&EPA
United States
Environmental Protection
Agency
Office of Water
4304
EPA822-B-01-009
December 2001
Ambient Water Quality
Criteria Recommendations
Information Supporting the Development
of State and Tribal Nutrient Criteria
Lakes and Reservoirs in
Nutrient Ecoregion IV
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EPA-822-B-01-009
AMBIENT WATER QUALITY CRITERIA RECOMMENDATIONS
INFORMATION SUPPORTING THE DEVELOPMENT OF STATE AND TRIBAL
NUTRIENT CRITERIA
FOR
LAKES AND RESERVOIRS IN NUTRIENT ECOREGION IV
Great Plains Grass and Shrublands
including all or parts of the States of:
North Dakota, Montana, Wyoming, Nebraska, Colorado,
Kansas, Oklahoma, New Mexico, 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 IV. 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)(l) 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
IV
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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 Secchi for lakes and reservoirs in Nutrient Ecoregion IV,
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:
• Historical and recent nutrient data in Nutrient Ecoregion IV. Data sets from Legacy
STORET, EPA Region 8 - Montana and Wyoming, EPA Region 8 - South Dakota, and
EPA Region 8 - North Dakota were used to assess nutrient conditions from 1990 to 2000.
• Reference sites/reference conditions in Nutrient Ecoregion IV. 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.
• 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.
• 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.
• Downstream effects of criteria. EPA encourages the RTAG to assess the potential effects
of the proposed criteria on downstream water quality and uses.
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In addition, EPA followed specific QA/QC procedures during data collection and analysis.
All data were reviewed for duplications. All data were from ambient waters that were not
located directly outside a permitted discharger. The following States indicated that their data
were sampled and analyzed using either standard methods or EPA-approved methods: North
Dakota, South Dakota, Montana, Wyoming, Colorado, Kansas, Oklahoma, and Texas. Nebraska
indicated that standard or EPA-approved methods were used for some specific nutrient
parameters.
The following tables contain a summary of aggregate and level III Ecoregion values for
TN, TP, water column chlorophyll a, and Secchi.
BASED ON 25th PERCENTILES ONLY
Nutrient Parameters
Total phosphorus (|ig/L)
Total nitrogen (mg/L) (reported)
Chlorophyll a (|ig/L) (spectrophotometric
method)
Secchi (m)
Aggregate Nutrient Ecoregion IV
Reference Conditions
20
0.44
2
2
For subecoregions 26, 28, 30, 31, 43, and 44 the ranges of nutrient parameter reference
conditions are as follows:
BASED ON 25th PERCENTILE ONLY
Nutrient Parameters
Total phosphorus (|ig/L)
Total nitrogen (mg/L) (calculated)
Chlorophyll a (|ig/L) (spectrophotometric
method)
Secchi (m)
Range of Level III Subecoregions
Reference Conditions
10-47*
0.39-0.68*
0.6-9.3*
0.4-2.8*
* 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-82-B-01-009.
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ACKNOWLEDGMENTS
The authors thankfully acknowledge the contributions of the following State and Federal
reviewers: EPA Regions 6, 7, and 8; the States of North Dakota, South Dakota, Montana,
Wyoming, Nebraska, Colorado, Kansas, Oklahoma, New Mexico, and Texas; the Tribes within
the Ecoregion; EPA headquarters personnel from the Office of Wetlands, Oceans, and
Watersheds, Office of Wastewater Management, Office of General Counsel, Office of Research
and Development, and Office of Science and Technology. EPA also acknowleges 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 8
3.2 Geographical Boundaries of Aggregate Ecoregion IV 9
3.3 Level III Subecoregions Within Aggregate Ecoregion IV 9
3.4 Suggested Ecoregional Subdivisions or Adjustments 12
4.0 Data Review for Lakes and Reservoirs in Aggregate Ecoregion IV 12
4.1 Data Sources 13
4.2 Historical Data from Aggregate Ecoregion IV (TP, TN, Chi a, and Secchi) 13
4.3 QA/QC of Data Sources 13
4.4 Data for All Lakes/Reservoirs Within Aggregate Ecoregion IV 13
4.5 Statistical Analysis of Data 16
4.6 Classification of Lake/Reservoir Type 16
4.7 Summary of Data Reduction Methods 23
5.0 Reference Sites and Conditions in Aggregate Ecoregion IV 26
6.0 Models Used to Predict or Verify Response Parameters 26
7.0 Framework for Refining Recommended Nutrient Criteria for Lakes and Reservoirs in
Aggregate Ecoregion IV 27
7.1 Example Worksheet for Developing Aggregate Ecoregion and
Subecoregion Nutrient Criteria 27
7.2 Setting Seasonal Criteria 28
7.3 When Data/Reference Conditions Are Lacking 28
7.4 Site-Specific Criteria Development 29
8.0 Literature Cited 29
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9.0 Appendices 30
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-l
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within
Aggregate Ecoregion B-l
Appendix C—Quality Control/Quality Assurance Rules C-l
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LIST OF TABLES AND FIGURES
Tables
Table 1 Lake and reservoir records for Aggregate Ecoregion IV—Great Plains
Grass and Shrublands 15
Table 2 Reference conditions for Aggregate Ecoregion IV lakes and reservoirs 17
Table 3a-f Reference conditions for Ecoregion IV lakes and reservoirs 18
Table 4 Changes in temperate lake attributes according to trophic state 22
Figures
Figure la Fourteen nutrient Ecoregions as delineated by Omernik (2000) 4
Figure Ib Level III Ecoregions of the United States 5
Figure 2 Aggregate Ecoregion IV 10
Figure 3 Aggregate Ecoregion IV with level III ecoregions shown 11
Figure 4 Map of sampling locations within each level III ecoregion 14
Figure 5a Illustration of data reduction process for lake data 24
Figure 5b Illustration of reference condition calculation 25
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XIV
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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 over enrichment 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 offish, 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
1
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criteria values for a specific waterbody type. In addition, EPA is committed to working with
States and Tribes to develop more refined and localized nutrient criteria based on approaches
described in the waterbody guidance manuals and this document.
Overview of the Nutrient Criteria Development Process
For each nutrient Ecoregion, EPA developed a set of recommendations for two causal
variables (total nitrogen and total phosphorus) and two early indicator response variables
(chlorophyll a [chl a] and 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
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only some instances), the best assurance of a representative and effective criterion is a balanced
incorporation of all five elements.
Because some parts of the country have naturally different soil and parent material nutrient
content, and different precipitation regimes, the application of the criterion development process
should reflect this regional variation. Therefore, an ecoregional approach was chosen. Initially,
the continental United States was divided into 14 separate Ecoregions of similar geographical
characteristics and similar nutrient condition (Figure la). 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 Ib 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 large-
scale aggregates is not without its drawbacks: variability is high because of the lumping of many
waterbody classes, seasons, and years worth of multipurpose data over a large geographic area.
For these reasons, the Agency recommends that States and Tribes develop nutrient criteria at the
level III ecoregional scale and at the waterbody-class scale, where those data are readily
available. Data analyses and recommendations on both the large Aggregate Ecoregion scale and
the more refined scales (level III Ecoregions and waterbody classes), where data were available
to make such assessments, are presented for comparison and completeness of analysis.
Comparison of Nutrient Criteria to Biological Criteria
Biological criteria are quantitative expressions of the desired condition of the aquatic
community. Such criteria can be based on data from sites that represent the least impacted
attainable condition for a particular waterbody type in an Ecoregion, subecoregion, or watershed.
EPA's nutrient criteria recommendations and biological criteria recommendations have many
similarities in their basic approaches to development and data requirements. Both are
empirically derived from statistical analysis of field-collected data and expert evaluation of
current reference conditions and historical information. Both use direct measurements from the
environment to integrate the effects of complex processes that vary according to type and
location of waterbody. The resulting criteria recommendations, in both cases, are efficient uses
of existing resources and are holistic indicators of the water quality necessary to protect uses.
States and authorized Tribes can develop and apply nutrient and biological criteria in
tandem, with each providing important and useful information to interpret both the nutrient
enrichment levels and the biological condition of sampled waterbodies. For example, using the
same reference sites for both types of criteria can lead to efficiencies in both sample design and
data analysis. In one effort, environmental managers can obtain information to support
assessment of biological and nutrient condition, either through evaluating existing data sets or
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
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Draft Aggregations of Level III Ecoregions
for the National Nutrient Strategy
I I I. Willamette and Central Valleys
^1 n. Western Forested Mountains
I I HI. XericWest
I I IV. Great Plains Grass and Shniblands
I I V. South Central Cultivated Great Plains
• VI. Corn Belt and Northern Great Plains
I I Vn. Mostly Glaciated Dairy Region
I I Vffl. Nutrient Poor Largely Glaciated Upper Midwest and Northeast
I I DC. Southeastern Temperate Forested Plains and Hills
I I X. Texas-Louisiana Coastal and Mississippi Alluvial Plains
CH XI. Central and Eastern Forested Uplands
I I Xn. Southern Coastal Plain
I I Xm. Southern Florida Coastal Plain
I I XIV. Eastern Coastal Plain
Projection
jc/jo/yiQiy1»ibs^312.nuti1anLiinVLi8_nutrtent_region8.aml /Avallace/Bandi/pba>j334.niitiBntfnuti1ant_iagions_g_pO_v1.ai 2flfflQQQ
Figure la. Fourteen nutrient Ecoregions as delineated by Omernik (2000). Ecoregions were based on geology, land use,
ecosystem type, and nutrient conditions.
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Level III Ecoregions of the United States
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I N. Mlmc,Mi. CicjlPUm is Ul,- \t.BM/ll.ji, a S.Hilliciacn. \Vn.-,.nsm I ill I'l.uii,
tLNelini*aSa«IHffl. 0 ; X.fllicni MiliiKiMa Wcllmh [jL,f«imJ Com Brll Ham.
] SO I N'onliem I jkei lid F.wflc
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63
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72 II
73
t . Mi"i"ip|:i VjBcy 1
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77 Ninth (
Is1 M,, ,tl. \: -mi ,.h.
M ,,ir n, 'u. !.i|, : , .
SO N«ilKm> H ! -:n >•..! I: ,i
81 v u i, I--, .:: ,i
Plmiis
Figure Ib. Level III Ecoregions of the United States.
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nutrient assessment. To investigate the effectiveness of this tandem approach, EPA has initiated
pilot projects in both freshwater and marine environments to pursue the relationship between
nutrient overenrichment and apparent declines in diversity of benthic invertebrates and fish.
2.0 BEST USE OF THIS INFORMATION
EPA recommendations published under section 304(a) of the CWA serve several purposes,
including providing guidance to States and Tribes in adopting water quality standards for
nutrients and ultimately controlling discharges or releases of pollutants. The recommendations
also provide guidance to EPA when it determines that it is necessary to promulgate Federal
water quality standards under section 303(c). Other uses include identification of
overenrichment problems, management planning, project evaluation, and determination of status
and trends of water resources.
State water quality inventories and listings of impaired waters consistently rank nutrient
overenrichment as a top contributor to use impairments. EPA's water quality standards
regulations at 40 CFR § 131.11 (a) require States and Tribes to adopt criteria that contain
sufficient parameters and constituents to protect the designated uses of their waters. In addition,
States and Tribes need quantifiable targets for nutrients to assess attainment of uses, develop
water quality-based permit limits and source control plans, and establish targets for total
maximum daily loads (TMDLs).
EPA expects States and Tribes to address nutrient overenrichment in their water quality
standards and to build on existing State and Tribal efforts where possible. States and Tribes can
address nutrient overenrichment through establishment of numerical criteria or use of narrative
criteria statements (e.g., "free from excess nutrients that cause or contribute to undesirable or
nuisance aquatic life or produce adverse physiological response in humans, animals, or plants").
In the case of narrative criteria, EPA expects that States and Tribes will establish procedures to
quantitatively translate these statements for both assessment and source control purposes.
Ecoregional nutrient criteria are developed to represent surface waters that are minimally
impacted by human activities and thus protect against the adverse effects of nutrient
overenrichment from cultural eutrophication. EPA's recommended process for developing such
criteria includes physical classification of waterbodies, determination of current reference
conditions, evaluation of historical data and other information (such as published literature), use
of models to simulate physical and ecological processes or determine empirical relationships
among causal and response variables (if necessary), expert judgment, and evaluation of
downstream effects. EPA has used elements of this process to produce the information
contained in this document. The causal (total nitrogen, total phosphorus) and biological and
physical response (chlorophyll a, 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
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modification. EPA has also published methods for modifying 304(a) criteria, such as the water
effect ratio, on a site-specific basis where conditions warrant modification to achieve the
intended level of protection. For nutrients, however, EPA expects that it will usually be
necessary for States and authorized Tribes to be more precise in identifying the nutrient levels
that protect aquatic life and recreational uses. This can be achieved through criteria modified to
reflect a smaller geographic scale than an Ecoregion, such as a subecoregion, the State or Tribe
level, or a specific class of waterbodies. Criteria can be refined by grouping data or performing
analyses at these smaller geographic scales. Refinement can also occur through further
consideration of other elements such as published literature or models.
EPA expects that the values presented in this document generally represent nutrient levels
that protect against the adverse effects of cultural overenrichment and are based on information
available to the Agency at the time of this publication. However, States and Tribes should
critically evaluate this information in light of the specific uses that need to be protected. For
example, more sensitive uses may require more stringent criteria to ensure adequate protection.
On the other hand, overly stringent levels of protection against cultural eutrophication may
actually fall below the natural load of nutrients for certain waterbodies. In cases such as these,
the level of nutrients specified may not be sufficient to support a productive fishery. In the
criteria derivation process, it is important to distinguish between the natural load associated with
a specific waterbody using historical data and expert judgment and current reference conditions.
These elements of the criteria derivation process are best addressed by States and Tribes with
access to information and local expertise. Therefore, EPA strongly encourages States and Tribes
to use the information contained in this document to develop more refined criteria according to
the methods described in EPA's technical guidance manuals for specific waterbody types.
To assist in further refinement of nutrient criteria, EPA has established 10 RTAGs (experts
from EPA Regional Offices and States/Tribes). In refining criteria, States and authorized Tribes
need to provide documentation of data and analyses, along with a defensible rationale, for any
new or revised nutrient criteria they submit to EPA for review and approval. As part of EPA's
review of State and Tribal standards, EPA intends to seek assurance from the RTAG that
proposed criteria are sufficient to protect uses.
In using the information and recommendations in this document and elsewhere to develop
numerical criteria or procedures to translate narrative criteria, EPA encourages States and Tribes
to:
• 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.
• 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.
• Identify appropriate periods of duration (how long) and frequency (how often) of
occurrence in addition to magnitude (how much). EPA does not recommend identifying
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nutrient concentrations that must be met at all times; rather a seasonal or annual averaging
period (e.g., based on weekly or biweekly measurements) is considered appropriate.
However, these central tendency measures should apply each season or each year, except
under the most extraordinary conditions (e.g., a 100-year flood).
3.0 AREA COVERED BY THIS DOCUMENT
This chapter provides a general description of the Aggregate Ecoregion and its
geographical boundaries. Descriptions of the level III subecoregions contained within the
Aggregate Ecoregion are also provided.
3.1 Description of Aggregate Ecoregion IV
Ecoregion IV is composed of disjunct, grassy, rolling high plains, hills, plateaus, buttes,
stabilized sand dunes, and badlands. Northernmost parts were once glaciated and contain
hummocky moraines that are studded with wetlands. The average annual freeze-free growing
season ranges from only 90 days in the north to 200 days in the south. Rainfall can vary widely
from year to year. The average annual precipitation ranges from 10 inches to 24 inches; overall,
the Great Plains Grass and Shrublands (IV) is drier than adjoining portions of the Western
Forested Mountains (II), Corn Belt - Northern Great Plains (VI), and South Central Cultivated
Great Plains (V). Both intermittent and ephemeral streams are common; perennial streams also
occur but usually originate outside the region in the Western Forested Mountains (II).
The natural vegetation is dominantly and characteristically short grass prairie with areas of
savanna also occurring such as on the Edwards Plateau of Texas and on the stony hills of eastern
Montana; woodland is commonly found along stream courses. The region's short grass prairie is
distinct from the forests of Ecoregion II, the sagebrush, shadscale, and creosote bush of
Ecoregion III, and the tall grass prairie of the Corn Belt and Northern Great Plains (VI).
Today, most of Ecoregion IV is rangeland and is not arable. Cropland is much less
common than in the Corn Belt and Northern Great Plains (VI) and the South Central Cultivated
Great Plains (V) because of the low and erratic precipitation, limited opportunities for irrigation,
and limitations imposed by its soils. Cattle, sheep, and horse grazing are common and have
impacted vegetation; when overgrazed, parts of the region are subject to wind erosion. Cattle
feedlots and their affects occur throughout the region but their density is far less than in
Ecoregion V. Although land use is dominated by grazing activities, some cropland agriculture
occurs such as on irrigated land adjacent to rivers and on the till, terraces, and lake plains of
north-central Montana.
Much of Ecoregion IV is underlain by moderately soluble sandstone, siltstone, and shale
rocks or glacial drift. Rock and soil type have significantly impacted water quality within
Ecoregion IV; together rocks, glacial drift, and soils significantly affect the alkalinity, dissolved
solid sulfate, salt, and suspended sediment concentrations of streams. Some of these contain
easily dissolved minerals and readily contribute dissolved solids to streams. High sulfate
concentrations in stream water occur over broad areas and are the product of soil leaching. High
-------
suspended sediment concentrations in stream water are found in steep, sparsely vegetated
watersheds composed of highly erodible, fine-grained material (USGS, 1993).
Throughout the Great Plains Grass and Shrublands (IV), measured nitrogen and phosphorus
levels in streams are generally much lower than in regions dominated by cropland agriculture or
urban-suburb an development. Where cropland agriculture does occur, fertilizers are used; in
these places, both runoff and irrigation return flow carry residues of nitrogen and phosphorus to
streams. Locally, however, industries, coal mining, oil production, livestock operations, and
municipalities have affected stream quality (USGS, 1993).
3.2 Geographical Boundaries of Aggregate Ecoregion IV
Ecoregion IV is a fragmented region composed of four separate segments in the central
portion of the United States where Great Plains grass and shrubs prevail (Figure 2). The largest
and most northern segment includes eastern Montana and Wyoming, western North and South
Dakota, and continues southwards to central Nebraska.
A second segment begins in southeastern Colorado, continues south to northeastern New
Mexico and extends east as a narrow strip running through northern Texas and extending down
to central Texas. From Texas the thin segment continues to stretch north to include small
portions of western Oklahoma and southwestern Kansas.
A third segment encompasses a portion of eastern Kansas and runs south into a small
section of central Oklahoma. The remaining segment encompasses a portion south central
Texas.
3.3 Level III Subecoregions Within Aggregate Ecoregion IV
There are six level III subecoregions contained within Aggregate Ecoregion IV (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.
26. Southwestern Tablelands
Unlike most adjacent Great Plains ecological regions, little of the Southwestern Tablelands
is in cropland. Much of this elevated tableland is in subhumid grassland and semiarid grazing
land. The potential natural vegetation in this region is grama-buffalo grass with some mesquite-
buffalo grass in the southeast and shinnery (midgrass prairie with open low and shrubs) along the
Canadian River.
28. Flint Hills
The Flint Hills is a region of limestone and shale open hills with relatively narrow steep
valleys. In contrast to surrounding ecological regions that are mostly in cropland, most of the
Flint Hills is grazed by beef cattle. Potential natural vegetation in the region is tallgrass prairie.
-------
Aggregate Nutrient Ecoregion 4
Washington
Louisiana
Aggregate Ecoregion
State Boundaries
200 0
N
+
Figure 2. Aggregate Ecoregion IV.
10
-------
Aggregate Nutrient Ecoregion 4
Level III Ecoregions
orth Dakota
Minnesota
Wisconsin
Illinois Indiana
Missouri
Kentucky
Tennessee
Arkansas
Mississippi
}
Louisiana
Level III Ecoregions
| | 26
| | 28
| | 30
| 1 31
| | 43
I I 44
State Boundaries
200
200 Miles
N
4-
Figure 3. Aggregate Ecoregion IV with level III ecoregions shown.
11
-------
30. Edwards Plateau
This Ecoregion is largely a dissected plateau that is hillier in the south and east where it is
easily distinguished from bordering ecological regions by a sharp fault line. The region contains
a sparse network of perennial streams, but they are relatively clear and cool compared to those of
surrounding areas. Originally covered by juniper-oak savanna and mesquite-oak savanna, most
of the region is used for grazing beef cattle, sheep, goats, and wildlife. Hunting leases are a
major source of income.
31. Southern Texas Plains
This rolling to moderately dissected plain was once covered with grassland and savanna
vegetation. Having been subject to long continued grazing, thorny brush is now the predominant
vegetation type. This "brush country," as it is called locally, has its greatest extent in Mexico
and contains a greater and more distinct diversity of animal life than that found elsewhere in
Texas.
43. Northwestern Great Plains
The Northwestern Great Plains Ecoregion encompasses the Missouri Plateau section of the
Great Plains. It is a semiarid rolling plain of shale and sandstone punctuated by occasional
buttes. Native grasslands, largely replaced on level ground by spring wheat and alfalfa, persist in
rangeland areas on broken topography. Agriculture is restricted by the erratic precipitation and
limited opportunities for irrigation.
44. Nebraska Sandhills
The Nebraska Sandhills comprise one of the most distinct and homogenous Ecoregions in
North America. One of the largest areas of grass stabilized sand dunes in the world, this region
is generally devoid of cropland agriculture, and except for some riparian areas in the north and
east, the region is treeless. Large portions of this Ecoregion contain numerous lakes and
wetlands and have a lack of streams.
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, 200Ib) 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 IV
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
12
-------
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 8 - Montana and Wyoming, EPA
Region 8 - South Dakota, and EPA Region 8 - North Dakota were used to assess nutrient
conditions from 1990 to 2000. EPA recommends that the RTAGs identify additional data
sources that can be used to supplement the data sets listed above. In addition, the RTAGs may
utilize published literature values to support quantitative and qualitative analyses.
4.2 Historical Data from Aggregate Ecoregion IV (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 IV were contacted regarding the quality of their data and
information on the methods used to sample and analyze their waters. The following States
indicated standard methods or approved EPA methods were used: North Dakota, South Dakota,
Montana, Wyoming, Colorado, Kansas, Oklahoma, and Texas. Nebraska indicated that standard
or EPA-approved methods were used for some specific nutrient parameters. New Mexico did
not provide information prior to the publication of this document.
4.4 Data for All Lakes and Reservoirs Within Aggregate Ecoregion IV
Figure 4 shows the location of the sampling stations within each subecoregion. Table 1
presents all data records for all parameters for Aggregate Ecoregion IV and subecoregions within
the Aggregate Ecoregion.
13
-------
Aggregate Nutrient Ecoregion 4
Lake and Reservoir Stations
• Stations
Level III Ecoregions
26
28
30
31
43
44
State Boundaries
200 0
200 Miles
Figure 4. Map of sampling locations within each level III ecoregion.
14
-------
Table 1. Lake and Reservoir records* for Aggregate Ecoregion IV—Great Plains Grass and Shrublands
# of lakes
# of lake stations
Aggregate
Ecoregion IV
162
285
Sub ecoR 26
29
42
Sub ecoR 28
40
54
Sub ecoR 30
14
43
SubecoRSl
2
4
Sub ecoR 43
59
124
Sub ecoR 44
18
18
Key nutrient parameters
(listed below)
- # of records for Secchi
depth
- # of records for
chlorophyll a (all
methods)
- # of records for total
Kjeldhal nitrogen
(TKN)
- # of records for nitrite
+ nitrate (NO2+NO3)
- # of records for total
nitrogen (TN)
- # of records for total
phosphorus (TP)
Total # of records for
key nutrient parameters
2582
693
1,798
1,453
7
2,247
8,780
276
104
106
127
7
261
881
202
178
409
342
—
480
1,611
1486
363
680
417
—
788
3,734
27
28
19
—
—
32
106
544
20
528
508
—
634
2,234
47
—
56
59
—
52
214
Definitions: (1) # of records refers to the total count of observations for that parameter over the entire decade (1990-1999) for that particular aggregate or subecoregion. These
are counts for all seasons over that decade. (2) # of lake stations refers to the total number of lake and reservoir stations within the aggregate or subecoregion from which nutrient
data were collected. Since lakes and reservoirs can cross ecoregional boundaries, it is important to note that only those portions of a lake or reservoir (and data associated with
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 Nutrient database. This does not
imply that this is the total of lakes within the Ecoregion. States and Tribes should determine the representativeness of the tabular data by comparing this information with any
additional material they may have.
-------
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 Mathew Liebman, U.S. EPA Region 1 Nutrient Criteria Coordinator
to Geoffrey Grubbs [U.S. EPA, 2000c]. New York State has also presented evidence that the
25th percentile and the 75th percentile compare well based on user perceptions of water
resources (NYSDEC, 2000).
Tables 2 and 3a-f 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-f 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-f 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.
16
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Table 2. Reference conditions for Aggregate Ecoregion IV lakes and reservoirs
Parameter
TKN (mg/L)
NO2+NO3-N (mg/L)
TN (mg/L) - calculated
TN (mg/L) - reported
TP (ng/L)
Secchi (meters)
Chlorophyll a (ng/L) - F
Chlorophyll a (ng/L) - S
Chlorophyll a (ng/L) - T
No. of lakes
N*
115
98
2
127
113
—
65
2
Reported values
Min
0.08
—
0.44
2
0.1
—
0.2
2.04
Max
3.90
1.71
0.49
580
4.63
—
37.5
3.04
25th percentiles based on all
seasons data for the decade
P25f all seasons}
0.44
0.01
0.45
0.44 (zz)
20
2
—
2
2.04 (zz)
Reference lakes§
P75 all seasons
*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.
f 75th percentile for Secchi.
J 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 ng/L, summer 15 ng/L, fall 12 ng/L, and winter 5 ng/L, the median value of all
seasons P25 will be 1 Ijig/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."
17
-------
Table 3a. Reference conditions for Ecoregion IV lakes and reservoirs
subecoregion 26
Parameter
TKN (mg/L)
NO2+NO3-N (mg/L)
TN (mg/L) - calculated
TN (mg/L) - reported
TP(ng/L)
Secchi (meters)
Chlorophyll a (ng/L) - F
Chlorophyll a (ng/L) - S
Chlorophyll a (ng/L) - T
No. of lakes
N*
17
12
2
21
20
—
11
2
Reported values
Min
0.27
0.01
0.44
2
0.3
—
0.7
2
Max
3.54
0.18
0.49
145
2.9
—
18.6
3
25th percentiles based on all
seasons data for the decade
P25f all seasons}
0.38
0.01
0.39
0.44 (zz)
20
1.7
—
1.2
2
Reference lakes§
P75 all seasons
Table 3b. Reference conditions for Ecoregion IV lakes and reservoirs
subecoregion 28
Parameter
TKN (mg/L)
NO2+NO3-N (mg/L)
TN (mg/L) - calculated
TN (mg/L) - reported
TP(^g/L)
Secchi (meters)
Chlorophyll a (ng/L) - F
Chlorophyll a (ng/L) - S
Chlorophyll a (ng/L) - T
No. of lakes
N*
34
32
—
36
34
—
34
—
Reported values
Min
0.48
0.01
—
4
0.2
—
1
—
Max
2.37
1.40
—
550
0.7
—
56
—
25th percentiles based on all
seasons data for the decade
P25f all seasons}
0.65
0.03
0.68
—
31
0.4
—
5.5
—
Reference lakes§
P75 all seasons
18
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Table 3c. Reference conditions for Ecoregion IV lakes and reservoirs
subecoregion 30
Parameter
TKN (mg/L)
NO2+NO3-N (mg/L)
TN (mg/L) - calculated
TN (mg/L) - reported
TP(ng/L)
Secchi (meters)
Chlorophyll a (ng/L) - F
Chlorophyll a (ng/L) - S
Chlorophyll a (ng/L) - T
No. of lakes
N*
13
12
—
13
14
—
13
—
Reported values
Min
0.26
0.03
—
2
0.8
—
0.5
—
Max
0.71
0.27
—
60
3.3
—
12.1
—
25th percentiles based on all
seasons data for the decade
P25f all seasons}
0.35
0.04
0.39
—
10
2.1
—
1.7
—
Reference lakes§
P75 all seasons
Table 3d. Reference conditions for Ecoregion IV lakes and reservoirs
subecoregion 31
Parameter
TKN (mg/L)
NO2+NO3-N (mg/L)
TN (mg/L) - calculated
TN (mg/L) - reported
TP(^g/L)
Secchi (meters)
Chlorophyll a (ng/L) - F
Chlorophyll a (ng/L) - S
Chlorophyll a (ng/L) - T
No. of lakes
N*
2
—
—
2
2
—
2
—
Reported values
Min
0.88
—
—
47
0.89
—
9.34
—
Max
0.90
—
—
75
0.89
—
10.85
—
25th percentiles based on all
seasons data for the decade
P25f all seasons}
0.88 (zz)
—
—
—
47 (zz)
0.89 (zz)
—
9.34 (zz)
—
Reference lakes§
P75 all seasons
19
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Table 3e. Reference conditions for Ecoregion IV lakes and reservoirs
subecoregion 43
Parameter
TKN (mg/L)
NO2+NO3-N (mg/L)
TN (mg/L) - calculated
TN (mg/L) - reported
TP(ng/L)
Secchi (meters)
Chlorophyll a (ng/L) - F
Chlorophyll a (ng/L) - S
Chlorophyll a (ng/L) - T
No. of lakes
N*
43
40
—
49
37
—
5(z)
—
Reported values
Min
0.24
0.03
—
16
0.4
—
0.5
—
Max
3.21
0.36
—
415
4.6
—
1.6
—
25th percentiles based on all
seasons data for the decade
P25f all seasons}
0.41
0.05
0.46
—
32
2.8
—
0.6
—
Reference lakes§
P75 all seasons
20
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Table 3f. Reference conditions for Ecoregion IV lakes and reservoirs
subecoregion 44
Parameter
TKN (mg/L)
NO2+NO3-N (mg/L)
TN (mg/L) - calculated
TN (mg/L) - reported
TP(ug/L)
Secchi (meters)
Chlorophyll a (ug/L) - F
Chlorophyll a (ug/L) - S
Chlorophyll a (ug/L) - T
No. of lakes
N*
14
16
—
10
13
—
—
—
Reported values
Min
0.46
0.00
—
5
0.2
—
—
—
Max
2.34
0.38
—
237
2.9
—
—
—
25th percentiles based on all
seasons data for the decade
P25f all seasons}
0.68
0.00
0.68
—
37
1
—
—
—
Reference lakes§
P75 all seasons
* 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.
f 75th percentile for Secchi.
J 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 ug/L, summer 15 ug/L, fall 12 ug/L, and winter 5 ug/L, the median value of all
seasons' P25 will be 11 ug/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 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."
21
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Table 4. Changes in temperate lake attributes according to trophic state (adapted from
Carlson and Simpson, 1995)
TSI
Value
<30
30-40
40-50
50-60
60-70
70-80
>80
SD(m)
>8
8-4
4-2
2-1
0.5-1
0.25-
0.5
0.25
TP
(MS^L)
<6
6-12
12-24
24-48
48-96
96-192
192-
384
Attributes
Oligotrophy: Clear water,
oxygen throughout the year
in the hypolimnion
Hypolimnia of shallower
lakes may become anoxic
Mesotrophy: Water
moderately clear but
increasing probability of
hypolimnetic anoxia during
summer
Eutrophy: Anoxic
hypolimnia, macrophyte
problems possible
Blue-green algae dominate,
algal scums and
macrophyte problems
Hypereutrophy (light
limited). Dense algae and
macrophytes
Algal scums, few
macrophytes
Water Supply
Iron and manganese
evident during the
summer. THM
precursors exceed 0.1
mg/L and turbidity >1
NTU
Iron, manganese, taste,
and odor problems
worsen
Recreation
Weeds, algal
scums, and
low
transparency
discourage
swimming and
boating
Fisheries
Salmonid
fisheries
dominate
Salmonid
fisheries in
deep lakes
Hypolimnetic
anoxia results
in loss of
salmonids.
Walleye may
predominate
Warm-water
fisheries only.
Bass may be
dominant
Rough fish
dominate,
summer fish
kills possible
Note: This table is provided to allow the reader to make comparisons between the ecoregional crriteria provided in this
document and traditional nutrient and biological endpoints.
22
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4.7 Summary of Data Reduction Methods
All descriptive statistics were calculated using the medians for each lake within Ecoregion
IV 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 the 25th percentile for the Aggregate Ecoregion or consider the lowest 25th percentile
from a subecoregion (level III) within the aggregate nutrient Ecoregion. Without data, one
may assume that the subecoregion in question is as sensitive as the most sensitive
subecoregion within the aggregate.
2. TN calculated: When reported total nitrogen (TN) median values are lacking or very low
in comparison to TKN and Nitrate/Nitrite-N values, the medians for TKN and
nitrite/nitrate-N are added, resulting in a calculated TN value. The number of samples (N)
for calculated TN is not filled in because it is represented by two subsamples of data: TKN
and nitrite/nitrate-N. Therefore, N/A is placed in this box.
3. TN reported: This is the median based on reported values for TN from the database.
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 periphyton-
dominated 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).
23
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Data Reduction
and Analysis
ECOREG
Moon
Swan Lake
Lake Data Sandy
Data Reservoir
Marsh Data
Fish Lake
Reservoir Data Clear
Lake
Bear Data
Reservoir
Data
WINTER
SPRING
Data Reduced
to
Median Value
for Each Unique
Water Body*
ALL OBSERVATIONS
SUMMER
FALL
Rainy Lake Median
Fish Reservoir Median
Moon Lake..
Rainy Lake Median
Fish Reservoir Median
Moon Lake .
Rainy Lake Median
Fish Reservoir Median
Moon Lake .
Rainy Lake Median
Fish Reservoir Median
Moon Lake ...
DESCRIPTIVE
STATISTICS
BY YEAR
Ra
Ra
Ra
Ra
I
Fish
Fish
Fish
Fish
Moon Lake Yearly Median 90
Moon Lake Yearly Median 91
Moon Lake Yearly Median 92
Moon Lake Yearly Median. . .
DESCRIPTIVE
STATISTICS
BY YEAR
Ra
Ra
Ra
Ra
Fish
Fish
Fish
Fish
i
Moon Lake Yearly Median 90
Moon Lake Yearly Median 91
Moon Lake Yearly Median 92
Moon Lake Yearlv Median .
DESCRIPTIVE
STATISTICS
YEARS COMBINED
DESCRIPTIVE
STATISTICS
YEARS COMBINED
DESCRIPTIVE
STATISTICS
BY YEAR
DESCRIPTIVE
STATISTICS
BY YEAR
Ra
Ra
Ra
Ra
Fish
Fish
Fish
Fish
Moon Lake Yearly Median 90
Moon Lake Yearly Median 91
Moon Lake Yearly Median 92
Moon Lake Yearly Median . .
Ri
Ri
R:
Ri
FisI
FisI
FisI
FisI
I
Moon Lake Yearly Median 90
Moon Lake Yearly Median 91
Moon Lake Yearly Median 92
Moon Lake Yearly Median . .
DESCRIPTIVE
STATISTICS
YEARS COMBINED
DESCRIPTIVE
STATISTICS
YEARS COMBINED
*Unique Water Body - is a water body that is unique to a state, a subecoregion, a county, the year, and the season.
Figure 5a. Illustration of data reduction process for lake data.
-------
Select 25th Percentile
from Distribution
of Median
Values
25%
Winter
TP
TN
TKN
NO2+NO3
Chi a
DO
SECCHI
25%
25%
25%
Spring
Summer
Calculate Median
Value of the
25th Percentiles
for the Four Seasons
Half values
Below Median
Half values
Above Median
1
25%
Season A
1
25%
Season B
1
25%
Season C
1
25%
Season D
25%
Fall
Median = Reference Condition for the Ecoregion
Figure 5b. Illustration of reference condition calculation.
-------
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 IV
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 lakes.
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-f in Section 4.0.
• RTAG discussion and rationale for selection of reference sites and conditions in Ecoregion
IV. 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.
26
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7.0 FRAMEWORK FOR REFINING RECOMMENDED NUTRIENT CRITERIA FOR
LAKES AND RESERVOIRS IN AGGREGATE ECOREGION IV
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-f 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:
Reference condition:
Models:
27
-------
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
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.
28
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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, 200Ib), 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.
U.S. EPA. 2000a. Nutrient Criteria Technical Guidance Manual: Lakes and Reservoirs. U.S.
Environmental Protection Agency, Washington, DC. EPA-822-BOO-001.
U.S. EPA. 2000b. Nutrient Criteria Technical Guidance Manual: Rivers and Streams. U.S.
Environmental Protection Agency, Washington, DC. EPA-822-BOO-002.
U.S. EPA. 2000c. Memorandum from Matthew Liebman to Geoffrey Grubbs, December 15,
2000, regarding comments on draft ambient water quality recommendations for development of
numeric nutrient criteria.
USGS (U.S. Geological Survey). 1993. National Water Summary 1990-1991. Water Supply
Paper 2400. U.S. Government Printing Office, Washington, D.C. 589 pages.
29
-------
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
30
-------
APPENDIX A
Descriptive Statistics Data Tables for Aggregate Ecoregion
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Decade and Season
from 1990 to 1997
Chloro_A_Phyto_Spec_A_ug_L
N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P7;
FALL 31
SPRING 22
SUMMER 65
WINTER 18
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-l
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Decade and Season
from 1992 to 1997
Chloro A Trich unco ug L
MAX STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL 1
SPRING 1
SUMMER 2
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-2
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Decade and Season
from 1991 to 2000
DIP_ug_L
MAX STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL 8 39.06 8.5000 149.00 45.59 16.12 117
SUMMER
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-3
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Decade and Season
from 1998 to 1999
Dissolved Oxygen percent sat
N MEAN MIN MAX STDDEV STDERR CV
SUMMER 8 89.04 75.600 104.15 8.71 3.08 10
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-4
-------
STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL 4 0
SPRING 26
SUMMER 61 7.16 .30000 15.00 2.16 0.28 30 3.10 6.50 7.40 8.15
WINTER 33
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-5
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Decade and Season
from 1990 to 2000
Nitrite_Nitrate_NO2_NO3_mg_L
MAX STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL
SPRING
SUMMER
WINTER
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-6
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Decade and Season
from 1990 to 2000
Nitrogen_Tot_Kj eldhal_mg_L
STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL
SPRING
SUMMER
WINTER
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-7
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Decade and Season
from 1990 to 2000
SECCHI_m
STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL 64 1.31
SPRING 41 1.61
SUMMER 113 1.25
WINTER 44 1.72
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-8
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Decade and Season
from 1992 to 1997
Total Nitrogen mg L
MAX STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL 1
SPRING 1
SUMMER 2 1.99 .44000 3.53 2.18 1.55 110
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-9
-------
10
STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL 68
SPRING 44 65.54 2.5000 570.00 94.46 14.24 144 2.50 17
SUMMER 127
WINTER 42
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-10
-------
Aggregate Nutrient Ecoregion: IV 11
Lakes and Reservoirs
Descriptive Statistics by Decade and Season
from 1991 to 2000
pH_S_U
MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95
FALL
SUMMER
Appendix A—Descriptive Statistics Data Tables for Aggregate Ecoregion A-l 1
-------
APPENDIX B
Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1990 to 1997
Chloro_A_Phyto_Spec_A_ug_L
MEAN
STDDEV
STDERR
P2J
MEDIAN
P7;
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SUMMER
34
13
11
1
1
2
1
83
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-l
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1992 to 1997
Chloro A Trich unco ug L
STDDEV
STDERR
P5
P2J
P7J
FALL
SPRING
SUMMER
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-2
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1991 to 2000
DIP_ug_L
season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL 8 39.06 8.5000 149.00 45.6 16.1 117
SUMMER
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion B-3
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1998 to 1999
Dissolved Oxygen percent sat
N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75
SUMMER 8 89.04 75.600 104.15 8.71 3.08 10 75.6 83.4 88.9 94.1
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion B-4
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1990 to 2000
Dissolved Oxygen mg L
STDDEV
STDERR
P5
P2J
P7J
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SUMMER
12
14
13
1
1
2
1
17
•-J
34
14
.23
131
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-5
-------
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
N
11
12
13
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1990 to 2000
Nitrite_Nitrate_NO2_NO3_mg_L
STDDEV
STDERR
P5
P2J
P7J
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1990 to 2000
Nitrogen_Tot_Kj eldhal_mg_L
STDDEV
STDERR
P5
P2J
P7J
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
12
11
34
8
11
13
12
1
1
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-7
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1990 to 2000
SECCHI m
STDDE\.
STDERR
P5
P2J
P7J
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
11
34
FALL
SPRING
SUMMER
WINTER
12
14
13
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1992 to 1997
Total Nitrogen mg L
season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P7J
FALL 1
SPRING 1
SUMMER 2 1.99 .44000 3.53 2.18 1.55 110 0.44 0.44 1.99 3.53
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion B-9
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1990 to 2000
Total Phosphorus ug L
STDDEV
STDERR
P5
P2J
P7J
10
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
19
14
21
8
11
13
12
1
1
114
123
113
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-10
-------
Aggregate Nutrient Ecoregion: IV 11
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Decade and Season
from 1991 to 2000
pH_S_U
MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P75 P95
FALL
SUMMER
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion B-l 1
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 1997
Chloro_A_Phyto_Spec_A_ug_L
N
MEAN
MAX STDDEV STDERR
P2J
MEDIAN
P7;
1990
1990
1990
1991
1991
1991
1991
1992
1992
1992
1993
1993
1993
1993
1994
1994
1995
1995
1995
1996
1996
1996
1997
1997
1997
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SUMMER
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
1
•-j
4
6
2
5
4
2
5
4
4
3
4
1
1
4
1
5
2
1
3
2
1
1
1
FALL
SUMMER
FALL
SPRING
SUMMER
FALL
SPRING
2
11
2
3
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-12
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 1997
Chloro A Phyto Spec A ug L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
1992
1993
1994
1994
1994
1995
1996
1997
1990
1990
1990
1990
1991
1991
1991
1991
1992
1992
1992
1992
1993
1993
1993
1993
1994
1994
1995
1995
1996
1996
1996
SUMMER
SUMMER
FALL
SPRING
SUMMER
SUMMER
SUMMER
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
SUMMER
WINTER
SPRING
SUMMER
WINTER
4
16
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12
8
8
8
10
8
3
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97
.13
. 65
. 70
. 49
. 00
. 82
1990 FALL
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-I:
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 1997
Chloro A Phyto Spec A ug L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
1990 SPRING
1990 SUMMER
1991 FALL
1991 SPRING
1991 SUMMER
1991 WINTER
1992 FALL
1992 SPRING
1992 SUMMER
1992 WINTER
1993 FALL
1993 SUMMER
1994 SUMMER
1991 SUMMER
1992 FALL
1992 SUMMER
2.19
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-14
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1992 to 1997
Chloro A Trich unco ug L
STDDEV STDERR CV P5 P25 MEDIAN P7J
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion B-15
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1991 to 2000
DIP_ug_L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
00
00
.00
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-16
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1998 to 1999
Dissolved Oxygen percent sat
subecoregion year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P7J
4 85.94 75.600 93.55 7.84 3.92 9
4 92.14 82.200 104.15 9.48 4.74 10
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion B-17
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Dissolved Oxygen mg L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
28
28
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
FALL
SUMMER
WINTER
FALL
SUMMER
SUMMER
WINTER
SPRING
SUMMER
WINTER
FALL
SPRING
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
1
6
3
2
4
4
1
4
3
2
3
1
1
5
3
2
2
1
1
2
1
7
10
12
10
•-j
10
12
9
8
10
13
10.
6.
11.
8.
5 .
12.
9 .
7 .
13.
9 .
4 .
8.
9 .
5 .
5.
10.
8.
•-J
11.
10.
8.
5.
•-J
6.
8.
6.
7 .
5 .
8.
7 .
~->
5 .
.40
. 73
.43
.65
.23
.14
. 00
.23
. 57
. 75
.78
. 90
. 40
. 46
. 03
. 43
.20
.10
.70
.10
. 70
. 49
.78
.23
.30
.16
. 57
.52
.51
.18
. 69
. 53
10.400
5.6000
11.400
8.5000
1 . 0000
12.100
9. 0000
4 . 1000
13.400
9.5000
.30000
8. 9000
9 . 4000
1. 0000
. 10000
10.150
7.8000
7.1000
11.700
6. 9500
8 . 7000
. 10000
2.0000
1.3000
6.7000
2.5500
4 . 8000
1 . 6000
8 . 0000
5 . 5000
4. 9000
.45000
10.
10
1
34
1
4
81
48
44
10.
6.
11.
8.
3.
12.
9 .
5.
13.
9 .
0.
8.
9 .
5 .
0 .
10.
•-j
•-J
11.
.40
.60
.40
.50
.15
.10
. 00
. 70
.40
.50
.30
. 90
. 40
.20
.10
.15
.80
.10
.70
10.
6.
11.
8.
6 .
12.
9 .
7 .
13.
9 .
6.
8.
9 .
6 .
7 .
10.
8.
•-J
11.
.40
.80
.40
.65
.15
.13
. 00
.35
.60
. 75
.85
. 90
. 40
. 60
.20
. 43
.20
.10
.70
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-18
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Dissolved Oxygen mg L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
WINTER
FALL
SPRING
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
SUMMER
SUMMER
FALL
SPRING
8
1
10
12
10
1
5
11
3
5
5
5
1
4
5
4
1
1
1
1
1
1
1
1
1
1
1
2
1
1
2
1
8.22
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-19
-------
Des
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
:riptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Dissolved Oxygen mg L
MIN MAX STDDEV STDERR CV P5
1990
1990
1991
1991
1991
1991
1992
1992
1992
1993
1993
1993
1993
1994
1994
1994
1994
1995
1995
1995
1995
1996
1996
1996
1996
1997
1998
1999
2000
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
WINTER
SUMMER
SUMMER
SUMMER
4
6
10
1
21
2
6
12
4
6
4
14
4
4
6
12
4
5
^
12
1
6
3
5
2
4
4
4
2
5 .
10.
9 .
9
7 .
11.
9 .
8.
9
9 .
10.
•-j
12.
8.
11.
7 .
11.
8.
10.
•-J
11.
8.
9 .
7 .
10.
9 .
8.
8.
7 .
. 98
.19
. 02
.20
.12
. 68
.15
.16
.00
.60
.20
2 6
. 70
. 83
.33
. 65
. 53
.76
. 95
. 7 9
.30
. 48
. 50
.78
.15
.05
.10
.20
. 93
1.
•-J
6.
9
4 .
10
8.
6 .
2 .
8.
9
2
11
8.
9 .
5 .
10
8.
10
6.
11
7 .
9 .
6 .
10
8.
^
~->
7 .
3000
4000
0650
2000
2150
. 000
7000
9170
8000
8000
6500
9300
. 500
5000
7000
0670
.500
3000
.350
4170
.300
5000
0000
7000
.150
0000
2800
1500
2400
11.
71
P2J
P7J
44
44
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-20
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Nitrite_Nitrate_NO2_NO3_mg_L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
10
FALL
SPRING
SUMMER
FALL
SPRING
SUMMER
WINTER
SUMMER
WINTER
FALL
FALL
SPRING
SUMMER
WINTER
SPRING
WINTER
FALL
SPRING
SUMMER
.11000
.26000
.02500
.01000
.01000
.02000
.02500
.05000
.07000
.02000
.02500
.02000
.00250
.00625
.00250
.00250
.02500
.10000
.02500
FALL
SUMMER
FALL
SPRING
SUMMER
SUMMER
SUMMER
FALL
SUMMER
WINTER
WINTER
SUMMER
FALL
.17
1.19
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-21
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Nitrite_Nitrate_NO2_NO3_mg_L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
11
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
SUMMER
WINTER
WINTER
SUMMER
WINTER
FALL
SUMMER
FALL
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
.02000
. 10000
.02500
.02500
.01000
.08000
.01000
.02500
.48000
.01000
.45000
.08000
.14000
.13000
.00250
.12000
.07000
47
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-22
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Nitrite_Nitrate_NO2_NO3_mg_L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
12
WINTER
FALL
SPRING
SUMMER
FALL
SUMMER
WINTER
FALL
SPRING
SUMMER
SUMMER
SUMMER
SUMMER
WINTER
FALL
SUMMER
FALL
SPRING
SUMMER
FALL
SUMMER
FALL
SUMMER
FALL
SUMMER
FALL
SPRING
SUMMER
WINTER
16
8
^
2
1
2
1
1
1
1
2
2
1
1
1
1
0.
124
141
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-23
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Nitrogen_Tot_Kj eldhal_mg_L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
1990
1990
1991
1991
1991
1991
1992
1992
1993
1993
1993
1993
1994
1994
1995
1995
1995
1995
1996
1996
1996
1997
1997
1997
1990
1990
1991
1991
1991
1992
1993
1994
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SUMMER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
FALL
SUMMER
FALL
SPRING
SUMMER
SUMMER
SUMMER
FALL
3
1
~->
5
3
4
2
1
8
3
9
1
1
5
1
2
~->
2
2
3
2
1
1
1
2
2
2
3
5
2
16
8
0.
0.
1.
1.
0 .
0 .
1.
1.
0.
0.
1.
0.
0 .
0 .
0 .
0 .
0.
0.
0.
0.
0 .
0 .
0 .
0 .
1.
0.
0.
1.
1.
0 .
0 .
0.
. 57
.36
. 46
. 22
. 41
.74
. 89
. 00
.60
.38
.30
.34
. 42
. 44
. 60
. 45
.60
.34
. 44
.85
. 47
.25
.20
.33
. 63
97
. 62
. 91
.10
. 7 5
. 80
.88
.44000
.35500
.60000
.50000
. 30000
. 30000
. 30000
1 . 0000
.29000
.36000
.30000
.34000
. 42000
.39000
. 60000
. 30000
.30000
.33000
.40000
.34000
. 44000
.24500
. 20000
. 33000
1.5500
.54500
.61000
1. 4500
. 50000
. 29000
. 02500
.60000
0.39
12
0.80
0.36
1.10
0.70
0 . 60
1.15
3.48
1. 00
0.85
0.43
1.30
0.34
0. 42
0.48
0 . 60
0 . 60
0.85
0.36
0.48
1. 62
0 . 50
0.25
0.20
0.33
1.
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-24
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Nitrogen_Tot_Kj eldhal_mg_L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
14
1994
1994
1994
1995
1995
1995
1996
1997
1997
1997
1990
1990
1990
1990
1991
1991
1991
1991
1992
1992
1992
1992
1993
1993
1993
1993
1994
1994
1995
1995
1995
1996
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
SUMMER
FALL
SPRING
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
SPRING
SUMMER
WINTER
SPRING
1
8
2
1
4
1
11
6
6
13
8
7
7
9
8
6
10
9
3
10
10
8
3
6
12
5
2
8
2
3
3
2
1.
0.
0.
0.
0 .
1.
0 .
1.
1.
0.
0.
0 .
0 .
0 .
0 .
0.
0.
0.
0.
0 .
0 .
0 .
0 .
0.
0.
0.
0.
0 .
0 .
0 .
0 .
0
. 90
. 98
9 9
.81
. 63
. 03
.54
. 48
.15
. 91
.54
. 43
.51
.51
. 80
. 44
.67
.48
.70
. 40
.52
. 50
. 41
.36
.32
. 21
. 22
.37
.18
. 46
. 42
33
1. 9000
.02500
.02500
.81000
. 02500
1 . 0300
. 02500
. 80000
.42500
.17250
.30000
. 30000
.30000
. 30000
. 15000
.30000
.30000
.30000
.44500
. 05000
. 05000
.34000
. 24000
.25000
.17000
.14000
.12500
. 05000
. 05000
. 31000
. 25000
'0000
.15
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-25
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Nitrogen_Tot_Kj eldhal_mg_L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
15
1990
1990
1990
1991
1991
1991
1993
1993
1990
1990
1991
1991
1992
1992
1992
1993
1993
1993
1993
1994
1994
1994
1994
1995
1995
1995
1996
1996
1996
1996
FALL 1
SPRING 1
SUMMER 1
SPRING 1
SUMMER 1
WINTER 1
FALL 1
SUMMER 1
SUMMER 1
WINTER 4
FALL 8
SUMMER 22
FALL 2
SUMMER 20
WINTER 2
FALL 1
SPRING 1
SUMMER 9
WINTER 1
FALL 1
SPRING 1
SUMMER 9
WINTER 1
FALL 3
SPRING 1
SUMMER 9
FALL 1
SPRING 1
SUMMER 2
WINTER 1
1.
0 .
1.
0 .
1.
0.
0.
0.
3.
2.
0 .
1.
1
1
^
0.
0 .
0 .
0 .
0 .
0.
0.
0.
0.
0 .
0 .
0 .
0 .
0.
0.
.20
. 90
.25
. 80
.10
. 90
.61
. 21
. 02
.34
. 88
.25
56
33
.10
. 12
. 83
. 66
.33
.33
. 4 2
.87
.28
.30
.27
.39
.24
. 50
.54
.28
1.2000
. 90000
1.2500
. 80000
1 . 1000
. 90000
.61000
.21000
3.0200
1. 4600
. 52500
.39500
30000
23500
2. 6800
.11750
. 82500
.23100
.33000
.32500
. 42000
.20700
.28000
.24000
. 27000
. 25550
. 24000
. 50000
.47000
.27500
1.
0 .
1.
0 .
1.
0.
0.
0.
3.
4 .
1.
3.
0
3 .
^
0.
0 .
1.
0 .
0 .
0.
2 .
0.
0.
0 .
0 .
0 .
0 .
0.
0.
.20
. 90
.25
. 80
.10
. 90
.61
. 21
. 02
.19
.33
. 60
. 83
. 02
.51
. 12
. 83
. 49
.33
.33
. 4 2
. 7 9
.28
.41
.27
. 69
.24
. 50
.60
.28
3.
1.
0 .
0 .
0.
0.
2 .
0.
0 .
0 .
0 .
0 .
0.
0.
0.
0.
0 .
0 .
0 .
0 .
0.
0.
. 02
. 46
.53
. 42
.30
. 25
.68
. 12
. 83
.23
.33
.33
. 4 2
. 21
.28
. 2 4
.27
.26
.24
. 50
.47
.28
3.
1.
0 .
0 .
0.
0.
2 .
0.
0 .
0 .
0 .
0 .
0.
0.
0.
0.
0 .
0 .
0 .
0 .
0.
0.
. 02
. 62
. 65
.53
.30
.58
.68
. 12
. 83
.36
.33
.33
. 4 2
. 35
.28
. 2 4
.27
.30
.24
. 50
.47
.28
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-26
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Nitrogen_Tot_Kj eldhal_mg_L
MIN MAX STDDEV STDERR CV P5
P2J
P7J
43
43
43
43
43
43
FALL
SPRING
SUMMER
SUMMER
SUMMER
SUMMER
WINTER
FALL
SUMMER
FALL
SUMMER
FALL
SUMMER
FALL
SUMMER
FALL
SUMMER
FALL
SPRING
SUMMER
WINTER
14
8
3
2
2
1
1
1
1
2
2
1
1
1
1
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-27
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
SECCHI m
STDDEV STDERR
P2J
P7J
1990
1990
1990
1990
1991
1991
1991
1991
1992
1992
1992
1992
1993
1993
1993
1993
1994
1994
1994
1994
1995
1995
1995
1995
1996
1996
1996
1996
1997
1997
1997
1998
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
SUMMER
2
4
9
4
2
5
6
4
2
4
6
^
10
5
10
2
^
2
~->
1
3
3
8
2
1
2
4
2
2
3
3
1
1.0000
.30480
.23000
1.0000
.90000
.22860
.80000
.90000
1.2000
.12700
.10000
.40000
.30000
.40000
.20000
.80000
.90000
2.4000
.13000
3.1000
.55000
.40000
.45000
1.3500
2000
7000
0000
9000
0250
6250
1250
1
1.
0.
0.
1.
0 .
0 .
0 .
0 .
1.
0.
0.
0.
0 .
0.
0 .
0 .
0.
2 .
0.
3 .
0 .
0 .
0 .
1.
1.
2 .
0.
1.
1.
1.
1.
2.
.00
.30
.23
.00
. 90
.23
. 80
. 90
.20
.13
.10
.40
.30
. 40
.20
. 80
. 90
.40
.13
.10
. 55
. 40
. 45
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. 50
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-28
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
SECCHI m
STDDEV STDERR
P2J
P7J
FALL
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SUMMER
SUMMER
FALL
SPRING
SUMMER
WINTER
SUMMER
SUMMER
FALL
SPRING
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
2
^
1
2
2
11
1
3
3
16
•-J
1
7
1
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10
2
2
9
8
10
12
10
8
11
12
9
8
10
13
8
2
.30000
.21000
.20000
.40000
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.15240
.40000
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.46000
.15000
.12000
.30000
.50000
.20000
.30000
.12000
.32500
.22500
.35000
.93980
.61000
.65000
.92710
1.3716
1.3700
.82500
1.0160
.93980
.91440
1.1500
.50800
1.1400
.15
1.14
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-29
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
SECCHI m
MAX STDDEV STDERR
P2J
P7J
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
WINTER
FALL
SPRING
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SUMMER
SUMMER
FALL
SPRING
10
12
10
2
5
12
3
5
5
5
1
4
5
4
1
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
5
4
11
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-30
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
SECCHI m
MAX STDDEV STDERR
P2J
P7J
1990
1990
1991
1991
1991
1991
1992
1992
1992
1992
1993
1993
1993
1993
1994
1994
1994
1994
1995
1995
1995
1995
1996
1996
1996
1996
1997
1997
1997
1997
1998
1998
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
T
3
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6
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3
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-31
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
SECCHI m
MAX STDDEV STDERR
P2J
P7J
WINTER
FALL
SUMMER
FALL
SPRING
SUMMER
FALL
SUMMER
FALL
SUMMER
FALL
SUMMER
SPRING
SUMMER
WINTER
13
8
3
1
1
1
1
1
1
1
2
1
1
1
.15
.10160
.22860
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1.7272
.15240
.86360
1.3208
1.2700
.45720
.90170
1.2192
.76200
.96520
.77470
1.0414
.15
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-32
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1992 to 1997
Total Nitrogen mg L
year season N MEAN MIN MAX STDDEV STDERR CV P5 P25 MEDIAN P7J
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Total Phosphorus ug L
MIN MAX STDDEV STDERR CV P5
1990
1990
1990
1990
1991
1991
1991
1991
1992
1992
1992
1992
1993
1993
1993
1993
1994
1994
1995
1995
1995
1995
1996
1996
1996
1996
1997
1997
1997
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
2
2
10
4
9
8
8
7
1
2
8
4
9
3
10
1
2
6
2
2
8
2
1
2
4
2
2
1
2
P2J
P7J
1990 FALL
1990 SUMMER
1991 FALL
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-34
-------
SPRING
SUMMER
SUMMER
SUMMER
FALL
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
SUMMER
FALL
SPRING
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
SPRING
N
10
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Total Phosphorus ug L
MIN MAX STDDEV STDERR CV P5
2
1
4
1
11
13
P2J
P7J
25 .
32.
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26.
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116
106
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92
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137
61
15
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-35
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Total Phosphorus ug L
N MEAN MIN MAX STDDEV STDERR CV P5
P2J
P7J
SUMMER
SPRING
SUMMER
WINTER
SPRING
SUMMER
WINTER
FALL
SUMMER
WINTER
FALL
SUMMER
FALL
SUMMER
WINTER
FALL
SPRING
SUMMER
11
FALL
SPRING
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SUMMER
SUMMER
1
1
2
1
1
1
1
1
1
2
1
1
1
1
4
11
3
23
2
3
1
11
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-36
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Total Phosphorus ug L
N MEAN MIN MAX STDDEV STDERR CV P5
P2J
P7J
WINTER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
FALL
SPRING
SUMMER
WINTER
FALL
SPRING
SUMMER
SUMMER
SUMMER
SUMMER
WINTER
FALL
SUMMER
FALL
SUMMER
FALL
SUMMER
FALL
SUMMER
FALL
SUMMER
FALL
SPRING
SUMMER
1
12
1
1
11
1
2
1
10
8
3
2
2
1
1
1
1
2
2
1
1
1
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-37
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1990 to 2000
Total Phosphorus ug L
subecoregion year season N
44 1997 WINTER 1
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion B-38
-------
Aggregate Nutrient Ecoregion: IV
Lakes and Reservoirs
Descriptive Statistics by Subecoregion, Year and Season
from 1991 to 2000
pH_S_U
MIN MAX STDDEV STDERR CV P5
P2J
P7J
Appendix B—Descriptive Statistics Data Tables for Level III Subecoregions Within Aggregate Ecoregion
B-39
-------
APPENDIX C
Quality Control/Quality Assurance Rules
-------
-------
INDUS
CORPORATION
Knowledge-Based Solutions
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
Appendix C—Quality Control/Quality Assurance Rules
-------
-------
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001
CONTENTS
1.0 BACKGROUND C-l
1.1 Purpose C-l
1.2 References C-l
2.0 QA/QC PROCEDURES C-l
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-l 1
5.2.1 Aggregate Nutrient Ecoregion 1 C-l 1
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 STORE! Nutrient Data Set C-l6
APPENDIX B Process for Adding Aggregate Nutrient Ecoregions and Level III
Ecoregions C-22
APPENDIX C Glossary C-23
Appendix C—Quality Control/Quality Assurance Rules C-iii
-------
-------
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001
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 Water-
Quality Assessment (NAWQA) data, and other relevant nutrient data from universities and
States/Tribes into the database. The data imported into the Nutrient Criteria Database 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
Appendix C—Quality Control/Quality Assurance Rules C-l
-------
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001
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
C-2 Appendix C—Quality Control/Quality Assurance Rules
-------
9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001
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.
Appendix C—Quality Control/Quality Assurance Rules C-3
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9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001
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.
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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.
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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 Pet' 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.
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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 Pet' 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.
Appendix C—Quality Control/Quality Assurance Rules C-7
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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
- Spring: April to May
- Summer: June to August
- Fall: September to October
- Winter: November to March
• Aggregate nutrient ecoregions: 1, 2, 3, 4, 5, 9, 10, 11, 12, 13, and 14
- Spring: March to May
- Summer: June to August
- Fall: September to November
- 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)
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5.1 Lakes and Reservoirs
5.1.1 Aggregate Nutrient Ecoregion 3
Data Sources:
Legacy STORE!
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)
Appendix C—Quality Control/Quality Assurance Rules C-9
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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
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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)
Appendix C—Quality Control/Quality Assurance Rules C-l 1
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Turbidity (NTU)
Turbidity (JCU)
pH
Level III ecoregions:
O 'f
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
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5.2.3 Aggregate Nutrient Ecoregion 5
Data sources:
Legacy STORE!
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
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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)
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Nitrogen, Total Kjeldhal (TKN) (mg/L)
Organ! c_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
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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)
TN - mg/1 (600)
TKN - mg/1 (625)
Total Ammonia (NH3 +NH4) - mg/1 (6 1 0)
Total NO2+NO3 - mg/1 (630)
Total Nitrite - mg/1 (615)
Total Nitrate - mg/1 (620)
Organic N - mg/L (605)
TP - mg/1 (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 Data Items Included
(STORET Item Name)
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)
RF ION/OFF tag (ONOFF)
Sample Data Items
Included
(STORET Item Name)
Sample Date (DATE)
Sample Time (TIME)
Sample Depth (DEPTH)
Composite Sample Code
(SAMPMETH)
+ If data record available at a station included data only for this or other such marked parameters, data record was
deleted from data set.
The following set of retrieval rules were applied to the retrieval process:
• Data were retrieved for waterbodies specified only as 'lake', 'stream', 'reservoir', or
'estuary' under "Station Type" parameter. Any stations specified as 'well,' 'spring,' or
'outfall' were eliminated from the retrieved data set.
• Data were retrieved for station types described as 'ambient' (e.g., no pipe or facility
discharge data) under the "Station Type" parameter.
• Data were retrieved that were designated as 'water' samples only. This includes 'bottom'
and 'vertically integrated' water samples.
• Data were retrieved that were designated as either 'grab' samples and 'composite' samples
(mean result only).
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• 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 STORE!'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
blank - Data not remarked.
A - Value reported is the mean of two or more determinations.
B - Results based upon colony counts outside the acceptable ranges.
C -Calculated. Value stored was not measured directly, but was
calculated from other data available.
D - Field measurement.
E - Extra sample taken in compositing process.
F - In the case of species, F indicates female sex.
G - Value reported is the maximum of two or more determinations.
H - Value based on field kit determination; results may not be accurate.
I - The value reported is less than the practical quantification limit and
greater than or equal to the method detection limit.
J - Estimated. Value shown is not a result of analytical measurement.
Keep or Delete Data Point
Keep
Keep
Delete
Keep
Keep
Delete
Delete
Delete
Delete
Keep, but used one-half the
reported value as the new value.
Delete
Appendix C—Quality Control/Quality Assurance Rules
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TABLE 2: STORET REMARK CODE RULES
K - Off-scale low. Actual value not known, but known to be less than
value shown.
L - Off-scale high. Actual value not known, but known to be greater
than value shown.
M -Presence of material verified, but not quantified. Indicates a positive
detection, at a level too low to permit accurate quantification.
N -Presumptive evidence of presence of material.
O -Sample for, but analysis lost. Accompanying value is not meaningful
for analysis.
P -Too numerous to count.
Q -Sample held beyond normal holding time.
R -Significant rain in the past 48 hours.
S -Laboratory test.
T -Value reported is less than the criteria of detection.
U -Material was analyzed for, but not detected. Value stored is the limit
of detection for the process in use.
V -Indicates the analyte was detected in both the sample and associated
method blank.
W -Value observed is less than the lowest value reportable under remark
"T."
X -Value is quasi vertically -integrated sample.
Y -Laboratory analysis from unpreserved sample. Data may not be
accurate.
Z -Too many colonies were present to count.
Keep, but used one-half the reported
value as the new value.
Keep
Keep, but used one half the reported
value as the new value.
Delete
Delete
Delete
Delete
Delete
Keep
Keep, but replaced reported value with
0.
Keep, but replaced reported value with
0.
Delete
Keep, but replaced reported value with
0.
No data point with this remark code in
data set.
Delete
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
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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
Appendix C—Quality Control/Quality Assurance Rules C-19
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9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001
• 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
C-20 Appendix C—Quality Control/Quality Assurance Rules
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9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001
nutrient data set contains the following:
41,174 station records
919,895 sample records
Appendix C—Quality Control/Quality Assurance Rules C-21
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9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001
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.
C-22 Appendix C—Quality Control/Quality Assurance Rules
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9 Nutrient Ecoregion/Waterbody Type Summary Chapters, Contract # 68-C-99-226, TO# 07 August 27, 2001
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
Appendix C—Quality Control/Quality Assurance Rules C-23
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