DEFINING AND RESTORING BIOLOGICAL INTEGRITYIN WILDERNESS LAKES

Abstract

Restoring ecosystems to some previous “natural” state is often impeded by the lack of information on what goal is to be attained. However, a target for restoration of lake ecosystems can be established by developing a multimetric tool for the assessment of biological integrity. Our study identified a set of recurring responses to disturbance that indicate impaired biological integrity in lakes that include properties of species composition, taxonomic diversity, and functional organization of the lake communities. We then tested these hypothesized responses 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. We also tested the feasibility of restoring biological integrity through fish-community manipulation in three additional lakes utilizing these integrity indicators as a recovery target. Six indicators of biological integrity were sensitive to disturbance in Adirondack wilderness lakes including dominance of native fish, relative abundance of Daphnia, dominant phytoplankton taxa, number of zooplankton species, dominance of large-bodied zooplankton, and zooplankton biomass. Adirondack wilderness lakes with high biological integrity were characterized by native fish communities, by zooplankton communities with relatively greater species richness, biomass, and larger species, particularly Daphnia and other cladocerans, and by phytoplankton communities with few dinoflagellates. Additionally, a shift to indigenous fish fauna in lakes impacted by nonnatives 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. Overall, our research suggests that ecosystem-scale indicators of biological integrity in lakes are powerful tools for identifying disturbance, providing target conditions for ecosystem recovery, and identifying disturbed lakes that would increase biological integrity through fish-community manipulation.