7.59 5.3500 10.90 1.97 0.66 26 5.35 6.28 6.60 9.30 10 20 FALL 23 7.19 .50000 11.30 2.28 0.48 32 4.15 6.70 7.30 8.38 10 20 SPRING 22 7.53 2.2000 10.10 1.81 0.39 24 4.25 7.30 7.75 8.78 9. 20 SUMMER 35 6.81 3.6000 11.05 1.53 0.26 23 4.55 6.00 6.73 7.45 10 20 WINTER 3 8.36 6.4750 10.60 2.09 1.20 25 6.48 6.48 8.00 10.6 10 22 FALL 2 7.80 7.2000 8.40 0.85 0.60 11 7.20 7.20 7.80 8.40 8. 22 SPRING 1 6.30 6.3000 6.30 . . . 6.30 6.30 6.30 6.30 6. 22 SUMMER 4 5.57 1.0500 9.34 3.91 1.96 70 1.05 2.33 5.95 8.82 9. 24 FALL 2 11.35 8.0000 14.70 4.74 3.35 42 8.00 8.00 11.4 14.7 14 24 SPRING 2 8.43 7.5000 9.35 1.31 0.93 16 7.50 7.50 8.43 9.35 9. 24 SUMMER 4 8.25 4.8000 13.40 3.66 1.83 44 4.80 5.90 7.40 10.6 13 24 WINTER 2 9.70 9.6000 9.80 0.14 0.10 1 9.60 9.60 9.70 9.80 9. 80 FALL 1 10.43 10.425 10.43 . . . 10.4 10.4 10.4 10.4 10 80 SPRING 1 9.95 9.9500 9.95 . . . 9.95 9.95 9.95 9.95 9. 80 SUMMER 5 7.12 5.7500 9.08 1.37 0.61 19 5.75 5.95 7.00 7.80 9. 80 WINTER 1 12.00 12.000 12.00 . . . 12.0 12.0 12.0 12.0 12 81 FALL 1 5.70 5.7000 5.70 . . . 5.70 5.70 5.70 5.70 5. Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1999 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 FALL 1 0.06 .05500 0.06 . . . 0.06 0.06 0.06 0.06 0. 6 SPRING 1 0.18 .17750 0.18 . . . 0.18 0.18 0.18 0.18 0. 6 SUMMER 1 0.02 .01750 0.02 . . . 0.02 0.02 0.02 0.02 0. 10 FALL 9 0.13 .01750 0.25 0.08 0.03 58 0.02 0.08 0.13 0.18 0. 10 SPRING 10 0.26 .00150 0.67 0.22 0.07 83 0.00 0.16 0.21 0.29 0. 10 SUMMER 12 0.10 .00150 0.31 0.10 0.03 99 0.00 0.01 0.07 0.17 0. 10 WINTER 8 0.32 .19000 0.44 0.09 0.03 29 0.19 0.24 0.33 0.39 0. 12 FALL 2 1.92 1.7250 2.11 0.27 0.19 14 1.73 1.73 1.92 2.11 2. 12 SPRING 2 1.68 1.3200 2.03 0.50 0.36 30 1.32 1.32 1.68 2.03 2. 12 SUMMER 2 1.75 1.4000 2.10 0.49 0.35 28 1.40 1.40 1.75 2.10 2. 12 WINTER 2 1.71 1.4850 1.94 0.32 0.23 19 1.49 1.49 1.71 1.94 1. 13 FALL 4 0.09 .00250 0.36 0.18 0.09 191 0.00 0.00 0.01 0.18 0. 13 SPRING 1 0.63 .63000 0.63 . . . 0.63 0.63 0.63 0.63 0. 13 SUMMER 10 0.11 .00050 0.73 0.23 0.07 208 0.00 0.00 0.01 0.09 0. 13 WINTER 2 0.90 .01000 1.79 1.26 0.89 140 0.01 0.01 0.90 1.79 1. 18 SUMMER 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 20 FALL 9 0.07 .00250 0.34 0.11 0.04 155 0.00 0.00 0.05 0.07 0. 20 SPRING 2 0.01 .00500 0.01 0.00 0.00 24 0.01 0.01 0.01 0.01 0. 20 SUMMER 6 0.02 .00000 0.12 0.05 0.02 203 0.00 0.01 0.01 0.01 0. 20 WINTER 2 0.14 .13000 0.14 0.01 0.01 5 0.13 0.13 0.14 0.14 0. 22 FALL 7 0.08 .02500 0.13 0.04 0.02 57 0.03 0.03 0.08 0.11 0. 22 SPRING 8 0.08 .01000 0.28 0.10 0.04 126 0.01 0.02 0.03 0.13 0. 22 SUMMER 11 0.08 .00000 0.36 0.11 0.03 147 0.00 0.01 0.04 0.09 0. 22 WINTER 2 0.17 .14000 0.20 0.04 0.03 25 0.14 0.14 0.17 0.20 0. 24 FALL 2 0.04 .01750 0.06 0.03 0.02 78 0.02 0.02 0.04 0.06 0. 24 SPRING 16 0.78 .01000 3.68 1.24 0.31 160 0.01 0.01 0.03 1.23 3. 24 SUMMER 8 0.46 .01000 3.20 1.11 0.39 243 0.01 0.02 0.06 0.15 3. 24 WINTER 5 0.27 .01000 1.31 0.58 0.26 210 0.01 0.01 0.01 0.04 1. 80 FALL 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 SPRING 1 0.02 .02000 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 SUMMER 3 0.00 .00100 0.01 0.00 0.00 79 0.00 0.00 0.01 0.01 0. 80 WINTER 1 0.03 .03000 0.03 . . . 0.03 0.03 0.03 0.03 0. 81 FALL 1 0.02 .01750 0.02 . . . 0.02 0.02 0.02 0.02 0.

Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1999 Nitrogen_Tot_Kjeldhal_mg_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 FALL 1 0.45 .45000 0.45 . . . 0.45 0.45 0.45 0.45 0. 6 SPRING 4 0.40 .20000 0.60 0.23 0.12 58 0.20 0.20 0.40 0.60 0. 6 SUMMER 1 0.45 .45000 0.45 . . . 0.45 0.45 0.45 0.45 0. 6 WINTER 1 1.95 1.9500 1.95 . . . 1.95 1.95 1.95 1.95 1. 10 FALL 8 0.83 .39000 1.34 0.32 0.11 39 0.39 0.66 0.72 1.10 1. 10 SPRING 9 0.68 .25000 1.15 0.24 0.08 35 0.25 0.63 0.69 0.70 1. 10 SUMMER 13 0.83 .23500 1.68 0.39 0.11 47 0.24 0.58 0.82 0.97 1. 10 WINTER 7 0.70 .43000 1.16 0.26 0.10 37 0.43 0.51 0.64 0.93 1. 12 FALL 2 0.26 .00000 0.52 0.37 0.26 141 0.00 0.00 0.26 0.52 0. 12 SPRING 2 0.28 .00000 0.56 0.40 0.28 141 0.00 0.00 0.28 0.56 0. 12 SUMMER 9 0.29 .00000 0.45 0.16 0.05 54 0.00 0.17 0.36 0.42 0. 12 WINTER 2 0.33 .00000 0.66 0.46 0.33 141 0.00 0.00 0.33 0.66 0. 13 FALL 20 0.64 .07250 2.23 0.50 0.11 78 0.11 0.29 0.55 0.85 1. 13 SPRING 32 0.54 .02500 2.90 0.63 0.11 118 0.03 0.20 0.35 0.60 2. 13 SUMMER 42 0.71 .07000 3.19 0.61 0.09 85 0.18 0.39 0.57 0.90 1. 13 WINTER 9 1.12 .34000 2.48 0.82 0.27 73 0.34 0.48 0.90 1.40 2. 18 FALL 2 0.30 .30000 0.30 0.00 0.00 0 0.30 0.30 0.30 0.30 0. 18 SPRING 1 0.38 .38000 0.38 . . . 0.38 0.38 0.38 0.38 0. 18 SUMMER 5 0.47 .32500 0.70 0.17 0.08 36 0.33 0.33 0.40 0.60 0. 20 FALL 17 0.70 .02500 2.96 0.67 0.16 96 0.03 0.33 0.50 0.90 2. 20 SPRING 24 0.39 .02500 3.19 0.65 0.13 168 0.03 0.08 0.18 0.47 0. 20 SUMMER 26 0.42 .02500 2.83 0.54 0.11 127 0.06 0.19 0.30 0.45 0. 20 WINTER 4 0.30 .06250 0.54 0.23 0.12 78 0.06 0.10 0.30 0.49 0. 22 FALL 7 0.47 .18000 1.02 0.35 0.13 75 0.18 0.19 0.39 0.90 1. 22 SPRING 8 0.58 .02500 1.68 0.63 0.22 109 0.03 0.13 0.36 0.99 1. 22 SUMMER 12 0.72 .02500 2.20 0.59 0.17 81 0.03 0.32 0.63 0.95 2. 22 WINTER 2 0.22 .22000 0.22 0.00 0.00 0 0.22 0.22 0.22 0.22 0. 24 FALL 4 0.63 .22500 1.40 0.53 0.26 83 0.23 0.31 0.45 0.95 1. 24 SPRING 12 1.32 .41000 3.51 0.96 0.28 72 0.41 0.54 1.00 1.75 3. 24 SUMMER 10 0.66 .24000 1.20 0.34 0.11 52 0.24 0.38 0.59 0.89 1. 24 WINTER 5 0.41 .29000 0.74 0.18 0.08 44 0.29 0.34 0.35 0.36 0. 80 FALL 1 0.11 .11250 0.11 . . . 0.11 0.11 0.11 0.11 0. 80 SPRING 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 80 SUMMER 4 0.46 .27500 0.70 0.20 0.10 44 0.28 0.29 0.43 0.62 0. Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1999 Nitrogen_Tot_Kjeldhal_mg_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 80 WINTER 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 81 FALL 1 0.50 .50000 0.50 . . . 0.50 0.50 0.50 0.50 0.

 Data were not always available for all years. 
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1998 SECCHI_m subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 FALL 2 1.38 .75000 2.00 0.88 0.63 64 0.75 0.75 1.38 2.00 2. 6 SPRING 2 1.47 1.0775 1.86 0.55 0.39 37 1.08 1.08 1.47 1.86 1. 6 SUMMER 2 1.18 .94000 1.42 0.34 0.24 29 0.94 0.94 1.18 1.42 1. 10 FALL 4 1.94 1.5250 2.30 0.33 0.17 17 1.53 1.69 1.96 2.19 2. 10 SPRING 4 1.52 1.1250 2.40 0.60 0.30 40 1.13 1.14 1.28 1.90 2. 10 SUMMER 7 1.45 .10000 2.50 0.71 0.27 49 0.10 1.35 1.50 1.80 2. 10 WINTER 3 2.31 2.0000 2.63 0.31 0.18 14 2.00 2.00 2.30 2.63 2. 12 SUMMER 15 1.98 .50000 4.60 1.30 0.34 66 0.50 1.13 1.50 2.20 4. 13 FALL 19 1.37 .17500 7.00 1.68 0.39 122 0.18 0.30 0.83 2.20 7. 13 SPRING 23 1.38 .10000 4.30 1.41 0.29 102 0.10 0.23 0.60 2.88 4. 13 SUMMER 36 1.57 .02500 5.50 1.36 0.23 87 0.20 0.33 1.28 2.36 4. 13 WINTER 5 0.98 .50000 1.70 0.48 0.21 49 0.50 0.60 1.00 1.10 1. 18 FALL 5 2.55 1.1049 4.50 1.54 0.69 61 1.10 1.45 1.78 3.90 4. 18 SPRING 2 2.30 1.6000 3.00 0.99 0.70 43 1.60 1.60 2.30 3.00 3. 18 SUMMER 9 2.57 .68580 5.70 1.66 0.55 65 0.69 1.50 2.35 3.00 5. 20 FALL 18 3.10 1.4000 5.20 1.16 0.27 37 1.40 2.30 2.73 3.90 5. 20 SPRING 19 2.58 .96000 4.03 0.93 0.21 36 0.96 1.90 2.55 3.20 4. 20 SUMMER 33 2.75 .90000 7.80 1.42 0.25 52 0.90 2.10 2.40 3.15 5. 20 WINTER 2 2.64 2.1000 3.18 0.76 0.54 29 2.10 2.10 2.64 3.18 3. 22 FALL 7 2.22 .75000 4.28 1.30 0.49 59 0.75 0.85 2.10 3.23 4. 22 SPRING 5 2.04 .80000 4.00 1.27 0.57 62 0.80 1.10 1.85 2.43 4. 22 SUMMER 8 1.88 .15000 3.80 1.34 0.47 71 0.15 0.75 1.85 2.95 3. 24 FALL 4 1.26 .54000 2.67 1.00 0.50 79 0.54 0.55 0.93 1.98 2. 24 SPRING 10 0.86 .20000 2.84 0.81 0.26 95 0.20 0.30 0.73 1.00 2. 24 SUMMER 5 1.02 .20000 3.00 1.14 0.51 112 0.20 0.33 0.74 0.83 3. 24 WINTER 2 2.20 .81000 3.59 1.96 1.39 89 0.81 0.81 2.20 3.59 3. 80 FALL 1 2.90 2.9000 2.90 . . . 2.90 2.90 2.90 2.90 2. 80 SUMMER 6 2.15 .50000 4.60 1.39 0.57 65 0.50 1.50 1.80 2.70 4. 81 FALL 1 1.76 1.7563 1.76 . . . 1.76 1.76 1.76 1.76 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: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1998 Total_Nitrogen_mg_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 10 FALL 3 0.28 .26500 0.29 0.01 0.01 5 0.27 0.27 0.28 0.29 0. 10 SPRING 3 0.49 .46000 0.52 0.03 0.02 6 0.46 0.46 0.51 0.52 0. 10 SUMMER 3 0.27 .27000 0.28 0.00 0.00 1 0.27 0.27 0.27 0.28 0. 10 WINTER 3 0.47 .45250 0.48 0.01 0.01 3 0.45 0.45 0.47 0.48 0. 13 FALL 7 0.89 .18000 2.28 0.70 0.26 78 0.18 0.32 0.81 1.18 2. 13 SPRING 4 1.20 .52000 2.72 1.04 0.52 86 0.52 0.53 0.79 1.88 2. 13 SUMMER 7 1.16 .47000 2.42 0.78 0.29 67 0.47 0.48 0.69 1.93 2. 13 WINTER 3 1.20 .60000 2.32 0.97 0.56 81 0.60 0.60 0.68 2.32 2. 22 FALL 7 0.56 .29000 1.07 0.33 0.13 59 0.29 0.30 0.46 1.00 1. 22 SPRING 8 0.71 .16500 1.96 0.65 0.23 92 0.17 0.29 0.48 1.02 1. 22 SUMMER 9 0.73 .15500 2.41 0.69 0.23 94 0.16 0.32 0.65 0.71 2. 22 WINTER 2 0.39 .36000 0.42 0.04 0.03 11 0.36 0.36 0.39 0.42 0. 24 FALL 2 0.42 .28125 0.56 0.20 0.14 47 0.28 0.28 0.42 0.56 0. 24 SPRING 11 1.55 .45000 4.33 1.31 0.40 85 0.45 0.57 0.89 1.90 4. 24 SUMMER 5 0.97 .80000 1.30 0.20 0.09 20 0.80 0.84 0.93 0.99 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: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1999 Total_Phosphorus_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 FALL 5 316.00 75.000 495.00 186 83.1 59 75.0 160 420 430 4 6 SPRING 7 97.86 30.000 165.00 60.5 22.9 62 30.0 30.0 120 150 1 6 SUMMER 6 199.58 35.000 357.50 103 41.9 51 35.0 185 200 220 3 6 WINTER 4 216.25 190.00 260.00 32.0 16.0 15 190 193 208 240 2 10 FALL 11 93.48 30.000 260.00 77.7 23.4 83 30.0 35.5 55.0 132 2 10 SPRING 12 66.71 40.000 150.00 31.5 9.09 47 40.0 41.5 60.3 79.3 1 10 SUMMER 17 104.43 26.750 410.00 105 25.5 101 26.8 35.0 62.5 95.0 4 10 WINTER 10 77.30 30.000 156.00 44.4 14.0 57 30.0 32.8 78.5 114 1 12 FALL 2 85.00 20.000 150.00 91.9 65.0 108 20.0 20.0 85.0 150 1 12 SPRING 2 82.50 15.000 150.00 95.5 67.5 116 15.0 15.0 82.5 150 1 12 SUMMER 18 85.14 .00000 260.00 80.2 18.9 94 0.00 20.0 62.5 165 2 12 WINTER 2 91.25 27.500 155.00 90.2 63.8 99 27.5 27.5 91.3 155 1 13 FALL 26 153.49 15.000 755.00 182 35.8 119 15.0 35.0 88.8 185 6 13 SPRING 33 81.44 2.5000 730.00 140 24.4 172 6.25 20.0 42.5 70.0 4 13 SUMMER 49 85.43 6.2500 690.00 140 20.0 164 6.25 25.0 30.0 80.0 4 13 WINTER 10 213.50 40.000 800.00 263 83.3 123 40.0 60.0 90.0 220 8 18 FALL 6 30.00 10.000 100.00 34.5 14.1 115 10.0 12.5 18.8 20.0 1 18 SPRING 3 9.58 2.5000 20.00 9.21 5.32 96 2.50 2.50 6.25 20.0 20 18 SUMMER 11 192.50 10.000 1200.00 384 116 199 10.0 10.0 20.0 110 12 20 FALL 25 40.63 2.5000 390.00 82.8 16.6 204 2.50 4.38 10.0 32.5 1 20 SPRING 24 41.70 1.5000 265.00 58.9 12.0 141 2.50 9.06 23.8 42.5 1 20 SUMMER 38 15.57 .00000 75.00 18.6 3.01 119 0.00 2.50 10.0 15.0 62 20 WINTER 6 6.88 2.5000 10.00 3.69 1.51 54 2.50 2.50 8.13 10.0 10 22 FALL 10 36.00 .00000 135.00 41.5 13.1 115 0.00 10.0 20.0 60.0 1 22 SPRING 6 43.96 2.5000 135.00 58.5 23.9 133 2.50 2.50 11.9 100 1 22 SUMMER 15 57.50 2.5000 200.00 51.1 13.2 89 2.50 20.0 45.0 70.0 2 22 WINTER 2 30.00 30.000 30.00 0.00 0.00 0 30.0 30.0 30.0 30.0 30 24 FALL 4 22.81 10.000 50.00 18.7 9.33 82 10.0 10.6 15.6 35.0 50 24 SPRING 16 283.79 15.625 1630.00 467 117 164 15.6 25.0 55.0 260 16 24 SUMMER 9 31.53 11.250 65.00 19.0 6.33 60 11.3 20.0 20.0 35.0 65 24 WINTER 6 43.33 20.000 70.00 16.0 6.54 37 20.0 40.0 42.5 45.0 70 80 FALL 1 82.50 82.500 82.50 . . . 82.5 82.5 82.5 82.5 82 80 SPRING 1 90.00 90.000 90.00 . . . 90.0 90.0 90.0 90.0 90 80 SUMMER 7 83.21 20.000 140.00 42.0 15.9 50 20.0 52.5 80.0 130 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: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1990 to 1999 Total_Phosphorus_ug_L subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 80 WINTER 1 90.00 90.000 90.00 . . . 90.0 90.0 90.0 90.0 90 81 FALL 1 20.00 20.000 20.00 . . . 20.0 20.0 20.0 20.0 20

Data were not always available for all years.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Decade and Season from 1991 to 1999 pH_S_U subecoregion season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 10 FALL 8 8.42 8.0000 9.05 0.34 0.12 4 8.00 8.19 8.38 8.58 9. 10 SPRING 8 8.38 8.1000 8.70 0.20 0.07 2 8.10 8.25 8.34 8.53 8. 10 SUMMER 9 8.39 7.2750 9.30 0.65 0.22 8 7.28 8.03 8.30 8.80 9. 10 WINTER 8 8.19 8.0250 8.60 0.19 0.07 2 8.03 8.08 8.10 8.28 8. 12 FALL 2 8.18 8.1700 8.18 0.01 0.00 0 8.17 8.17 8.18 8.18 8. 12 SPRING 2 8.04 7.9400 8.13 0.13 0.10 2 7.94 7.94 8.04 8.13 8. 12 SUMMER 11 8.33 7.8350 9.48 0.45 0.14 5 7.84 8.08 8.18 8.50 9. 12 WINTER 2 8.13 8.0675 8.18 0.08 0.06 1 8.07 8.07 8.13 8.18 8. 13 SUMMER 4 8.32 8.2400 8.51 0.13 0.06 2 8.24 8.24 8.27 8.41 8. 18 SUMMER 2 7.61 7.3150 7.91 0.42 0.30 6 7.32 7.32 7.61 7.91 7. 20 SUMMER 2 8.25 8.1050 8.40 0.21 0.15 3 8.11 8.11 8.25 8.40 8. 22 SUMMER 2 8.22 8.0500 8.39 0.24 0.17 3 8.05 8.05 8.22 8.39 8. 80 SUMMER 3 7.22 6.3000 7.88 0.82 0.47 11 6.30 6.30 7.48 7.88 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: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Chloro_A_Fluor_cor_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 1996 FALL 1 2.80 2.8000 2.80 . . . 2.80 2.80 2.80 2.80 2. 6 1996 WINTER 1 4.50 4.5000 4.50 . . . 4.50 4.50 4.50 4.50 4. 6 1997 FALL 1 46.50 46.500 46.50 . . . 46.50 46.50 46.50 46.50 46. 6 1997 SUMMER 1 32.00 32.000 32.00 . . . 32.00 32.00 32.00 32.00 32. 10 1994 FALL 3 5.88 4.6000 7.45 1.45 0.83 25 4.60 4.60 5.60 7.45 7. 10 1994 SPRING 3 7.23 5.3500 10.55 2.88 1.66 40 5.35 5.35 5.80 10.55 10. 10 1994 SUMMER 3 2.85 2.3000 3.35 0.53 0.30 18 2.30 2.30 2.90 3.35 3. 10 1995 FALL 3 8.07 7.1000 8.70 0.85 0.49 11 7.10 7.10 8.40 8.70 8. 10 1995 SPRING 3 5.53 5.3000 5.80 0.25 0.15 5 5.30 5.30 5.50 5.80 5. 10 1995 SUMMER 3 1.70 1.5000 1.80 0.17 0.10 10 1.50 1.50 1.80 1.80 1. 10 1995 WINTER 3 2.42 1.4500 3.20 0.89 0.51 37 1.45 1.45 2.60 3.20 3. 10 1998 SUMMER 1 0.90 .90000 0.90 . . . 0.90 0.90 0.90 0.90 0. 12 1997 SUMMER 3 28.20 20.600 40.50 10.75 6.21 38 20.60 20.60 23.50 40.50 40. 12 1998 SUMMER 8 14.94 1.2000 47.60 16.91 5.98 113 1.20 2.25 7.35 25.75 47. 13 1997 SUMMER 3 2.40 1.7000 3.40 0.89 0.51 37 1.70 1.70 2.10 3.40 3. 13 1998 SUMMER 1 5.50 5.5000 5.50 . . . 5.50 5.50 5.50 5.50 5. 18 1997 SUMMER 1 5.30 5.3000 5.30 . . . 5.30 5.30 5.30 5.30 5. 18 1998 SUMMER 1 4.00 4.0000 4.00 . . . 4.00 4.00 4.00 4.00 4. 20 1999 SUMMER 2 1.50 .00000 3.00 2.12 1.50 141 0.00 0.00 1.50 3.00 3. 22 1999 SUMMER 1 2.50 2.5000 2.50 . . . 2.50 2.50 2.50 2.50 2. 80 1990 SPRING 1 6.80 6.8000 6.80 . . . 6.80 6.80 6.80 6.80 6. 80 1990 SUMMER 1 2.15 2.1500 2.15 . . . 2.15 2.15 2.15 2.15 2. 80 1991 SUMMER 2 3.55 .70000 6.40 4.03 2.85 114 0.70 0.70 3.55 6.40 6. 80 1992 FALL 1 1.90 1.9000 1.90 . . . 1.90 1.90 1.90 1.90 1. 80 1992 SUMMER 2 4.05 2.8000 5.30 1.77 1.25 44 2.80 2.80 4.05 5.30 5. 80 1993 FALL 1 3.60 3.6000 3.60 . . . 3.60 3.60 3.60 3.60 3. 80 1993 SUMMER 1 4.40 4.4000 4.40 . . . 4.40 4.40 4.40 4.40 4. 80 1994 FALL 1 28.00 28.000 28.00 . . . 28.00 28.00 28.00 28.00 28. 80 1994 SPRING 1 4.40 4.4000 4.40 . . . 4.40 4.40 4.40 4.40 4. 80 1995 FALL 1 10.00 10.000 10.00 . . . 10.00 10.00 10.00 10.00 10. 80 1995 SPRING 1 2.40 2.4000 2.40 . . . 2.40 2.40 2.40 2.40 2. 80 1995 SUMMER 1 7.10 7.1000 7.10 . . . 7.10 7.10 7.10 7.10 7.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Chloro_A_Fluor_cor_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 80 1996 FALL 1 3.90 3.9000 3.90 . . . 3.90 3.90 3.90 3.90 3. 80 1996 SPRING 1 4.70 4.7000 4.70 . . . 4.70 4.70 4.70 4.70 4. 80 1996 SUMMER 1 23.00 23.000 23.00 . . . 23.00 23.00 23.00 23.00 23. 80 1997 FALL 1 6.60 6.6000 6.60 . . . 6.60 6.60 6.60 6.60 6. 80 1997 SPRING 1 3.60 3.6000 3.60 . . . 3.60 3.60 3.60 3.60 3. 80 1997 SUMMER 2 4.30 3.4000 5.20 1.27 0.90 30 3.40 3.40 4.30 5.20 5. 80 1998 SUMMER 1 3.80 3.8000 3.80 . . . 3.80 3.80 3.80 3.80 3.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1997 Chloro_A_Phyto_Spec_A_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  13 1990 FALL 5 25.32 3.0000 83.40 33.56 15.01 133 3.00 6.60 8.50 25.10 83 13 1990 SPRING 4 3.28 2.6000 3.80 0.54 0.27 16 2.60 2.85 3.35 3.70 3 13 1990 SUMMER 21 11.53 1.8000 45.50 13.63 2.97 118 2.00 4.00 5.50 12.50 43 13 1991 FALL 1 9.40 9.4000 9.40 . . . 9.40 9.40 9.40 9.40 9 13 1991 SPRING 6 14.60 2.1000 23.70 9.84 4.02 67 2.10 2.75 18.38 22.30 23 13 1991 SUMMER 6 43.30 9.3500 94.20 31.50 12.86 73 9.35 19.05 37.35 62.50 94 13 1991 WINTER 2 29.90 29.900 29.90 0.00 0.00 0 29.90 29.90 29.90 29.90 29 13 1992 FALL 11 11.11 2.6000 41.35 10.97 3.31 99 2.60 4.80 7.45 13.30 41 13 1992 SPRING 16 4.88 .80000 19.00 4.80 1.20 98 0.80 1.75 2.90 6.98 19 13 1992 SUMMER 7 11.03 1.2500 41.55 13.96 5.28 127 1.25 3.50 5.10 12.00 41 13 1992 WINTER 2 7.65 2.8000 12.50 6.86 4.85 90 2.80 2.80 7.65 12.50 12 13 1993 FALL 3 2.50 1.7000 3.00 0.70 0.40 28 1.70 1.70 2.80 3.00 3 13 1993 SPRING 1 0.80 .80000 0.80 . . . 0.80 0.80 0.80 0.80 0 13 1993 SUMMER 6 11.12 .90000 27.35 10.13 4.14 91 0.90 4.65 7.15 19.50 27 13 1994 FALL 1 23.60 23.600 23.60 . . . 23.60 23.60 23.60 23.60 23 13 1994 SPRING 1 6.00 6.0000 6.00 . . . 6.00 6.00 6.00 6.00 6 13 1994 SUMMER 21 11.42 1.6500 52.60 13.97 3.05 122 1.70 2.15 4.20 18.80 37 13 1994 WINTER 1 8.40 8.4000 8.40 . . . 8.40 8.40 8.40 8.40 8 13 1995 FALL 4 8.85 2.4000 15.70 6.82 3.41 77 2.40 3.00 8.65 14.70 15 13 1995 SPRING 1 12.35 12.350 12.35 . . . 12.35 12.35 12.35 12.35 12 13 1995 SUMMER 8 8.58 3.5000 16.30 4.59 1.62 54 3.50 5.43 7.23 11.75 16 13 1995 WINTER 1 27.20 27.200 27.20 . . . 27.20 27.20 27.20 27.20 27 13 1996 FALL 8 9.44 1.9000 26.50 7.82 2.77 83 1.90 4.80 6.50 12.28 26 13 1996 SUMMER 20 4.88 1.1500 37.70 8.06 1.80 165 1.23 1.60 2.53 3.40 23 18 1991 SUMMER 3 5.92 1.4000 8.30 3.91 2.26 66 1.40 1.40 8.05 8.30 8 18 1992 SPRING 1 2.10 2.1000 2.10 . . . 2.10 2.10 2.10 2.10 2 18 1993 SUMMER 4 3.91 1.0000 7.40 2.72 1.36 69 1.00 1.90 3.63 5.93 7 18 1994 SUMMER 1 1.50 1.5000 1.50 . . . 1.50 1.50 1.50 1.50 1 18 1995 FALL 2 6.13 2.4000 9.85 5.27 3.73 86 2.40 2.40 6.13 9.85 9 18 1995 SPRING 2 1.35 .30000 2.40 1.48 1.05 110 0.30 0.30 1.35 2.40 2 18 1995 SUMMER 4 2.04 .85000 3.85 1.41 0.70 69 0.85 0.93 1.73 3.15 3 18 1996 SUMMER 3 1.48 .60000 2.55 0.99 0.57 67 0.60 0.60 1.30 2.55 2
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1997 Chloro_A_Phyto_Spec_A_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  20 1990 FALL 2 17.18 13.050 21.30 5.83 4.13 34 13.05 13.05 17.18 21.30 21 20 1990 SPRING 3 3.72 1.9000 4.95 1.61 0.93 43 1.90 1.90 4.30 4.95 4 20 1990 SUMMER 10 3.20 1.2000 8.10 2.30 0.73 72 1.20 1.90 2.13 5.20 8 20 1991 FALL 3 2.90 .40000 6.10 2.91 1.68 100 0.40 0.40 2.20 6.10 6 20 1991 SPRING 9 2.68 1.5000 4.85 1.14 0.38 43 1.50 2.00 2.10 3.00 4 20 1991 SUMMER 14 2.44 .90000 5.65 1.18 0.32 48 0.90 1.70 2.45 2.70 5 20 1991 WINTER 1 1.65 1.6500 1.65 . . . 1.65 1.65 1.65 1.65 1 20 1992 FALL 7 3.17 .20000 8.00 2.74 1.03 86 0.20 1.00 2.10 5.20 8 20 1992 SPRING 7 2.44 .30000 7.30 2.55 0.97 105 0.30 0.55 1.25 4.50 7 20 1992 SUMMER 6 1.98 .70000 2.80 0.86 0.35 43 0.70 1.20 2.30 2.60 2 20 1993 FALL 6 1.18 .30000 3.10 1.24 0.51 106 0.30 0.30 0.48 2.40 3 20 1993 SPRING 3 1.55 1.0000 1.90 0.48 0.28 31 1.00 1.00 1.75 1.90 1 20 1993 SUMMER 14 2.25 .00000 6.90 2.05 0.55 91 0.00 0.70 1.53 4.10 6 20 1994 FALL 7 10.31 1.3000 40.70 14.30 5.41 139 1.30 1.40 5.40 15.65 40 20 1994 SUMMER 11 5.91 .70000 42.20 12.10 3.65 205 0.70 1.10 2.50 3.20 42 20 1995 FALL 12 3.07 .90000 7.50 2.02 0.58 66 0.90 1.78 2.23 4.45 7 20 1995 SPRING 2 1.75 1.1000 2.40 0.92 0.65 53 1.10 1.10 1.75 2.40 2 20 1995 SUMMER 20 5.90 .50000 58.30 12.58 2.81 213 0.70 1.38 2.50 4.80 34 20 1995 WINTER 1 1.20 1.2000 1.20 . . . 1.20 1.20 1.20 1.20 1 20 1996 FALL 4 1.38 1.1000 1.60 0.21 0.10 15 1.10 1.25 1.40 1.50 1 20 1996 SPRING 3 1.83 .50000 3.40 1.46 0.85 80 0.50 0.50 1.60 3.40 3 20 1996 SUMMER 8 6.59 .85000 33.80 11.37 4.02 173 0.85 1.15 1.93 5.95 33 20 1996 WINTER 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0 22 1990 FALL 1 3.15 3.1500 3.15 . . . 3.15 3.15 3.15 3.15 3 22 1990 SPRING 1 2.73 2.7300 2.73 . . . 2.73 2.73 2.73 2.73 2 22 1990 SUMMER 1 11.45 11.450 11.45 . . . 11.45 11.45 11.45 11.45 11 22 1991 FALL 2 2.54 .72000 4.36 2.57 1.82 101 0.72 0.72 2.54 4.36 4 22 1991 SPRING 2 2.11 1.2150 3.00 1.26 0.89 60 1.22 1.22 2.11 3.00 3 22 1991 SUMMER 2 4.05 1.1450 6.96 4.11 2.91 101 1.15 1.15 4.05 6.96 6 22 1993 SUMMER 1 5.42 5.4200 5.42 . . . 5.42 5.42 5.42 5.42 5 22 1995 FALL 1 2.33 2.3300 2.33 . . . 2.33 2.33 2.33 2.33 2 22 1995 SPRING 1 2.71 2.7100 2.71 . . . 2.71 2.71 2.71 2.71 2
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1997 Chloro_A_Phyto_Spec_A_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 22 1995 SUMMER 1 2.83 2.8250 2.83 . . . 2.83 2.83 2.83 2.83 2. 24 1990 FALL 3 14.10 9.4400 22.00 6.88 3.97 49 9.44 9.44 10.87 22.00 22. 24 1990 SPRING 2 43.83 38.690 48.97 7.27 5.14 17 38.69 38.69 43.83 48.97 48. 24 1990 SUMMER 3 13.71 2.5000 23.30 10.49 6.06 77 2.50 2.50 15.32 23.30 23. 24 1991 SPRING 1 0.63 .62500 0.63 . . . 0.63 0.63 0.63 0.63 0. 24 1991 SUMMER 2 7.25 1.0000 13.50 8.84 6.25 122 1.00 1.00 7.25 13.50 13. 24 1992 FALL 1 0.25 .25000 0.25 . . . 0.25 0.25 0.25 0.25 0. 24 1992 SPRING 4 1.74 .25000 4.67 1.99 1.00 115 0.25 0.54 1.02 2.94 4. 24 1992 SUMMER 2 11.13 .25000 22.00 15.38 10.88 138 0.25 0.25 11.13 22.00 22. 24 1992 WINTER 1 17.00 17.000 17.00 . . . 17.00 17.00 17.00 17.00 17. 24 1993 FALL 1 0.25 .25000 0.25 . . . 0.25 0.25 0.25 0.25 0. 24 1993 SPRING 3 8.91 1.9600 21.00 10.51 6.07 118 1.96 1.96 3.78 21.00 21. 24 1993 SUMMER 2 17.70 2.5000 32.90 21.50 15.20 121 2.50 2.50 17.70 32.90 32. 24 1993 WINTER 1 22.51 22.510 22.51 . . . 22.51 22.51 22.51 22.51 22. 24 1994 SPRING 1 14.39 14.390 14.39 . . . 14.39 14.39 14.39 14.39 14. 24 1995 SUMMER 4 41.26 .79000 155.80 76.39 38.20 185 0.79 1.56 4.23 80.97 155. 24 1995 WINTER 1 3.50 3.5000 3.50 . . . 3.50 3.50 3.50 3.50 3. 24 1996 SPRING 1 0.25 .25000 0.25 . . . 0.25 0.25 0.25 0.25 0. 24 1996 SUMMER 1 15.40 15.400 15.40 . . . 15.40 15.40 15.40 15.40 15. 24 1997 FALL 1 9.27 9.2650 9.27 . . . 9.27 9.27 9.27 9.27 9. 24 1997 SPRING 1 4.64 4.6350 4.64 . . . 4.64 4.64 4.64 4.64 4. 24 1997 SUMMER 1 7.26 7.2600 7.26 . . . 7.26 7.26 7.26 7.26 7.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1997 Chloro_A_Trich_unco_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 10 1993 SUMMER 2 38.50 11.000 66.00 38.89 27.50 101 11.00 11.00 38.50 66.00 66. 10 1996 SUMMER 1 131.00 131.00 131.00 . . . 131.00 131.00 131.00 131.00 131. 10 1997 SUMMER 1 1.00 1.0000 1.00 . . . 1.00 1.00 1.00 1.00 1. 12 1990 SUMMER 4 41.94 1.0600 130.00 59.54 29.77 142 1.06 6.23 18.35 77.65 130. 12 1991 SUMMER 3 8.15 4.7000 14.70 5.68 3.28 70 4.70 4.70 5.05 14.70 14. 12 1992 SUMMER 2 11.15 8.0000 14.30 4.45 3.15 40 8.00 8.00 11.15 14.30 14. 12 1993 SUMMER 2 2.40 .80000 4.00 2.26 1.60 94 0.80 0.80 2.40 4.00 4. 12 1994 SUMMER 3 26.05 2.8000 57.55 28.29 16.33 109 2.80 2.80 17.80 57.55 57. 12 1995 SUMMER 2 11.25 7.2000 15.30 5.73 4.05 51 7.20 7.20 11.25 15.30 15. 12 1996 SUMMER 4 9.41 2.4000 13.50 4.85 2.43 52 2.40 6.40 10.88 12.43 13. 12 1997 SUMMER 4 25.64 12.200 52.20 18.22 9.11 71 12.20 13.93 19.08 37.35 52. 22 1990 FALL 1 3.43 3.4300 3.43 . . . 3.43 3.43 3.43 3.43 3. 22 1990 SPRING 1 2.65 2.6450 2.65 . . . 2.65 2.65 2.65 2.65 2. 22 1990 SUMMER 1 9.18 9.1750 9.18 . . . 9.18 9.18 9.18 9.18 9. 22 1991 FALL 2 2.59 .74000 4.44 2.61 1.85 101 0.74 0.74 2.59 4.44 4. 22 1991 SPRING 2 2.10 1.2350 2.97 1.23 0.87 58 1.24 1.24 2.10 2.97 2. 22 1991 SUMMER 2 4.26 1.3500 7.17 4.11 2.91 97 1.35 1.35 4.26 7.17 7. 22 1993 SUMMER 1 5.48 5.4800 5.48 . . . 5.48 5.48 5.48 5.48 5. 22 1995 FALL 2 2.33 .40000 4.25 2.72 1.93 117 0.40 0.40 2.33 4.25 4. 22 1995 SPRING 1 2.74 2.7400 2.74 . . . 2.74 2.74 2.74 2.74 2. 22 1995 SUMMER 1 2.94 2.9350 2.94 . . . 2.94 2.94 2.94 2.94 2. 24 1990 FALL 2 10.65 10.145 11.15 0.71 0.50 7 10.15 10.15 10.65 11.15 11. 24 1990 SPRING 2 47.04 42.080 51.99 7.01 4.95 15 42.08 42.08 47.04 51.99 51. 24 1990 SUMMER 2 21.66 17.020 26.30 6.56 4.64 30 17.02 17.02 21.66 26.30 26. 24 1992 SPRING 3 2.35 .95000 4.69 2.04 1.18 87 0.95 0.95 1.42 4.69 4. 24 1993 SPRING 2 3.34 2.7600 3.92 0.82 0.58 25 2.76 2.76 3.34 3.92 3. 24 1995 SUMMER 2 1.66 .95000 2.37 1.00 0.71 60 0.95 0.95 1.66 2.37 2. 24 1997 FALL 1 10.32 10.315 10.32 . . . 10.32 10.32 10.32 10.32 10. 24 1997 SPRING 1 6.91 6.9050 6.91 . . . 6.91 6.91 6.91 6.91 6. 24 1997 SUMMER 1 8.14 8.1350 8.14 . . . 8.14 8.14 8.14 8.14 8. 80 1990 SUMMER 1 18.00 18.000 18.00 . . . 18.00 18.00 18.00 18.00 18. 80 1993 SUMMER 1 0.60 .60000 0.60 . . . 0.60 0.60 0.60 0.60 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1997 Chloro_A_Trich_unco_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 80 1995 SUMMER 2 32.30 3.1000 61.50 41.30 29.20 128 3.10 3.10 32.30 61.50 61. 80 1996 SUMMER 1 26.20 26.200 26.20 . . . 26.20 26.20 26.20 26.20 26.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1991 to 1999 DIP_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 10 1994 FALL 3 9.00 3.0000 17.00 7.21 4.16 80 3.00 3.00 7.00 17.00 17. 10 1994 SPRING 3 1.67 1.0000 3.00 1.15 0.67 69 1.00 1.00 1.00 3.00 3. 10 1994 SUMMER 3 4.33 3.0000 5.00 1.15 0.67 27 3.00 3.00 5.00 5.00 5. 10 1994 WINTER 3 12.67 11.500 13.50 1.04 0.60 8 11.50 11.50 13.00 13.50 13. 10 1995 FALL 2 2.00 2.0000 2.00 0.00 0.00 0 2.00 2.00 2.00 2.00 2. 10 1995 SPRING 3 11.50 10.000 14.00 2.18 1.26 19 10.00 10.00 10.50 14.00 14. 10 1995 SUMMER 3 5.33 4.0000 6.00 1.15 0.67 22 4.00 4.00 6.00 6.00 6. 10 1995 WINTER 3 18.00 13.500 24.50 5.77 3.33 32 13.50 13.50 16.00 24.50 24. 10 1998 FALL 5 62.00 2.0000 138.00 51.67 23.11 83 2.00 35.00 51.50 83.50 138. 10 1998 SUMMER 5 54.80 .00000 139.00 71.53 31.99 131 0.00 4.00 4.00 127.00 139. 10 1998 WINTER 3 74.00 40.000 122.00 42.76 24.68 58 40.00 40.00 60.00 122.00 122. 10 1999 SPRING 5 33.70 19.500 47.00 11.45 5.12 34 19.50 26.00 33.00 43.00 47. 10 1999 WINTER 4 58.88 22.000 88.00 31.31 15.66 53 22.00 33.00 62.75 84.75 88. 12 1991 FALL 2 65.00 20.000 110.00 63.64 45.00 98 20.00 20.00 65.00 110.00 110. 12 1991 SPRING 2 65.00 20.000 110.00 63.64 45.00 98 20.00 20.00 65.00 110.00 110. 12 1991 SUMMER 2 80.00 20.000 140.00 84.85 60.00 106 20.00 20.00 80.00 140.00 140. 12 1991 WINTER 2 67.50 20.000 115.00 67.18 47.50 100 20.00 20.00 67.50 115.00 115. 12 1992 WINTER 2 72.50 15.000 130.00 81.32 57.50 112 15.00 15.00 72.50 130.00 130.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 1990 FALL 1 4.05 4.0500 4.05 . . . 4.05 4.05 4.05 4.05 4. 6 1990 SPRING 3 9.07 7.0000 10.20 1.79 1.03 20 7.00 7.00 10.00 10.20 10. 6 1990 SUMMER 1 5.90 5.9000 5.90 . . . 5.90 5.90 5.90 5.90 5. 6 1991 FALL 1 6.40 6.4000 6.40 . . . 6.40 6.40 6.40 6.40 6. 6 1991 SPRING 1 7.60 7.6000 7.60 . . . 7.60 7.60 7.60 7.60 7. 6 1991 SUMMER 1 3.55 3.5500 3.55 . . . 3.55 3.55 3.55 3.55 3. 10 1990 FALL 3 8.47 5.5000 10.00 2.57 1.48 30 5.50 5.50 9.90 10.00 10. 10 1990 SPRING 3 10.70 8.3000 12.60 2.19 1.27 20 8.30 8.30 11.20 12.60 12. 10 1990 SUMMER 3 8.17 3.3000 13.50 5.12 2.95 63 3.30 3.30 7.70 13.50 13. 10 1991 FALL 2 10.50 10.400 10.60 0.14 0.10 1 10.40 10.40 10.50 10.60 10. 10 1991 SPRING 2 10.05 8.9000 11.20 1.63 1.15 16 8.90 8.90 10.05 11.20 11. 10 1991 SUMMER 2 7.85 6.6000 9.10 1.77 1.25 23 6.60 6.60 7.85 9.10 9. 10 1991 WINTER 1 12.20 12.200 12.20 . . . 12.20 12.20 12.20 12.20 12. 10 1992 FALL 2 9.85 8.6000 11.10 1.77 1.25 18 8.60 8.60 9.85 11.10 11. 10 1992 SPRING 2 8.88 8.3000 9.45 0.81 0.57 9 8.30 8.30 8.88 9.45 9. 10 1992 SUMMER 2 7.85 6.9000 8.80 1.34 0.95 17 6.90 6.90 7.85 8.80 8. 10 1992 WINTER 2 10.45 9.1000 11.80 1.91 1.35 18 9.10 9.10 10.45 11.80 11. 10 1993 FALL 1 6.00 6.0000 6.00 . . . 6.00 6.00 6.00 6.00 6. 10 1993 SPRING 2 9.15 9.0000 9.30 0.21 0.15 2 9.00 9.00 9.15 9.30 9. 10 1993 SUMMER 6 6.10 1.5000 9.60 2.75 1.12 45 1.50 5.30 6.20 7.80 9. 10 1993 WINTER 2 9.90 8.2000 11.60 2.40 1.70 24 8.20 8.20 9.90 11.60 11. 10 1994 FALL 4 6.93 .85000 9.60 4.08 2.04 59 0.85 4.60 8.63 9.25 9. 10 1994 SPRING 4 10.29 7.0000 11.95 2.23 1.11 22 7.00 9.03 11.10 11.55 11. 10 1994 SUMMER 4 9.66 9.0500 10.60 0.66 0.33 7 9.05 9.28 9.50 10.05 10. 10 1994 WINTER 3 11.23 10.500 11.70 0.64 0.37 6 10.50 10.50 11.50 11.70 11. 10 1995 FALL 4 8.81 8.0000 9.35 0.61 0.30 7 8.00 8.35 8.95 9.28 9. 10 1995 SPRING 4 11.23 9.9000 11.80 0.89 0.45 8 9.90 10.70 11.60 11.75 11. 10 1995 SUMMER 4 8.99 8.0000 9.50 0.69 0.34 8 8.00 8.53 9.23 9.45 9. 10 1995 WINTER 3 11.72 11.650 11.85 0.12 0.07 1 11.65 11.65 11.65 11.85 11. 10 1996 SUMMER 2 9.88 8.7500 11.00 1.59 1.13 16 8.75 8.75 9.88 11.00 11. 10 1997 SUMMER 1 6.00 6.0000 6.00 . . . 6.00 6.00 6.00 6.00 6. 10 1998 FALL 5 9.02 7.3500 10.90 1.27 0.57 14 7.35 8.70 9.05 9.10 10.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  10 1998 SPRING 2 8.35 8.2000 8.50 0.21 0.15 3 8.20 8.20 8.35 8.50 8 10 1998 SUMMER 7 7.89 3.4000 9.50 2.11 0.80 27 3.40 7.70 8.60 9.40 9 10 1998 WINTER 3 11.40 11.000 11.80 0.40 0.23 4 11.00 11.00 11.40 11.80 11 10 1999 SPRING 5 10.72 9.9600 11.32 0.57 0.25 5 9.96 10.48 10.59 11.25 11 10 1999 WINTER 4 13.18 12.660 13.85 0.49 0.25 4 12.66 12.86 13.11 13.51 13 12 1990 SUMMER 5 8.32 6.7000 9.50 1.28 0.57 15 6.70 7.20 9.00 9.20 9 12 1991 FALL 2 7.65 6.7000 8.60 1.34 0.95 18 6.70 6.70 7.65 8.60 8 12 1991 SPRING 2 8.20 7.8000 8.60 0.57 0.40 7 7.80 7.80 8.20 8.60 8 12 1991 SUMMER 6 6.72 4.7000 8.40 1.34 0.55 20 4.70 5.85 6.78 7.80 8 12 1991 WINTER 2 8.55 8.1000 9.00 0.64 0.45 7 8.10 8.10 8.55 9.00 9 12 1992 SUMMER 3 7.87 5.0500 10.10 2.58 1.49 33 5.05 5.05 8.45 10.10 10 12 1992 WINTER 2 9.00 8.6000 9.40 0.57 0.40 6 8.60 8.60 9.00 9.40 9 12 1993 SUMMER 2 7.48 6.8500 8.10 0.88 0.62 12 6.85 6.85 7.48 8.10 8 12 1994 SUMMER 4 6.31 5.4000 7.60 1.08 0.54 17 5.40 5.43 6.13 7.20 7 12 1995 SUMMER 3 7.23 5.4500 8.60 1.62 0.93 22 5.45 5.45 7.65 8.60 8 12 1996 SUMMER 5 6.91 4.5000 8.20 1.45 0.65 21 4.50 6.75 7.40 7.70 8 12 1997 SUMMER 5 6.52 4.0000 8.10 1.80 0.80 28 4.00 5.25 7.50 7.75 8 13 1990 FALL 6 8.52 3.8000 13.20 3.63 1.48 43 3.80 6.70 7.45 12.50 13 13 1990 SPRING 6 9.00 7.8500 13.00 1.99 0.81 22 7.85 8.00 8.13 8.90 13 13 1990 SUMMER 21 7.23 5.8000 9.15 0.90 0.20 12 6.00 6.65 7.00 7.75 8 13 1991 FALL 1 7.00 7.0000 7.00 . . . 7.00 7.00 7.00 7.00 7 13 1991 SPRING 8 8.08 7.0000 9.00 0.69 0.24 9 7.00 7.50 8.18 8.63 9 13 1991 SUMMER 6 7.90 6.5500 9.65 1.28 0.52 16 6.55 7.10 7.38 9.35 9 13 1991 WINTER 3 9.38 7.5000 10.75 1.69 0.97 18 7.50 7.50 9.90 10.75 10 13 1992 FALL 11 8.25 5.6000 11.30 1.54 0.46 19 5.60 7.00 8.10 8.70 11 13 1992 SPRING 16 8.07 4.4500 12.50 2.15 0.54 27 4.45 6.68 7.80 9.60 12 13 1992 SUMMER 7 8.69 7.6000 10.40 0.91 0.34 10 7.60 8.00 8.60 9.15 10 13 1992 WINTER 2 5.90 2.2000 9.60 5.23 3.70 89 2.20 2.20 5.90 9.60 9 13 1993 FALL 3 8.15 7.4000 9.65 1.30 0.75 16 7.40 7.40 7.40 9.65 9 13 1993 SPRING 2 7.08 6.8000 7.35 0.39 0.27 5 6.80 6.80 7.08 7.35 7 13 1993 SUMMER 8 7.63 5.5000 9.50 1.29 0.46 17 5.50 6.65 7.88 8.48 9 13 1994 FALL 2 6.70 5.7000 7.70 1.41 1.00 21 5.70 5.70 6.70 7.70 7
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  13 1994 SPRING 1 7.00 7.0000 7.00 . . . 7.00 7.00 7.00 7.00 7 13 1994 SUMMER 20 6.32 2.4000 8.55 1.51 0.34 24 2.70 5.88 6.80 7.18 8 13 1994 WINTER 1 2.50 2.5000 2.50 . . . 2.50 2.50 2.50 2.50 2 13 1995 FALL 3 5.58 3.5500 7.70 2.08 1.20 37 3.55 3.55 5.50 7.70 7 13 1995 SPRING 4 7.55 5.8000 9.10 1.37 0.68 18 5.80 6.60 7.65 8.50 9 13 1995 SUMMER 8 6.49 2.1000 8.20 2.07 0.73 32 2.10 5.80 6.95 8.05 8 13 1995 WINTER 1 4.50 4.5000 4.50 . . . 4.50 4.50 4.50 4.50 4 13 1996 FALL 8 6.70 1.8500 10.65 2.48 0.88 37 1.85 5.95 6.70 7.90 10 13 1996 SUMMER 20 6.72 2.1000 10.50 1.89 0.42 28 3.18 6.00 6.90 7.80 10 18 1991 SUMMER 2 5.15 2.4000 7.90 3.89 2.75 76 2.40 2.40 5.15 7.90 7 18 1992 SPRING 1 8.35 8.3500 8.35 . . . 8.35 8.35 8.35 8.35 8 18 1993 SUMMER 4 9.43 8.4000 10.40 0.93 0.47 10 8.40 8.65 9.45 10.20 10 18 1994 SUMMER 3 9.30 6.6000 10.90 2.35 1.36 25 6.60 6.60 10.40 10.90 10 18 1995 FALL 4 4.95 1.6500 7.20 2.48 1.24 50 1.65 3.08 5.48 6.83 7 18 1995 SUMMER 6 5.97 2.5500 8.20 2.05 0.84 34 2.55 5.35 5.88 7.95 8 18 1996 FALL 2 7.05 6.9000 7.20 0.21 0.15 3 6.90 6.90 7.05 7.20 7 18 1996 SUMMER 2 7.90 6.7000 9.10 1.70 1.20 21 6.70 6.70 7.90 9.10 9 20 1990 FALL 1 7.30 7.3000 7.30 . . . 7.30 7.30 7.30 7.30 7 20 1990 SPRING 5 8.07 7.4500 9.20 0.67 0.30 8 7.45 7.75 7.95 8.00 9 20 1990 SUMMER 13 7.38 4.3000 11.05 1.88 0.52 25 4.30 6.20 7.55 8.60 11 20 1991 FALL 5 8.24 5.4500 11.30 2.49 1.12 30 5.45 6.80 7.25 10.40 11 20 1991 SPRING 12 6.78 .30000 9.15 2.78 0.80 41 0.30 6.28 7.78 8.45 9 20 1991 SUMMER 14 6.58 4.9000 9.30 1.38 0.37 21 4.90 5.40 6.55 7.35 9 20 1991 WINTER 1 4.55 4.5500 4.55 . . . 4.55 4.55 4.55 4.55 4 20 1992 FALL 5 8.21 6.3000 10.00 1.65 0.74 20 6.30 6.70 8.55 9.50 10 20 1992 SPRING 10 6.18 2.0000 9.55 2.61 0.82 42 2.00 4.00 6.60 8.20 9 20 1992 SUMMER 6 6.92 6.2500 7.45 0.51 0.21 7 6.25 6.30 7.10 7.30 7 20 1992 WINTER 1 10.60 10.600 10.60 . . . 10.60 10.60 10.60 10.60 10 20 1993 FALL 8 7.68 4.1500 11.30 1.99 0.70 26 4.15 7.10 7.55 8.35 11 20 1993 SPRING 3 8.18 8.0500 8.30 0.13 0.07 2 8.05 8.05 8.20 8.30 8 20 1993 SUMMER 12 6.67 3.5500 7.80 1.18 0.34 18 3.55 6.35 6.90 7.45 7 20 1994 FALL 6 7.75 6.8000 9.10 0.97 0.39 12 6.80 6.85 7.58 8.60 9
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  20 1994 SPRING 1 8.10 8.1000 8.10 . . . 8.10 8.10 8.10 8.10 8 20 1994 SUMMER 11 6.12 2.7000 9.05 1.92 0.58 31 2.70 4.55 6.30 7.45 9 20 1994 WINTER 1 6.80 6.8000 6.80 . . . 6.80 6.80 6.80 6.80 6 20 1995 FALL 11 5.19 .20000 9.80 3.20 0.96 62 0.20 2.80 6.70 7.85 9 20 1995 SPRING 3 9.67 8.6000 10.95 1.19 0.69 12 8.60 8.60 9.45 10.95 10 20 1995 SUMMER 22 6.82 4.2000 10.70 1.57 0.34 23 4.70 5.55 6.98 7.45 9 20 1995 WINTER 1 9.20 9.2000 9.20 . . . 9.20 9.20 9.20 9.20 9 20 1996 FALL 5 7.35 4.3500 8.65 1.72 0.77 23 4.35 7.70 7.85 8.20 8 20 1996 SPRING 7 7.79 6.5500 9.35 1.09 0.41 14 6.55 7.25 7.30 9.30 9 20 1996 SUMMER 10 7.43 4.8000 10.50 1.91 0.60 26 4.80 5.95 6.85 8.55 10 20 1996 WINTER 1 8.40 8.4000 8.40 . . . 8.40 8.40 8.40 8.40 8 20 1997 SPRING 1 10.10 10.100 10.10 . . . 10.10 10.10 10.10 10.10 10 20 1999 SUMMER 2 6.42 6.1500 6.69 0.38 0.27 6 6.15 6.15 6.42 6.69 6 22 1990 FALL 1 7.20 7.2000 7.20 . . . 7.20 7.20 7.20 7.20 7 22 1990 SUMMER 1 1.70 1.7000 1.70 . . . 1.70 1.70 1.70 1.70 1 22 1991 SUMMER 1 2.70 2.7000 2.70 . . . 2.70 2.70 2.70 2.70 2 22 1992 SUMMER 1 0.40 .40000 0.40 . . . 0.40 0.40 0.40 0.40 0 22 1993 SUMMER 2 4.15 3.6000 4.70 0.78 0.55 19 3.60 3.60 4.15 4.70 4 22 1994 SUMMER 1 0.40 .40000 0.40 . . . 0.40 0.40 0.40 0.40 0 22 1995 FALL 1 8.40 8.4000 8.40 . . . 8.40 8.40 8.40 8.40 8 22 1995 SUMMER 1 0.10 .10000 0.10 . . . 0.10 0.10 0.10 0.10 0 22 1996 SPRING 1 6.30 6.3000 6.30 . . . 6.30 6.30 6.30 6.30 6 22 1999 SUMMER 2 8.82 8.3000 9.34 0.74 0.52 8 8.30 8.30 8.82 9.34 9 24 1990 FALL 2 10.50 6.3000 14.70 5.94 4.20 57 6.30 6.30 10.50 14.70 14 24 1990 SPRING 1 9.10 9.1000 9.10 . . . 9.10 9.10 9.10 9.10 9 24 1990 SUMMER 1 7.80 7.8000 7.80 . . . 7.80 7.80 7.80 7.80 7 24 1990 WINTER 1 9.60 9.6000 9.60 . . . 9.60 9.60 9.60 9.60 9 24 1991 FALL 1 8.00 8.0000 8.00 . . . 8.00 8.00 8.00 8.00 8 24 1991 SPRING 1 10.25 10.250 10.25 . . . 10.25 10.25 10.25 10.25 10 24 1991 SUMMER 2 7.60 7.4000 7.80 0.28 0.20 4 7.40 7.40 7.60 7.80 7 24 1991 WINTER 1 10.00 10.000 10.00 . . . 10.00 10.00 10.00 10.00 10 24 1992 FALL 1 8.45 8.4500 8.45 . . . 8.45 8.45 8.45 8.45 8
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 24 1992 SPRING 1 9.60 9.6000 9.60 . . . 9.60 9.60 9.60 9.60 9. 24 1992 SUMMER 2 8.45 7.2000 9.70 1.77 1.25 21 7.20 7.20 8.45 9.70 9. 24 1992 WINTER 2 12.40 10.550 14.25 2.62 1.85 21 10.55 10.55 12.40 14.25 14. 24 1993 FALL 1 7.70 7.7000 7.70 . . . 7.70 7.70 7.70 7.70 7. 24 1993 SPRING 1 7.50 7.5000 7.50 . . . 7.50 7.50 7.50 7.50 7. 24 1993 SUMMER 2 6.65 5.2000 8.10 2.05 1.45 31 5.20 5.20 6.65 8.10 8. 24 1993 WINTER 1 9.80 9.8000 9.80 . . . 9.80 9.80 9.80 9.80 9. 24 1994 FALL 1 8.40 8.4000 8.40 . . . 8.40 8.40 8.40 8.40 8. 24 1994 SPRING 2 7.03 6.1500 7.90 1.24 0.88 18 6.15 6.15 7.03 7.90 7. 24 1994 SUMMER 2 7.45 7.0000 7.90 0.64 0.45 9 7.00 7.00 7.45 7.90 7. 24 1994 WINTER 1 8.90 8.9000 8.90 . . . 8.90 8.90 8.90 8.90 8. 24 1995 SUMMER 3 8.00 4.8000 13.40 4.70 2.72 59 4.80 4.80 5.80 13.40 13. 24 1995 WINTER 2 8.80 8.2500 9.35 0.78 0.55 9 8.25 8.25 8.80 9.35 9. 24 1996 SPRING 1 9.10 9.1000 9.10 . . . 9.10 9.10 9.10 9.10 9. 24 1996 SUMMER 1 6.60 6.6000 6.60 . . . 6.60 6.60 6.60 6.60 6. 80 1990 FALL 1 10.70 10.700 10.70 . . . 10.70 10.70 10.70 10.70 10. 80 1990 SPRING 1 9.80 9.8000 9.80 . . . 9.80 9.80 9.80 9.80 9. 80 1990 SUMMER 2 7.63 6.2000 9.05 2.02 1.43 26 6.20 6.20 7.63 9.05 9. 80 1991 FALL 1 12.55 12.550 12.55 . . . 12.55 12.55 12.55 12.55 12. 80 1991 SUMMER 2 8.00 7.0000 9.00 1.41 1.00 18 7.00 7.00 8.00 9.00 9. 80 1992 FALL 1 10.75 10.750 10.75 . . . 10.75 10.75 10.75 10.75 10. 80 1992 SPRING 1 10.30 10.300 10.30 . . . 10.30 10.30 10.30 10.30 10. 80 1992 SUMMER 2 9.15 9.0000 9.30 0.21 0.15 2 9.00 9.00 9.15 9.30 9. 80 1992 WINTER 1 12.50 12.500 12.50 . . . 12.50 12.50 12.50 12.50 12. 80 1993 FALL 1 10.35 10.350 10.35 . . . 10.35 10.35 10.35 10.35 10. 80 1993 SPRING 1 9.85 9.8500 9.85 . . . 9.85 9.85 9.85 9.85 9. 80 1993 SUMMER 2 7.43 5.0500 9.80 3.36 2.38 45 5.05 5.05 7.43 9.80 9. 80 1993 WINTER 1 11.85 11.850 11.85 . . . 11.85 11.85 11.85 11.85 11. 80 1994 FALL 1 10.50 10.500 10.50 . . . 10.50 10.50 10.50 10.50 10. 80 1994 SPRING 1 9.95 9.9500 9.95 . . . 9.95 9.95 9.95 9.95 9. 80 1994 SUMMER 1 8.20 8.2000 8.20 . . . 8.20 8.20 8.20 8.20 8. 80 1994 WINTER 1 12.00 12.000 12.00 . . . 12.00 12.00 12.00 12.00 12.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Dissolved_Oxygen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 80 1995 FALL 1 10.20 10.200 10.20 . . . 10.20 10.20 10.20 10.20 10. 80 1995 SPRING 1 10.85 10.850 10.85 . . . 10.85 10.85 10.85 10.85 10. 80 1995 SUMMER 3 7.15 5.9500 8.90 1.55 0.89 22 5.95 5.95 6.60 8.90 8. 80 1995 WINTER 1 11.80 11.800 11.80 . . . 11.80 11.80 11.80 11.80 11. 80 1996 FALL 1 9.50 9.5000 9.50 . . . 9.50 9.50 9.50 9.50 9. 80 1996 SPRING 1 10.35 10.350 10.35 . . . 10.35 10.35 10.35 10.35 10. 80 1996 SUMMER 2 7.43 5.7500 9.10 2.37 1.67 32 5.75 5.75 7.43 9.10 9. 80 1996 WINTER 1 12.80 12.800 12.80 . . . 12.80 12.80 12.80 12.80 12. 80 1997 FALL 1 10.30 10.300 10.30 . . . 10.30 10.30 10.30 10.30 10. 80 1997 SPRING 1 9.75 9.7500 9.75 . . . 9.75 9.75 9.75 9.75 9. 80 1997 SUMMER 1 9.40 9.4000 9.40 . . . 9.40 9.40 9.40 9.40 9. 80 1997 WINTER 1 12.40 12.400 12.40 . . . 12.40 12.40 12.40 12.40 12. 80 1998 WINTER 1 11.50 11.500 11.50 . . . 11.50 11.50 11.50 11.50 11. 81 1990 FALL 1 4.70 4.7000 4.70 . . . 4.70 4.70 4.70 4.70 4. 81 1991 FALL 1 6.70 6.7000 6.70 . . . 6.70 6.70 6.70 6.70 6.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 1990 FALL 1 0.10 .10000 0.10 . . . 0.10 0.10 0.10 0.10 0. 6 1990 SPRING 1 0.03 .02500 0.03 . . . 0.03 0.03 0.03 0.03 0. 6 1990 SUMMER 1 0.03 .02500 0.03 . . . 0.03 0.03 0.03 0.03 0. 6 1991 FALL 1 0.01 .01000 0.01 . . . 0.01 0.01 0.01 0.01 0. 6 1991 SPRING 1 0.33 .33000 0.33 . . . 0.33 0.33 0.33 0.33 0. 6 1991 SUMMER 1 0.01 .01000 0.01 . . . 0.01 0.01 0.01 0.01 0. 10 1990 FALL 1 0.05 .05075 0.05 . . . 0.05 0.05 0.05 0.05 0. 10 1990 SPRING 2 0.01 .00150 0.03 0.02 0.01 126 0.00 0.00 0.01 0.03 0. 10 1990 SUMMER 2 0.01 .00150 0.01 0.00 0.00 99 0.00 0.00 0.01 0.01 0. 10 1992 FALL 1 0.01 .00575 0.01 . . . 0.01 0.01 0.01 0.01 0. 10 1992 SUMMER 3 0.01 .00500 0.01 0.00 0.00 8 0.01 0.01 0.01 0.01 0. 10 1993 FALL 1 0.02 .01750 0.02 . . . 0.02 0.02 0.02 0.02 0. 10 1993 SUMMER 1 0.00 .00150 0.00 . . . 0.00 0.00 0.00 0.00 0. 10 1994 FALL 4 0.10 .00800 0.20 0.08 0.04 82 0.01 0.04 0.09 0.15 0. 10 1994 SPRING 4 0.12 .01300 0.20 0.08 0.04 69 0.01 0.06 0.13 0.18 0. 10 1994 SUMMER 4 0.03 .00150 0.05 0.02 0.01 80 0.00 0.01 0.03 0.04 0. 10 1994 WINTER 3 0.25 .22000 0.28 0.03 0.02 11 0.22 0.22 0.26 0.28 0. 10 1995 FALL 4 0.04 .01950 0.08 0.03 0.01 81 0.02 0.02 0.02 0.05 0. 10 1995 SPRING 4 0.36 .27500 0.53 0.11 0.06 31 0.28 0.29 0.32 0.43 0. 10 1995 SUMMER 4 0.10 .10000 0.11 0.00 0.00 5 0.10 0.10 0.10 0.11 0. 10 1995 WINTER 3 0.42 .37500 0.49 0.06 0.03 14 0.38 0.38 0.41 0.49 0. 10 1998 FALL 5 0.19 .12500 0.25 0.06 0.02 30 0.13 0.14 0.18 0.24 0. 10 1998 SUMMER 5 0.19 .11000 0.31 0.08 0.03 39 0.11 0.15 0.18 0.22 0. 10 1998 WINTER 3 0.25 .16000 0.40 0.13 0.08 52 0.16 0.16 0.19 0.40 0. 10 1999 SPRING 5 0.39 .16000 0.67 0.24 0.11 63 0.16 0.19 0.29 0.62 0. 10 1999 WINTER 4 0.41 .19000 0.71 0.23 0.11 56 0.19 0.24 0.37 0.58 0. 12 1991 FALL 2 1.92 1.7250 2.11 0.27 0.19 14 1.73 1.73 1.92 2.11 2. 12 1991 SPRING 2 1.68 1.3200 2.03 0.50 0.36 30 1.32 1.32 1.68 2.03 2. 12 1991 SUMMER 2 1.75 1.4000 2.10 0.49 0.35 28 1.40 1.40 1.75 2.10 2. 12 1991 WINTER 2 1.75 1.5000 1.99 0.35 0.25 20 1.50 1.50 1.75 1.99 1. 12 1992 WINTER 2 1.68 1.4700 1.90 0.30 0.21 18 1.47 1.47 1.68 1.90 1. 13 1991 FALL 1 0.00 .00250 0.00 . . . 0.00 0.00 0.00 0.00 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 13 1991 SUMMER 2 0.37 .00250 0.73 0.51 0.36 140 0.00 0.00 0.37 0.73 0. 13 1991 WINTER 1 0.01 .01000 0.01 . . . 0.01 0.01 0.01 0.01 0. 13 1992 FALL 1 0.65 .64750 0.65 . . . 0.65 0.65 0.65 0.65 0. 13 1992 SUMMER 6 0.05 .00050 0.24 0.10 0.04 203 0.00 0.00 0.00 0.03 0. 13 1993 FALL 1 0.08 .08000 0.08 . . . 0.08 0.08 0.08 0.08 0. 13 1993 SPRING 1 0.63 .63000 0.63 . . . 0.63 0.63 0.63 0.63 0. 13 1993 SUMMER 2 0.01 .00500 0.01 0.00 0.00 0 0.01 0.01 0.01 0.01 0. 13 1993 WINTER 1 1.79 1.7850 1.79 . . . 1.79 1.79 1.79 1.79 1. 13 1994 SUMMER 1 0.17 .17000 0.17 . . . 0.17 0.17 0.17 0.17 0. 13 1995 FALL 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 13 1996 FALL 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 13 1996 SUMMER 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 18 1991 SUMMER 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 20 1991 FALL 5 0.08 .00250 0.34 0.15 0.07 175 0.00 0.00 0.00 0.07 0. 20 1992 FALL 2 0.05 .05000 0.05 0.00 0.00 0 0.05 0.05 0.05 0.05 0. 20 1992 SPRING 1 0.01 .00700 0.01 . . . 0.01 0.01 0.01 0.01 0. 20 1995 FALL 1 0.10 .10000 0.10 . . . 0.10 0.10 0.10 0.10 0. 20 1995 SUMMER 2 0.01 .00500 0.01 0.00 0.00 0 0.01 0.01 0.01 0.01 0. 20 1996 FALL 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 20 1996 SPRING 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 20 1996 SUMMER 2 0.01 .00500 0.01 0.00 0.00 0 0.01 0.01 0.01 0.01 0. 20 1996 WINTER 2 0.14 .13000 0.14 0.01 0.01 5 0.13 0.13 0.14 0.14 0. 20 1999 SUMMER 2 0.06 .00000 0.12 0.08 0.06 141 0.00 0.00 0.06 0.12 0. 22 1990 FALL 1 0.13 .13000 0.13 . . . 0.13 0.13 0.13 0.13 0. 22 1990 SPRING 1 0.28 .27500 0.28 . . . 0.28 0.28 0.28 0.28 0. 22 1990 SUMMER 2 0.19 .02500 0.36 0.24 0.17 123 0.03 0.03 0.19 0.36 0. 22 1991 FALL 2 0.06 .05000 0.08 0.02 0.01 28 0.05 0.05 0.06 0.08 0. 22 1991 SPRING 3 0.08 .01000 0.20 0.11 0.06 135 0.01 0.01 0.03 0.20 0. 22 1991 SUMMER 3 0.06 .03500 0.09 0.03 0.02 55 0.04 0.04 0.04 0.09 0. 22 1992 FALL 2 0.11 .11000 0.11 0.00 0.00 0 0.11 0.11 0.11 0.11 0. 22 1992 SPRING 1 0.01 .01000 0.01 . . . 0.01 0.01 0.01 0.01 0. 22 1992 SUMMER 2 0.09 .01000 0.17 0.11 0.08 126 0.01 0.01 0.09 0.17 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 22 1993 SPRING 3 0.04 .01000 0.06 0.03 0.02 67 0.01 0.01 0.06 0.06 0. 22 1993 SUMMER 5 0.07 .01000 0.21 0.08 0.04 116 0.01 0.01 0.04 0.09 0. 22 1993 WINTER 2 0.17 .14000 0.20 0.04 0.03 25 0.14 0.14 0.17 0.20 0. 22 1995 FALL 2 0.03 .02500 0.03 0.00 0.00 0 0.03 0.03 0.03 0.03 0. 22 1995 SPRING 1 0.03 .02500 0.03 . . . 0.03 0.03 0.03 0.03 0. 22 1995 SUMMER 1 0.03 .02500 0.03 . . . 0.03 0.03 0.03 0.03 0. 22 1999 SUMMER 2 0.00 .00000 0.00 0.00 0.00 . 0.00 0.00 0.00 0.00 0. 24 1990 FALL 2 0.04 .01000 0.06 0.04 0.03 101 0.01 0.01 0.04 0.06 0. 24 1990 SPRING 2 0.04 .01000 0.07 0.04 0.03 106 0.01 0.01 0.04 0.07 0. 24 1990 SUMMER 2 0.10 .09500 0.10 0.00 0.00 4 0.10 0.10 0.10 0.10 0. 24 1992 SPRING 5 1.58 .01000 2.89 1.26 0.57 80 0.01 0.56 1.79 2.64 2. 24 1992 SUMMER 2 0.01 .01000 0.01 0.00 0.00 0 0.01 0.01 0.01 0.01 0. 24 1992 WINTER 4 0.02 .01000 0.04 0.01 0.01 77 0.01 0.01 0.01 0.02 0. 24 1993 SPRING 8 0.47 .01000 3.68 1.30 0.46 276 0.01 0.01 0.01 0.02 3. 24 1995 SUMMER 4 0.86 .01000 3.20 1.56 0.78 182 0.01 0.02 0.11 1.70 3. 24 1995 WINTER 1 1.31 1.3050 1.31 . . . 1.31 1.31 1.31 1.31 1. 24 1996 SPRING 1 0.67 .67000 0.67 . . . 0.67 0.67 0.67 0.67 0. 24 1996 SUMMER 1 0.09 .08625 0.09 . . . 0.09 0.09 0.09 0.09 0. 24 1997 FALL 1 0.03 .02500 0.03 . . . 0.03 0.03 0.03 0.03 0. 24 1997 SPRING 1 0.06 .06250 0.06 . . . 0.06 0.06 0.06 0.06 0. 24 1997 SUMMER 1 0.03 .02500 0.03 . . . 0.03 0.03 0.03 0.03 0. 80 1990 FALL 1 0.02 .02000 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 1990 SPRING 1 0.02 .02000 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 1990 SUMMER 1 0.01 .01250 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1991 SUMMER 2 0.00 .00100 0.01 0.00 0.00 94 0.00 0.00 0.00 0.01 0. 80 1992 FALL 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1992 SPRING 1 0.03 .03000 0.03 . . . 0.03 0.03 0.03 0.03 0. 80 1992 SUMMER 2 0.01 .00500 0.01 0.00 0.00 0 0.01 0.01 0.01 0.01 0. 80 1992 WINTER 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1993 FALL 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1993 SPRING 1 0.08 .07500 0.08 . . . 0.08 0.08 0.08 0.08 0. 80 1993 SUMMER 1 0.04 .04000 0.04 . . . 0.04 0.04 0.04 0.04 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrite_Nitrate_NO2_NO3_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 80 1993 WINTER 1 0.06 .05500 0.06 . . . 0.06 0.06 0.06 0.06 0. 80 1994 FALL 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1994 SPRING 1 0.01 .01250 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1994 SUMMER 1 0.02 .02000 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 1994 WINTER 1 0.02 .02000 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 1995 FALL 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1995 SPRING 1 0.02 .01750 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 1995 SUMMER 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1995 WINTER 1 0.04 .04000 0.04 . . . 0.04 0.04 0.04 0.04 0. 80 1996 FALL 1 0.02 .02000 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 1996 SPRING 1 0.02 .02000 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 1996 SUMMER 1 0.01 .00500 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1996 WINTER 1 0.03 .03000 0.03 . . . 0.03 0.03 0.03 0.03 0. 80 1997 FALL 1 0.02 .02000 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 1997 SPRING 1 0.01 .01250 0.01 . . . 0.01 0.01 0.01 0.01 0. 80 1997 SUMMER 1 0.02 .02000 0.02 . . . 0.02 0.02 0.02 0.02 0. 80 1997 WINTER 1 0.03 .03000 0.03 . . . 0.03 0.03 0.03 0.03 0. 80 1998 WINTER 1 0.04 .04000 0.04 . . . 0.04 0.04 0.04 0.04 0. 81 1990 FALL 1 0.03 .02500 0.03 . . . 0.03 0.03 0.03 0.03 0. 81 1991 FALL 1 0.01 .01000 0.01 . . . 0.01 0.01 0.01 0.01 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 1990 FALL 1 0.40 .40000 0.40 . . . 0.40 0.40 0.40 0.40 0. 6 1990 SPRING 4 0.40 .20000 0.60 0.23 0.12 58 0.20 0.20 0.40 0.60 0. 6 1990 SUMMER 1 0.50 .50000 0.50 . . . 0.50 0.50 0.50 0.50 0. 6 1990 WINTER 1 1.80 1.8000 1.80 . . . 1.80 1.80 1.80 1.80 1. 6 1991 FALL 1 0.50 .50000 0.50 . . . 0.50 0.50 0.50 0.50 0. 6 1991 SPRING 1 0.60 .60000 0.60 . . . 0.60 0.60 0.60 0.60 0. 6 1991 SUMMER 1 0.40 .40000 0.40 . . . 0.40 0.40 0.40 0.40 0. 6 1994 WINTER 1 2.10 2.1000 2.10 . . . 2.10 2.10 2.10 2.10 2. 10 1990 FALL 3 0.87 .42000 1.28 0.43 0.25 50 0.42 0.42 0.91 1.28 1. 10 1990 SPRING 4 0.76 .25000 1.15 0.38 0.19 50 0.25 0.49 0.83 1.04 1. 10 1990 SUMMER 4 1.06 .47000 1.68 0.53 0.26 50 0.47 0.64 1.05 1.48 1. 10 1991 FALL 1 0.38 .38000 0.38 . . . 0.38 0.38 0.38 0.38 0. 10 1991 SPRING 2 0.87 .86000 0.87 0.01 0.01 1 0.86 0.86 0.87 0.87 0. 10 1991 SUMMER 2 1.03 .76000 1.30 0.38 0.27 37 0.76 0.76 1.03 1.30 1. 10 1991 WINTER 2 0.82 .48000 1.16 0.48 0.34 59 0.48 0.48 0.82 1.16 1. 10 1992 FALL 3 1.26 .37000 2.63 1.20 0.70 96 0.37 0.37 0.78 2.63 2. 10 1992 SPRING 2 0.75 .61500 0.88 0.18 0.13 25 0.62 0.62 0.75 0.88 0. 10 1992 SUMMER 5 1.41 .50000 3.68 1.33 0.60 95 0.50 0.62 0.70 1.54 3. 10 1992 WINTER 2 0.57 .56000 0.57 0.01 0.01 1 0.56 0.56 0.57 0.57 0. 10 1993 FALL 3 0.76 .40000 1.34 0.51 0.29 67 0.40 0.40 0.53 1.34 1. 10 1993 SPRING 2 0.63 .58000 0.67 0.06 0.05 10 0.58 0.58 0.63 0.67 0. 10 1993 SUMMER 6 0.69 .25000 1.01 0.31 0.13 46 0.25 0.44 0.71 1.00 1. 10 1993 WINTER 2 0.58 .43000 0.72 0.21 0.15 36 0.43 0.43 0.58 0.72 0. 10 1994 FALL 3 1.37 .29000 3.27 1.65 0.95 120 0.29 0.29 0.56 3.27 3. 10 1994 SPRING 3 0.78 .40000 1.33 0.48 0.28 62 0.40 0.40 0.63 1.33 1. 10 1994 SUMMER 3 1.19 .33000 1.97 0.82 0.47 69 0.33 0.33 1.26 1.97 1. 10 1994 WINTER 2 0.49 .44000 0.54 0.07 0.05 14 0.44 0.44 0.49 0.54 0. 10 1995 FALL 3 0.46 .22000 0.72 0.25 0.14 54 0.22 0.22 0.45 0.72 0. 10 1995 SPRING 3 0.79 .43500 1.11 0.34 0.20 43 0.44 0.44 0.83 1.11 1. 10 1995 SUMMER 3 0.72 .41000 1.09 0.34 0.20 48 0.41 0.41 0.65 1.09 1. 10 1995 WINTER 2 0.47 .35000 0.58 0.16 0.11 35 0.35 0.35 0.47 0.58 0. 10 1996 FALL 2 0.53 .42000 0.64 0.16 0.11 29 0.42 0.42 0.53 0.64 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  10 1996 SPRING 2 0.52 .50500 0.54 0.02 0.02 4 0.51 0.51 0.52 0.54 0 10 1996 SUMMER 4 0.43 .16000 0.73 0.28 0.14 65 0.16 0.19 0.41 0.66 0 10 1996 WINTER 2 0.39 .32000 0.46 0.10 0.07 25 0.32 0.32 0.39 0.46 0 10 1997 FALL 2 0.60 .47000 0.73 0.18 0.13 31 0.47 0.47 0.60 0.73 0 10 1997 SPRING 2 0.63 .55500 0.70 0.10 0.07 16 0.56 0.56 0.63 0.70 0 10 1997 SUMMER 3 0.61 .51000 0.81 0.17 0.10 28 0.51 0.51 0.52 0.81 0 10 1997 WINTER 2 0.37 .34000 0.40 0.04 0.03 11 0.34 0.34 0.37 0.40 0 10 1998 FALL 5 0.86 .67500 1.24 0.24 0.11 28 0.68 0.70 0.73 0.96 1 10 1998 SPRING 2 0.50 .37000 0.63 0.18 0.13 37 0.37 0.37 0.50 0.63 0 10 1998 SUMMER 7 0.88 .48000 1.32 0.29 0.11 33 0.48 0.58 0.94 1.10 1 10 1998 WINTER 3 0.57 .50000 0.64 0.07 0.04 12 0.50 0.50 0.56 0.64 0 10 1999 SPRING 5 0.70 .62500 0.84 0.09 0.04 12 0.63 0.63 0.69 0.70 0 10 1999 WINTER 4 0.84 .45000 1.16 0.30 0.15 36 0.45 0.63 0.87 1.05 1 12 1990 SUMMER 5 0.59 .12000 1.63 0.60 0.27 102 0.12 0.27 0.45 0.49 1 12 1991 FALL 2 0.26 .00000 0.52 0.37 0.26 141 0.00 0.00 0.26 0.52 0 12 1991 SPRING 2 0.28 .00000 0.56 0.40 0.28 141 0.00 0.00 0.28 0.56 0 12 1991 SUMMER 6 0.31 .00000 0.42 0.16 0.06 50 0.00 0.32 0.37 0.41 0 12 1991 WINTER 2 0.27 .00000 0.54 0.38 0.27 141 0.00 0.00 0.27 0.54 0 12 1992 SUMMER 3 0.37 .33000 0.40 0.04 0.02 10 0.33 0.33 0.37 0.40 0 12 1992 WINTER 2 0.39 .00000 0.77 0.54 0.39 141 0.00 0.00 0.39 0.77 0 12 1993 SUMMER 2 0.14 .11000 0.17 0.04 0.03 28 0.11 0.11 0.14 0.17 0 12 1994 SUMMER 4 0.37 .31500 0.45 0.06 0.03 15 0.32 0.33 0.35 0.40 0 12 1995 SUMMER 3 0.30 .28000 0.33 0.03 0.01 8 0.28 0.28 0.30 0.33 0 12 1996 SUMMER 5 0.17 .12000 0.24 0.05 0.02 28 0.12 0.13 0.17 0.20 0 12 1997 SUMMER 5 0.42 .32000 0.52 0.09 0.04 22 0.32 0.37 0.38 0.52 0 13 1990 FALL 2 0.62 .30000 0.93 0.45 0.32 72 0.30 0.30 0.62 0.93 0 13 1990 SPRING 7 0.37 .20000 0.75 0.19 0.07 50 0.20 0.20 0.36 0.40 0 13 1990 SUMMER 25 0.67 .10000 2.28 0.49 0.10 74 0.20 0.40 0.56 0.80 1 13 1990 WINTER 1 0.33 .33000 0.33 . . . 0.33 0.33 0.33 0.33 0 13 1991 FALL 2 0.52 .43500 0.61 0.12 0.09 23 0.44 0.44 0.52 0.61 0 13 1991 SPRING 9 0.69 .10000 2.90 0.87 0.29 126 0.10 0.20 0.48 0.75 2 13 1991 SUMMER 7 1.01 .19000 3.19 1.00 0.38 99 0.19 0.33 0.78 0.93 3
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  13 1991 WINTER 4 1.04 .57000 1.40 0.38 0.19 37 0.57 0.74 1.10 1.35 1 13 1992 FALL 14 0.68 .07250 2.18 0.56 0.15 83 0.07 0.27 0.52 0.93 2 13 1992 SPRING 18 0.43 .02500 2.63 0.58 0.14 133 0.03 0.18 0.29 0.50 2 13 1992 SUMMER 13 0.45 .07000 1.59 0.38 0.11 84 0.07 0.24 0.41 0.51 1 13 1992 WINTER 3 1.33 .34000 2.93 1.40 0.81 106 0.34 0.34 0.71 2.93 2 13 1993 FALL 2 1.96 1.8500 2.08 0.16 0.11 8 1.85 1.85 1.96 2.08 2 13 1993 SPRING 2 1.87 .82500 2.91 1.47 1.04 79 0.83 0.83 1.87 2.91 2 13 1993 SUMMER 2 1.67 .89000 2.45 1.10 0.78 66 0.89 0.89 1.67 2.45 2 13 1993 WINTER 1 2.28 2.2800 2.28 . . . 2.28 2.28 2.28 2.28 2 13 1994 FALL 3 1.34 .57000 2.72 1.20 0.69 90 0.57 0.57 0.72 2.72 2 13 1994 SPRING 3 1.23 .45500 2.66 1.24 0.71 101 0.46 0.46 0.57 2.66 2 13 1994 SUMMER 5 1.32 .57000 3.05 0.99 0.44 75 0.57 0.90 0.95 1.16 3 13 1994 WINTER 3 1.56 .33000 2.31 1.07 0.62 69 0.33 0.33 2.03 2.31 2 13 1995 FALL 2 2.08 1.2600 2.90 1.16 0.82 56 1.26 1.26 2.08 2.90 2 13 1995 SPRING 4 1.10 .26000 2.64 1.07 0.53 97 0.26 0.40 0.75 1.80 2 13 1995 SUMMER 2 1.73 .89000 2.56 1.18 0.84 68 0.89 0.89 1.73 2.56 2 13 1995 WINTER 3 1.27 .34000 2.76 1.30 0.75 102 0.34 0.34 0.72 2.76 2 13 1996 FALL 4 1.11 .57500 2.27 0.78 0.39 70 0.58 0.63 0.81 1.60 2 13 1996 SPRING 3 1.09 .36000 2.53 1.24 0.72 114 0.36 0.36 0.38 2.53 2 13 1996 SUMMER 4 1.13 .19000 2.91 1.25 0.62 111 0.19 0.27 0.70 1.98 2 13 1996 WINTER 3 1.40 .48000 2.91 1.32 0.76 95 0.48 0.48 0.80 2.91 2 13 1997 FALL 7 0.64 .14000 1.40 0.43 0.16 67 0.14 0.30 0.60 0.99 1 13 1997 SPRING 3 1.31 .53000 2.43 0.99 0.57 76 0.53 0.53 0.97 2.43 2 13 1997 SUMMER 7 0.75 .22000 1.42 0.39 0.15 53 0.22 0.45 0.68 0.99 1 13 1997 WINTER 2 0.50 .34000 0.65 0.22 0.16 44 0.34 0.34 0.50 0.65 0 13 1998 SPRING 4 1.35 .59000 3.19 1.24 0.62 92 0.59 0.64 0.81 2.06 3 13 1998 WINTER 3 0.50 .29000 0.70 0.21 0.12 41 0.29 0.29 0.52 0.70 0 18 1991 SUMMER 3 0.54 .33000 0.70 0.19 0.11 35 0.33 0.33 0.60 0.70 0 18 1992 SPRING 1 0.38 .38000 0.38 . . . 0.38 0.38 0.38 0.38 0 18 1995 FALL 2 0.30 .30000 0.30 0.00 0.00 0 0.30 0.30 0.30 0.30 0 18 1995 SUMMER 2 0.35 .30000 0.40 0.07 0.05 20 0.30 0.30 0.35 0.40 0 18 1996 FALL 2 0.30 .30000 0.30 0.00 0.00 0 0.30 0.30 0.30 0.30 0
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  18 1996 SUMMER 1 0.35 .35000 0.35 . . . 0.35 0.35 0.35 0.35 0 20 1990 FALL 1 0.60 .60000 0.60 . . . 0.60 0.60 0.60 0.60 0 20 1990 SPRING 6 0.34 .02500 0.80 0.30 0.12 88 0.03 0.15 0.23 0.60 0 20 1990 SUMMER 13 0.39 .06250 0.85 0.28 0.08 73 0.06 0.20 0.30 0.70 0 20 1991 FALL 6 0.50 .02500 1.22 0.46 0.19 93 0.03 0.22 0.31 0.90 1 20 1991 SPRING 10 0.17 .02500 0.60 0.18 0.06 111 0.03 0.03 0.10 0.25 0 20 1991 SUMMER 14 0.24 .02500 0.56 0.16 0.04 67 0.03 0.10 0.23 0.35 0 20 1991 WINTER 1 0.70 .70000 0.70 . . . 0.70 0.70 0.70 0.70 0 20 1992 FALL 8 0.68 .26500 1.18 0.32 0.11 48 0.27 0.45 0.61 0.92 1 20 1992 SPRING 12 0.27 .02500 0.93 0.28 0.08 104 0.03 0.03 0.22 0.37 0 20 1992 SUMMER 6 0.27 .17000 0.42 0.10 0.04 36 0.17 0.19 0.26 0.35 0 20 1992 WINTER 1 0.06 .06250 0.06 . . . 0.06 0.06 0.06 0.06 0 20 1993 FALL 3 0.52 .30000 0.71 0.21 0.12 40 0.30 0.30 0.56 0.71 0 20 1993 SPRING 3 0.29 .15500 0.43 0.14 0.08 48 0.16 0.16 0.27 0.43 0 20 1993 SUMMER 1 0.40 .40000 0.40 . . . 0.40 0.40 0.40 0.40 0 20 1994 FALL 2 0.25 .14000 0.35 0.15 0.11 61 0.14 0.14 0.25 0.35 0 20 1994 SPRING 1 0.10 .10000 0.10 . . . 0.10 0.10 0.10 0.10 0 20 1994 SUMMER 2 0.19 .18500 0.20 0.01 0.01 6 0.19 0.19 0.19 0.20 0 20 1994 WINTER 2 0.28 .10000 0.45 0.25 0.18 90 0.10 0.10 0.28 0.45 0 20 1995 FALL 2 2.21 .79000 3.63 2.01 1.42 91 0.79 0.79 2.21 3.63 3 20 1995 SPRING 4 0.65 .02500 1.62 0.69 0.34 106 0.03 0.20 0.47 1.09 1 20 1995 SUMMER 4 0.75 .02500 2.02 0.88 0.44 119 0.03 0.16 0.47 1.33 2 20 1995 WINTER 2 0.28 .18000 0.38 0.14 0.10 50 0.18 0.18 0.28 0.38 0 20 1996 FALL 2 1.43 .58500 2.28 1.20 0.85 84 0.59 0.59 1.43 2.28 2 20 1996 SPRING 2 2.03 .87000 3.19 1.64 1.16 81 0.87 0.87 2.03 3.19 3 20 1996 SUMMER 2 2.22 .78000 3.65 2.03 1.44 92 0.78 0.78 2.22 3.65 3 20 1997 SPRING 1 5.26 5.2600 5.26 . . . 5.26 5.26 5.26 5.26 5 22 1990 FALL 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0 22 1990 SPRING 1 1.68 1.6800 1.68 . . . 1.68 1.68 1.68 1.68 1 22 1990 SUMMER 2 0.78 .66000 0.90 0.17 0.12 22 0.66 0.66 0.78 0.90 0 22 1991 FALL 2 0.70 .38500 1.02 0.45 0.32 64 0.39 0.39 0.70 1.02 1 22 1991 SPRING 3 0.53 .02500 1.47 0.81 0.47 155 0.03 0.03 0.09 1.47 1
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 22 1991 SUMMER 3 0.61 .02500 1.19 0.58 0.34 96 0.03 0.03 0.60 1.19 1. 22 1992 FALL 2 0.19 .18000 0.19 0.01 0.01 4 0.18 0.18 0.19 0.19 0. 22 1992 SPRING 1 0.43 .43000 0.43 . . . 0.43 0.43 0.43 0.43 0. 22 1992 SUMMER 4 0.51 .02500 1.00 0.47 0.24 92 0.03 0.11 0.52 0.92 1. 22 1993 SPRING 3 0.29 .17000 0.38 0.11 0.06 37 0.17 0.17 0.31 0.38 0. 22 1993 SUMMER 7 0.71 .25000 2.20 0.69 0.26 97 0.25 0.28 0.40 0.90 2. 22 1993 WINTER 2 0.22 .22000 0.22 0.00 0.00 0 0.22 0.22 0.22 0.22 0. 22 1994 SUMMER 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 22 1995 FALL 2 0.65 .40000 0.90 0.35 0.25 54 0.40 0.40 0.65 0.90 0. 22 1995 SPRING 1 0.43 .43000 0.43 . . . 0.43 0.43 0.43 0.43 0. 22 1995 SUMMER 1 0.50 .50000 0.50 . . . 0.50 0.50 0.50 0.50 0. 22 1996 SPRING 1 0.60 .60000 0.60 . . . 0.60 0.60 0.60 0.60 0. 24 1990 FALL 3 0.77 .40000 1.40 0.55 0.32 72 0.40 0.40 0.50 1.40 1. 24 1990 SPRING 2 0.57 .55000 0.58 0.02 0.02 4 0.55 0.55 0.57 0.58 0. 24 1990 SUMMER 2 0.90 .89000 0.91 0.01 0.01 1 0.89 0.89 0.90 0.91 0. 24 1991 SUMMER 1 1.80 1.8000 1.80 . . . 1.80 1.80 1.80 1.80 1. 24 1992 SPRING 2 2.09 1.6300 2.54 0.64 0.46 31 1.63 1.63 2.09 2.54 2. 24 1992 SUMMER 3 0.42 .30000 0.57 0.14 0.08 33 0.30 0.30 0.38 0.57 0. 24 1992 WINTER 4 0.33 .29000 0.36 0.03 0.01 9 0.29 0.32 0.34 0.35 0. 24 1993 FALL 1 0.23 .22500 0.23 . . . 0.23 0.23 0.23 0.23 0. 24 1993 SPRING 7 1.36 .41000 3.51 1.09 0.41 80 0.41 0.53 0.85 1.86 3. 24 1993 SUMMER 2 0.63 .24000 1.03 0.56 0.39 88 0.24 0.24 0.63 1.03 1. 24 1993 WINTER 1 0.49 .49000 0.49 . . . 0.49 0.49 0.49 0.49 0. 24 1994 SPRING 1 1.40 1.4000 1.40 . . . 1.40 1.40 1.40 1.40 1. 24 1995 SUMMER 4 0.87 .50000 1.20 0.37 0.19 43 0.50 0.55 0.89 1.19 1. 24 1995 WINTER 1 0.98 .98000 0.98 . . . 0.98 0.98 0.98 0.98 0. 24 1996 SPRING 1 0.89 .88500 0.89 . . . 0.89 0.89 0.89 0.89 0. 24 1996 SUMMER 1 1.20 1.1950 1.20 . . . 1.20 1.20 1.20 1.20 1. 24 1997 FALL 1 0.40 .39500 0.40 . . . 0.40 0.40 0.40 0.40 0. 24 1997 SPRING 1 0.35 .35000 0.35 . . . 0.35 0.35 0.35 0.35 0. 24 1997 SUMMER 1 0.57 .56500 0.57 . . . 0.57 0.57 0.57 0.57 0. 80 1990 FALL 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Nitrogen_Tot_Kjeldhal_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 80 1990 SPRING 1 0.40 .40000 0.40 . . . 0.40 0.40 0.40 0.40 0. 80 1990 SUMMER 2 0.44 .25000 0.63 0.27 0.19 61 0.25 0.25 0.44 0.63 0. 80 1991 FALL 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 80 1991 SUMMER 1 0.40 .40000 0.40 . . . 0.40 0.40 0.40 0.40 0. 80 1992 FALL 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 80 1992 SPRING 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 80 1992 SUMMER 2 0.30 .20000 0.40 0.14 0.10 47 0.20 0.20 0.30 0.40 0. 80 1992 WINTER 1 0.30 .30000 0.30 . . . 0.30 0.30 0.30 0.30 0. 80 1993 FALL 1 0.18 .17500 0.18 . . . 0.18 0.18 0.18 0.18 0. 80 1993 SPRING 1 0.45 .45000 0.45 . . . 0.45 0.45 0.45 0.45 0. 80 1993 SUMMER 2 0.28 .25500 0.30 0.03 0.02 11 0.26 0.26 0.28 0.30 0. 80 1993 WINTER 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 80 1994 FALL 1 0.23 .22500 0.23 . . . 0.23 0.23 0.23 0.23 0. 80 1994 SPRING 1 0.35 .35000 0.35 . . . 0.35 0.35 0.35 0.35 0. 80 1994 SUMMER 1 0.30 .30000 0.30 . . . 0.30 0.30 0.30 0.30 0. 80 1994 WINTER 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 80 1995 FALL 1 0.25 .25000 0.25 . . . 0.25 0.25 0.25 0.25 0. 80 1995 SPRING 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 80 1995 SUMMER 3 0.41 .22000 0.70 0.26 0.15 63 0.22 0.22 0.30 0.70 0. 80 1995 WINTER 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 80 1996 FALL 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 80 1996 SPRING 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 80 1996 SUMMER 2 0.37 .20000 0.54 0.24 0.17 65 0.20 0.20 0.37 0.54 0. 80 1996 WINTER 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 80 1997 FALL 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 80 1997 SPRING 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 80 1997 SUMMER 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 80 1997 WINTER 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 80 1998 WINTER 1 0.05 .05000 0.05 . . . 0.05 0.05 0.05 0.05 0. 81 1990 FALL 1 0.60 .60000 0.60 . . . 0.60 0.60 0.60 0.60 0. 81 1991 FALL 1 0.40 .40000 0.40 . . . 0.40 0.40 0.40 0.40 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 SECCHI_m subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 1990 FALL 1 2.00 2.0000 2.00 . . . 2.00 2.00 2.00 2.00 2. 6 1990 SPRING 1 1.10 1.1000 1.10 . . . 1.10 1.10 1.10 1.10 1. 6 1990 SUMMER 1 1.32 1.3200 1.32 . . . 1.32 1.32 1.32 1.32 1. 6 1991 SPRING 1 1.06 1.0550 1.06 . . . 1.06 1.06 1.06 1.06 1. 6 1991 SUMMER 1 1.51 1.5100 1.51 . . . 1.51 1.51 1.51 1.51 1. 6 1993 FALL 1 1.34 1.3350 1.34 . . . 1.34 1.34 1.34 1.34 1. 6 1994 FALL 1 0.48 .48000 0.48 . . . 0.48 0.48 0.48 0.48 0. 6 1994 SPRING 1 1.86 1.8550 1.86 . . . 1.86 1.86 1.86 1.86 1. 6 1994 SUMMER 1 0.43 .43000 0.43 . . . 0.43 0.43 0.43 0.43 0. 6 1997 FALL 1 0.75 .75000 0.75 . . . 0.75 0.75 0.75 0.75 0. 6 1997 SUMMER 1 1.45 1.4500 1.45 . . . 1.45 1.45 1.45 1.45 1. 10 1992 FALL 1 1.50 1.5000 1.50 . . . 1.50 1.50 1.50 1.50 1. 10 1993 FALL 1 3.10 3.1000 3.10 . . . 3.10 3.10 3.10 3.10 3. 10 1993 SUMMER 3 1.33 .00000 2.20 1.17 0.68 88 0.00 0.00 1.80 2.20 2. 10 1994 FALL 4 1.69 .60000 2.35 0.76 0.38 45 0.60 1.20 1.90 2.18 2. 10 1994 SPRING 4 1.96 1.3500 3.70 1.16 0.58 59 1.35 1.38 1.40 2.55 3. 10 1994 SUMMER 4 1.53 1.2000 1.80 0.25 0.13 16 1.20 1.35 1.55 1.70 1. 10 1994 WINTER 3 3.13 2.7000 3.50 0.40 0.23 13 2.70 2.70 3.20 3.50 3. 10 1995 FALL 4 2.08 1.2500 3.55 1.01 0.51 49 1.25 1.48 1.75 2.68 3. 10 1995 SPRING 4 1.08 .90000 1.40 0.24 0.12 22 0.90 0.90 1.00 1.25 1. 10 1995 SUMMER 4 1.40 1.2000 1.80 0.28 0.14 20 1.20 1.20 1.30 1.60 1. 10 1995 WINTER 3 1.48 .50000 2.05 0.85 0.49 58 0.50 0.50 1.90 2.05 2. 10 1996 SUMMER 1 0.60 .60000 0.60 . . . 0.60 0.60 0.60 0.60 0. 10 1997 SUMMER 1 0.20 .20000 0.20 . . . 0.20 0.20 0.20 0.20 0. 10 1998 SUMMER 1 2.50 2.5000 2.50 . . . 2.50 2.50 2.50 2.50 2. 12 1990 SUMMER 4 2.63 .50000 7.00 2.96 1.48 113 0.50 0.85 1.50 4.40 7. 12 1991 SUMMER 3 2.20 1.5000 2.60 0.61 0.35 28 1.50 1.50 2.50 2.60 2. 12 1992 SUMMER 2 1.03 .80000 1.25 0.32 0.23 31 0.80 0.80 1.03 1.25 1. 12 1993 SUMMER 2 3.10 1.6000 4.60 2.12 1.50 68 1.60 1.60 3.10 4.60 4. 12 1994 SUMMER 3 1.55 1.4000 1.80 0.22 0.13 14 1.40 1.40 1.45 1.80 1. 12 1995 SUMMER 2 2.15 1.2000 3.10 1.34 0.95 62 1.20 1.20 2.15 3.10 3. 12 1996 SUMMER 4 2.80 2.7000 3.00 0.14 0.07 5 2.70 2.70 2.75 2.90 3.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 SECCHI_m subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  12 1997 SUMMER 7 1.41 .50000 2.40 0.61 0.23 43 0.50 1.00 1.50 1.80 2 12 1998 SUMMER 8 1.91 .50000 4.25 1.49 0.53 78 0.50 1.00 1.25 3.00 4 13 1990 FALL 5 2.14 .10000 7.00 2.97 1.33 139 0.10 0.30 0.30 3.00 7 13 1990 SPRING 5 1.26 .30000 3.00 1.19 0.53 94 0.30 0.50 0.50 2.00 3 13 1990 SUMMER 22 1.20 .02500 4.50 1.34 0.29 112 0.03 0.20 0.45 1.80 4 13 1991 FALL 1 0.30 .30000 0.30 . . . 0.30 0.30 0.30 0.30 0 13 1991 SPRING 6 1.64 .10000 4.30 2.01 0.82 122 0.10 0.15 0.60 4.10 4 13 1991 SUMMER 6 0.81 .13000 1.50 0.47 0.19 59 0.13 0.60 0.73 1.15 1 13 1991 WINTER 2 0.55 .50000 0.60 0.07 0.05 13 0.50 0.50 0.55 0.60 0 13 1992 FALL 10 0.73 .15000 2.20 0.65 0.21 90 0.15 0.20 0.50 1.00 2 13 1992 SPRING 15 1.31 .10000 4.00 1.31 0.34 100 0.10 0.28 0.60 2.75 4 13 1992 SUMMER 6 1.69 .30000 2.55 0.89 0.36 53 0.30 1.00 1.90 2.50 2 13 1992 WINTER 2 1.05 1.0000 1.10 0.07 0.05 7 1.00 1.00 1.05 1.10 1 13 1993 FALL 3 2.05 1.1500 3.60 1.35 0.78 66 1.15 1.15 1.40 3.60 3 13 1993 SPRING 1 3.00 3.0000 3.00 . . . 3.00 3.00 3.00 3.00 3 13 1993 SUMMER 8 1.60 .22500 3.50 1.27 0.45 79 0.23 0.23 1.78 2.53 3 13 1994 FALL 2 2.25 1.1000 3.40 1.63 1.15 72 1.10 1.10 2.25 3.40 3 13 1994 SPRING 1 3.60 3.6000 3.60 . . . 3.60 3.60 3.60 3.60 3 13 1994 SUMMER 19 1.29 .22500 3.00 0.94 0.22 73 0.23 0.38 1.20 2.20 3 13 1995 FALL 4 2.10 .25000 4.00 1.79 0.89 85 0.25 0.60 2.08 3.60 4 13 1995 SPRING 1 1.95 1.9500 1.95 . . . 1.95 1.95 1.95 1.95 1 13 1995 SUMMER 7 1.51 .40000 2.90 0.89 0.34 59 0.40 0.75 1.40 2.20 2 13 1995 WINTER 1 1.70 1.7000 1.70 . . . 1.70 1.70 1.70 1.70 1 13 1996 FALL 9 0.76 .26000 1.40 0.43 0.14 56 0.26 0.40 0.63 1.10 1 13 1996 SUMMER 20 1.92 .30000 4.33 1.13 0.25 59 0.36 0.99 2.00 2.74 3 13 1997 SUMMER 3 4.83 4.5000 5.50 0.58 0.33 12 4.50 4.50 4.50 5.50 5 13 1998 SUMMER 1 1.50 1.5000 1.50 . . . 1.50 1.50 1.50 1.50 1 18 1991 SUMMER 3 2.95 1.4500 4.40 1.48 0.85 50 1.45 1.45 3.00 4.40 4 18 1992 SPRING 1 3.00 3.0000 3.00 . . . 3.00 3.00 3.00 3.00 3 18 1993 SUMMER 4 3.40 2.0000 5.50 1.59 0.80 47 2.00 2.18 3.05 4.63 5 18 1994 SUMMER 1 1.90 1.9000 1.90 . . . 1.90 1.90 1.90 1.90 1 18 1995 FALL 4 1.93 .99060 3.90 1.33 0.66 69 0.99 1.18 1.41 2.68 3
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 SECCHI_m subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  18 1995 SPRING 1 1.60 1.6000 1.60 . . . 1.60 1.60 1.60 1.60 1 18 1995 SUMMER 6 3.19 .68580 5.70 1.94 0.79 61 0.69 1.37 3.30 4.80 5 18 1996 FALL 3 2.63 1.2192 4.50 1.69 0.97 64 1.22 1.22 2.18 4.50 4 18 1996 SUMMER 4 4.01 2.2860 6.40 1.82 0.91 45 2.29 2.62 3.68 5.40 6 18 1997 SUMMER 1 1.50 1.5000 1.50 . . . 1.50 1.50 1.50 1.50 1 18 1998 SUMMER 1 0.75 .75000 0.75 . . . 0.75 0.75 0.75 0.75 0 20 1990 SPRING 5 2.03 .96000 3.60 1.19 0.53 59 0.96 1.10 1.50 3.00 3 20 1990 SUMMER 13 2.03 .90000 3.00 0.71 0.20 35 0.90 1.75 2.10 2.55 3 20 1991 FALL 3 3.33 2.4000 5.20 1.62 0.93 48 2.40 2.40 2.40 5.20 5 20 1991 SPRING 11 2.59 1.8000 4.00 0.76 0.23 29 1.80 2.00 2.40 2.75 4 20 1991 SUMMER 13 2.58 .75000 5.05 1.31 0.36 51 0.75 1.70 2.40 3.05 5 20 1991 WINTER 1 2.80 2.8000 2.80 . . . 2.80 2.80 2.80 2.80 2 20 1992 FALL 5 2.79 1.3000 6.50 2.14 0.96 77 1.30 1.65 1.80 2.70 6 20 1992 SPRING 9 3.15 1.0000 6.00 1.57 0.52 50 1.00 2.00 3.00 4.00 6 20 1992 SUMMER 6 2.78 1.2000 4.10 1.25 0.51 45 1.20 1.80 2.73 4.10 4 20 1992 WINTER 1 2.10 2.1000 2.10 . . . 2.10 2.10 2.10 2.10 2 20 1993 FALL 6 3.20 2.5000 4.20 0.68 0.28 21 2.50 2.80 2.90 3.90 4 20 1993 SPRING 3 2.83 2.2000 3.60 0.71 0.41 25 2.20 2.20 2.70 3.60 3 20 1993 SUMMER 11 1.93 1.2000 4.30 0.86 0.26 45 1.20 1.30 1.70 2.05 4 20 1994 FALL 9 2.99 1.8000 5.30 1.21 0.40 41 1.80 2.25 2.40 3.80 5 20 1994 SUMMER 10 3.50 .90000 7.80 2.15 0.68 61 0.90 2.30 3.00 4.00 7 20 1995 FALL 12 3.34 1.4000 5.80 1.39 0.40 42 1.40 2.25 2.80 4.53 5 20 1995 SPRING 2 2.78 1.4000 4.15 1.94 1.38 70 1.40 1.40 2.78 4.15 4 20 1995 SUMMER 22 3.03 1.0000 5.70 1.19 0.25 39 1.20 2.35 2.98 3.30 4 20 1996 FALL 4 2.23 1.6000 3.00 0.68 0.34 30 1.60 1.66 2.16 2.80 3 20 1996 SPRING 5 3.10 1.1000 4.50 1.50 0.67 48 1.10 1.90 3.90 4.10 4 20 1996 SUMMER 8 3.07 1.8000 4.50 0.98 0.35 32 1.80 2.43 2.88 3.84 4 20 1996 WINTER 1 3.55 3.5500 3.55 . . . 3.55 3.55 3.55 3.55 3 22 1990 FALL 1 0.85 .85000 0.85 . . . 0.85 0.85 0.85 0.85 0 22 1990 SPRING 1 2.43 2.4250 2.43 . . . 2.43 2.43 2.43 2.43 2 22 1990 SUMMER 1 0.50 .50000 0.50 . . . 0.50 0.50 0.50 0.50 0 22 1991 FALL 2 3.75 3.2250 4.28 0.74 0.53 20 3.23 3.23 3.75 4.28 4
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 SECCHI_m subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 22 1991 SPRING 3 2.32 1.1000 4.00 1.51 0.87 65 1.10 1.10 1.85 4.00 4. 22 1991 SUMMER 2 2.95 2.4000 3.50 0.78 0.55 26 2.40 2.40 2.95 3.50 3. 22 1992 FALL 3 2.15 1.5000 2.85 0.68 0.39 31 1.50 1.50 2.10 2.85 2. 22 1992 SUMMER 3 2.10 1.0000 3.80 1.49 0.86 71 1.00 1.00 1.50 3.80 3. 22 1993 SUMMER 1 0.15 .15000 0.15 . . . 0.15 0.15 0.15 0.15 0. 22 1995 FALL 1 0.75 .75000 0.75 . . . 0.75 0.75 0.75 0.75 0. 22 1995 SPRING 1 0.80 .80000 0.80 . . . 0.80 0.80 0.80 0.80 0. 22 1995 SUMMER 1 2.20 2.2000 2.20 . . . 2.20 2.20 2.20 2.20 2. 24 1990 FALL 4 1.18 .54000 2.10 0.77 0.38 65 0.54 0.55 1.04 1.81 2. 24 1990 SPRING 3 1.02 .20000 2.29 1.11 0.64 109 0.20 0.20 0.58 2.29 2. 24 1990 SUMMER 3 1.20 .20000 2.65 1.29 0.74 107 0.20 0.20 0.75 2.65 2. 24 1990 WINTER 1 3.00 3.0000 3.00 . . . 3.00 3.00 3.00 3.00 3. 24 1991 FALL 1 2.67 2.6650 2.67 . . . 2.67 2.67 2.67 2.67 2. 24 1991 SPRING 1 3.58 3.5750 3.58 . . . 3.58 3.58 3.58 3.58 3. 24 1991 SUMMER 2 2.11 .71500 3.50 1.97 1.39 93 0.72 0.72 2.11 3.50 3. 24 1991 WINTER 1 3.66 3.6600 3.66 . . . 3.66 3.66 3.66 3.66 3. 24 1992 FALL 1 3.00 3.0000 3.00 . . . 3.00 3.00 3.00 3.00 3. 24 1992 SPRING 6 1.12 .20000 3.40 1.23 0.50 110 0.20 0.30 0.65 1.50 3. 24 1992 SUMMER 2 1.88 .76000 3.00 1.58 1.12 84 0.76 0.76 1.88 3.00 3. 24 1992 WINTER 2 2.20 .81000 3.59 1.96 1.39 89 0.81 0.81 2.20 3.59 3. 24 1993 SPRING 2 0.74 .70000 0.78 0.05 0.04 7 0.70 0.70 0.74 0.78 0. 24 1993 SUMMER 2 1.62 .61500 2.63 1.42 1.01 88 0.62 0.62 1.62 2.63 2. 24 1993 WINTER 1 0.83 .82500 0.83 . . . 0.83 0.83 0.83 0.83 0. 24 1994 FALL 1 2.67 2.6650 2.67 . . . 2.67 2.67 2.67 2.67 2. 24 1994 SPRING 2 1.24 .64000 1.83 0.84 0.60 68 0.64 0.64 1.24 1.83 1. 24 1994 SUMMER 2 2.01 .84000 3.18 1.65 1.17 82 0.84 0.84 2.01 3.18 3. 24 1994 WINTER 1 3.40 3.4000 3.40 . . . 3.40 3.40 3.40 3.40 3. 24 1995 SUMMER 2 0.55 .33000 0.78 0.31 0.22 57 0.33 0.33 0.55 0.78 0. 24 1995 WINTER 2 2.52 .70500 4.34 2.57 1.82 102 0.71 0.71 2.52 4.34 4. 24 1996 SPRING 1 0.75 .75000 0.75 . . . 0.75 0.75 0.75 0.75 0. 24 1996 SUMMER 1 0.62 .61500 0.62 . . . 0.62 0.62 0.62 0.62 0. 24 1997 FALL 1 1.08 1.0750 1.08 . . . 1.08 1.08 1.08 1.08 1.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 SECCHI_m subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 24 1997 SPRING 1 0.95 .95000 0.95 . . . 0.95 0.95 0.95 0.95 0. 24 1997 SUMMER 1 0.90 .90000 0.90 . . . 0.90 0.90 0.90 0.90 0. 80 1990 SUMMER 1 1.30 1.3000 1.30 . . . 1.30 1.30 1.30 1.30 1. 80 1991 SUMMER 1 4.60 4.6000 4.60 . . . 4.60 4.60 4.60 4.60 4. 80 1993 FALL 1 2.90 2.9000 2.90 . . . 2.90 2.90 2.90 2.90 2. 80 1993 SUMMER 1 3.70 3.7000 3.70 . . . 3.70 3.70 3.70 3.70 3. 80 1995 SUMMER 2 2.20 1.7000 2.70 0.71 0.50 32 1.70 1.70 2.20 2.70 2. 80 1996 SUMMER 1 1.90 1.9000 1.90 . . . 1.90 1.90 1.90 1.90 1. 80 1997 SUMMER 1 1.50 1.5000 1.50 . . . 1.50 1.50 1.50 1.50 1. 80 1998 SUMMER 1 0.50 .50000 0.50 . . . 0.50 0.50 0.50 0.50 0. 81 1990 FALL 1 1.76 1.7563 1.76 . . . 1.76 1.76 1.76 1.76 1.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 Total_Nitrogen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 10 1994 FALL 3 0.28 .25000 0.30 0.03 0.01 9 0.25 0.25 0.28 0.30 0. 10 1994 SPRING 3 0.42 .38500 0.45 0.03 0.02 7 0.39 0.39 0.42 0.45 0. 10 1994 SUMMER 3 0.25 .24000 0.25 0.01 0.00 2 0.24 0.24 0.25 0.25 0. 10 1994 WINTER 3 0.38 .36000 0.39 0.02 0.01 5 0.36 0.36 0.39 0.39 0. 10 1995 FALL 3 0.28 .28000 0.28 0.00 0.00 0 0.28 0.28 0.28 0.28 0. 10 1995 SPRING 3 0.57 .53500 0.59 0.03 0.02 5 0.54 0.54 0.59 0.59 0. 10 1995 SUMMER 3 0.30 .29000 0.30 0.01 0.00 2 0.29 0.29 0.30 0.30 0. 10 1995 WINTER 3 0.55 .51500 0.60 0.04 0.03 8 0.52 0.52 0.54 0.60 0. 13 1990 FALL 1 0.96 .96000 0.96 . . . 0.96 0.96 0.96 0.96 0. 13 1990 SPRING 1 0.39 .38500 0.39 . . . 0.39 0.39 0.39 0.39 0. 13 1990 SUMMER 2 1.37 .38000 2.35 1.39 0.99 102 0.38 0.38 1.37 2.35 2. 13 1990 WINTER 1 0.34 .34000 0.34 . . . 0.34 0.34 0.34 0.34 0. 13 1991 FALL 1 0.63 .62500 0.63 . . . 0.63 0.63 0.63 0.63 0. 13 1991 SPRING 1 0.52 .52000 0.52 . . . 0.52 0.52 0.52 0.52 0. 13 1991 SUMMER 1 0.36 .36000 0.36 . . . 0.36 0.36 0.36 0.36 0. 13 1991 WINTER 1 0.60 .60000 0.60 . . . 0.60 0.60 0.60 0.60 0. 13 1992 FALL 2 1.57 .87000 2.26 0.98 0.70 63 0.87 0.87 1.57 2.26 2. 13 1992 SPRING 2 1.59 .52000 2.66 1.51 1.07 95 0.52 0.52 1.59 2.66 2. 13 1992 SUMMER 1 0.48 .48000 0.48 . . . 0.48 0.48 0.48 0.48 0. 13 1992 WINTER 1 0.72 .72000 0.72 . . . 0.72 0.72 0.72 0.72 0. 13 1993 FALL 2 2.04 1.9500 2.13 0.13 0.09 6 1.95 1.95 2.04 2.13 2. 13 1993 SPRING 2 1.94 .88000 3.00 1.50 1.06 77 0.88 0.88 1.94 3.00 3. 13 1993 SUMMER 2 1.72 .92000 2.51 1.12 0.80 66 0.92 0.92 1.72 2.51 2. 13 1993 WINTER 1 2.32 2.3200 2.32 . . . 2.32 2.32 2.32 2.32 2. 13 1994 FALL 2 1.77 .74500 2.80 1.45 1.03 82 0.75 0.75 1.77 2.80 2. 13 1994 SPRING 2 1.60 .49000 2.72 1.57 1.11 98 0.49 0.49 1.60 2.72 2. 13 1994 SUMMER 2 1.98 .59000 3.36 1.96 1.39 99 0.59 0.59 1.98 3.36 3. 13 1994 WINTER 2 1.44 .36000 2.52 1.53 1.08 106 0.36 0.36 1.44 2.52 2. 13 1995 FALL 2 2.12 1.2900 2.95 1.17 0.83 55 1.29 1.29 2.12 2.95 2. 13 1995 SPRING 2 1.74 .57000 2.92 1.66 1.17 95 0.57 0.57 1.74 2.92 2. 13 1995 SUMMER 1 2.48 2.4800 2.48 . . . 2.48 2.48 2.48 2.48 2. 13 1995 WINTER 2 1.79 .75000 2.82 1.46 1.04 82 0.75 0.75 1.79 2.82 2.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 Total_Nitrogen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 13 1996 FALL 4 1.16 .61000 2.31 0.78 0.39 67 0.61 0.69 0.87 1.63 2. 13 1996 SPRING 3 1.10 .37500 2.54 1.24 0.72 112 0.38 0.38 0.40 2.54 2. 13 1996 SUMMER 4 1.14 .20000 2.92 1.24 0.62 109 0.20 0.29 0.72 1.99 2. 13 1996 WINTER 2 0.79 .68000 0.90 0.16 0.11 20 0.68 0.68 0.79 0.90 0. 13 1997 FALL 7 0.70 .18000 1.58 0.47 0.18 68 0.18 0.32 0.66 1.00 1. 13 1997 SPRING 3 1.35 .54000 2.45 0.99 0.57 73 0.54 0.54 1.07 2.45 2. 13 1997 SUMMER 7 0.78 .32000 1.47 0.39 0.15 49 0.32 0.47 0.69 1.00 1. 13 1997 WINTER 2 0.59 .45500 0.72 0.19 0.13 32 0.46 0.46 0.59 0.72 0. 13 1998 SPRING 4 1.45 .60000 3.21 1.19 0.59 82 0.60 0.78 1.00 2.13 3. 13 1998 WINTER 3 0.51 .30000 0.71 0.21 0.12 40 0.30 0.30 0.53 0.71 0. 22 1990 FALL 1 0.33 .33000 0.33 . . . 0.33 0.33 0.33 0.33 0. 22 1990 SPRING 1 1.96 1.9550 1.96 . . . 1.96 1.96 1.96 1.96 1. 22 1990 SUMMER 1 1.02 1.0200 1.02 . . . 1.02 1.02 1.02 1.02 1. 22 1991 FALL 2 0.77 .46000 1.07 0.43 0.31 56 0.46 0.46 0.77 1.07 1. 22 1991 SPRING 3 0.72 .16500 1.51 0.70 0.40 96 0.17 0.17 0.50 1.51 1. 22 1991 SUMMER 2 0.43 .15500 0.71 0.39 0.28 91 0.16 0.16 0.43 0.71 0. 22 1992 FALL 2 0.30 .29000 0.30 0.01 0.01 2 0.29 0.29 0.30 0.30 0. 22 1992 SPRING 1 0.47 .47000 0.47 . . . 0.47 0.47 0.47 0.47 0. 22 1992 SUMMER 1 0.14 .14000 0.14 . . . 0.14 0.14 0.14 0.14 0. 22 1993 SPRING 3 0.34 .23000 0.44 0.11 0.06 31 0.23 0.23 0.35 0.44 0. 22 1993 SUMMER 5 0.82 .29000 2.41 0.90 0.40 110 0.29 0.32 0.40 0.69 2. 22 1993 WINTER 2 0.39 .36000 0.42 0.04 0.03 11 0.36 0.36 0.39 0.42 0. 22 1995 FALL 2 0.75 .50000 1.00 0.35 0.25 47 0.50 0.50 0.75 1.00 1. 22 1995 SPRING 1 0.53 .53000 0.53 . . . 0.53 0.53 0.53 0.53 0. 22 1995 SUMMER 1 0.65 .65000 0.65 . . . 0.65 0.65 0.65 0.65 0. 24 1990 FALL 2 0.50 .44000 0.56 0.08 0.06 17 0.44 0.44 0.50 0.56 0. 24 1990 SPRING 2 0.62 .62000 0.62 0.00 0.00 0 0.62 0.62 0.62 0.62 0. 24 1990 SUMMER 2 1.00 .98500 1.01 0.01 0.01 1 0.99 0.99 1.00 1.01 1. 24 1992 SPRING 2 3.00 1.6700 4.33 1.88 1.33 63 1.67 1.67 3.00 4.33 4. 24 1993 SPRING 7 1.41 .45000 3.64 1.12 0.42 79 0.45 0.57 0.89 1.90 3. 24 1995 SUMMER 3 1.01 .80000 1.30 0.26 0.15 26 0.80 0.80 0.93 1.30 1. 24 1997 FALL 1 0.12 .12250 0.12 . . . 0.12 0.12 0.12 0.12 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1998 Total_Nitrogen_mg_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 24 1997 SPRING 1 0.45 .45000 0.45 . . . 0.45 0.45 0.45 0.45 0. 24 1997 SUMMER 1 0.68 .67500 0.68 . . . 0.68 0.68 0.68 0.68 0.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 6 1990 FALL 1 120.00 120.00 120.00 . . . 120.00 120.00 120.00 120.00 120. 6 1990 SPRING 3 40.00 30.000 60.00 17.32 10.00 43 30.00 30.00 30.00 60.00 60. 6 1990 SUMMER 1 40.00 40.000 40.00 . . . 40.00 40.00 40.00 40.00 40. 6 1991 FALL 1 30.00 30.000 30.00 . . . 30.00 30.00 30.00 30.00 30. 6 1991 SPRING 1 30.00 30.000 30.00 . . . 30.00 30.00 30.00 30.00 30. 6 1991 SUMMER 1 30.00 30.000 30.00 . . . 30.00 30.00 30.00 30.00 30. 6 1992 FALL 3 553.33 490.00 640.00 77.67 44.85 14 490.00 490.00 530.00 640.00 640. 6 1992 WINTER 3 266.67 250.00 300.00 28.87 16.67 11 250.00 250.00 250.00 300.00 300. 6 1993 FALL 3 343.33 330.00 350.00 11.55 6.67 3 330.00 330.00 350.00 350.00 350. 6 1993 SPRING 3 196.67 190.00 200.00 5.77 3.33 3 190.00 190.00 200.00 200.00 200. 6 1993 SUMMER 3 206.67 200.00 220.00 11.55 6.67 6 200.00 200.00 200.00 220.00 220. 6 1993 WINTER 3 201.67 190.00 220.00 16.07 9.28 8 190.00 190.00 195.00 220.00 220. 6 1994 FALL 1 8.00 8.0000 8.00 . . . 8.00 8.00 8.00 8.00 8. 6 1994 SPRING 4 87.50 20.000 130.00 47.17 23.58 54 20.00 60.00 100.00 115.00 130. 6 1994 SUMMER 1 185.00 185.00 185.00 . . . 185.00 185.00 185.00 185.00 185. 6 1994 WINTER 3 150.00 150.00 150.00 0.00 0.00 0 150.00 150.00 150.00 150.00 150. 6 1996 FALL 1 490.00 490.00 490.00 . . . 490.00 490.00 490.00 490.00 490. 6 1996 SUMMER 1 185.00 185.00 185.00 . . . 185.00 185.00 185.00 185.00 185. 6 1996 WINTER 1 260.00 260.00 260.00 . . . 260.00 260.00 260.00 260.00 260. 6 1997 FALL 1 160.00 160.00 160.00 . . . 160.00 160.00 160.00 160.00 160. 6 1997 SPRING 1 220.00 220.00 220.00 . . . 220.00 220.00 220.00 220.00 220. 6 1997 SUMMER 1 530.00 530.00 530.00 . . . 530.00 530.00 530.00 530.00 530. 10 1990 FALL 3 73.33 30.000 120.00 45.09 26.03 61 30.00 30.00 70.00 120.00 120. 10 1990 SPRING 4 80.00 40.000 150.00 49.67 24.83 62 40.00 45.00 65.00 115.00 150. 10 1990 SUMMER 4 197.50 40.000 640.00 295.11 147.56 149 40.00 45.00 55.00 350.00 640. 10 1991 FALL 2 35.00 20.000 50.00 21.21 15.00 61 20.00 20.00 35.00 50.00 50. 10 1991 SPRING 2 65.00 50.000 80.00 21.21 15.00 33 50.00 50.00 65.00 80.00 80. 10 1991 SUMMER 2 80.00 80.000 80.00 0.00 0.00 0 80.00 80.00 80.00 80.00 80. 10 1991 WINTER 2 70.00 60.000 80.00 14.14 10.00 20 60.00 60.00 70.00 80.00 80. 10 1992 FALL 3 105.00 10.000 265.00 139.37 80.47 133 10.00 10.00 40.00 265.00 265. 10 1992 SPRING 2 50.00 30.000 70.00 28.28 20.00 57 30.00 30.00 50.00 70.00 70. 10 1992 SUMMER 5 128.00 40.000 380.00 142.37 63.67 111 40.00 50.00 80.00 90.00 380.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 10 1992 WINTER 2 60.00 10.000 110.00 70.71 50.00 118 10.00 10.00 60.00 110.00 110. 10 1993 FALL 3 130.00 60.000 260.00 112.69 65.06 87 60.00 60.00 70.00 260.00 260. 10 1993 SPRING 2 65.00 40.000 90.00 35.36 25.00 54 40.00 40.00 65.00 90.00 90. 10 1993 SUMMER 6 137.50 30.000 410.00 144.91 59.16 105 30.00 45.00 75.00 190.00 410. 10 1993 WINTER 2 60.00 40.000 80.00 28.28 20.00 47 40.00 40.00 60.00 80.00 80. 10 1994 FALL 6 78.83 20.000 275.00 96.65 39.46 123 20.00 41.00 43.50 50.00 275. 10 1994 SPRING 6 93.50 29.000 370.00 136.13 55.58 146 29.00 30.00 33.50 65.00 370. 10 1994 SUMMER 6 119.00 20.000 510.00 193.03 78.80 162 20.00 22.00 46.00 70.00 510. 10 1994 WINTER 5 43.60 24.000 110.00 37.21 16.64 85 24.00 25.00 29.00 30.00 110. 10 1995 FALL 6 45.92 26.500 110.00 32.57 13.30 71 26.50 27.00 31.00 50.00 110. 10 1995 SPRING 6 63.00 35.000 120.00 29.33 11.97 47 35.00 51.00 56.00 60.00 120. 10 1995 SUMMER 6 66.92 30.000 210.00 70.97 28.97 106 30.00 31.50 35.00 60.00 210. 10 1995 WINTER 5 49.40 30.000 90.00 24.07 10.76 49 30.00 36.50 38.50 52.00 90. 10 1996 FALL 2 100.00 80.000 120.00 28.28 20.00 28 80.00 80.00 100.00 120.00 120. 10 1996 SPRING 2 55.00 40.000 70.00 21.21 15.00 39 40.00 40.00 55.00 70.00 70. 10 1996 SUMMER 4 82.50 50.000 110.00 25.00 12.50 30 50.00 65.00 85.00 100.00 110. 10 1996 WINTER 2 45.00 20.000 70.00 35.36 25.00 79 20.00 20.00 45.00 70.00 70. 10 1997 FALL 2 105.00 70.000 140.00 49.50 35.00 47 70.00 70.00 105.00 140.00 140. 10 1997 SPRING 2 70.00 55.000 85.00 21.21 15.00 30 55.00 55.00 70.00 85.00 85. 10 1997 SUMMER 3 156.67 70.000 300.00 125.03 72.19 80 70.00 70.00 100.00 300.00 300. 10 1997 WINTER 2 55.00 30.000 80.00 35.36 25.00 64 30.00 30.00 55.00 80.00 80. 10 1998 FALL 5 115.30 39.000 204.00 60.60 27.10 53 39.00 88.50 113.00 132.00 204. 10 1998 SPRING 2 67.50 55.000 80.00 17.68 12.50 26 55.00 55.00 67.50 80.00 80. 10 1998 SUMMER 8 98.13 34.000 257.00 88.66 31.35 90 34.00 36.50 55.00 155.50 257. 10 1998 WINTER 3 136.67 89.000 169.00 42.15 24.33 31 89.00 89.00 152.00 169.00 169. 10 1999 SPRING 5 72.20 56.000 84.00 11.56 5.17 16 56.00 64.50 78.00 78.50 84. 10 1999 WINTER 4 107.75 77.000 143.00 27.94 13.97 26 77.00 87.00 105.50 128.50 143. 12 1990 SUMMER 5 68.00 10.000 115.00 44.24 19.79 65 10.00 35.00 80.00 100.00 115. 12 1991 FALL 2 85.00 20.000 150.00 91.92 65.00 108 20.00 20.00 85.00 150.00 150. 12 1991 SPRING 2 82.50 15.000 150.00 95.46 67.50 116 15.00 15.00 82.50 150.00 150. 12 1991 SUMMER 6 91.67 20.000 190.00 71.04 29.00 77 20.00 25.00 75.00 165.00 190. 12 1991 WINTER 2 85.00 20.000 150.00 91.92 65.00 108 20.00 20.00 85.00 150.00 150.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  12 1992 SUMMER 3 61.67 50.000 85.00 20.21 11.67 33 50.00 50.00 50.00 85.00 85 12 1992 WINTER 2 97.50 35.000 160.00 88.39 62.50 91 35.00 35.00 97.50 160.00 160 12 1993 SUMMER 2 40.00 20.000 60.00 28.28 20.00 71 20.00 20.00 40.00 60.00 60 12 1994 SUMMER 4 110.00 90.000 160.00 33.67 16.83 31 90.00 90.00 95.00 130.00 160 12 1995 SUMMER 3 86.67 75.000 95.00 10.41 6.01 12 75.00 75.00 90.00 95.00 95 12 1996 SUMMER 5 54.00 25.000 80.00 20.43 9.14 38 25.00 45.00 60.00 60.00 80 12 1997 SUMMER 8 134.38 45.000 310.00 102.94 36.39 77 45.00 57.50 77.50 225.00 310 12 1998 SUMMER 8 65.63 .00000 210.00 81.39 28.78 124 0.00 0.00 42.50 115.00 210 13 1990 FALL 2 60.00 40.000 80.00 28.28 20.00 47 40.00 40.00 60.00 80.00 80 13 1990 SPRING 7 41.43 20.000 75.00 25.61 9.68 62 20.00 20.00 25.00 70.00 75 13 1990 SUMMER 24 107.15 1.5000 680.00 167.91 34.28 157 10.00 25.00 45.00 110.00 560 13 1990 WINTER 1 30.00 30.000 30.00 . . . 30.00 30.00 30.00 30.00 30 13 1991 FALL 2 165.00 80.000 250.00 120.21 85.00 73 80.00 80.00 165.00 250.00 250 13 1991 SPRING 9 66.11 10.000 175.00 52.31 17.44 79 10.00 30.00 50.00 90.00 175 13 1991 SUMMER 7 86.07 2.5000 240.00 80.36 30.37 93 2.50 30.00 60.00 130.00 240 13 1991 WINTER 4 80.00 60.000 100.00 16.33 8.16 20 60.00 70.00 80.00 90.00 100 13 1992 FALL 14 222.50 30.000 760.00 195.29 52.19 88 30.00 80.00 185.00 320.00 760 13 1992 SPRING 18 71.94 2.5000 700.00 159.27 37.54 221 2.50 10.00 35.00 55.00 700 13 1992 SUMMER 14 42.32 6.2500 120.00 43.37 11.59 102 6.25 10.00 30.00 75.00 120 13 1992 WINTER 3 268.33 70.000 620.00 305.38 176.31 114 70.00 70.00 115.00 620.00 620 13 1993 FALL 6 302.50 10.000 660.00 270.37 110.38 89 10.00 60.00 272.50 540.00 660 13 1993 SPRING 4 237.50 50.000 700.00 310.95 155.48 131 50.00 55.00 100.00 420.00 700 13 1993 SUMMER 11 143.18 10.000 800.00 223.68 67.44 156 10.00 30.00 80.00 150.00 800 13 1993 WINTER 2 470.00 220.00 720.00 353.55 250.00 75 220.00 220.00 470.00 720.00 720 13 1994 FALL 4 432.50 75.000 860.00 396.92 198.46 92 75.00 95.00 397.50 770.00 860 13 1994 SPRING 3 296.67 30.000 800.00 436.16 251.82 147 30.00 30.00 60.00 800.00 800 13 1994 SUMMER 23 105.33 2.5000 650.00 183.85 38.34 175 10.00 15.00 25.00 90.00 630 13 1994 WINTER 3 473.33 60.000 800.00 377.54 217.97 80 60.00 60.00 560.00 800.00 800 13 1995 FALL 6 270.83 15.000 750.00 307.17 125.40 113 15.00 50.00 125.00 560.00 750 13 1995 SPRING 4 347.50 40.000 840.00 373.73 186.87 108 40.00 57.50 255.00 637.50 840 13 1995 SUMMER 9 203.61 2.5000 580.00 230.38 76.79 113 2.50 30.00 70.00 440.00 580 13 1995 WINTER 3 350.00 50.000 880.00 460.33 265.77 132 50.00 50.00 120.00 880.00 880
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  13 1996 FALL 14 170.09 10.000 760.00 229.01 61.21 135 10.00 15.00 57.50 325.00 760 13 1996 SPRING 3 306.67 50.000 790.00 418.85 241.82 137 50.00 50.00 80.00 790.00 790 13 1996 SUMMER 24 79.27 2.5000 700.00 155.35 31.71 196 10.00 17.50 25.00 45.00 325 13 1996 WINTER 3 326.67 40.000 840.00 445.57 257.25 136 40.00 40.00 100.00 840.00 840 13 1997 FALL 7 149.29 20.000 705.00 247.53 93.56 166 20.00 30.00 40.00 110.00 705 13 1997 SPRING 3 273.33 30.000 730.00 395.77 228.50 145 30.00 30.00 60.00 730.00 730 13 1997 SUMMER 10 130.50 10.000 760.00 225.05 71.17 172 10.00 30.00 52.50 116.00 760 13 1997 WINTER 2 415.00 30.000 800.00 544.47 385.00 131 30.00 30.00 415.00 800.00 800 13 1998 SPRING 4 207.50 20.000 690.00 322.63 161.32 155 20.00 30.00 60.00 385.00 690 13 1998 SUMMER 1 30.00 30.000 30.00 . . . 30.00 30.00 30.00 30.00 30 13 1998 WINTER 3 290.00 30.000 780.00 424.62 245.15 146 30.00 30.00 60.00 780.00 780 18 1991 SUMMER 3 13.33 10.000 20.00 5.77 3.33 43 10.00 10.00 10.00 20.00 20 18 1992 SPRING 1 20.00 20.000 20.00 . . . 20.00 20.00 20.00 20.00 20 18 1993 SUMMER 4 15.00 10.000 20.00 5.77 2.89 38 10.00 10.00 15.00 20.00 20 18 1994 SUMMER 3 620.00 10.000 1200.00 595.57 343.85 96 10.00 10.00 650.00 1200.0 120 18 1995 FALL 4 36.25 10.000 100.00 42.70 21.35 118 10.00 12.50 17.50 60.00 100 18 1995 SPRING 2 4.38 2.5000 6.25 2.65 1.88 61 2.50 2.50 4.38 6.25 6 18 1995 SUMMER 6 14.58 2.5000 20.00 7.14 2.92 49 2.50 10.00 17.50 20.00 20 18 1996 FALL 4 16.25 10.000 20.00 4.79 2.39 29 10.00 12.50 17.50 20.00 20 18 1996 SUMMER 4 13.75 10.000 25.00 7.50 3.75 55 10.00 10.00 10.00 17.50 25 18 1997 SUMMER 1 55.00 55.000 55.00 . . . 55.00 55.00 55.00 55.00 55 18 1998 SUMMER 1 110.00 110.00 110.00 . . . 110.00 110.00 110.00 110.00 110 20 1990 FALL 1 50.00 50.000 50.00 . . . 50.00 50.00 50.00 50.00 50 20 1990 SPRING 6 26.08 1.5000 60.00 20.71 8.46 79 1.50 10.00 25.00 35.00 60 20 1990 SUMMER 13 22.42 8.0000 65.00 18.76 5.20 84 8.00 10.00 10.00 25.00 65 20 1991 FALL 6 80.83 2.5000 390.00 153.63 62.72 190 2.50 2.50 10.00 70.00 390 20 1991 SPRING 12 65.10 2.5000 480.00 134.99 38.97 207 2.50 8.13 22.50 30.00 480 20 1991 SUMMER 14 8.39 2.5000 30.00 7.99 2.13 95 2.50 2.50 6.25 10.00 30 20 1991 WINTER 1 40.00 40.000 40.00 . . . 40.00 40.00 40.00 40.00 40 20 1992 FALL 9 130.00 20.000 350.00 104.61 34.87 80 20.00 55.00 110.00 175.00 350 20 1992 SPRING 12 36.15 2.5000 150.00 41.87 12.09 116 2.50 4.38 25.00 50.00 150 20 1992 SUMMER 6 15.63 2.5000 45.00 15.53 6.34 99 2.50 6.25 10.00 20.00 45
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75  20 1992 WINTER 1 2.50 2.5000 2.50 . . . 2.50 2.50 2.50 2.50 2 20 1993 FALL 8 8.13 2.5000 20.00 6.78 2.40 83 2.50 2.50 6.25 12.50 20 20 1993 SPRING 3 30.00 10.000 50.00 20.00 11.55 67 10.00 10.00 30.00 50.00 50 20 1993 SUMMER 16 6.88 2.5000 20.00 6.49 1.62 94 2.50 2.50 2.50 10.00 20 20 1994 FALL 9 25.56 2.5000 120.00 38.60 12.87 151 2.50 2.50 6.25 20.00 120 20 1994 SPRING 1 2.50 2.5000 2.50 . . . 2.50 2.50 2.50 2.50 2 20 1994 SUMMER 11 30.23 2.5000 145.00 41.06 12.38 136 2.50 10.00 15.00 25.00 145 20 1994 WINTER 2 6.25 2.5000 10.00 5.30 3.75 85 2.50 2.50 6.25 10.00 10 20 1995 FALL 13 11.92 2.5000 60.00 15.71 4.36 132 2.50 2.50 6.25 10.00 60 20 1995 SPRING 4 29.38 2.5000 75.00 32.56 16.28 111 2.50 6.25 20.00 52.50 75 20 1995 SUMMER 23 13.10 2.5000 65.00 16.59 3.46 127 2.50 2.50 10.00 15.00 45 20 1995 WINTER 3 5.00 2.5000 10.00 4.33 2.50 87 2.50 2.50 2.50 10.00 10 20 1996 FALL 6 17.29 2.5000 45.00 14.84 6.06 86 2.50 10.00 13.13 20.00 45 20 1996 SPRING 8 14.53 2.5000 55.00 17.27 6.11 119 2.50 4.38 10.00 15.00 55 20 1996 SUMMER 10 26.63 2.5000 80.00 30.16 9.54 113 2.50 6.25 10.00 50.00 80 20 1996 WINTER 4 9.06 6.2500 10.00 1.88 0.94 21 6.25 8.13 10.00 10.00 10 20 1997 SPRING 1 100.00 100.00 100.00 . . . 100.00 100.00 100.00 100.00 100 20 1999 SUMMER 2 0.00 .00000 0.00 0.00 0.00 . 0.00 0.00 0.00 0.00 0 22 1990 FALL 1 25.00 25.000 25.00 . . . 25.00 25.00 25.00 25.00 25 22 1990 SPRING 1 135.00 135.00 135.00 . . . 135.00 135.00 135.00 135.00 135 22 1990 SUMMER 2 55.00 40.000 70.00 21.21 15.00 39 40.00 40.00 55.00 70.00 70 22 1991 FALL 2 35.00 10.000 60.00 35.36 25.00 101 10.00 10.00 35.00 60.00 60 22 1991 SPRING 3 8.75 2.5000 21.25 10.83 6.25 124 2.50 2.50 2.50 21.25 21 22 1991 SUMMER 3 39.17 2.5000 70.00 34.13 19.70 87 2.50 2.50 45.00 70.00 70 22 1992 FALL 5 45.00 .00000 135.00 57.45 25.69 128 0.00 10.00 10.00 70.00 135 22 1992 SPRING 1 2.50 2.5000 2.50 . . . 2.50 2.50 2.50 2.50 2 22 1992 SUMMER 5 52.00 10.000 120.00 44.53 19.91 86 10.00 15.00 50.00 65.00 120 22 1993 SUMMER 7 72.86 20.000 200.00 68.00 25.70 93 20.00 20.00 40.00 110.00 200 22 1993 WINTER 2 30.00 30.000 30.00 0.00 0.00 0 30.00 30.00 30.00 30.00 30 22 1994 SUMMER 1 50.00 50.000 50.00 . . . 50.00 50.00 50.00 50.00 50 22 1995 FALL 2 20.00 20.000 20.00 0.00 0.00 0 20.00 20.00 20.00 20.00 20 22 1995 SPRING 1 20.00 20.000 20.00 . . . 20.00 20.00 20.00 20.00 20
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 22 1995 SUMMER 1 20.00 20.000 20.00 . . . 20.00 20.00 20.00 20.00 20. 22 1996 SPRING 1 180.00 180.00 180.00 . . . 180.00 180.00 180.00 180.00 180. 22 1999 SUMMER 2 60.00 50.000 70.00 14.14 10.00 24 50.00 50.00 60.00 70.00 70. 24 1990 FALL 4 20.63 2.5000 50.00 20.85 10.43 101 2.50 6.25 15.00 35.00 50. 24 1990 SPRING 3 27.08 6.2500 50.00 21.95 12.67 81 6.25 6.25 25.00 50.00 50. 24 1990 SUMMER 3 20.83 2.5000 35.00 16.65 9.61 80 2.50 2.50 25.00 35.00 35. 24 1990 WINTER 1 20.00 20.000 20.00 . . . 20.00 20.00 20.00 20.00 20. 24 1991 FALL 1 15.00 15.000 15.00 . . . 15.00 15.00 15.00 15.00 15. 24 1991 SPRING 1 20.00 20.000 20.00 . . . 20.00 20.00 20.00 20.00 20. 24 1991 SUMMER 2 52.50 50.000 55.00 3.54 2.50 7 50.00 50.00 52.50 55.00 55. 24 1991 WINTER 1 15.00 15.000 15.00 . . . 15.00 15.00 15.00 15.00 15. 24 1992 FALL 1 40.00 40.000 40.00 . . . 40.00 40.00 40.00 40.00 40. 24 1992 SPRING 6 391.67 10.000 960.00 422.35 172.42 108 10.00 60.00 215.00 890.00 960. 24 1992 SUMMER 5 35.50 2.5000 70.00 30.12 13.47 85 2.50 20.00 20.00 65.00 70. 24 1992 WINTER 6 41.67 20.000 70.00 16.33 6.67 39 20.00 35.00 40.00 45.00 70. 24 1993 FALL 1 20.00 20.000 20.00 . . . 20.00 20.00 20.00 20.00 20. 24 1993 SPRING 8 263.13 25.000 1630.00 558.69 197.53 212 25.00 25.00 27.50 172.50 1630 24 1993 SUMMER 2 50.00 40.000 60.00 14.14 10.00 28 40.00 40.00 50.00 60.00 60. 24 1993 WINTER 1 45.00 45.000 45.00 . . . 45.00 45.00 45.00 45.00 45. 24 1994 SPRING 1 65.00 65.000 65.00 . . . 65.00 65.00 65.00 65.00 65. 24 1995 SUMMER 3 33.33 20.000 60.00 23.09 13.33 69 20.00 20.00 20.00 60.00 60. 24 1995 WINTER 1 45.00 45.000 45.00 . . . 45.00 45.00 45.00 45.00 45. 24 1996 SPRING 1 40.00 40.000 40.00 . . . 40.00 40.00 40.00 40.00 40. 24 1996 SUMMER 1 65.00 65.000 65.00 . . . 65.00 65.00 65.00 65.00 65. 24 1997 FALL 1 20.00 20.000 20.00 . . . 20.00 20.00 20.00 20.00 20. 24 1997 SPRING 1 25.00 25.000 25.00 . . . 25.00 25.00 25.00 25.00 25. 24 1997 SUMMER 1 20.00 20.000 20.00 . . . 20.00 20.00 20.00 20.00 20. 80 1990 FALL 1 70.00 70.000 70.00 . . . 70.00 70.00 70.00 70.00 70. 80 1990 SPRING 1 100.00 100.00 100.00 . . . 100.00 100.00 100.00 100.00 100. 80 1990 SUMMER 2 72.50 60.000 85.00 17.68 12.50 24 60.00 60.00 72.50 85.00 85. 80 1991 FALL 1 115.00 115.00 115.00 . . . 115.00 115.00 115.00 115.00 115. 80 1991 SUMMER 2 50.00 20.000 80.00 42.43 30.00 85 20.00 20.00 50.00 80.00 80.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1990 to 1999 Total_Phosphorus_ug_L subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 80 1992 FALL 1 95.00 95.000 95.00 . . . 95.00 95.00 95.00 95.00 95. 80 1992 SPRING 1 90.00 90.000 90.00 . . . 90.00 90.00 90.00 90.00 90. 80 1992 SUMMER 2 60.00 50.000 70.00 14.14 10.00 24 50.00 50.00 60.00 70.00 70. 80 1992 WINTER 1 140.00 140.00 140.00 . . . 140.00 140.00 140.00 140.00 140. 80 1993 FALL 1 80.00 80.000 80.00 . . . 80.00 80.00 80.00 80.00 80. 80 1993 SPRING 1 120.00 120.00 120.00 . . . 120.00 120.00 120.00 120.00 120. 80 1993 SUMMER 2 110.00 70.000 150.00 56.57 40.00 51 70.00 70.00 110.00 150.00 150. 80 1993 WINTER 1 115.00 115.00 115.00 . . . 115.00 115.00 115.00 115.00 115. 80 1994 FALL 1 95.00 95.000 95.00 . . . 95.00 95.00 95.00 95.00 95. 80 1994 SPRING 1 90.00 90.000 90.00 . . . 90.00 90.00 90.00 90.00 90. 80 1994 WINTER 1 80.00 80.000 80.00 . . . 80.00 80.00 80.00 80.00 80. 80 1995 FALL 1 85.00 85.000 85.00 . . . 85.00 85.00 85.00 85.00 85. 80 1995 SPRING 1 85.00 85.000 85.00 . . . 85.00 85.00 85.00 85.00 85. 80 1995 SUMMER 3 71.67 55.000 90.00 17.56 10.14 25 55.00 55.00 70.00 90.00 90. 80 1995 WINTER 1 100.00 100.00 100.00 . . . 100.00 100.00 100.00 100.00 100. 80 1996 FALL 1 80.00 80.000 80.00 . . . 80.00 80.00 80.00 80.00 80. 80 1996 SPRING 1 80.00 80.000 80.00 . . . 80.00 80.00 80.00 80.00 80. 80 1996 SUMMER 2 100.00 60.000 140.00 56.57 40.00 57 60.00 60.00 100.00 140.00 140. 80 1996 WINTER 1 90.00 90.000 90.00 . . . 90.00 90.00 90.00 90.00 90. 80 1997 FALL 1 65.00 65.000 65.00 . . . 65.00 65.00 65.00 65.00 65. 80 1997 SPRING 1 70.00 70.000 70.00 . . . 70.00 70.00 70.00 70.00 70. 80 1997 SUMMER 2 70.00 60.000 80.00 14.14 10.00 20 60.00 60.00 70.00 80.00 80. 80 1997 WINTER 1 90.00 90.000 90.00 . . . 90.00 90.00 90.00 90.00 90. 80 1998 SUMMER 1 130.00 130.00 130.00 . . . 130.00 130.00 130.00 130.00 130. 80 1998 WINTER 1 80.00 80.000 80.00 . . . 80.00 80.00 80.00 80.00 80. 81 1990 FALL 1 30.00 30.000 30.00 . . . 30.00 30.00 30.00 30.00 30. 81 1991 FALL 1 10.00 10.000 10.00 . . . 10.00 10.00 10.00 10.00 10.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ec

 Aggregate Nutrient Ecoregion: III  Lakes and Reservoirs Descriptive Statistics by Subecoregion, Year and Season from 1991 to 1999 pH_S_U subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P 10 1994 FALL 3 8.27 8.1000 8.50 0.21 0.12 3 8.10 8.10 8.20 8.50 8. 10 1994 SPRING 3 8.53 8.5000 8.55 0.03 0.02 0 8.50 8.50 8.55 8.55 8. 10 1994 SUMMER 3 8.20 8.2000 8.20 0.00 0.00 0 8.20 8.20 8.20 8.20 8. 10 1994 WINTER 3 8.10 8.0000 8.20 0.10 0.06 1 8.00 8.00 8.10 8.20 8. 10 1995 FALL 3 8.25 8.1500 8.30 0.09 0.05 1 8.15 8.15 8.30 8.30 8. 10 1995 SPRING 3 7.98 7.9500 8.00 0.03 0.02 0 7.95 7.95 8.00 8.00 8. 10 1995 SUMMER 3 7.85 7.8000 7.90 0.05 0.03 1 7.80 7.80 7.85 7.90 7. 10 1995 WINTER 3 8.02 8.0000 8.05 0.03 0.02 0 8.00 8.00 8.00 8.05 8. 10 1998 FALL 5 8.51 8.0000 9.05 0.40 0.18 5 8.00 8.35 8.40 8.75 9. 10 1998 SUMMER 6 8.58 7.2750 9.30 0.74 0.30 9 7.28 8.30 8.70 9.20 9. 10 1998 WINTER 3 8.13 8.0000 8.30 0.15 0.09 2 8.00 8.00 8.10 8.30 8. 10 1999 SPRING 5 8.45 8.1000 8.70 0.22 0.10 3 8.10 8.40 8.50 8.55 8. 10 1999 WINTER 4 8.33 8.2000 8.60 0.19 0.09 2 8.20 8.20 8.25 8.45 8. 12 1991 FALL 2 8.18 8.1700 8.18 0.01 0.00 0 8.17 8.17 8.18 8.18 8. 12 1991 SPRING 2 8.04 7.9400 8.13 0.13 0.10 2 7.94 7.94 8.04 8.13 8. 12 1991 SUMMER 2 8.12 8.1000 8.14 0.03 0.02 0 8.10 8.10 8.12 8.14 8. 12 1991 WINTER 2 8.09 7.9650 8.21 0.17 0.12 2 7.97 7.97 8.09 8.21 8. 12 1992 WINTER 2 8.16 8.1550 8.17 0.01 0.01 0 8.16 8.16 8.16 8.17 8. 12 1997 SUMMER 3 8.86 8.5850 9.38 0.45 0.26 5 8.59 8.59 8.61 9.38 9. 12 1998 SUMMER 8 8.34 7.8350 9.58 0.55 0.20 7 7.84 7.98 8.22 8.47 9. 13 1997 SUMMER 3 8.26 8.2400 8.30 0.03 0.02 0 8.24 8.24 8.24 8.30 8. 13 1998 SUMMER 1 8.51 8.5100 8.51 . . . 8.51 8.51 8.51 8.51 8. 18 1997 SUMMER 1 7.91 7.9100 7.91 . . . 7.91 7.91 7.91 7.91 7. 18 1998 SUMMER 1 7.32 7.3150 7.32 . . . 7.32 7.32 7.32 7.32 7. 20 1999 SUMMER 2 8.25 8.1050 8.40 0.21 0.15 3 8.11 8.11 8.25 8.40 8. 22 1999 SUMMER 2 8.22 8.0500 8.39 0.24 0.17 3 8.05 8.05 8.22 8.39 8. 80 1991 SUMMER 1 6.30 6.3000 6.30 . . . 6.30 6.30 6.30 6.30 6. 80 1997 SUMMER 1 7.88 7.8800 7.88 . . . 7.88 7.88 7.88 7.88 7. 80 1998 SUMMER 1 7.48 7.4800 7.48 . . . 7.48 7.48 7.48 7.48 7.
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