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Restoration of Aquatic Ecosystems: Science, Technology, and Public Policy
bioaccumulate contaminants because of differences in diet and growth rate. Therefore, contamination may determine which fish are exploited and the composition of the remaining stock. Fisheries management decisions also can affect the amounts of contaminants in fish at the top of the food chain by manipulating the composition of the fish stock (see Lake Michigan case study, Appendix A). Reproduction of piscivorous birds and mammals was severely affected by dichlorodiphenyltrichloroethane (DDT) in some ecosystems (NRC, 1986). Organochlorine contaminants remain a threat to populations of waterfowl raptorial birds, minks, and otters, and wildlife populations depend on the extent to which contaminants can be remediated.
INTEGRATED AQUATIC SYSTEMS
Lake restorations must be viewed in a watershed context. Abatement of eutrophication, siltation, and contaminant problems is far simpler, and generally more effective, when inputs can be controlled or reduced. This chapter has described many in-lake techniques that can ameliorate symptoms of eutrophication. Reduction of inputs enhances the long-term effectiveness of in-lake approaches.
Lake restoration has strong interactions with restoration of other watershed components. Restoration of influent streams affects the input of sediment, solutes (including nutrients and contaminants), and water to the lake. The surrounding wetlands affect water and solute fluxes and habitats for fish spawning. Conversely, lake restoration affects wetlands by influencing macrophyte distribution, water levels, and wave and ice impacts on littoral areas. Lake restorations and stream restorations interact through the life cycles of migratory fish.
From a technical standpoint, the watershed is the most logical scale at which to undertake restoration. However, institutional constraints, and occasional ecological surprises, can make watershed restoration more difficult than it appears. Institutional complexities are best illustrated by the Lake Michigan case study (Appendix A), in which the major participants include international commissions, two U.S. federal agencies, and water quality managers and fisheries managers from five states. The Lake Apopka case study (Appendix A) illustrates unexpected ecological consequences of watershed change. Draining, diking, and canal building left the lake vulnerable to the effects of a 1947 hurricane that unprooted and drastically reduced aquatic vegetation. Subsequent algal blooms left the water so turbid that macrophytes could not be reestablished. Fishery management contributed to water quality problems via deliberate, massive kills of