Trophic State and Eutrophication - Freshwater Ecology: Concepts and Environmental Applications - page 351

Methods for Controlling Causes and Symptoms of Eutrophication by Phytoplankton a TABLE 17.2

Method Explanation Positive aspects Negative aspects

Control of cause
Control of point sources Bans on phosphorus in detergents; tertiary Clean up at source Tertiary treatment can be expensive; generally

sewage treatment ineffective in lakes in which hypolimnion

goes anoxic

Control of nonpoint sources Control of watershed disturbance; feedlot Clean up at source; potential for Can be politically unpopular; generally

effluent; intact riparian zones long-term improvement ineffective in lakes in which hypolimnion

goes anoxic

In-lake control
Dilution and flushing Use of low-nutrient water to dilute nutrients Where practical can be an easy, Requires large supply of low-nutrient water;

and phytoplankton inexpensive solution usually only practical in smaller lakes

Destratification, mixing Keeping O 2 in the hypolimnion keeps Rapid results Energy required to mix and destratify lakes;

phosphorus in sediments; deeper mixing not practical on large lakes; can select against

increases light limitation of phytoplankton desirable cold water fish

Hypolimnetic release Release nutrient-rich water from hypolimnion Easy to implement in reservoirs with Costly to pump water, greater nutrient input to

possibility of hypolimnetic release downstream systems

Biomanipulation Manipulate food web by increasing piscivores Can lead to rapid increases in water Unpredictable results; does not work on

or decreasing planktivores to increase numbers quality with minimal costs extremely eutrophic systems; may lead to

of zooplankton that graze phytoplankton excessive macrophyte growth in shallow

systems

Alum Alum seals phosphate in hypolimnion; flocculates Rapid response May need repeated application; may be cost-

and settles phytoplankton prohibitive in large lakes

Copper treatment Copper kills phytoplankton Acts within days Repeated treatment necessary; can lead to

sediment contamination and negative effects
on nontarget species

a After Cooke et al. (1993).