United States
Environmental Protection
Agency
Environmental Research
Laboratory
Corvallis OR 97330
Research and Development
EPA-600/S3-83-057 Dec. 1983
SERA Project Summary
Response of Skinner Lake
(Indiana) to Agricultural Drainage
C. D. McNabb, B. J. Premo, F. C. Payne, T. R. Batterson, and J. R Craig
Agricultural runoff has been shown
to be relatively rich in plant nutrients
that promote high densities in algae
populations in lakes. Decomposition
of these algae stresses the oxygen
system, which in very productive lakes
results in release of water quality de-
grading substances from sediments,
and causes shifts in animal and plant
populations toward less desirable spe-
cies. Turbidity in the water is increased
in the process. For lakes in the north
central States, phosphorus is most
commonly the key nutrient responsi-
ble for development of excessive algae
densities. Various agricultural land
management practices are known to
promote conservation of this and other
nutrients on the land.
From measurements over an annual
cycle in 1978-79, a phosphorus runoff-
algae density model was developed for
a lake at the bottom of an agricultural
watershed in northern Indiana. Like
other models in the literature, this
model stated that mean total phos-
phorus and chlorophyll a concentra-
tions in the epilimnion of the lake in
the ice-free period of the year were
predictable from mean total phospho-
rus in inflowing streams and residence
time of water in thejake (t^,). For this
particular system, [TP]epLand [chl a]epj
were predictable from [TP]streams and
tyy measured during spring and summer,
rather than over a longer interval of the
year. Measurement of the last two
variables during the period of spring
runoff just prior to thermal stratifica-
tion of the lake when the flushing
coefficient (p) equaled 1, and continued
through the duration of stratification,
was sufficient
Land management practices were
implemented on erosion-sensitive por-
tions of the watershed between 1978
and 1981. These included conserva-
tion tillage, terraces, livestock exclu-
sion, grassed waterways, diversions.
group tile mains, settling basins, and
stabilizing stream banks with vegeta-
tion. The model was tested in 1982 on
the assumption that this work would
change [~n*lrtmam& and alter total phos-
phorus and chlorophyll a concentra-
tions in the lake. It proved to be area-
sonable predictor of UPlapj and [chl a]^
for the ice-free period of the year. In the
absence of unusual rain events and by
design of the model, tw in 1979 and
1982 were nearly the same; 0.60 and
0.65 respectively. [TFJ^r^,,,,, was 127
mg rtv3 in 1979 and 100 mg rtv3 in
1982. Total phosphorus and chloro-
phyll a concentrations in the lake were
reduced between years from 63 to 54
mg nv3 and 15 to 10 mg nr3 respec-
tively. The model predicted 55 mg nr3
UPlepi and 13 mg nv3 [chl a]^, for
When a lake model can be calibrated
to fit specific characteristics of a water-
shed, it becomes a powerful manage-
ment tool. It focuses attention of plan-
ners on management alternatives most
likely to achieve intended goals. This
study showed that proper manage-
ment of an agricultural watershed can
improve water quality of a receiving
lake. Maintenance of established land-
use practices and implementation of
others at key sites on the watershed
will likely result in continued improve-
ment of this lake.
This Project Summary was developed
by EPA's Environmental Research Lab-
oratory, Corvallis, OR, to announce key
findings of the research project that is
fully documented in a separate report
-------
of the same title (see Project Report
ordering information at back).
Introduction
During 1978-1981, various land man-
agement practices were put in place on the
agricultural watershed of Skinner Lake in
Noble County, Indiana. The objective was
to reverse the process of eutrophication in
the lake. Studies reported here were con-
ducted to evaluate the effectiveness of the
program.
Skinner Lake had an average depth of
4.4 m, a maximum depth of 10 m and
surface area of 49.4 ha. One hundred
twenty-five permanent residences line the
shore of the lake. Lake level was controlled
by a concrete sill dam that was con-
structed in 1962. The lake discharged to
the Croft Drain that entered the South
Branch of the Elkhart River some 8.3 km
downstream.
Stable thermal stratification during sum-
mer was characteristic of Skinner Lake. It
existed from mid-May through mid-Octo-
ber. Figure 1 shows a typical temperature
regime for the ice-free season. The hy-
polimnion approached anaerobic condi-
tions rapidly as stratification became es-
tablished (Figure 2). Relative areal oxygen
deficits in the hypolimnion calculated for
the interval 1 May through 15 May in
1978 and 1979 were in the range of 700-
900 mg m"2 day"1. Lakes with areal oxy-
gen deficits greater than 550 mg m"2 day"1
have been considered highly fertile or
eutrophic. Other expressions of eutrophy
for Skinner Lake included extensive growth
of aquatic macrophytes such as Nymphaea
odorata. Ceratophyllum demersum, and
Myriophyllum spicatum, and blooms of
blue-green algae (Aphanizomenon sp.).
The dominant fish in Skinner Lake in-
cluded small sunfish (Lepomis spp.) and
crapp\es(Pomoxisspp.), and a large rough
fish population composed of the white
sucker (Catastomus commersoni) and the
golden shiner (Notemigonus crysoleucas).
The lake's turbidity, algal blooms, macro-
phytes and low oxygen conditions were
blamed for a general decline in fishing
quality over the last two decades.
The Watershed
The area of Skinner Lake watershed was
3649 hectares, 68% of which was used
• for agriculture. The remaining 32% was in
woodlands and wetlands. The Rimmell
inlet was the most important continuously
discharging surface flow to Skinner Lake
(Figure 3). Eighty-two percent of the
watershed (3091 ha) was within the
Rimmell drainage system. Land there was
put to varied crop and livestock use. Sub-
April May June July August September October November Dec.
Figure 1. Temperature isopleths (°C) for Skinner Lake during the ice-free season of 1979.
7
8
9
10
10 11 12
April May June July August September October November Dec.
Figure 2. Dissolved oxygen isopleths (mg I -') for Skinner Lake during the
ice-free season of 1979.
Figure 3. The Skinner Lake watershed in Noble County, Indiana. Section boundaries
form the grid shown.
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surface tiles were widely employed for
drainage. Three smaller streams carrying
tile and surface runoff entered the lake
from agricultural land: the Hardendorff
system drained 1 80 ha, the Riddle stream
107 ha, and the Weimer stream 42 ha of
the watershed. The overflow from nearby
Sweet Lake ran along a 0.8 km channel
through a woodland to Skinner Lake. The
Croft-Sweet system drained 229 ha of
watershed.
The particular land treatment practices
implemented on the watershed of Skinner
Lake from 1978 to 1981 were chosen
from the data and experience generated by
the nonpoint-source pollution study of
Black Creek in nearby Allen County, Indiana
These included settling basins, conser-
vation tillage, group tile mains, terraces,
livestock exclusion, diversions, grassed
waterways, and planting vegetation on
critical erosion sites. The work accom-
plished is shown in Figure 4.
Phosphorus - Algae Model
The product of the evaluation studies
was a model which described the quan-
titative relationship between phosphorus
concentration in inputs to the lake and
algal biomass in the lake in the ice-free
period of the year. This model was based
on eutrophication models that were devel-
oped in the literature over the past several
decades. More specifically, it resulted from
a modification of a model developed by
Vollenweider and Kerekes from data of
200 lakes in 50 countries participating in
the Organization for Economic Coopera-
tion and Development (OECD) Coopera-
tive Program on Lake Eutrophication.
Skinner Lake was considered phosphorus
limited, ratherthan nitrogen limited, on the
strength of high ratios of [TN]/[TP]. These
ranged from 19 to 220 in Skinner Lake
during 1979.
Modifications were made to the Vollen-
weider and Kerekes model by considering
(1) major sources contributing to [TP] in
loading to Skinner Lake, (2) seasonal dif-
ferences in [TP] in input and water resi-
dence time of the lake (tw), and (3) dif-
ferences in epilimnetic and hypolimnetic
[TP] during summer, and their relation to
[cnta].
Atmospheric bulk loading to Skinner
Lake over a 12-month interval in 1978-
1979 amounted to 0.04 g TP nr2. While
this measurement fell within the range
predicted for the geographical region, it
constituted only 1 A% of the annual load-
ing. Septic tank loading was estimated
using a constant, 0.08 kgTPcapuf1 yr1.
There were 125 cottages and approxi-
mately 375 people served by septic tanks
Minimum tillage
Pasture & hay seedings
Settling & lake basins
Tile
I Terrace
MM Tree plantings
••«•••••• Diversion
----- Watershed boundaries
sssss=5t Grassed waterway
• Water control structure
• Animal waste pit
Figure 4 (a). Land management practices applied to the west portion of the Skinner Lake
watershed during 1979-1981.
around Skinner Lake. By this constant,
they contributed 30 kg TP yr"1 . This septic
tank loading comprised 2% of the 1 978-
79 annual TP load.
Estimates of internal phosphorus loading
were calculated for intervals of the ice- free
period of 1 979 from the following:
Tpinternai = A
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Figure 4 (b). Land management practices applied to the east portion of the Skinner Lake
watershed during 1979-1981.
streams and t^ These are illustrated in
Table 1 and in Figure 5 for the principal
stream discharging to Skinner Lake. Be-
cause of the high flushing rate during the
spring overturn period (Table 1), TP inputs
from streams during the preceding winter
and period ofjjpring snow-melt had little
influence on [TP] in the lake during spring
overturn and the following summer.
Table 1. Flushing Coefficients (p = Volume
Outflow/Volume Lake) of Skinner
Lake during Periods of
1978-1979
Period (p)
Fall Overturn and Winter 0.02
9/6/78 - 2/6/79
Snow Melt 1.30
2/6 - 3/20/79
Spring Overturn 1.06
3/20 - 5/22/79
Summer Stratification 0.17
5/22 - 9/6/79
Whole Year 2.55
9/6/78 - 9/6/79
The following model fit the 1978-1979
data for Skinner Lake:
(1)[TPep,]ss=[TPstrearnl^s
1 + ^ss 2
In the model, ss is the period of spring
overturn and summer stratification where
the length of the spring period is defined
as the interval prior to the onset of strati-
fication during which the flushing coef-
ficient (p) of the laj
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1000-
ioo -4
IS:
0.1
1
'\
10
100
Residence Time
£ represents plot of Skinner Lake coordinates of 1979.
• represents plot of Skinner Lake coordinates of 1982.
Aa probable case for Skinner Lake with diversion of Rimmell stream around lake to outlet stream;
&[> probable case for Skinner Lake if settling basin on Rimmell stream removed 100% TP in
stream discharge.
Figure 6. Diagramatic representation of the Skinner Lake model.
Skinner Lake, diverting the stream would
have increased tw from 0.63 to 2.35.
The net effect of diverting the Rimmell
would have been to reduce the [TP.DJSS
from 63 mg nr3 to 45 mg m'3, and [chla]ss
from 1 5 mg nr3 to 11 mg rrr3. Another
alternative for reducing the effect of runoff
and nutrients on the lake was a settling
basin on the Rimmell stream just above its
inlet to Skinner Lake. On the basis of 1979
data, if the basin removed 100% of panic-
ulate phosphorus from the water, [TPstream]ss
would have been reduced from 127 mg
nr3to52 mgm-^lTPepJss fram63 mg nr3
to 20 mg rrr3, and[chla]ssfrom 15 mg nr3
to 7.5 mg m"3. As shown in Figure 6, this
would represent a considerable improve-
ment in water quality at Skinner Lake.
Expectations in these examples provide
a focus for considering costs and benefits
of various strategies for land management
and lake improvement. Results of this
study call attention to the need for site-
specific information on which to base
cost-benefit judgements.
year variability in the systems. It should be
noted that by definition of variables in the
Skinner Lake model, comparable portions
of the water-year in 1979 and 1982 were
used in this study. Between-year differ-
ences in rain events on the watershed, for
example, differences in the intensity of
individual events and associated differ-
ences in erosional runoff, were minimized
by the model. The time interval over which
tWs was calculated was nearly the same
for both years, as was the value to t^,
(0.63 in 1979 and 0.65 in 1982]S
Unusually intense storms did not occur in
those intervals in either year. It is probable
that land management was the primary
cause for the improvement observed in
Skinner Lake during this study. However,
ordinary between-year variability was not
measured in the system during years prior
to land treatment and only a continuing
trend of improvement with maintenance
of existing practices and implementation
of others on the watershed in the years
ahead will confirm this.
Applications
A calibrated model fit to a specific lake's
characteristics becomes a useful manage-
ment tool. One treatment considered by
planners of the Skinner Lake project was
diversion of the Rimmell stream directly to
the lake's outlet Contours of the existing
landscape favored such an approach. Com-
pensation for disrupting intervening land
use would have been costly. The Skinner
Lake model could predict the effect of this
strategy if, for example, it had been imple-
mented in 1979. Figure 6 shows that
diversion_pf the Rimmell would not have
lowered [TPstream]ss appreciably. Other in-
lets were important m determining total
[TpstreaJss- Because the Rimmell pro-
vided a large percentage of inflow water to
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C. D. McNabb, B. J. Premo. F. C. Payne. T. R. Batterson, and J. R. Craig are with
Department of Fisheries and Wildlife, East Lansing. Ml 48824.
Spencer A. Peterson is the EPA Project Officer (see below).
The complete report, entitled "Response of Skinner Lake (Indiana) to Agricultural
Drainage," (Order No. PB 83-233 676; Cost: $10.00, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
Corvallis, OR 97333
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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* U.S. GOVERNMENT PRINTING OFFICE: 1984-759-102/808
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