Restoring Biological Integrity in Wilderness Lakes of New York

Amy L. Harig Department of Fishery and Wildlife Biology, Colorado State University, Fort Collins

Restoring ecosystems to some previous "natural" state is often impeded by the lack of information on what goal is to be attained (Karr 1991). However, a target for restoration of lake ecosystems can be established by developing indictors for the assessment of biological integrity. I identified properties of species composition, taxonomic diversity, and functional organization of lake communities that indicate impaired biological integrity, then tested these hypothesized indicators in 12 small, isolated Adirondack lakes impacted by nonnative fish species from collections of fish, benthic invertebrates, zooplankton, and phytoplankton over a 3-yr period. Six indicators were sensitive to disturbance by nonnative fish introductions including the dominance of native fish, relative abundance of Daphnia, dominant phytoplankton taxa, number of zooplankton species, dominance of large-bodied zooplankton, and zooplankton biomass. I then utilized these integrity indicators as a recovery target to test the feasibility of restoring biological integrity through fish community manipulation in three additional lakes impacted by nonnative fish introductions. The restoration of indigenous fish fauna had a top-down, cascading effect on the zooplankton and phytoplankton, shifting their communities from being similar to lakes with poor biological integrity to characteristics more consistent with high integrity lakes. Specifically, the restored lakes were characterized by zooplankton communities with relatively greater species richness, biomass, and larger species, particularly Daphnia and other cladocerans, in addition to a native fish community. Overall, our research suggests that ecosystem-scale indicators of biological integrity in lakes are powerful tools for identifying disturbance and providing target conditions for ecosystem recovery. Furthermore, these indicators could be used to identify disturbed lakes with the greatest chance of recovering attributes of high biological integrity through fish-community manipulation.

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