c/EPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Corvalhs OR 97330
EPA-600/3-79-103
September 1 979
Research and Development
Non-Point Source—
Stream Nutrient
Level Relationships:
A Nationwide Study
Supplement 1:
Nutrient Map
Reliability
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development U S Environmental
Protection Agency have been grouped into nine series These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields
The nine series are
1 Environmental Health Effects Research
2 Environmental Protection Technology
3 Ecological Research
4 Environmental Monitoring
5 Socioeconornic Environmental Studies
6 Scientific and Technical Assessment Reports (STAR)
7 Interagency Energy-Environment Research and Development
8 Special Reports
9 Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series This series
describes research on the effects of pollution on humans, plan! and animal spe-
cies, and materials Problems are assessed for their long- and short-term influ-
ences Investigations include formation transport, and pathway studies to deter-
mine the fate of pollutants and their effects This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161
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EPA-600/3-79-103
September 1979
NONPOINT SOURCE—STREAM NUTRIENT LEVEL
RELATIONSHIPS: A NATIONWIDE STUDY
SUPPLEMENT 1: NUTRIENT MAP RELIABILITY
By
Theodore R. McDowell and
James M. Omerm'k
Streams Branch
Freshwater Division
Corvallis Environmental Research Laboratory
Corvallis, Oregon 97330
CORVALLIS ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
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DISCLAIMER
This report has been reviewed by the Corvallis Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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FOREWORD
Effective regulatory and enforcement actions by the Environmental Protec-
tion Agency would be virtually impossible without sound scientific data on
pollutants and their impact on environmental stability and human health.
Responsibility for building this data base has been assigned to EPA's Office
of Research and Development and its 15 major field installations, one of which
is the Corvallis Environmental Research Laboratory (CERL).
The primary mission of the Corvallis Laboratory is research on the ef-
fects of environmental pollutants on terrestrial, freshwater, and marine
ecosystems; the behavior, effects and control of pollutants in lake and stream
systems; and the development of predictive models on the movement of pollu-
tants in the biosphere.
This report clarifies the reliability and applicability of an earlier
CERL study that related phosphorus and nitrogen levels in stream to the non-
point influences present in their drainage areas and also demonstrated the
regionalities in stream nutrient levels in the conterminous United States. As
such the information provided herein should be of interest and utility to
water quality managers.
Thomas A. Murphy
Director, CERL
m
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ABSTRACT
The National Eutrophication Survey (NES) national maps of nonpoint
source-related nitrogen and phosphorus concentrations in streams were evalu-
ated for applicability and reliability. Interpretations on these maps, which
were based on data from 928 sampling sites associated with nonpoint source
watersheds and the relationships of these data to general land use and other
macro-watershed characteristics, were compared with a nationwide set of non-
point source stream nutrient data collected largely by the U.S. Geological
Survey (USGS).
In most areas where comparisons could be made the mapped interpretations
agreed relatively well with USGS data. Where disagreements did occur regard-
ing nitrogen concentrations, NES mapped interpretations tended to be higher
than USGS values more often than lower; where disagreements occurred regarding
phosphorus concentrations, the reverse was apparent.
Revised reliability map insets based on these analyses are provided for
maps of total nitrogen and total phosphorus concentrations.
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CONTENTS
Foreword iii
Abstract iv
Figures vi
Sections
1. Introduction 1
2. Conclusions 4
3. Background 5
History and Objectives of the EPA/NES-NPS Study 5
Data Collection and Analysis 5
NPS Assessment Methodology 7
Strengths and Limitations of the NES Tributary Sampling
Data 9
4. Approach 11
Selection of Comparable Data Sources 11
Data Acquisition and Handling 12
Data Comparisons 13
5. Results 16
Total N Comparisons 16
Areas of Agreement 16
Areas of Disagreement 20
Total P Comparisons 21
Areas of Agreement 21
Areas of Disagreement 22
Revised Reliability Maps 26
References 29
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FIGURES
Number Page
1. Distribution of individual NES nonpoint source study watersheds. ... 6
2. Relationships between general land use and nutrient concentrations
in streams 8
3. Distribution of USGS nonpoint source watersheds used for stream
nutrient concentration comparisons 14
4. Area! comparisons of NPS stream nitrogen concentration data 17
5. Areal comparisons of NPS stream phosphorus concentration data 22
6. Revised reliability map insets for EPA-NES mapped interpretations of
total nitrogen and total phosphorus concentrations in streams from
nonpoint sources 27
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SECTION 1
INTRODUCTION
The primary objective of the Federal Water Pollution Control Act Amend-
ments of 1972 (PL 92-500) is "...to restore and maintain the chemical, physi-
cal, and biological integrity of the Nation's waters". Section 208 of PL
92-500 requires that each state identify areas which have substantial water
quality control problems. It appears evident that these problem areas should
be identified on the basis of local and regional variations in the sources and
concentrations of specific pollutants. Accurate identification of sources and
reliable assessment of the contribution of each source to pollution are essen-
tial if effective pollution control strategies are to be implemented.
Historically, the principal strategy employed to protect water quality
has been to control pollution from urban-industrial point* sources. However,
it is now recognized that in many cases water quality cannot be adequately
protected without also controlling nonpoint sources* of pollution (i.e.,
pollution resulting from agricultural, silvicultural, mining, and construction
activities). Section 208 of PL 92-500 requires that state and local govern-
ments develop areawide waste treatment management plans which identify point
and nonpoint sources of water pollution. For areas in which pollution from
nonpoint sources (NPS) is a problem, the plans must include procedures for
controlling that pollution to the extent feasible.
Pollution from nonpoint sources varies spatially and temporally due to
natural as well as anthropogenic influences. Agencies reponsible for "208
planning" must be able to identify geographic variations in water quality and
determine whether those variations are related to changes in "natural," back-
ground conditions or to pollution from man-related point and/or nonpoint
sources. These distinctions must be made both at a general, regional level to
identify areas with water quality problems and at a site-specific, local level
to identify and control sources of pollution.
Unfortunately, the water quality data needed for 208 planning have not
been collected in many areas. Planning agencies lacking data often do not
have the time, money, and/or expertise required to conduct systematic water
sampling programs. Expediency has forced many agencies to use water quality
prediction models to estimate concentrations of various pollutants, particu-
* According to Pisano (1976), point sources are: 1) discrete and confined;
i.e., effluent from a pipe; and 2) controlled through best practices tech-
nology for industry and secondary waste treatment for municipalities. Paisano
defines nonpoint sources as: 1) dispersed, diffuse and intermittent; 2)
influenced by local climatic, hydrologic, and terrestrial conditions; and 3)
controlled through land management and conservation practices.
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larly those attributable to nonpoint sources. Generally, these models are
based on empirically-derived relationships between land use or other basin
characteristics and concentrations of selected water quality parameters (e.g.,
nutrients such as nitrogen and phosphorus*). The state-of-the-art for models
used to predict concentrations of nitrogen and phosphorus in streams is par-
ticularly primitive, relying primarily on regression equations (i.e., Dillon
and Kirchner, 1975; Omernik, 1976; 1977) or on adaptations of the Universal
Soil Loss Equation** (i.e., McElroy et a]_. , 1976). The reliability of these
empirical models is questionable, particularly when the models are extended
beyond the design and geographic limits of the original studies. Therefore,
those concerned with accurate local assessments of nonpoint source pollution
may find that the reliability of these empirical models is unsatisfactory. On
the other hand, those concerned with regional variations in stream nutrient
levels, or with the preliminary identification of areas with potential water
quality control problems, may find that obtaining the detailed land use,
soils, terrain, and climatic data required by these empirical models is exorb-
itantly expensive and time consuming (and unwarranted considering the level of
information needed). Clearly, alternative NPS assessment methodology is
needed.
One alternative to the assessment methodology mentioned above has re-
cently been developed. This alternative is based on a set of maps which
illustrate ranges in mean annual NFS-related nutrient concentrations that one
might generally expect in streams draining any area within the conterminous
United States (Omernik, 1977). The maps were compiled by comparing patterns
of land use in the United States (U.S. Geological Survey, 1970) with water
quality data mapped for 928 NFS-type watersheds sampled for the Environmental
Protection Agency's (EPA) National Eutrophication Survey (NES). Apparent
regional relationships between land use patterns (and other human-related
activities such as fertilizer usage and livestock densities) and nutrient
concentrations in streams sampled for the NES were used to classify areas
according to the range in mean annual concentration of total nitrogen (N),
inorganic nitrogen (IN), and total phosphorus (P) expected in streams in each
area. Therefore, concentrations illustraced on the NES maps do not represent
actual nutrient concentrations in a particular stream at a particular time;
however, general areal patterns of NFS-related stream nutrient levels can be
interpreted from the NES maps in the same manner that one can interpret the
areal distribution of precipitation from an isometric map.
* Nitrogen and phosphorus are usually the limiting factors influencing eutro-
phication (the nutrient enrichment of water bodies), and are generally con-
sidered to be the nutrients having the greatest potential for affecting water
quality.
** The Universal Soil Loss Equation (USLE; see Wischmeier and Smith, 1965)
was originally developed to estimate long-term average annual soil loss due to
sheet and rill erosion on agricultural fields in the midwest; however, it has
been extended beyond the original design by McElroy e_t al. (1976) to estimate
NPS concentrations of sediment, nutrients and other chemicals in streams.
Problems encountered when using the USLE to predict NPS pollutant levels are
discussed by Wischmeier (1976), Omernik (1977), U.S. Forest Service (in
press), and McDowell (1979).
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OBJECTIVES
The purpose of this paper is to evaluate the utility and the reliability
of the NES maps of stream nutrient concentrations attributable to nonpoint
sources. We will clarify the utility of the NES maps by briefly reviewing
their basis, strengths (including possible applications), and limitations.
Most of this paper, however, is concerned with clarifying the reliability of
the NES map interpretations. Reliability is evaluated by comparing the NES
map interpretations with mapped patterns of mean annual total nitrogen and
total phosphorus concentrations primarily determined by the U.S. Geological
Survey (USGS). The NES map of inorganic nitrogen concentration was not evalu-
ated because of a lack of suitable data for comparison. Only those USGS
stations monitoring NPS-type watersheds are used in the comparisons. Results
of the comparisons are mapped and discussed. Finally, new reliability maps
are presented to clarify the spatial variations in reliability associated with
each NES map examined.
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SECTION 2
CONCLUSIONS
The NES maps can be valuable tools for individuals or agencies concerned
with regional comparisons of NPS-related stream nutrient levels. However, the
strengths, limitations, and reliability of NES map interpretations should be
considered carefully before those interpretations are used to estimate NPS-
related stream nutrient levels in any basin or region. Although NES map
interpretations are not an equivalent substitute for stream nutrient data
(particularly for assessments of streams draining small watersheds), agencies
lacking such data could use the NES maps either to make regional NPS assess-
ments or to identify potential problem areas that may require sampling pro-
grams.
Data from 330 USGS stations monitoring total nitrogen concentrations and
601 monitoring total phosphorus concentrations were used to evaluate the
reliability of the NES map interpretations. In most areas where comparisons
could be made, NES map interpretations agree relatively well with mean annual
nutrient concentrations calculated from USGS water quality data, particularly
in areas where streams had also been sampled for the NES and in regions with
relatively homogeneous environmental (soils, geology, climate, terrain) and
land use characteristics. Results of these comparisons tend to confirm the
conclusion of the NES-NPS study that there is a strong relationship between
land use and stream nutrient levels (Omernik, 1977).
Assessment of the NES map of Total N concentrations reveals that USGS
data and NES map interpretations disagree only in a few areas. Areas of
apparent disagreement tend to be small, with the exception of areas in New
York, Wyoming, Arizona, and northern California. Where disagreements do
occur, NES map interpretations of mean annual Total N concentrations tend to
be higher than USGS values more often than lower.
NES map interpretations are in general agreement with Total P data from
nearly 80 percent of the 601 USGS stations used in the comparisons. In nearly
all cases of disagreement, NES map interpretations are lower than the mean
annual Total P concentrations calculated from USGS water quality data. The
most notable areas of disagreement are located along the Atlantic and Gulf
Coastal Plains, particularly in Florida and New Jersey, and along the Appa-
lachian system, primarily in Pennsylvania and Kentucky.
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SECTION 3
BACKGROUND
HISTORY AND OBJECTIVES OF THE EPA/NES-NPS STUDY
The NFS-stream nutrient maps were produced by interpreting data from the
Environmental Protection Agency's National Eutrophication Survey (NES). The
NPS assessment portion of the NES was undertaken to study the relationship
between watershed land use characteristics and lake trophic conditions. It
was hoped that this subproject of the NES would result in "...a quick, rela-
tively accurate method of assessing nutrient loadings to lakes based on anal-
ysis of land use in their watersheds" (Omernik, 1976; 1977). Originally,
aerial photography and topographic maps were to have been used to identify and
map land use types in each drainage area associated with the approximately 800
lakes sampled for the NES. However, for a variety of reasons, the analysis
was limited to nonpoint source-stream nutrient level relationships using only
those tributary sampling sites associated with NPS-type watersheds. Of the
more than 4000 NES tributary sampling sites, 928 met this criterion.
The principal objectives of the NES-NPS land use study were: 1) to
investigate the relationships between nonpoint watershed characteristics and
stream nutrient levels; 2) to "...develop a means for predicting stream nitro-
gen and phosphorus levels based on land use and related geographical charac-
teristics"; and 3) to investigate and define regionalizes in the relation-
ships between macro-watershed characteristics and stream nutrient levels and
provide "...some accountability for these regionalities in the predictive
methods" (Omernik, 1977).
DATA COLLECTION AND ANALYSIS
Generally, of the 928 NPS-type watersheds included in the study, each was
sampled approximately once a month for one year. However, the NES sampling
program consisted of three phases, and not all watersheds were sampled in the
same year. Sampling began in 1972 at 133 sites in the northeast; in 1973 at
340 sites in the east and southeast; and in 1974 at 455 sites in the west and
midwest (Figure 1). Stream samples were collected by National Guard units in
each state and sent to the Corvallis (Oregon) Environmental Research Labora-
tory for nutrient analysis. Sample collection, preservation, storage, and
analyses were done according to methods described in NES Working Paper No. 175
(U.S. EPA, 1975).
Comparable data collected from a relatively large number of watersheds
dispersed across the conterminous United States provided a unique opportunity
to examine the regionalities of land use—stream nutrient level relationships.
Two methods were used to analyze the NES data. First, regression analysis was
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used to examine the relationships between areally-expressed watershed charac-
teristics (delineated from aerial photography and topographic maps) and the
mean annual concentrations of total nitrogen (total Kjeldahl-N + N02 + N03),
inorganic nitrogen (NH3 + N02 + N03), total phosphorus, and orthophosphorus
(P04 as P; technically, soluble reactive phosphorus) calculated for each
stream. Good correlations were found between general land use and nutrient
concentrations in streams. Nutrient concentrations were much lower in streams
draining forested watersheds than in those draining agricultural or urban
watersheds (Figure 2). The second method involved mapping the location and
nutrient concentrations of each of the 928 sampling sites. The area! patterns
of the nutrient concentrations were then overlaid and compared with general
land use patterns, as well as patterns of other macro-watershed characteris-
tics (e.g., fertilizer use, farm animal density, and acid rainfall) that in
many areas appeared to correlate spatially with certain nutrient forms. Then
areas, which frequently coincided with land use map units on the USGS national
map (1970), were assigned what appeared to be the most appropriate range in
mean annual nutrient concentrations. Separate maps were constructed to illus-
trate ranges for total nitrogen, inorganic nitrogen, and total phosphorus.
NPS ASSESSMENT METHODOLOGY
The analysis of NES data resulted in two methods that can be used to
predict NPS stream nutrient levels:
1. Regional regression equations in which general land use data (per-
cent of drainage area occupied by selected land use types) are used
as the independent variables; and
2. Mapped interpretations of national and regional patterns of land
use-stream nutrient level relationships.
Both methods provide only limited prediction capabilities, particularly
when applied for NPS assessments of small watersheds which tend to exhibit
greater variability than larger drainage areas (Onstad et al. , 1977).
Although neither may be adequate for precise assessments of local NPS stream
nutrient levels, they may be quite useful for regional comparisons when other
data are unavailable.
The second NPS assessment method is particularly interesting for several
reasons:
1. It is the first attempt to produce national maps illustrating gen-
eral NPS-stream nutrient patterns;
2. It requires no detailed data collection, only basin delineation and
calculation of areally weighted means for mapped nutrient classes
within the basin (the mean of the areally weighted class means
represents that part of the mean annual nutrient levels in the basin
attributable to nonpoint sources);
3. It can be used (or, unfortunately, misused) by almost anyone re-
gardless of their level of expertise, although interpretations will
be improved with knowledge of important NPS relationships and addi-
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N
68 > 90% Forest
77 > 75% Forest
295 > 50% Forest
21 > 50% Cleared
Unproductive
103 Mixed
39 >50% Range
144 > 50% Agriculture
11 > 40% Urban
72 > 75% Agriculture
74 > 90% Agriculture
. 108
Land Use
vs.
Mean Total Nitrogen and Mean
Inorganic Nitrogen Stream Concentrations
Data from 904 ' Nonpomt source —type watersheds
distributed throughout the United States
inorganic nitrogen concentration
.839
total nitrogen concentration
i.o
2.0 3.0 4.0
Milligrams per Liter
5.0
6.0
N
68 > 90% Forest
77 > 75% Forest
295 > 50% Forest
21
> 50% Cleared
Unproductive
Mixed
103
39 > 50% Range
144 > 50% Agriculture
11 > 40% Urban
72 > 75% Agriculture
74 > 90% Agriculture
Land Use
vs.
Mean Total Phosphorus and Mean
Orthophosphorus Stream Concentrations
Data irom 904 "Nonpomt source —type" watersheds
distributed throughout the United States
'thophosphorus concentration
.034
total phosphorus concentration
.02 .04 .06 .08 .10 .12
Milligrams per Liter
.14
.16
.18
.20
Figure 2. Relationships between general land use and nutrient concentrations
in streams.
8
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tional local information. The step by step procedure for utilizing the stream
nutrient maps is illustrated and explained by Omernik (1977, pp. 8-10).
The usefulness of these maps can best be illustrated by comparison with
another small-scale graphic more familiar to most people—an isometric map of
mean annual precipitation. One should not use a precipitation map to predict
the precipitation that will occur during a particular year at a given loca-
tion. Rather, the map illustrates patterns of long term mean conditions.
Many parts of the United States seldom experience a truly "normal year" cli-
matically. Generally, precipitation totals are somewhat higher or somewhat
lower than the mean; and (occasionally) totals deviate extremely from the mean
conditions. Admittedly, precipitation maps may provide a more accurate indi-
cator of their subject than the nutrient maps because of their more extensive
data base (from both temporal and spatial standpoints). However, precipita-
tion maps are compiled using data from different geographical locations to-
gether with knowledge of apparent associations of these data with physio-
graphic characteristics, water bodies, ocean currents, latitude, and other
environmental factors. For example, precipitation patterns in mountainous
areas, where data are scarce or lacking, are drawn to reflect the expected
orographic effects of elevation and exposure to weather systems. Much the
same kind of qualitative analysis was employed in compiling the nutrient maps.
They are based on values from stream samples from nearly 1000 locations
throughout the United States, as well as knowledge of the apparent associa-
tions between the nutrient data and other spatial phenomena such as land use.
Although the nutrient data were collected for only one year at each sampling
site, there were generally a sufficient number of data sites to indicate re-
gional patterns.
Strengths and Limitations of the NES Tributary Sampling Data
The NES data provide a good base for identifying geographic variations in
NPS stream nutrient levels. NES stream sampling was conducted nationwide and
data were collected for 928 NPS-type watersheds (unaffected by point sources).
Due to their number, their wide distribution, and the great variations in
drainage characteristics, it may be stated that the watersheds examined in the
study are representative of NPS-type watersheds in many parts of the conterm-
inous United States. Consistent definition and analysis of water-quality
parameters at the EPA Corvallis Laboratory and consistent interpretation of
basin characteristics permitted direct comparisons of geographic variations in
stream nutrient levels, and facilitated the statistical analysis of land
use—stream nutrient level relationships.
However, the NES data have several important limitations. Each of the
928 sites was sampled periodically for one year, and data were not flow-
weighted. Therefore, the mean annual concentrations reported for each water-
shed do not reflect or explain year-to-year, month-to-month, or storm-to-storm
variations in stream nutrient levels. Erroneous and unrepresentative assess-
ments may result if the NES maps are used to predict nutrient levels at a
given time in a specific stream. This problem will be most pronounced if the
NES maps are used to predict nutrient levels in streams draining small water-
sheds which tend to exhibit greater hydro!ogic variability than large basins
(Onstad et aj_. , 1977). For example, the Lakes Region Planning Commission
(LRPC) monitored nutrient levels in 14 streams draining into Lake Winnni-
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pesakee, New Hampshire and found that mean annual nutrient concentrations
varied markedly from stream to stream (Lakes Region Planning Commission,
1977). In general, land use patterns were similar in the watersheds associ-
ated with the 14 stream sampling sites. Eleven of those streams were also
monitored by the NES in 1972, and mean nutrient concentrations again varied
between streams (from 0.011 to 0.035 mg Total P/l). However, when Total P
concentrations were averaged for those 11 streams to produce a single mean for
the entire basin, the 1972 basin mean calculated from NES data (0.019 mg Total
P/l) was in close agreement with the 1976 basin mean calculated from LRPC data
(0.016 mg Total P/l) for the same streams. These findings suggest that annual
variability may not be a serious problem if the NES maps are used only for
regional comparisons or to estimate stream nutrient levels averaged over time
and over a large basin.
Another major limitation of the NES-NPS data base is the lack of sampling
sites in several large areas of the country (i.e., the southwest, the inter-
mountain west, and the coastal plains of the southeast). Many areas in the
west were not sampled because they lacked sufficient precipitation to produce
perennial streams and lakes, and lake eutrophication was the primary concern
of the NES.
Even in regions .that supported perennial streams, streams were not samp-
led unless they could be readily associated with a definable drainage area.
Regions dominated by plains, particularly those in the southeast, including
most of Florida, often lacked sufficient relief to identify topographic di-
vides on maps. Bayous, canals, and interbasin water transfers further compli-
cated the identification of discrete drainage areas.
Finally, since the main purpose of the NES-NPS nutrient study was to
examine relationships between land use and stream nutrient levels, land use
characteristics had to be classified and delineated for each drainage area
used in the analysis. Because of project limitations, the only feasible way
to evaluate land use in the 928 watersheds was to use maps and aerial photog-
raphy. Therefore, it was mandatory that complete, current photo coverage be
available for all watersheds used in the study. Unfortunately, data from many
NES sampling sites could not be used because those sites were located in areas
which lacked usable aerial photography.
Limitations associated with the NES data have caused concern regarding
the reliability of the mapped interpretations of NPS stream nutrient levels.
Although reliability insets were provided for each map, they were compiled
using no data other than that collected for the NES. The reliability assess-
ments were based on the distribution of NES stream sampling sites and the
apparent spatial correlations of these data with NPS watershed characteris-
tics. Recognizing problems inherent in the original reliability assessment,
the decision was made to examine other data sources to reevaluate the reli-
ability of the NES map interpretations. Nutrient concentration values from
such data sources would increase the number of data points and possibly pro-
vide data for areas not sampled by the NES.
10
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SECTION 4
APPROACH
SELECTION OF COMPARABLE DATA SOURCES
Collection of a data base comparable to the NES/NPS stream nutrient data
was essential for evaluating the reliability of the NES map interpretations.
Several criteria were established to insure that the best available, most
comparable data would be selected for the evaluation. Data from other studies
would be used only if the following conditions were met:
1. At least six Total N and/or Total P concentrations were determined
at each stream sampling site per year.
2. The sampling sites were on streams draining watersheds not influ-
enced by point sources.
3. The sampling sites were on streams draining watersheds without major
areas of indirect drainage (i.e., data from streams with greater
than 50% of the basin draining to upstream reservoirs and lakes
would not be used).
4. The sampling sites were on streams draining watersheds with defin-
able topographic divides.
Drainage characteristics and potential point sources were identified from
U.S. Geological Survey maps (scale, 1:250,000) and surface water records (by
state and year).
A review of NPS water-quality literature revealed that the parameters
sampled, sampling procedures, and data reporting varied markedly between indi-
vidual water quality studies (e.g., studies reviewed by the U.S. Forest
Service [1977]). Many private, state, and Federal studies of stream nutrient
concentrations reported values for inorganic and/or dissolved forms of N and
P, but not for Total N or Total P. The period of record and sample frequency
also varied between studies, further complicating data comparisons.
The U.S. Geological Survey had the only data source reviewed which was
based on a national network of stream sampling sites, many of which poten-
tially met the data selection criteria. USGS water quality records can be
quite useful for data comparisons because the agency employs standard sampl-
ing, analytical, and reporting procedures. Also, USGS water quality data are
accessible through the STORET computer system—the same national system that
stores the NES data. The number of USGS water quality stations, the compara-
bility of USGS data, and the lack of consistently comparable data from other
11
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sources made USGS water quality records the best source of stream nutrient
data to evaluate the reliability of the NES map interpretations.
DATA ACQUISITION AND HANDLING
An initial search of the STORET system was made to identify USGS water
quality monitoring stations with nutrient concentration data comparable to
those recorded for NES stream sampling sites. A list was compiled of all USGS
stations recording six or more Total N and/or Total P concentrations during
any year since 1969. The location of each station was plotted on a USGS
l:3,168,000-scale base map. Using additional USGS 1:250,000-scale maps and
USGS surface water records, those stations located on reservoirs, lakes,
canals, bayous, or on rivers affected by urban-industrial centers were identi-
fied and eliminated from the list. It was assumed that the remaining USGS
stations monitored streams draining NPS-type watersheds.
After the initial screening, another search of the STORET system was
conducted to obtain additional information regarding each USGS station remain-
ing on the list, including:
1. The station number and name.
2. The water year(s) (October-September) since October 1969 during
which Total N and/or Total P were measured.
3. The number of Total N samples recorded each water year.
4. Means of Total N concentrations (calculated for each water year with
^ 6 samples of Total N).
5. The mean concentration of Total N, calculated over the period of
record, as the mean of the annual means of Total N concentrations
for all water years with ^ 6 samples of Total N.
6. The number of Total P samples recorded each water year.
7. Means of Total P concentrations, calculated for each water year with
^ 6 samples of Total P.
8. The mean concentration of Total P, calculated over the period of
record, as the mean of the annual means of Total P concentrations
for all water years with ^ 6 samples of Total P.
The location of each remaining USGS station was plotted on two USGS
l:3,168,000-scale base maps. Each USGS station monitored for Total N and the
mean concentration of Total N for that station were color coded and plotted on
one map. Mean concentrations of Total P were plotted on a second map. The
watersheds of all stations were rechecked for potential point sources and
areas of indirect drainage using USGS 1:250,000-scale topographic maps and
USGS surface water records again for the screening process. However, it was
infeasible to conduct a more detailed analysis of land use and other watershed
chararacteristies associated with each USGS station as was done for NES-NPS
sites. Although there may be some uncertainty regarding the effectiveness of
12
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the screening process, it was assumed that the remaining USGS stations pro-
vided the best available, most comparable data base for evaluating the relia-
bility of the nutrient maps.
An effort was made to obtain the greatest number and the widest distrib-
ution of USGS stations possible and, especially, to obtain representation for
areas where NES-NPS data were lacking, thus enabling a test of the map inter-
pretations for these areas. However, some large areas of the country had no
USGS stations meeting the selection criteria, while some small areas had too
many stations to map individually on the small-scale base maps. The shortage
of sites monitoring Total N was particularly noticeable. Only 330 USGS sta-
tions monitoring Total N concentrations met all selection criteria, while 601
stations monitoring Total P concentrations passed the screening process.
Nutrient data from a small number of streams sampled in other studies were
added to fill data gaps for a few key areas. The number of supplemental sites
(35 monitoring Total P and 18 monitoring Total N) was restricted to minimize
the possibility of data incompatability often encountered when comparing data
from a number of studies using different collection, analysis, and reporting
procedures. Supplemental sites selected for this study were located in the
following states: Ohio (Weidner et al. , 1969; Taylor et al_. , 1971); Oklahoma
(Olness et aJL , 1975); South Dakota (Dornbush et aJL , 1974); Iowa (Jones
et al_. , 1976); Washington (Sylvester, 1961); and Oregon (U.S. EPA, unpublished
data). Most of the supplemental studies monitored nutrient runoff from small
agricultural and/or forested watersheds. The distribution of all non-NES
sites used for comparisons are illustrated in Figure 3.
DATA COMPARISONS
After screening, nutrient concentrations from each of the remaining
stations were compared with nutrient concentrations illustrated on the NES
maps (the sets of nutrient-concentration classes used on the maps are shown in
Table 1).
TABLE 1. NES-NPS STREAM NUTRIENT CONCENTRATION MAP CLASSES (Omernik, 1977)
Total Nitrogen Concentrations*
(milligrams/liter)
Total Phosphorus Concentrations*
(milligrams/liter)
Map Unit
Map Class
Map Unit
Map Class
1
2
3
4
5
6
7
8
9
10
S 0.500
0.
0.
0.
1.
1.
1.
2.
3.
501
701
901
101
401
701
001
001
to
to
to
to
to
to
to
to
0.
0.
1.
1.
1.
2.
3.
5.
700
900
100
400
700
000
000
000
1
2
3
4
5
6
7
8
9
S 0.010
0.
0.
0.
0.
0.
0.
0.
on
016
021
031
051
071
101
to
to
to
to
to
to
to
0.
0.
0.
0.
0.
0.
0.
015
020
030
050
070
100
200
> 0.200
> 5.000
Representative of mean annual values.
13
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DISTRIBUTION OF U S G S
NONPOINT SOURCE WATERSHEDS' USED
FOR TOTAL NITROGEN COMPARISONS
Each of the small dotl represent! a
dromage CK.a
Each of the large doll represents
seven or more sampling sites in close
proximity to one another but generally on
different streams
•less than 6% are from non-U S G S sources
DISTRIBUTION OF U S G S
NONPOINT SOURCE WATERSHEDS* USED
FOR TOTAL PHOSPHOROUS COMPARISONS
t«d
Each of Ih* imoll dot* r*pre»nii
itr*o«n templing lit* and ill onotie
Each of th« larg* dori r«pr«i«nti
i«v*n or mar* tamplmg iilei in (lose
prOHimilY lo o»* another but generally on
different irreami
•leu than 6% ore from non-U SGS tourcet
Figure 3. Distribution of USGS nonpoint source watersheds used for stream
nutrient concentration comparisons.
14
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If several stream sampling stations were in close proximity and within
the same NES map unit, nutrient concentrations representative jof the majority
of those sites were used for the comparison. Comparisons revealed that Total
N or Total P data from stream sampling stations in some areas disagreed with
the Total N or Total P concentrations illustrated for those areas on the NES
maps. Apparent disagreements were noted directly on the NES map, and areas
were classified according to the following scheme:
1. General agreement—differences between NES map values and comparable
concentrations were within ± 1 map class of NES map interpretations
excluding obvious outliers;
2. Comparable concentrations were mostly higher (S 2 map classes) than
NES map unit interpretations;
3. Comparable concentrations were mostly lower (^ 2 map classes) than
NES map interpretations; or
4. The areas had insufficient data to make comparisons (i.e., areas
with too few of the supplemental USGS stations and/or too few of the
original NES sites to assess the reliability of the NES map inter-
pretations).
Areas were identified on the basis of the criteria listed above, but the
boundaries for each area were drawn to correspond with regional land use
patterns, NES map unit boundaries, and the general distribution of sampling
stations within each region. Results of these comparisons are illustrated on
Figures 4 and 5 (see Section 5).
15
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SECTION 5
RESULTS
TOTAL N COMPARISONS
With some important exceptions, Total N concentrations illustrated on the
NES map were in general agreement with mean concentrations calculated from
USGS water quality data. However, it should be noted that few of the USGS
stream sampling stations were located in areas that had not been sampled for
the NES; therefore, several large areas still lacked the nutrient data needed
to assess the reliability of the NES map interpretations. The paucity of USGS
and NES sampling stations was particularly acute in areas west of the hun-
dredth meridian and in the Gulf and southeastern coastal plains.
Areas of Agreement
Areas of agreement were defined as all areas in which mean annual Total N
concentration calculated from USGS water quality records were within ± 1 map
class of the concentrations illustrated for those areas on the NES map (Figure
4). This definition was later expanded to include those areas intensively
sampled for the NES but with too few USGS stations to make meaningful compar-
isons. This decision was made because pre'iminary comparisons revealed that
USGS data and concentrations illustrated on the NES map were generally in
close agreement in those areas where interpretations were based on Total N
data from a large number of NES sampling sites. Understandably, NES map
interpretations should be more reliable in those areas than in areas not
sampled in the original survey.
Northern Florida was an important area of agreement because no streams in
Florida had been selected in the NES/NPS study since lack of relief precluded
accurate watershed delineation. Nutrient concentrations illustrated on the
NES maps were assigned mainly on the basis of land use-stream nutrient level
relationships observed in other poorly drained parts of the southeast. Total
N concentrations for Florida USGS stations were in general agreement with NES
map values, apparently supporting the conclusion in the NES-NPS study that
Total N concentrations in streams are closely correlated with watershed land
use (Omernik, 1977). Although this area is considered part of the southeast
coastal plain, drainage and land use characteristics differ from those in the
coastal plains of neighboring states. Therefore, relationships observed in
northern Florida may not apply in other areas, particularly since small areas
of disagreement did exist along Florida's northwest coast and the Georgia-
Florida border.
16
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AREAL COMPARISONS OF MEAN ANNUAL
TOTAL NITROGEN CONCENTRATIONS ILLUSTRATED
ON THE EPA/NES MAP (OMERNIK.1977) WITH
CONCENTRATIONS MEASURED AT SELECTED US OS
STREAM SAMPLING STATIONS
Areot for which
of insufho.nt d
Figure 4. Area! comparisons of stream nitrogen concentration data.
One relatively large area of agreement extends along the Appalachian
Mountains and the Piedmont* from northern Alabama and Georgia through Penn-
sylvania. The central portion of this region is comprised of alternating
ridge and valley systems and is primarily forest land with limited areas of
crop and pasture land. To the east of the ridge and valley system is the
Piedmont, and the Appalachian plateaus are to the west. Various mixtures of
cropland, pasture, woodland, and forest are found in these two areas.
Although land use and terrain were quite variable throughout the Appalachian
system, Total N concentrations calculated from USGS stream samples generally
agree with concentrations illustrated for the same areas on the NES maps.
Data comparisons reveal only three relatively small enclaves of disagreement
which will be discussed later. However, it should be noted that although many
streams in the region were sampled by the NES for Total N concentrations,
relatively few were sampled by USGS.
Another region of apparent agreement, but with considerably more NES
sites than USGS sites, includes most of New England and northern New York
* Names and descriptions of physiographic provinces are from Fenneman (1946);
descriptions of regional vegetation patterns are from Bailey (1976).
17
-------
Northern hardwoods and spruce forests are the dominant cover type, but several
areas are important agriculturally. USGS stations monitoring Total N concen-
trations were found only in Connecticut and Massachusetts, and much of Maine
and the Atlantic coastal areas were lacking sufficient data to make the de-
sired comparisons. Due to the general homogeneity of the region, the large
number of NES sites, and the general agreement between NES map interpretations
and USGS stream nutrient values from Connecticut and Massachusetts, as well as
Lakes Region Planning Commission (1977) values from New Hampshire, it is
likely that the NES map interpretations of Total N concentrations are fairly
reliable for much of New England.
The largest area of apparent agreement between USGS and NES stream nu-
trient values is centered in the agricultural midwest from Ohio to Nebraska
and from North Dakota to central Texas. This region is characterized by large
homogeneous agricultural subregions of mainly cropland with grazing more
important on the western margins. Regional homogeneity and a dense network of
NES sites provided the basis for NES map interpretations which agree quite
well with Total N concentrations recorded for USGS stream sampling stations.
However, the number of USGS stations in this region was small, and the sta-
tions were widely dispersed. Enclaves with insufficient data for comparisons
are located along the Mississippi River in western Illinois and eastern
Arkansas, along the Missouri River in western Iowa and northern Missouri, and
along the Ohio River in southern Indiana and Kentucky.
Another region of agreement extends from central Missouri into northern
Louisiana and east Texas. The Ozark Plateaus, a mix of hardwood forests and
agricultural lands, dominates the northern half of the region. The southern
half; which includes the lowland plains of Louisiana and east Texas, is pri-
marily forest land mixed with some cropland and pasture. Total nitrogen was
monitored at only a few USGS stream sampling sites in the region; however,
mean concentrations calculated for those sites are in general agreement with
NES map interpretations. Although some areas exhibit a great deal of varia-
bility, many of the region's streams were sampled for the NES, and the varia-
bility was considered when developing the NES map.
West of the hundredth meridian, regions with insufficient data are ex-
tensive, and areas of agreement are rather limited. One area of agreement
includes the semiarid high plains of southeastern Montana, northeastern
Wyoming, and the western edges of Nebraska and South Dakota. The area is
primarily used for grazing, but forests and cropland are important in some
locations. Nutrients were sampled in some of the area streams during the NES,
and several more were sampled for Total N by USGS. Total N concentrations
illustrated on the NES map were in general agreement with USGS data except for
one area in southeastern Montana.
The Southern Rocky Mountains, located primarily in Colorado but extending
into Wyoming and New Mexico, comprise another area of apparent agreement in
the West. The area is a mixture of sagebrush, semiarid grassland, forest and
alpine vegetation. Grazing is a major land use, with irrigated agriculture
also important in some locations. Only a few of this area's streams were
sampled for the NES, and only four were sampled for Total N by USGS. However,
sampling sites were widely distributed, and data from those sites are in
agreement with NES map interpretations.
18
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The Middle Rocky Mountains in northern Utah and along the Idaho-Wyoming
border and the Northern Rocky Mountains in western Montana and northern Idaho
were also areas of apparent agreement. These areas differ with regard to
geologic structure, vegetation, and climate. The Middle Rockies group is a
complex anticlinal system and is covered primarily with semiarid brush, wood-
land, and some forest. The more extensive northern group is not anticlinal
and is primarily forested. Grazing is important in both areas, but other land
use characteristics differ between the two mountain subsystems. The NES
sampled nutrient concentrations in many streams in both areas, whereas only a
small number of USGS stream stations recorded Total N concentrations in either
area; however, Total N data from the USGS stations fell within the ranges
illustrated on the NES map. Therefore, the NES map classifications were
considered to be reasonably representative of mean Total N concentrations in
streams flowing from the Rocky Mountains.
In the Pacific Northwest, a zone of apparent agreement was found to
extend from the areas of irrigated and dryland agriculture along the Snake
River on the Oregon-Idaho border, into and along the northern parts of the
Palouse Hills and Columbia Basin in Idaho and Washington, and into the intens-
ively farmed Willamette Valley of western Oregon. As was the case with some
of the other regions, the quality of these assessments is somewhwat limited by
the fact that representative USGS data were extremely scarce, although NES-NPS
stream data for nitrogen concentrations were numerous.
The Cascade Range of Washington and Oregon was another area of the
Pacific Northwest identified as a zone of apparent agreement, again based
mainly on the number and distribution of NES sites. None of the USGS sampling
stations in this area were sampled for Total N. However, based on the NES
data and relationships observed by USGS in other forested mountain regions of
the West (including the Olympic and the Sierra Nevada Mountain Ranges where
mean annual Total N concentrations were generally less than 0.5 mg/1), the NES
map classifications were considered to be representative of Total N concentra-
tions in streams draining the Cascade Range.
In the Sierra Nevada Range of California, Total N concentrations reported
by USGS were in good agreement with concentrations illustrated on the NES map.
This was also true for the foothill areas on the west side of the Range. In
general, nutrient classes illustrated for forested areas, whether in mountain
or lowlands, were in good agreement with data reported for USGS stream sampl-
ing stations. Therefore, Total N data reported for streams draining the
coastal forests of northern California fell within the range of concentrations
illustrated on the NES map. This area of agreement extended along the Cali-
fornia Coast Range from the humid redwood forests in northern California to
the drier woodland and rangeland north of San Francisco Bay.
Total N data from other USGS sampling sites were also in agreement with
NES map interpretations. However, some of those sites were quite isolated
(Figure 3), and data from one or two isolated sampling sites could not be used
to make valid reliability assessments for an entire region.
19
-------
Areas of Disagreement
Generally, NES map interpretations corresponded reasonably well with mean
annual Total N concentrations calculated from USGS water quality data. Areas
of apparent disagreement were usually small and often surrounded by larger
areas of agreement (Figure 4). Although the direction of disagreement was not
consistent, NES map interpretations of Total N concentrations tended to be
higher than USGS values more often than lower. For example, the largest area
of disagreement was in southeastern New York State. There, mean annual Total
N concentrations reported by the USGS were substantially lower (generally,
0.29 to 0.75 mg/1) than those illustrated on the NES map (0.07 to 1.7 mg/1).
The 1972-73 NES stream samples from this area were collected during a period
when weather patterns were extremely atypical. Tropical storm Agnes passed
through the area during the sampling perioo, and the exceptionally heavy
precipitation which accompanied the storm may have washed large quantities of
nitrogen from the atmosphere and/or land surface into area streams.
Another area of apparent disagreement centers on Atlanta, Georgia. Total
N concentrations in streams sampled by the USGS were consistently higher
(generally 1.69 to 4.47 mg/1) than those illustrated for that area on the NES
map (0.9 to 1.4 mg/1). One possible explanation may be the rapid expansion of
the urban and suourban fringe around Atlanta. The boundaries exhibited on the
National Land Use Map (USGS, 1970) and the distribution of population centers
illustrated on USGS topographic maps (1:250,000 scale) of the area are based
on outdated information, which can be very misleading in areas of rapid expan-
sion. Since there were no NES stream sampling sites in the immediate vicinity
of Atlanta, map interpretations based on the outdated land use patterns could
substantially underestimate nutrient inputs from areas influenced by recent
urban development. For this same area, the NES map interpretations for Total
P concentrations are also lower than USGS values, further suggesting that
urbanization is expanding into the woodland-agriculture fringe of Atlanta.
Other important areas of disagreement are apparent in the western United
States. The largest of these is along the southern margin of the Colorado
Plateaus and southeastern portion of the Basin and Range province. The up-
lands of this area are generally forested and receive significant amounts of
precipitation, but much of the lowland is desert plain. Here streams sampled
by the USGS consistently revealed lower mean annual concentrations of Total N
(0.26 to 0.67 mg/1) than were illustrated or the NES map (0.7 to 1.4 mg/1).
NES map interpretations for the region were based on samples collected from
only 2 streams; therefore, it is quite like'y, based on the USGS data, that
the NES map overestimates Total N concentrations in streams throughout the
entire region.
Another area of disagreement is in the southern portion of the Klamath
Mountains in northern California. Mean annual Total N concentrations calcu-
lated from USGS stream samples in the area were substantially lower (mostly
0.26 to 0.55 mg/1) than those illustrated on the NES map (0.7 to 0.9 mg/1).
Much of the region is forested, but grazing and cropland are important in some
locales. Whether the USGS, or the NES values, or both are representative of
this particular area is impossible to determine without a more detailed study
of the individual watersheds associated with the sampling sites and the region
as a whole.
20
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Another area of apparent disagreement is in the southern portion of the
Wyoming Basin, an arid to semiarid elevated plain. Grazing and mining are the
major activities in the region. The watersheds sampled by the USGS revealed
mean annual Total N concentrations consistantly higher (1.52 to 6.43 mg/1)
than those illustrated for the area on the NES map (1.1 to 1.4 mg/1). The NES
had no sample sites within the area of disagreement but had sampled five
streams in adjacent areas. Although topographic maps of the area did not
identify any point sources in the USGS-sampled watersheds, they may have been
influenced by point sources associated with recent mining activity— activity
too recent to show on the dated (1952-1961) 1:250,000-scale USGS topographic
maps of the area. Then too, Total N concentrations could be elevated in the
basin due to heavy grazing and/or local soil or geologic characteristics.
Other small areas of apparent disagreement are scattered throughout the
east, southeast, and midwest; however, these areas will not be discussed in
detail. Since these areas are small, the apparent NES map inaccuracies are
probably due to local variations in land use, climate, and terrain that cannot
be accounted for when illustrating general information on small-scale maps.
TOTAL P COMPARISONS
The 601 USGS stations used for evaluating the NES map of mean annual
Total P concentrations was nearly double the 330 used for evaluating the Total
N concentrations. Most of the additional USGS sites were located on streams
in the states of Washington, Arkansas, Pennsylvania, and Kansas, with smaller
numbers of additional sampling sites scattered through several other states.
Still, the reliability of NES map interpretations could not be evaluated in
several areas, particularly parts of the west and southeast, either because
Total P data had not been reported for those areas or because local sampling
stations did not meet the criteria established for this study. However, areas
without Total P data were generally smaller than those lacking Total N data.
Areas of Agreement
The areas of agreement appear quite similar for evaluations of both NES
maps, although some areas of agreement are slightly larger for Total P than
for the Total N evaluation due primarily to the increased number and wider
distribution of USGS stations sampling Total P (Figure 3). Since the areas
of agreement common to both comparisons have already been discussed in the
section on Total N, only those areas of agreement unique to the Total P com-
parisons (Figure 5) will be discussed here. Perhaps the most conspicuous area
of agreement unique to Figure 5 occurred in southeastern New York, an area
where USGS values of Total N concentrations had been substantially lower than
NES map interpretations. The high nitrogen concentrations in streams were
probably due to greater atmospheric washout of nitrogen in the period of
heavier precipitation, a condition that would not necessarily have the same
kind of effect on phosphorus concentrations in streams.
Similar patterns occurred in Arizona, northern California, and several
smaller areas in northeastern Mississippi, southwestern Georgia, southeastern
Montana, and southeastern South Carolina. Again, USGS water quality records
and NPS map interpretations were in general agreement regarding Total P con-
21
-------
AREAL COMPARISONS OF MEAN ANNUAL TOTAL
PHOSPHORUS CONCENTRATIONS ILLUSTRATED
ON THE EPA/NES MAP (OMERNIK, 1977) WITH
CONCENTRATIONS MEASURED AT SELECTED USGS
STREAM SAMPLING STATIONS
of iniufhi
USGS volu
EPA/NES mterpretationi
General agreement diff
map clou
USGS
than EPA/NES mterpr*
Figure 5. Areal comparisons of NFS stream phosphorus concentration data.
centrations, while in the same areas NES map interpretations were substan-
tially greater for stream concentrations of Total N.
Areas of Disagreement
Areas of apparent disagreement between USGS water quality data and NES
interpretations of Total-P concentrations were found in several parts of the
country (Figure 5). NES map interpretations underestimated (^ 2 map classes)
mean annual Total P concentrations for more than 100 of the 600 USGS stations
used in this study, but at only five stations were concentrations substan-
tially lower than those estimated using the NES maps. This consistent ten-
dency for NES map interpretations of Total P concentrations to be higher than
those reported by the USGS was most evident along the Atlantic Coastal Plain
from New Jersey to Florida and along the Appalachian System from western New
York to northeastern Georgia.
As mentioned previously, because NES-NPS data-were lacking for Florida,
NES map interpretations for that state had been based mainly on general land
use patterns and similarities with other parts of the southeast. The poorly
22
-------
drained, sandy plains of Florida are etched with shallow lakes, swamps, and
sinks; and, most significantly, phosphate deposits underlie much of the north
and central parts of the state (USGS, 1970, p. 184). The combination of these
factors apparently act to elevate Total P concentrations beyond levels that
would be expected given the area's general land use patterns.
NES map interpretations also indicate Total P concentrations in streams
draining the terraced coastal plain of North Carolina were considerably lower
than those which the USGS found. Here, land use is a mixture of forest, crop-
land, pasture, and swamp. Much of the area is poorly drained, and phosphate
deposits are found in some locations. Streams in this part of North Carolina
were not sampled for the NES; and map interpretations, based primarily on
general land use patterns (as was the case in Florida), appeared to be unrep-
resentative of mean annual Total P concentrations in streams draining other
parts of the Atlantic Coastal Plain. On the other hand, Total P data from
coastal plain streams in South Carolina agreed quite well with NES map inter-
pretations. Although regional characteristics appear to be quite similar
along the coastal plains of the southeast, local environmental conditions
often differ significantly between watersheds, particularly with regard to
soils, geology, and mineral availability.
This discontinuous pattern of apparent disagreement also extends into the
middle Atlantic Coastal Plain of New Jersey and the Piedmont of New Jersey and
southeastern Pennsylvania. Land use in both areas is a mixture of forests,
cropland, pasture, and urban developments, while bogs are important primarily
in the lowlands of New Jersey. Although some NES stream sampling sites were
located in New Jersey and adjacent coastal states, Total P data from nearly 50
USGS sampling stations in New Jersey and southeastern Pennsylvania revealed
that NES map interpretations (0.01 to 0.10 mg/1) consistently underestimated
Total P concentrations (0.04 to 2.50 mg/1) in both areas. Based on these
comparisons, it might be concluded that NES interpretations are relatively
unreliable for estimating NPS Total P concentrations in streams draining the
Atlantic Coastal Plains. However, much of this part of the United States is
very densely populated and industrialized. Because watersheds associated with
the USGS sites were not scrutinized as closely for point sources as were the
NES watersheds, there is a strong likelihood that point sources were partly
responsible for the higher USGS values.
Another major region of apparent disagreement stretched along the Appa-
lachian Plateau and the adjacent ridge and valley system from western New York
south to northeastern Tennessee. Land use throughout the region is a mixture
of forest, cropland, pasture, mining, and urban development. The two largest
areas of apparent disagreement within the region are located in western Penn-
sylvania and eastern Kentucky. Both are areas with substantial mining activ-
ity. Local nonpoint impacts from mining or other man-related activities might
have caused Total P values reported by the USGS to be substantially higher
than those shown on the NES map (0.08 to 1.10 mg/1 vs 0.01 to 0.10 mg/1).
However, it is also possible that for these areas the NES data and conclusions
relative to land use associations were inadequate to show regionalities due to
background environmental sources (i.e., soils, geology, vegetation). Unfor-
tunately, data are too sparse and the level of this assessment is too general
to permit definitive identification of nutrient sources. Morover, it should
be reerriphasized that this project was not, designed to identify specific non-
23
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point sources, only to evaluate the reliability of the NhS map interpreta-
tions.
NES map interpretations tend to be fairly reliable for estimating Total P
concentrations in streams draining the southern portion of the Appalachian
system (i.e., Tennessee, northeastern Alabama, and northwestern Georgia);
however, two areas of apparent disagreement are found in the southern portion
of the Piedmont, a zone of transition between the Appalachian system and the
coastal plain. Both areas are located in Georgia—the first around Atlanta
and the second in the northeastern corner of the state. Neither area was
sampled for the NES, although several streams in adjacent areas were. In both
areas NES map interpretations (0.01 to 0.10 mg/1) were considerably lower than
USGS-reported concentrations (0.12 to 0.89 mg/1). As in other urban growth
areas, development is expanding into the rural landscape around Atlanta. This
recent expansion and associated man-related effects may have been responsible,
at least in part, for the higher than expected stream nutrient levels in the
area (see page 30).
Moving to the middle of the nation, NES map interpretations are consider-
ably lower than Total P concentrations reported by the USGS (0.01 to 0.07 mg/1
vs 0.07 to 0.72 mg/1) for streams draining some parts of the Ozark Plateaus in
southwestern Missouri, northwestern Arkansas, and eastern Oklahoma. However,
data from several USGS stations in adjacent areas indicate that the NES map
interpretations are relatively representative of Total P concentrations ob-
served in streams draining most of the Ozarks. Therefore, apparent disagree-
ments between NES map interpretations and USGS data from other parts of the
Plateau may be attributable to local variations in land use and other water-
shed characteristics not distinguishable on generalized, small-scale maps (the
NES maps and the USGS national land use map were published at a scale of
1:7,500,000).
NES map interpretations of Total P concentrations were also lower than
values reported by the USGS (0.03 to 0.20 mg/1 vs 0.01 to 2.40 mg/1) in some
parts of southern Arkansas and east Texas. These areas of apparent disagree-
ment are located in the western portion of the Gulf Coastal Plain, where land
use is a mixture of forests, swamps, cropland, and pasture. Some of the
reason for the disagreement may lie with the fact that although the National
Land Use Map (USGS, 1970) neatly generalizes the region's land use character-
istics into distinct area! patterns (used for NES-NPS analyses), local water-
shed conditions can vary substantially from those illustrated on the USGS map.
Also, streams in these parts of the coastal plain had not been sampled for the
NES, but several streams in similar nearby areas of Texas and Louisiana had
been sampled.
Farther west there are several more relatively small areas where NES map
interpretations appear significantly lower than USGS values for Total P con-
centrations. One such area is in the southern portion of the Wyoming Basin.
Interestingly, the NES maps for Total N concentrations were also lower for
parts of this same area. This region is grazed extensively, and mining activ-
ities have been expanding rapidly in many parts of the region. Because dif-
ferences between NES interpretations and USGS nutrient concentrations are so
great, and because the region's resources are being developed so rapidly,
there is reason to suspect that some of the region's streams may be receiving
24
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substantial amounts of phosphorus from point and nonpoint sources associated
with mining and grazing.
A situation similar to that in Wyoming appears to exist in the southern
portion of the Colorado Plateaus, but comparisons are inconclusive because at
only two USGS stream sample stations in that part of Colorado and New Mexico
were Total P concentrations measured. Most of the Colorado Plateaus and
almost all of the Basin and Range provinces lack the stream nutrient data
needed to assess the reliability of the NES map interpretations.
Although there is a general shortage of Total P data for streams in the
arid and semi arid west, data are available for a large number of streams in
the western and irrigated portions of Washington State. Comparing NES map
interpretations with USGS Total P data, three relatively small areas of ap-
parent disagreement are found in or near Washington's major mountain systems.
The first extends south along the Washington coast, from the western slopes of
the Olympic Mountains in the north to Willapa Bay in the south. There, NES
map interpretations of mean annual concentrations of Total P were lower than
values calculated from the USGS water quality data (0.016 to 0.02 mg/1 vs 0.03
to 0.04 mg/1). Olympic National Park and its lush, relatively undisturbed
forests occupy much of the area, and Total P concentrations in streams drain-
ing the Park are not much different than those in adjacent areas influenced by
logging. Since NES map interpretations underestimate Total P concentrations
(based on comparisons with USGS data) in the undisturbed areas as well as in
the logged areas, NES map interpretations may be unreliable for that part of
Washington.
Other areas of apparent disagreement are located in Washington's Cascade
Mountains. These mountains are heavily forested, particularly on the western
slopes. Logging is the principal activity in much of the region. In these
areas, the USGS found much higher mean annual Total P stream concentrations
than were predicted by the NES maps. However, the areas are relatively small
and USGS data from adjacent areas agree fairly well with NES map interpreta-
tions. Again regional generalizations mandated by the 1:7,500,000 scale of
the NES maps appear to be inadequate for predicting Total-P concentrations in
particular streams draining small areas; therefore, using NES maps to make
such predictions may be considered inappropriate.
The last areas of apparent disagreement to be discussed are found in the
Sierra Nevada Mountains of California. The first is located along the Cali-
fornia-Nevada border around Lake Tahoe where NES map interpretations for mean
annual Total P concentrations were generally lower than the values reported by
the USGS (0.016 to 0.05 mg/1 vs 0.03 to 0.26 mg/1). Some of the difference
may be explained by the accelerated road building and construction around Lake
Tahoe that are reported to have increased nutrient and sediment concentrations
in a number of influent (re. groundwater) tributaries (Goldman, 1974).
Although recent urban and recreational development may explain elevated Total
P concentrations around Lake Tahoe, they do not explain why USGS Total P
concentrations sampled in the foothills of central California and in the
Sierras around Sequoia and Kings Canyon National Parks in southern California
are generally more than twice that predicted by the NES maps. Grazing and
development may be important factors influencing nutrient runoff in hills
outside the parks; but, other than recreational activity, environmental condi-
25
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tions (soils, geology, ana vegetation) are more likely to be responsible for
the higher nutrient concentrations in streams draining these National Parks.
Differences between NES map interpretations and USGS water quality data cannot
be attributed simply to isolated local variations in land use. Instead, the
differences appear to be of a regional nature; therefore, the NES map inter-
pretations should be considered unreliable for estimation of Total P concen-
trations in streams draining the Sierra Nevada Mountains in central and
southern California.
Three smal1 areas of apparent disagreement, one in the mountains of
northern Idaho and the other two in Wiscons~n and Minnesota, have been omitted
from this discussion. These areas were relatively small and were surrounded
by much larger areas where stream nutrient data from USGS water quality sta-
tions agreed quite well with concentrations illustrated on the NES maps.
Revised Reliability Maps
Based on NES-USGS data comparisons, and conclusions drawn from those
comparisons, new reliability maps have been constructed (Figure 6). These
maps reflect the following: 1) the distribution of NES stream sampling sites
used to develop the original NES map interpretations; 2) the distribution of
USGS stream sampling sites used to assess the reliability of the NES map
interpretations; and 3) the apparent areal patterns of agreement and disagree-
ment between NES map interpretations and stream nutrient data from both USGS
and NES stream sampling sites. The reliability maps provide qualitative
assessments of the dependability or relative representativeness of mean annual
nutrfent concentrations calculated from NES map interpretations.
The NES map interpretations represent nean annual nutrient concentrations
averaged over time for all streams in any region or major drainage basin
within the conterminous United States. The reliability maps do not indicate
the dependability of NES map interpretations for predicting stream nutrient
levels in a particular stream at a particular time. Although the influence of
NES map scale (1:7,500,000) and resolution cannot be illustrated on the relia-
bility maps, those factors must be considered major limitations on the relia-
bility of NES map interpretations, particularly when those interpretations are
used to estimate stream nutrient levels in areas which exhibit a great deal of
local variability in land use and other watershed characteristics.
26
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RELIABILITY
C J Very good
•ZH Good
TOTAL NITROGEN
RELIABILITY
Very good
; I Good
Fair
TOTAL PHOSPHORUS
Figure 6. Revised reliability map insets for EPA-NES mapped interpretations
of total nitrogen and total phosphorus in streams from nonpoint
sources.
27
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REFERENCES
Bailey, R. G. 1976. Ecoregions of the United States. Map, scale
1:7,500,000. U.S. Forest Service, Ogden, Utah.
Dillon, P. J. and W. B. Kirchner. 1975. The Effects of Geology and Land Use
on the Export of Phosphorus from Watersheds. Water Research 9:135-148.
Dornbush, J. N. , J. R. Anderson, and L. L. Harms. 1974. Quantification of
Pollutants in Agricultural Runoff. EPA Environmental Protection Tech-
nology Series EPA-660/2-74-005. U.S. Environmental Protection Agency,
Washington, D.C. 149 pp.
Fenneman, N. M. 1946. Physical Divisions of the United States. Map, scale
1:7,000,000. U.S. Geological Survey, Washington, D.C.
Goldman, C. R. 1974. Eutrophication of Lake Tahoe Emphasizing Water Quality.
EPA Ecological Research Series EPA-660/3-74-034. U.S. Environmental
Protection Agency, Pacific Northwest Environmental Research Laboratory,
Corvallis, Oregon. 408 pp.
Jones, J. R. , B. P. Borofka, and R. W. Bachmann. 1976. Factors Affecting
Nutrient Loads in Some Iowa Streams. Water Research 10:117-122.
Lakes Region Planning Commission. 1977. Methodology for Land Use Correla-
tions. Interim Report 5C2 from Task 5, Water Quality Modeling. Lakes
Region Planning Commission, Meredith, New Hampshire. 30 pp.
McDowell, T. R. 1979. Application of the Universal Soil Loss Equation to
Determine Sediment Yields from Forested Watersheds. Paper presented at
the 37th Annual Meeting of the Oregon Academy of Science, February 24,
1979, Mount Hood Community College, Gresham, Oregon. 35 pp.
McElroy, A. D. , S. Y. Chiu, J. W. Nebgen, A. Aleti, and F. W. Bennett. 1976.
Loading Functions for Assessment of Water Pollution from Nonpoint
Sources. EPA Environmental Protection Technology Series EPA-600/
2-76-151. U.S. Environmental Protection Agency, Washington, D.C. 445
pp.
Olness, A., S. J. Smith, E. D. Rhoades, and R. B. Menzel. 1975. Nutrient and
Sediment Discharge from Agricultural Watersheds in Oklahoma. Journal of
Environmental Quality 4(3):331-336.
29
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Omernik, J. M. 1976. The Influence of Land Use on Stream Nutrient Levels.
EPA Ecological Research Series EPA-600/3-76-014. U.S. Environmental
Protection Agency, Corvallis Environmental Research Laboratory, Corval-
lis, Oregon. 105 pp.
Omernik, J. M. 1977. Nonpoint Source-Stream Nutrient Level Relationships: A
Nationwide Study. EPA Ecological Research Series EPA-600/3-77-105. U.S.
Environmental Protection Agency, Corvallis Environmental Research Labora-
tory, Corvallis, Oregon. 151 pp.
Onstad, C. A., C. K. Mutchler, and A. J. Bowie. 1977. Predicting Sediment
Yield. In: National Symposium on Soil Erosion and Sedimentation by
Water. American Society of Agricultural Engineers Publication 4-77. pp.
43-58.
Pisano, M. 1976. Nonpoint Pollution: An EPA View of Areawide Water Quality
Management. Journal of Soil and Water Conservation 31(3):94-100.
Sylvester, R. 0. 1961. Nutrient Content of Drainage Water from Forested,
Urban and Agricultural Areas. In: Algae and Metropolitan Wastes. U.S.
Department of Health, Education, and Welfare Publication SEC TR W61-3,
Cincinnati, Ohio. pp. 80-87.
Taylor, A. W. , W. M. Edwards, and E. C. Simpson. 1971. Nutrients in Streams
Draining Woodland and Farmland near Coshocton, Ohio. Water Resources
Research 7(l):81-89.
U.S. Environmental Protection Agency. 1974. National Eutrophication Survey
Methods for Lakes Sampled in 1972. National Eutrophication Survey Work-
ing Paper No. 1. U.S. Environmental Protection Agency, Las Vegas En-
vironmental Research Center and Corvallis Environmental Research Center,
Corvallis, Oregon. 40 pp.
U.S. Environmental Protection Agency. 1975. National Eutrophication Survey
Methods 1973-1976. National Eutrophication Survey Working Paper No. 175.
U.S. Environmental Protection Agency, Las Vegas Environmental Research
Center and Corvallis Environmental Research Center, Corvallis, Oregon.
91 pp.
U.S. Forest Service. 1977. Non-Point Water Quality Modeling in Wildland
Management: A State-of-the-Art Assessment. Vol. II: Appendices. EPA
Ecological Research Series Report EPA-600/3-77-078. U.S. Environmental
Protection Agency, Environmental Research Laboratory, Athens, Georgia.
568 pp.
U.S. Forest Service. In Press. An Approach to Water Resources Evaluation
Non-Point Sources—Silviculture. U.S. Environmental Protection Agency,
Environmental Research Laboratory, Athens, GA.
U.S. Geological Survey. 1970. The National Atlas of the United States. U.S.
Government Printing Office, Washington, D.C. 417 pp.
30
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Weidner, R. 8. , A. G. Christiansen, S. R. Weibel, and R. B. Robeck. 1969.
Rural Runoff as a Factor in Stream Pollution. Journal Water Pollution
Control Federation 41(3):377-384.
Wischmeier, W. H. 1976. Use and Misuse of the Universal Soil Loss Equation.
Journal of Soil and Water Conservation 31(l):5-9.
Wischmeier, W. H. and D. D. Smith. 1965. Predicting Rainfall-Erosion Losses
from Cropland East of the Rocky Mountains. U.S. Department of Agricul-
ture. Agricultural Handbook 282, U.S. Government Printing Office, Wash-
ington, D.C.
31
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before < omp
iz:
1. REPORT NO.
EPA-600/3-79-1_03_ _
4. rtTLE AND SUBTITLE
NON-POINT SOURCE--STREAM NUTRIENT LEVEL RELATIONSHIPS:
A NATIONWIDE STUDY
SUPPLEMENT 1: NUTRIENT MAP RELIABILITY
3. RECIPIENT'S ACC.E3SION NO.
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S)
Theodore R. McDowell
James M. Omernik
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Corvallis Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Corvallis, Oregon 97330
5 REPORT DATE
September 1979 issuing date
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1BA820
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
same
13. TYPE OF REPORT AND PERIOD COVERED
inhouse --final
TiTlS PONSO RIN G AG EJ\JCY CO D E
EPA/600/02
15. SUPPLEMENTARY NOTES
This publication is a supplement to EPA-600/3-77-105: Nonpoint Source—Stream Nutrient
Level Relationships
16. ABSTRACT
The National Eutrophication Survey (NES) national maos of non-point source
nitrogen and phosphorus concentrations in streams were evaluated for applicability
and reliability. Interpretations on these maos which were based on data from
928 sampling sites associated with non-point source watersheds and the relationships
of these data to general land use, and other macro-watershed characteristics, were
compared with a nationwide set of non-point source stream nutrient data collected
largely by the U. S. Geological Survey (USGS).
In most areas where comparisons could be made the mapped interpretations agreed
relatively well with USGS data. Where disagreements did occur regardino nitronen
concentrations, NES mapped interpretations tended to be higher than USGS values
more often than lower; where disagreements occurred regarding phosphorus concen-
trations, the reverse was apparent.
Revised reliability map insets based on these analyses are provided for maps of
total nitrogen and total phosphorus concentrations.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
land use
nutrients
watersheds
phosphorus
nitrogen
loadings
concentrations
eutrophication
stream flow
soils
geology
lonpoint source nutrients
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
02/A, E
04/A,C
05/A,C,G
18. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (This Report)
Unclassified
20 SECURITY CLASS /This page)
Unclassified
21. NO. OF PAGES
10
22. PRICE
EPA Form 2220-1 (Rev. 4-77)
33
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