United States
Environmental Protection
Agency
Environmental Research
Laboratory
Corvallis OR 97333
Research and Development
EPA-600/S3-84-097 Nov. 1984
&EPA Project Summary
Effect of Dredging
Lilly Lake, Wisconsin
Russell C. Dunst, James G. Vennie, R. B. Corey, and A. E. Peterson
Lilly Lake is located in southeastern
Wisconsin. It has a surface area of 37 ha
and in 1977 had a maximum depth of
1.8 m and a calculated infilling rate of
0.5 cm per year. The basin contained up
to 10.7 m of lightweight, organic sedi-
ments. Recreational activity was severe-
ly restricted due to periodic winter fish
kills and dense growths of macrophytes
throughout the summer. During the
open water periods of 1978 and 1979,
683,000 m3 of sediment were removed
with a 30-cm cutterhead dredge and
transported via pipeline to two disposal
sites. The dredging operation deepened
the lake to a maximum of 6.6 m and
afforded an excellent opportunity to
evaluate the inlake and disposal site
effects of the project. The inlake portion
of the investigation included an assess-
ment of water quality, aquatic biology,
sediments, and hydrology before, dur-
ing, and after completion of dredging.
The evaluation of sediment disposal
emphasized the impact on the nearby
groundwater system and the value of
using hydrosoilsto enhance agricultural
crop production. The study began in
July, 1976 and extended through 1981,
with some work continuing into the
summer of 1982.
This Project Summary was developed
by EPA's Environmental Research Labo-
ratory, 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 order-
ing information at back).
Introduction
Lilly Lake is a 37 ha, natural, seepage
lake located in southeastern Wisconsin.
In the early 1970s, it was 1,8 m deep and
infilling at a rate of 0.5 cm/yr. The basin
contained up to 10.7 m of light-weight,
organic sediments, with a water content
of 90-98%. During July-October 1978
and May-August 1979, 683,900 m3 of
sediment were removed with a 30-cm
cutterhead dredge, deepening the lake to
6.6 m. Inlake water quality, aquatic
biology, sediment characteristics, and
hydrology were investigated before, dur-
ing, and after completion of the project
(1976-82).
Before dredging began, winter fish kills
were common, and rooted macrophytes
grew over the entire basin, reaching the
surface in most areas. The fish population
was dominated by slow growing bluegills,
and natural reproduction of gamef ish was
poor. Had oxygen resupply/production
been eliminated during the winter, dis-
solved oxygen concentrations would have
approached zero within 25 days. Water
quality was satisfactory in the summer.
Chlorophyll a levels averaged under 5
fjg/L, and at least 22 genera of algae
were present. Chlorophyceae were domi-
nant in terms of numbers and biomass.
Macrophytes were represented by 12
submergent species, with a combined
lakewide weighted average biomass of
685 and 335 g/m2 in 1976 and 1977,
respectively. These plants strongly influ-
enced inlake dynamics and were a major
problem in recreational usage of the lake.
In 1977, groundwater inflow contributed
17 and 2% of the water and phosphorus
loading to the lake, respectively.
During the dredging activity, lake levels
dropped 1.5 m. This produced an in-
creased groundwater inflow, including a
halt in the outflow, with flow reversal in
all of the previous outflow areas. As a
result, inlake water chemistry showed
more similarity to that of the groundwater,
which is illustrated by increases in con-
ductivity and total alkalinity. Because of
sediment disturbance, there were also
increases in ammonia nitrogen, total
phosphorus, and biological oxygen de-
-------
mand (5-day) levels. However, intake
dissolved oxygen concentrations were not
affected, and, in general, water quality
remained within tolerable limits. The fish
population did not appear to be stressed
by the prevailing conditions. Initially, the
algal population increased, peaking at 33
Aig/L of chlorophyll a. Changes were also
measured for gross primary productivity,
numbers of algal cells, and total biomass;
however, the population did not undergo
any major change in diversity or relative
composition. Apparently in response to
the algal expansion, the zooplankter
Bosmina longirostris greatly increased in
number during the same period.
Since completion of the dredging pro-
ject, the lake has refilled to pre-treatment
levels. Compared to earlier concentra-
tions, magnesium, sodium, potassium,
chloride, conductivity, and total alkalinity
were higher while total phosphorus was
lower. In 1981 sediment oxygen demand
and ammonia nitrogen release rates were
similar to 1977. Nevertheless, the inlake
water storage was increased by 2.3X, and
winter dissolved oxygen levels remained
above 7 mg/L at all depths. The ammonia
nitrogen was apparently being quickly
converted to other nitrogen forms (as in
1977), because only insignificant levels
were found in the water column. Soluble
reactive phosphorus release into the
water column was minimal due to the
toxic conditions, although it would be-
come a significant phosphorus source
under anoxia. In 1981, the lake was still
polymictic, but thermal gradients up to
8°C were present on occasion. Low
dissolved oxygen levels were found near
the bottom during these periods of re-
duced mixing. Bottom temperatures
reached 24°C; however, summer maxima
were depressed at all depths due to the
increased water volume.
By 1981, average summer chlorophyll
a levels were again under 5 /ug/L. Algal
diversity and density were similar to the
pre-dredging levels of 1978. There was a
shift in species composition, represented
by the appearance of six genera of
Chrysophyceae. These were co-dominant
with the Chlorophyceae in terms of bio-
mass. The benthic invertebrate commun-
ity was relatively sparse both before and
after dredging; however, numbers and
diversity were greater in 1981. The
populations of Hyalella azteca and Peri-
coma sp. were down, but Oligochaetes,
Caenis sp., and several genera of chiron-
omids responded to the improved inlake
conditions. Many of the latter are known
to be good fish food organisms. Dredging
and drawdown was a major disruption for
the rooted submergent vegetation. In
1980, species diversity was reduced to
six, and the lake bottom was inhabited
primarily by a macrophytic algae, Chara
sp. This is often a pioneer species for new
habitat. By 1982 the Chara sp. was being
replaced by rooted macrophytes, and the
diversity of species had increased some-
what. The plant community was still
evolving, but the existing characteristics
included: (1) growth over 75% of the lake
area, to a depth of 3.7 m; (2) top 1.2-1.8 m
of the water column weed-free, except in
the shallow, near shore area; (3) lakewide
weighted average biomass under 100
g/m2; and (4) lower biomass over sand
versus muck bottom. The lower biomass
over sand was also true before dredging
but is important because of the greatly
enlarged area of sand bottom post-
treatment.
Although dredging removed the phos-
phorus-rich upper sediments, resulting in
a major reduction in most phosphorus
forms (especially sodium hydroxide ex-
tractable phosphorus), the sediments
were still the most important reservoir of
phosphorus within the lake. However,
phosphorus transport directly into the
water column was minimal, based on a
combination of measurement and predic-
tive equation. Groundwaters furnished
46% of the water loading in 1981 but only
9% of the phosphorus. Several models
were used with the water and phosphorus
loadings before and after dredging to
predict a chlorophyll a level for the lake.
All of the models suggested that low
chlorophyll a concentrations would be
present in the lake, correlating well with
actual measurements.
The lake sediments were transported
via pipeline to two disposal sites. The
primary site, a modified abandoned gravel
pit, was used in 1978 and 1979, eventu-
ally receiving about 540,000 m3 of sedi-
ment. The remainder of the sediments
were placed in a low diked area on
agricultural land. This site was used in
1979 only. Changes to the groundwater
systems were monitored with observation
wells at both sites plus private drinking
water wells at the gravel pit. Parameters
of interest at both sites included water
levels, nitrate plus nitrite nitrogen, am-
monia nitrogen, pH, and conductivity. In
addition, chemical oxygen demand was
measured at the diked area and the
following at the gravel pit site: chloride,
total organic nitrogen, total dissolved
phosphorus, total phosphorus, arsenic,
barium, cadmium, copper, iron, lead,
mercury, selenium, silver, zinc, and
chromium.
The results were similar at each of the
disposal sites. The response time for i
particular well was related to soil perme-
ability and distance from the diked area oi
gravel pit basin. The greatest impact was
observed in wells located adjacent to the
sites, especially where permeable soils
were present. Impact duration was short
because the lake sediments quickly inhib-
ited continued seepage of water away
from the sites. In general, the surrounding
groundwater systems were not affected
significantly as a result of lake sediment
disposal. In 1983, the modified gravel pit
was still retaining water; however, the
sediments at the diked area were land-
spread, dried, and incorporated into the
terrestrial soils during 1980-81. By 1983
the area was growing corn.
Laboratory, greenhouse and field stu-
dies, begun in 1980 and terminated in
1982, were set up to determine the effects
of applications of sediment from the lake
on agricultural crops. The laboratory
studies included a survey of sediments
from 11 other Wisconsin lakes, and the
greenhouse study included three addi-
tional sediments so that chemical proper-
ties and plant responses to this sediment
could be compared with chemical proper-
ties and crop responses from other sedi-
ments.
The sediment survey included analyses
of the 12 sediments for pH, total carbon,
chemical oxygen demand, loss on ignition,
total nitrogen, ammonia nitrogen, total
phosphorus, organic phosphorus, phos-
phorus extracted with 0.5A4 sodium bi-
carbonate, phosphorus equilibrated in
0.01M calcium chloride, and total zinc,
manganese, copper, cadmium and lead.
A study of nitrogen and phosphorus
released or immobilized on incubation
was also included. Lilly Lake sediment
hadthe highest pH, total carbon, chemical
oxygen demand, loss on ignition, total
nitrogen and nitrogen release on three
month's incubation. It also showed the
greatest decrease in phosphorus equili-
brating in calcium chloride after incuba-
tion. The sediments showed wide ranges
in many of the factors, particularly in
those associated with pH and organic
matter content.
The four sediments used in the green-
house study were selected to give wide
ranges in pH (5.1 to7.7), chemical oxygen
demand(3.5to28.7 mg/L), total nitrogen
(0.35 to 2.69 mg/L) and carbon/phos-
phorus ratio(64-1420). Sediment concen-
trations equivalent to 0, 10, 30, 90 and
270 mT/ha were established in 1.5 dm3
pots of Plainfield sand and Withee silt
-------
loam. Corn was planted and harvested
after eight weeks.
Factors investigated in the greenhouse
experiment included yield, tissue concen-
trations of nitrogen, phosphorus, potas-
sium, calcium, magnesium, sulfur, iron,
manganese, copper, zinc, boron, and
plant uptake of nitrogen, phosphorus and
potassium. Statistical analyses showed
highly significant differences associated
with the soil used for all factors "except
yield and copper concentration. Differ-
ences associated with sediment source
were significant at the 5% level or greater
for all factors except phosphorus, potas-
sium and boron concentrations. However,
only concentrations and uptakes of nitro-
gen showed differences that were great
enough to be important from a practical
standpoint. The New Richmond flowage
sediment did increase the zinc concentra-
tion in the plant tissue more than the
other sediments, but the concentration
was not excessive.
Although there was a sizable, signifi-
cant variation in nitrogen concentration
and uptake associated with the different
sediments, there was no effect of applica-
tion rate beyond the first increment.
Application rate did significantly affect
calcium, magnesium, sulfur and manga-
nese concentrations, but except for man-
ganese the effects were not great. I ncreas-
ing rates of high pH Lilly Lake sediment
decreased manganese concentrations in
the plant, whereas increasing rates of the
acidic Lake Tomah sediment increased
manganese concentrations.
The field studies were set up on a Fox
silt loam in 1980. Lilly Lake sediment
additions equivalent to 0, 22.4, 44.8 and
39.6 mT/ha of dry sediments were made.
There were four replicates in a latin
square design. Sudan grass was planted
and was harvested twice. Even though
the site was an old alfalfa field, significant
yield and nitrogen uptake responses over
the control were obtained in both har-
vests. There were no significant differ-
ences between different rates of sediment
application.
The field experiment of 1981 and 1982
was on a Hebron silt loam at a different
site because sediment from an adjoining
lagoon was spread over the original site.
The same experimental design was used
at the new site which was previously in'
pasture, and corn was grown both years.
No significant differences in yield, or in
nitrogen or phosphorus concentrations or
uptakes occurred in 1981. Grain yields
could not be obtained in 1982 because of
cow damage, but concentrations of the
following elements were determined in
ear leaves at silking and in the corn grain:
nitrogen, phosphorus, potassium, calci-
um, magnesium, sulfur, zinc, iron, copper,
aluminum, manganese, cobalt, arsenic,
cadmium and lead. The only significant
effect associated with sediment addition
was an increase in the nitrogen concen-
tration in the grain at the highest sedi-
ment rate.
Both the greenhouse and field results
suggest that, of the factors measured, the
only beneficial effect to crops from the
application of Lilly Lake sediment would
be an increase in nitrogen availability
which would probably continue to be
effective for a number of years. No
harmful effects of sediment application
were apparent.
-------
Russell C. Dunst and James G. Vennie are with the Wisconsin Department of
Natural Resources, Madison, WI53707;R. B. Corey and A. E. Petersonare with
the University of Wisconsin, Madison, Wl 53701.
Spencer A. Peterson is the EPA Project Officer (see below).
The complete report, entitled "Effect of Dredging Lilly Lake, Wisconsin," {Order
No. PB 85-117 042; Cost: $ 13.00, 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
US GOVERNMENT PRINTING OFFICE, 559-016/7861
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES P>
EPA
PERMIT No G-35
Official Business
Penalty for Private Use $300
------- |