624 LIMNOLOGY
treatment, there is often a period of time when lake waters
cannot be used for swimming, fishing, or crop irrigation.
Copper sulfate and chelated copper compounds are gen-
erally used to control algal blooms. Copper is an essential
element, required in small amounts, for plant growth. High
concentrations of this metal can lead to inhibition of photosyn-
thesis and to plant death. The effectiveness of copper chelates
is enhanced by warm temperatures and sunlight, conditions
that stimulate copper uptake by sensitive plants. The effect of
copper treatment can be observed within 10 days, with full
effects manifested in four to six weeks. Several treatments may
be needed each season. An advantage of using copper com-
pounds for aquatic plant control is that there are no restrictions
in lake uses following treatment; copper compounds can even
be used in lakes that are drinking water supplies. However,
copper compounds must be used with extreme care because
copper is persistent in the environment. Yearly application
of copper to lakes can result in elevated copper concentrations
in sediments, where the copper can then be taken up by ben-
thic infauna and fish. The toxicity of copper to fish is higher in
soft than in hard water.Biological Methods The development and use of biologi-
cal methods of aquatic plant control is in its infancy. Interest
in biological control agents was stimulated by a desire to
find more “natural” means of long-term control of nuisance
aquatic plants as well as reduce the use of expensive equip-
ment or chemicals. The biological control method that is
used in many states is stocking the lake with sterile grass
carp (white amur), a vegetarian fish native to large rivers
of China and Russia. The fish are sterile because they are
triploid, i.e., they have an extra set of chromosomes. Grass
carp were first introduced into the United States in 1963 by
the state of Arkansas and are now legal in most states. The
objective of grass carp use is to end up with a lake that has
20 to 40 percent plant cover, not a lake that is totally devoid
of plants.
Grass carp are rapidly growing fish that live for at least
10 years. In general, they reach at least 10 pounds in weight
and have been known to reach 40 pounds in the southern
U.S. They feed from the top of the plant down and therefore
do not stir up lake sediments. They are most appropriately
used for lakewide, low-intensity control of submersed plants
such as water weed, water celery, and certain pondweeds.
Milfoil is less preferred and water lilies and watershield are
not eaten at all. Grass carp are dormant during the winter and
start intensive feeding when water temperatures reach 68F.
The appropriate stocking rate is usually determined by the
fisheries department of the particular state in which the lake
is located and will depend on the amount and type of plants
in the lake as well as spring and summer water temperatures.
Survival rates of the fish will vary depending on fish disease
and presence of predators such as ospreys and otters.
Grass carp are inexpensive compared to some other
aquatic plant control methods and offer long-term control.
However, there are numerous disadvantages to their use.
There is no control over how much the grass carp will eat.
Overstocking of grass carp could result in eradication ofbeneficial as well as nuisance plants or eradication of all
plants in the lake. Removing excess fish is difficult and
expensive. If native plants are not growing in a lake, other
plants such as invasive, non-native plants or algae will move
in to fill the void. Furthermore, the grass carp will add nutri-
ents to the lake through their wastes and through the decay of
their bodies when they die; this will contribute to the growth
of other plants in the lake.
In addition to no control over how much the grass carp will
eat, there is no control over where they will graze. The fish
may avoid areas of the lake experiencing heavy recreational
use (e.g., swimming docks), resulting in less plant removal
than desired for those areas. Substantial removal of vegeta-
tion by grass carp may not become apparent until three to five
years after introduction. Furthermore, all inlets and outlets to
the lake must be screened to prevent grass carp from migrat-
ing out of the lake into streams, rivers, and other lakes with
potential impacts on downstream, non-target plants.REFERENCESCarlson, R.E. 1977. “A Trophic State Index for Lakes.” Limnology and
Oceanography 22 , 361–368.
Cobbossee Watershed District. 1988. Cochnewagon Lake Restoration Proj-
ect: Hypolimnetic Alum Treatment. Preliminary Report No. 1: 1985–- Cobbossee Watershed District, Winthrop, ME.
Cooke, G.D. and R.E. Charlson. 1986. “Water Quality Management in a Drink-
ing Water Reservoir.” Lake and Reservoir Management 2 , 363–371.
Cooke, G.D., E.B. Welch, S.A. Peterson, and P.R. Newroth. 1986. Lake and
Reservoir Restoration. Butterworths, Boston, MA.
Cooke, G.D., E.B. Welch, A.B. Martin, D.G. Fulmer, J.B. Hyde, and G.D.
Schrieve. 1993a. “Effectiveness of Al, Ca, and Fe Salts for Control of
Internal Phosphorus Loading in Shallow and Deep Lakes.” Hydrobio-
logia 253 , 323–335.
Cooke, G.D., E.B., Welch, S.A. Peterson, and P.R. Newroth. 1993b. Res-
toration and Management of Lakes and Reservoirs. Lewis Publishers,
Boca Raton, FL.
Cooke, W. 1996. Crary Weed Roller Pilot Project Report. King County Sur-
face Water Management Division, Seattle, WA.
Dominie, D.R. 1978. Cobbossee Watershed District Lake Restoration
Report. Progress Report No. 4. Cobbossee Watershed District, East
Winthrop, ME.
Garrison, P.J. and D.R. Knauer. 1984. “Long-Term Evaluation of Three
Alum-Treated Lakes.” Lake and Reservoir Management, pp. 513–517.
EPA-440/5-84-001, U.S. Environmental Protection Agency, Washing-
ton, D.C.
Gibbons, M.V., H.L. Gibbons, and M.D. Sytsma. 1994. A Citizens ’ Manual
for Developing Integrated Aquatic Vegetation Management Plane. First
Edition. Washington State Department of Ecology, Olympia, WA.
Gulland, J.A. 1970. “Food Chain Studies and Some Problems in World
Fisheries.” Pp. 296–315 in J.H. Steele, ed., Marine Food Chains. Uni-
versity of California Press, Los Angeles.
KCM, Inc. 1994. Cottage Lake Nutrient Budget. Prepared for King County
Surface Water Management Division, Seattle, WA.
Kenefick, S.L., S.E. Hurdey, E.E. Prepas, N. Motkosky, and H.G. Peterson. - “Odorous Substances and Cyanobacterial Toxins in Prairie Drink-
ing Water Sources.” Water Science and Technology 25 (2), 147–154.
Kennedy, R.H. and G.D. Cooke, 1982. “Control of Lake Phosphorus with
Aluminum Sulfate. Dose Determination and Application Techniques.”
Water Research Bulletin 18 , 389–395.
Kozlovsky, D.G. 1968. “A Critical Evaluation of the Trophic Level Con-
cept. I. Ecological Efficiencies.” Ecology 49 , 48–60.
Lorenzen, M.W. and A. W. Fast. 1977. A Guide to Aeration/Circulation
Techniques for Lake Management. EPA-600/3-77-004, U.S. Environ-
mental Protection Agency, Washington, D.C.
C012_002_r03.indd 624C012_002_r03.indd 624 11/18/2005 10:36:49 AM11/18/2005 10:36:49 AM