LAKE EUTROPHICATION:
RESULTS FROM THE NATIONAL EUTROPHICATION SURVEY
. By
Jack H. Gakstatter, Marvin 0. All urn
and James M. Omernlk
Presented at the 26th Annual AIBS Meeting;
Oregon State University, CorvalUs, Oregon
August 17-22, 1975
Corvallis Environmental Research Laboratory
U.S. Environmental Protection Agency
Office of Research and Development
CorvalUs, Oregon 97330
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INTRODUCTION
In early 1972, the U.S. Environmental Protection Agency (EPA) initiated
the National Eutrophication Survey (NES) program to: (1) identify those
i
lakes and reservoirs in the contiguous United States that receive nutrients
from the discharges of municipal sewage treatment facilities, and (2) deter-
mine the significance of these point-source nutrient inputs to the nutrient
levels and the primary productivity of each system. After the program began,
additional federal legislation was passed (Public Law 92-500), and NES
objectives were broadened to include an assessment of the relationships of
non-point sources; e.g., land use, to lake nutrient levels and also to assist
in establishing water-quality criteria for nutrients.
Selection Criteria
Freshwater lakes and impoundments in the Survey were selected through
consultation with EPA Regional Offices and state pollution control agen-
cies, as well as related state agencies managing fisheries, water resources.
or public health. EPA established selection criteria to limit the type
and number of candidate water bodies, consistent with existing Agency
water goals and strategies. For 27 states of the eastern United States
where lakes were selected prior to passage of P.L. 92-500, strongest
emphasis was placed on lakes faced with actual or potential accelerated
eutrophication problems; i.e., an artificially increased rate of algal
and/or aquatic plant production. As a result, the selected lakes:
1. were impacted by one or more municipal sewage treatment
plants, either directly or by discharge to an Inlet tributary
within approximately 25 miles of the lake;
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2. were 100 acres or larger In size; and
3. had mean hydraulic retention times of at least 30 days. .
»t
However, these criteria were waived for a number of lakes of particular
interest to the states.
In the western states, these criteria were modified to reflect
revised water-research mandates, as well as to address more prevalent
non-point source problems in agricultural or undeveloped areas. Thus
each state was requested to submit a list of candidate lakes for the
Survey that:
1. were representative of the full range of water
quality (from oligotrophic* to eutrophic*);
2. were in the recreational, water supply, and/or
fish and wildlife propagation use-categories; and
3. were representative of the full scope of nutrient
pollution problems or sources (from municipal waste and/or
nutrient-rich industrial discharges, as well as from non-
point sources).
The size and retention time constraints applied in the eastern states
were retained as was the waiver provision.
In all cases, listings of potential candidate lakes or reservoirs,
prepared with the cooperation of the EPA Regional Offices, were made
available to the states to initiate the selection process.
In total, the Survey includes 812 lakes and reservoirs across the
contiguous 48 United States. Figure 1 shows the distribution of the
* Oligotrophic—low nutrient concentrations and primary productivity.
Eutrophic—high nutrient concentrations and primary productivity.
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1975-152
1973-250
GRAND TOTAL- 812
Figure 1. Number of lakes and reservoirs sampled 1n each state and yea'r of
sampling by the National Eutrophication Survey.
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lakes and reservoirs by state and the year during which each water body
was sampled.
GENERAL SURVEY METHODS
Several kinds of Information are required as a basis for management
decisions regarding the need for point or non-point source control of
phosphorus and perhaps other nutrients as well. The Survey purpose 1s
to collect the type of data which will provide a basis for such decisions
or at least to provide a data base which can be supplemented with more
detail, if required. First, an annual nutrient budget is estimated for
each water body, differentiating between inputs originating from point
and non-point sources; second, the existing trophic condition of the
water body is evaluated by sampling; and third, an algal assay 1s per-
formed to determine whether phosphorus, nitrogen, or some other element
is limiting primary productivity of the water body. The methods used to
gather this information are described below.
The operations aspects of the Survey are shared by branches of two
.EPA laboratories (46 people) and a small headquarters staff (3 people).
The Environmental Monitoring and Support Laboratory at Las Vegas, Nevada
(Las Vegas-EMSL) is responsible for sampling each lake, doing the associ-
ated analyses, evaluating a portion of the data, and reporting results.
The Corvallis Environmental Research Laboratory (CERL) at CorvalUs,
Oregon is.responsible for coordinating the sampling of streams and sewage
treatment plants, analyzing the samples, and performing the algal assay
on lake samples. CERL also has major responsibility for evaluating the
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lake, stream, and point-source data and Incorporating these data Into a
report on each lake. The headquarters staff (Washington, D.C.) makes, the
Initial contact with each state water pollution control agency to expiain
the function of the Survey and to cooperatively determine which lakes and
reservoirs will be Included. They also contact each State National Guard
to explain the function of the Survey and to request their assistance In
meeting Survey objectives by collecting monthly samples from selected
tributaries to surveyed lakes. In addition, the headquarters staff
provides general coordination and guidance to the operational aspects of
the program.
Because the Survey has to cover a large geographical area 1n a rela-
tively short period of time, pontoon-equipped UH-1H Bell helicopters with
automated and manually-operated instruments are used to measure the water
quality of each lake. Two helicopters - carrying a Hmnologlst and a
technician - are operated simultaneously, and a third helicopter is used
for ferrying parts, equipment, and people. The sampling teams from the
Las Vegas-EMSL are sopported by a mobile analytical laboratory, chemistry
technicians, electronic specialists, and other staff involved with heli-
copter maintenance or program coordination. The total staff 1n the field
usually ranges from 12 to 14 people.
Operating procedures involve establishing a work center at an airport
and then sampling all lakes within a 100-mile radius. When all of the
water bodies within the area are sampled, the support staff moves to a
new central location, and sampling begins on a different set of lakes. In
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this manner, 150 to 250 lakes have been sampled three times each year, and
the sampling will be completed on all of the 812 lakes In a four-year period.
Table 1 depicts the routine water-quality parameters which were sefexted
to characterize each lake and assess Its trophic condition. Parameter
selection was based on the relevance of each parameter as a measure of
potential and existing primary production. Both the number and the type
of parameters measured were also limited to a certain extent by the opera-
tional aspects of the Survey.
Table 1. Water-quality characteristics measured
Physical-Chemical
Alkalinity
Conductivity*
pH*
Dissolved oxygen
Phosphorus:
Ortho
Total
Nitrogen:
Ammonia
Kjeldahl
Nitrate
Seech1 depth
Temperature*
Biological
Algal assay
Chlorophyll a.
Algal count and
Identification
* Determined on-s1te with electronic probes.
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Concurrent with the lake sampling, the significant tributaries and
outlet(s) of each lake are sampled monthly, totaling about 4,200 sampling
sites nationwide. Volunteer National Guardsmen of each state, trained
on-site by EPA or state agency staff, collect and preserve the samples'^. ,.
at sites pre-selected by EPA personnel. The samples are shipped to CERL
for analysis of the various forms of nitrogen and phosphorus (see Table 1).
Through an interagency agreement, the U.S. Geological Survey estimates
flows for each sampled stream. These data are used in conjunction with
concentration values to determine nutrient loadings.
A voluntary sampling program was established through the respective
state water pollution control agencies to have plant operators collect
effluent samples from those municipal sewage treatment plants which
impact Survey lakes—about 1,000 treatment plants. The effluent samples
are collected monthly, preserved, and shipped to the Corvallis laboratory
for nitrogen and phosphorus analyses.
Specific procedures used In collecting, preserving, shipping, and
analyzing the various kinds of samples collected by the Survey are
described In National Eutrophication Survey Working Papers No. 1 (1974)
and 175 (1975).
Presently, the field portion of the Survey is almost completed with
the last samples scheduled for collection in November, 1975. Data
analysis is scheduled for completion in December, 1976.
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8
RESULTS AND DISCUSSION
Limiting Nutrients
For each of the surveyed lakes, an algal assay 1s performed on a
sample of lake water and, to supplement the assay findings, Inorganic
nitrogen to dissolved orthophosphorus ratios are determined from the
lake sampling results. For the 623 surveyed lakes 1n states east of
the Rocky Mountains, the assay demonstrated that with respect to algal
growth requirements, 67% were phosphorus-limited, 30% were nitrogen-
limited and 3% were either limited by an element other than phosphorus
or nitrogen or the results were not conclusive (Table 2).
Table 2. Summary of algal assay results for surveyed
water bodies in the 37 states east of the Rocky Mountains.
Limiting Nutrient
Phosphorus ,
Nitrogen
Other
Total
Number of Lakes
417
186
20
623
% of all Lakes
67
30
3
100%
A higher.percentage of phosphorus limited lakes would probably have
been found had the Survey not been mostly concerned with lakes which were
impacted by municipal wastes. The algal assay results should, therefore,
be evaluated with some caution because they reflect existing conditions
which often include man's impact on the nutrient regime.
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Municipal waste treatment plant effluents, for example, have an average
total nitrogen to total phosphorus ratio of about 2.5 to 1 whereas natural
waters usually have a ratio 1n excess of 15 to 1. The relative abundance
of phosphorus provided 1n municipal effluents could change a lake from
phosphorus-limited to nitrogen-limited. Such a lake could theoretically
be changed back to phosphorus-limited by reducing phosphorus Inputs.
Figure 2 Is an Indication of the significance of municipal wastes to
the total annual phosphorus load to some of the eastern lakes and reser-
voirs. Of the 234 water bodies Included 1n the frequency histogram, 135
receive more than 20% of their annual total phosphorus load from municipal
sources. If 80% of the phosphorus were removed from these discharges by
treatment, only 9 of the lakes would still receive more than 20% of their
total phosphorus load from municipal wastes as shown 1n Figure 3.
The reduction or removal of phosphorus originating from municipal
sources does not guarantee that the trophic status of the receiving lake
will be significantly improved. That determination can only be made on
a case-by-case basis In which many factors, such as background phosphorus
levels, the limiting nutrient, lake morphometry, etc., are considered.
It is apparent, however, that in many cases, eutrophlc conditions are
either the direct result of phosphorus from municipal wastes or at least
are worsened by phosphorus Inputs from these sources which could be
readily controlled.
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200
175
2 ISO
J 125
u.
° IOO
or
m 75
2
^
z 50
25
0-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 91-100
PERCENT OF TOTAL PHOSPHORUS LOAD FROM MUNICIPAL POINT SOURCES
Figure 2. A frequency histogram representing the percent of total annual
phosphorus load attributable to municipal wastes for,a-'number
of eastern U.S. lakes and reservoirs.
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200
175
s 150
u.
0
125
100
50
25
0-10 11-20 21-30 31-40 41-50 5I-6O 61-70 71-80 81-90 91-100
PERCENT OF TOTAL PHOSPHORUS LOAD FROM MUNICIPAL POINT SOURCES
FOLLOWING 80% REMOVAL
Figure 3. A frequency histogram representing the percent of total annual
phosphorus load attributable to municipal wastes after Q0%
effluent phosphorus reduction for a number of eastern.if.S lakes
*nd reservoirs.
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12
Trophic Condition of Survey Lakes
About 80% of the lakes and reservoirs Included 1n the first two
years of the Survey 1n the eastern United States were eutrophlc. Th'ts
was not unexpected since a large number of these water bodies were
impacted by municipal wastes.
The classical terms, oUgotrophlc, mesotrophlc, and eutrophlc were
used to describe the trophic condition of each water body. Based partly
on observations during the first year of the Survey and partly on litera-
ture values, some general guidelines were developed for each of four key
parameters to assist us in assigning a trophic classification to each
lake. These values are listed in Table 3.
Table 3. Key parameter values associated with
three lake trophic conditions.
Parameter
Total Phosphorus (yg/1)
Chlorophyll a (yg/l)
Seech i depth (meters)
Hypolimnetic Dissolved
Oxygen (% saturation)
OUgotrophic
<10
< 4
> 3.7
>80
Me so trophic
10-20
4-10
2.0-3.7
10-80
Eutrophlc
>20-25
>10
<2.0
<10
If each of the four parameters from a given lake were within the
range of a specific trophic condition (e.g., oUgotrophic) then it was
fairly certain that the Indicated trophic condition appropriately
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13
described the lake. Unfortunately, In many cases, all the parameter
values did not neatly fall wUMn one trophic classification; therefore,
a relative Index or ranking system was also used. This Index Included.
the four parameters shown 1n Table 3 (except that minimum dissolved
oxygen concentrations were used) plus Inorganic nitrogen and dissolved
orthophosphorus concentrations. The Index was based on percentile
rankings for each of the six parameters which were then added together
to produce a single index number. Using this system, a large number of
lakes could be ranked 1n general order from most oligotrophlc to most
eutrophic. There were enough well-studied lakes Included In the Survey
to allow us to determine approximately where the transition from oligo-
trophic to mesotrophic and from mesotrophic to eutrophic occurred in
the ordered list of lakes. This system was not without exception but
did prove useful. The Index is discussed 1n detail in National Eutrophi-
cation Survey Working Paper No. 24 (1974).
Phosphorus Loading - Trophic Condition Relationships
Another of the Survey objectives was to estimate annual phosphorus
and nitrogen loadings for each of the study lakes and to examine rela-
tionships between these nutrient inputs and the resulting trophic condi-
tions. Such relationships are needed by lake managers to predict trophic
responses which would result from either Increasing or decreasing phos-
phorus loads. They would also give regulatory agencies a firmer basis
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14
for allocating total phosphorus loads from point or non-point sources
so that the desired trophic condition of a lake or reservoir could be
maintained or achieved.
The Survey has not developed any original nutrient loading-lake
response relationships. However, the data have been applied to models
recently developed by other Investigators.
Prior to 1968 there were no models of general applicability which
related total phosphorus load to trophic condition In the receiving lake.
Now, however, there are at least three which seem very promising. These
models are presented and compared using data collected by the Survey
from twenty-three lakes and reservoirs. These twenty-three water bodies
represent a cross-section of trophic conditions, mean depths, and mean
hydraulic retention times. All are located in northeastern and north-
central states except for two reservoirs 1n Georgia and two in South
Carolina. In this group of lakes, six are oligotrophlc, nine are
mesotrophic, and eight are eutrophic.
The three relationships (or models) which will be compared were
developed by Vollenweider and Dillon (1974), Dillon (1975), and Larsen
and Herder (1975), respectively.
Vollenweider (1968), using existing data from a number of European
and North American lakes, was the first to relate total phosphorus
loading to lake trophic condition. He plotted annual total phosphorus
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15
loadings (g/m2/yr) against lake mean depths and empirically determined
the transition between oligotrophic, mesotrophic, and eutrophic loadings.
*'t
Although this approach worked reasonably well for lakes with detention
times of several months or longer, it did not account for the fact that
two lakes with identical mean depths could have quite different hydraulic
retention times and therefore different trophic responses to the same
loading rate. Subsequently, Vollenweider modified his initial relation-
ship and based his revised model on considerations of a mass balance
equation for phosphorus. The application of Vollenweider's revised
model to the Survey lakes is Illustrated in Figure 4.
The observed loadings and trophic conditions of the 23 Survey
lakes did not fit the Vollenweider relationship very well. Phosphorus
loadings for five of the eutrophic lakes plotted clearly within the
eutrophic zone of the Vollenweider relationship while loadings of two
eutrophic lakes plotted within the mesotrophic zone and one within the
oligotrophic zone. Loadings for five of the mesotrophic lakes fell
within the oligotrophic zone while the remainder were within the meso-
trophic portion of the Vollenweider relationship.
Vollenweider's work was extremely important not only because he
was the first to investigate the loading-response relationship but also
because his original ideas interested others 1n this type of approach.
Stimulated by Vollenweider's earlier work, Dillon (1975) used the
mass balance modeling approach to derive the relationship illustrated
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MEAN DEPTH (m) / MEAN HYDRAULIC RETENTION TIME (yrs.)
Figure 4. The Vollenweider relationship applied to a number of eastern U.S
lakes and reservoirs sampled b.y the Survey.
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17
in Figure 5. Dillon's approach relates lake mean depth to a factor
which Includes total annual phosphorus loading, the phosphorus retention
coefficient, and hydraulic flushing time. The 23 Survey lakes fit tne^.
Dillon relationship quite well as illustrated In Figure 5. Two
oligotrophic lakes plotted in the mesotrophic zone and two mesotrophic
lakes plotted in the oligotrophic zone; however, observed conditions
for the other lakes were as predicted by the Dillon relationship.
Larsen and Herder (1975), working independently of Dillon, also
solved a mass balance equation for phosphorus to develop a relationship
between the average incoming phosphorus concentration and the phosphorus
retention coefficient. The average incoming phosphorus concentration
is defined as the total annual phosphorus load divided by the total
hydraulic inflow which is also equivalent to:
where, L = annual total phosphorus areal load (g/m2/yr)
C * hydraulic flushing time (exchange/year)
z = mean depth (meters)
The Larsen and Merder relationship therefore Incorporates the same
variables as the Dillon relationship although the graphical solution of
the mass balance model for phosphorus is different. Figure 6 depicts
the 23 Survey lakes plotted against the Larsen-Merder relationship.
The fit is very good and the relative location of each point on the
graph is very similar to Figure 5, the Dillon relationship.
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EUTROPHIC
D27CI
D45I2./ A. 2313
02695
04315
A" 27 84
2782 / ° 3303
A2306
0 A1318
OLIGOTROPHIC"
O Oligotrophic Lakes
A Mesotrophic Lakes
D Eutrophic Lakes
' i i i i i i
0.0
10.0
MEAN DEPTH (METERS)
100.0
00
Figure 5. The Dillon relationship applied to a number of eastern U.S.
lakes and reservoirs sampled by the Survey.
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g
5
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o
§
oc
100.0 -
85
O
i
O
o
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<
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_ A J3I8
2306^2311 "OLIGOTROPHIC
O Oligotrophic Lakes
A Mesotrophic Lakes
D Eutrophic Lakes
O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
PHOSPHORUS RETENTION COEFFICIENT (
1.0
Figure 6. The Larsen-Mercier relationship applied to a numbef" of eastern
U.S. lakes and reservoirs sampled by the Survey.
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20
Since both the latter two models predict In-lake concentrations of
total phosphorus, the vertical distance from an observed point, reprer
senting a lake, to one of the transitional lines 1s at least a semi- *'-
quantitative measure of the degree of ollgotrophlc or eutrophy.
The vertical distance from a given point to a transitional line 1n
the Vollenwelder relationship has less meaning 1n terms of the degree
of ollgotrophy or eutrophy because the model does not directly relate
total phosphorus loading to 1n-lake phosphorus concentrations.
In summary, the models developed by Dillon and Larsen-Mercler,
which relate total phosphorus loads to lake phosphorus concentrations,
should prove to be useful lake management tools. The Vollenwelder model,
at this time, Is probably less precise because 1t considers only total
phosphorus loading without regard to In-lake processes which reduce the
effective phosphorus concentration; however, the model can be used to
determine approximate acceptable total phosphorus loads.
The Relationships of Land Use to Nutrient Levels
Another of the Survey objectives Is to examine, on a National scale,
the relationships of land use and other drainage area characteristics to
stream nutrient levels and subsequently lake trophic status.
Of the 4,200 sub-drainage areas sampled by the Survey across the
United States, about 1,000 were selected for a detailed study of land
use and other drainage area characteristics (see Figure 7). Criteria
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DI1T1IBUTION Of
N. E. S UNO USE
STUDY MAINAGt AM AS
Figure 7. The distribution of stream drainage areas selected by the
National Eutrophication Survey for land use studies.
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22
for selecting the 1,000 stream sampling sites and associated drainage
areas were:
1. Absence of Identifiable point sources.
2. Availability of usable aerial photography (scale 1:40,000 to
1:80,000) or existing land-use data.
3. Availability of accurate topographic maps for drainage area
delineation.
4. Sufficient land relief for clear delineation of drainage area
limits.
5. The need to encompass a variety of geographic and climatic
areas.
Note that few, if any, of the selected drainage areas were 1n Florida,
the Atlantic and Gulf coastal plains, or northern Minnesota. These areas
were excluded from consideration because of the difficulty of accurately
defining drainage area boundaries due to low topographic relief, and, in
many cases, because of the strong influence of ground water.
At the present time only the data from the eastern United States
(east of the Mississippi River) have been compiled, but the analysis
of these data is not complete. Therefore, only general results are
presented.
Figure 8 summarizes the data collected from 473 eastern U.S.
drainage areas for total phosphorus and total nitrogen concentrations
originating from different land use categories. The categories are
defined as follows:
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NU
or SUM
53 FOREST ^
170 MOSTLY FOREST
52 MIXED
11 MOSTLY URIAH
M MOSTLY ACR 1C.
91 AGRICULTURE
MEAN TOTAL PHOSPHORUS CONCENTRATIONS
vs
LAND USE
DATA ON, 473 SUBCMAINAGE AREAS IN
EASTERN UNITED STATES
| 0.014
j 0.031
] 0.040
0.066
0.066
0.03
MILLIGRAMS PER LITER
0.10
0.13S
O.IS
NUMMD
OF SUBS
53 FOREST ^
170 MOSTLY FMEST
52 MIXED
11 MOSTLY URMN
96 MOSTLY MRIC.
91 AGRICULTURE
MEAN TOTAL NITROGEN CONCENTRATIONS
vs
LAND USE
0*TA ON 473 SUBDRAINAGE *«E»S IN
EASTERN UNITED STATES
O.MO
1.2*1
l.tlJ
1.0
1.0
MIILIGRAMS PER LITER
ro
4.170
3.0
4.0
Figure 8. The relationship between total phosphorus and total nitrogen
concentrations in streans and land use in the eastern U.S.
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24
1. Forest; other types negligible
a. >75% forested (including forested wetland)
b. <7% agriculture
c. <2% urban
2. Mostly forest; other types present
a. >50% forest
b. not included in the forest category
3. Mostly agriculture; other types present
a. >50% agriculture
b. not included in the agriculture category
4. Agriculture; other types negligible
a. >75% agriculture
b. <7% urban
5. Urban
>39% urban
6. Mixed; not included in any of other categories
Streams draining predominately agricultural areas have total phos-
phorus concentrations averaging about 10 times higher than those
draining forested areas (Figure 8). The difference between total
nitrogen concentrations was not as marked. Streams in agricultural
areas averaged nearly 5 times higher total nitrogen concentrations
than those draining forested areas. It is Interesting to note that,
based on the mean concentration values, phosphorus would be expected
to be limiting in surface waters draining either forested or agricul-
tural areas. The total nitrogen to total phosphorus ratio changes
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25
from 60 to 1 for forested areas to 31 to 1 for agricultural areas.
Generally phosphorus Is the limiting nutrient when the N:P ratio
exceeds 14:1.
The nutrient loads per unit area of drainage for total phosphorus
and total nitrogen are shown in Figure 9. The differences In exports
for the different land use categories are not as pronounced as the
nutrient concentrations were. Total phosphorus export from agricul-
tural lands was only 3.7 times greater than from forested lands and
total nitrogen export only 2.2 times greater. The differences in
magnitude between stream loads and stream concentrations are due to
the differences in stream flows resulting from the two types of land
use. The data suggest that stream flow per unit of drainage area
is somewhat higher for forested than for agricultural areas. This
seems logical since forested areas frequently are those which are
unsuitable for agricultural purposes because of steeper slopes and
relatively thin soils.
The pattern for orthophosphorus concentrations was very similar
to that for total phosphorus as shown in Figure 10. Except with
predominately urban drainage areas, of which their were only eleven,
mean orthophosphorus concentrations represented 40 to 43% of the
total phosphorus concentrations regardless of overall land use.
Orthophosphorus concentrations in streams draining agricultural areas
were nearly 10 times the concentrations in streams draining forested
areas.
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S3 FOREST
170 MOSTLY[FOREST
52 MIXED
11 MOSTLY URIAH
M MOSTLY MRK.
91 MRICULTURE
TOTAL PHOSPHORUS EXPORT
vs
LAND USE
or tat
S3
170
S2
11
9C
91
I DATA ON if} SUICMAINAGE AREAS IN
CASTEm uxrrto rr«T»«
MOSUY FOREST
MIXED
MOSTLY URIAH
MOSTLY MRK.
•"••* rwm jnrat*
MRICULTURE
*^
| ••' Z
\ 17.4
| 1..4
I 30.1
|22.7
; | 30.*
i i
0 10 20 30 40
KILOGRAMS PER SQUARE KILOMETER PER YEAR
TOTAL NITROGEN EXPORT
LAND USE
OAT* ON 473 SUBONAINACE AREAS IN
EASTERN UNITED STATES
440.1
ro
7M.6
630.5
9*2.3
SOO
KILOGRAMS PER SQUARE KILOMETER PER YEAR
1000
Figure 9. The relationship between total phosphorus and total nitrogen,export
in streams and land use in the eastern U.S. •'•
-------
or sues
S3 FOKST
IT* MOSTLY FOKST
S2 MIXED
11 MOSTLY UMAM
M MOSTLY M*K.
M ACMCULTUM
MEAN ORTHOPHOSPHORUS CONCENTRATIONS
vs
LAND USE
DATA ON 471 SUBDKAINAGE AREAS 'N
EASTfftN UNITED STATES
J 0.006
| 0.014
| 0.017
0.033
O.OM
0.01
0.01
0.04
PER LITER
o.os
0.0*
OF SUIS
S3 FOKST _
170 MOSTLY FOKST
52 MIXED
11 MOSTLY UMUIM
M MOSTLY MMIC.
91 UtKULTURE
MEAN INOMANIC NITROGEN CONCENTRATIONS
LAND USE
DATA ON 473 SUBORAINAGE AHCAS IN
EASTERN UNITED STATES
0.131
rv>
J 0.347
J 0.»7*
I 154
J I.O49
J ».l»0
o.so
I.OO
1.50 3-00
MILLIGRAMS PER LITER
1.50
3.00
Figure 10. The relationship between orthophosphorus and inorganic nitrogen,
concentrations in streams and land use in the eastern U.S.
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28
Inorganic nitrogen exhibited quite a different pattern from
total nitrogen in that substantially higher (13.7X) concentrations
were observed in streams draining agricultural lands than In forested '"
lands (Figure 10). In streams drainage forested areas, Inorganic nitro-
gen constituted about 27% of the total nitrogen, however, this Increased
to 762 in streams draining predominately agricultural areas. Although
thp sample size (11 drainage areas) was relatively small, Inorganic
nitrogen made up about 98% of the total nitrogen In streams draining
mostly urban drainage areas. Inorganic nitrogen export was also signifi-
cantly higher (5.6X) from agricultural areas than from forested areas as
shown in Figure 11. The difference probably reflects the use of inorganic
nitrogen fertilizers and the high water solubility of inorganic nitrogen
compounds.
What conclusions can be drawn from these general results? First,
these data suggest that streams draining agricultural watershed have
higher nutrient levels and therefore would be expected to be more produc-
tive than those draining forested watersheds. The Increase in nutrient
levels is generally proportional to the Increasing percent of the land
in agriculture.
Second, the data indicate that the inorganic portion (orthophosphorus)
of the total phosphorus component stays roughly at the 4035 level regardless
of land use type, whereas, the Inorganic portion of the total nitrogen
component increases markedly from 27% for forested areas to 75% for
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NMMfR
OF sues
S3 FOREST
170 MOSTLY FOREST
52 MIXED
II MOSTLY URMN
M MOSTLY MRIC.
tl AGRICULTURE
OF SU*S
S3 FOREST
p'-v •'pr • —v •»,»-«
170 M9STLV FOREST
52 MIXED
11 MOSTLY URMH
M MSTLY MRK.
tl A6RKULTURE
ORTHOPHOSPHORUS EXPORT
vs
LAND USE
DATA OH «73 SUBCWAINAGE AREAS IN
EASTIRN UNITED STATES
TO
7.,
I..,
5 10
KILOGRAMS PER SQUARE KILOMETER PER YEAR
INORGANIC NITR06EN EXPORT
vs
LAND USE
DATA ON 47] SUBORAINAGE AREAS IN
EASTERN UNITED STATES
] S36 9
lS.O
»•>
200
400 «00
KILOGRAMS PER SQUARE KILOMETER PER YEAR
3 "•.«
800
Figure n. The relationship between orthophosphorus and inorganic nitrogen
export in streams and land use in the eastern U.S.
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30
agricultural areas. Inorganic nitrogen In streams draining mostly urban
areas represented a substantially larger fraction of the total nitrogen
(98%), however the number of test areas was relatively small (11). "•,„
Lastly, what uses can be made of the data derived from this segment
of the survey? Other than elucidating the land use-nutrient level -
eutrophication relationships, probably the two most important uses will
be: (1) to provide a basis for a quick and relatively accurate method
of determining nitrogen and phosphorus concentrations and loadings based
on land use and other non-point source types of geographical character-
istics, and (2) to provide a large nationwide collection of watershed
data for testing other methods of estimating nitrogen and phosphorus
levels in streams from non-point sources.
SUMMARY
The National Eutrophication Survey, which was Initiated In 1972
by the U.S. Environmental Protection Agency, is In the first stage of
collecting data from over 800 lakes and reservoirs in the contiguous
United States. In the eastern U.S., a large percentage of the surveyed
water bodies are impacted by municipal sewage treatment plant effluent
and are in various stages of enrichment. Phosphorus loads to a signifi-
cant number of these Impacted lakes and reservoirs could be substantially
reduced by controlling phosphorus inputs from municipal sources.
Primary production in 67% of the water bodies surveyed east of the
Rocky Mountains was phosphorus-limited and 30% were nitrogen-limited
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31
according to algal assay results. It Is believed that the apparent
nitrogen-limited condition was frequently the result of excessive phos-
phorus inputs from municipal sources.
Land use in the watershed was shown to be a significant factor in
determining levels of phosphorus and nitrogen 1n streams in selected
areas studied in the eastern United States. Average total phosphorus
concentrations were about 10 times greater 1n streams draining agricul-
tural areas than in streams draining forested areas; total nitrogen
concentrations were about five times greater. The percentage of total
nitrogen 1n the inorganic form was substantially higher in streams
draining agricultural lands than in those streams draining forested
lands.
Phosphorus loading data for 23 selected survey lakes were applied
to three general models relating annual total phosphorus loading rates
to lake trophic conditions. The "fit" of observed conditions to pre-
dictions made by each model was compared and discussed.
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32
REFERENCES CITED
Dillon, P. J. 1975. The phosphorus budget of Cameron Lake. Ontario:
the importance of flushing rate to the degree of eutrophy of lakes.
Limnol. Oceanogr. 20_: 28-39.
Larsen, D. P. and H. T. Mercler. 1975. Lake phosphorus loading graphs:
an alternative. National Eutrophlcation Survey Working Paper No.
174.
U.S. Environmental Protection Agency. 1974. Survey methods for lakes
sampled 1n 1972. National Eutrophication Survey Working Paper No. 1.
40 pp.
U.S. Environmental Protection Agency. 1975. Survey methods, 1973-1976.
National Eutrophlcation Survey Working Paper No. 175. 91 pp.
U.S. Environmental Protection Agency. 1974. An approach to a relative
trophic Index system for classifying lakes and reservoirs. National
EutropMcation Survey Working Paper No. 24. 44 pp.
Vollenweider, R. A. 1968. The scientific basis of lake and stream
eutrophlcation with particular reference to phosphorus and nitrogen
as factors in eutrophication. OECD, DAS/CSI/68-27. 159 pp.
Vollenweider, R. A. and P. J. Dillon. 1974. The application of the
phosphorus loading concept to eutrophication research. National
Research Council of Canada No. 13690. 42 pp.
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