Assessing biological integrity and determining anthropogenic stress thresholds of Great Lakes coastal wetlands

Great Lakes coastal margins, especially wetlands, are diverse, easily degraded habitats for which we lacked biological indicators of ecological integrity. Although human development has eradicated 80% of coastal wetlands, they currently comprise 2.16 x 10⁵ ha along the >16,000 km Great Lakes basin coastline. Wetlands were categorized according to hydrogeomorphology and dominant zones of emergent vegetation (wet meadow, Typha, Schoenoplectus). Surveys were conducted on suites of wetlands from all of the Lakes, subjectively ordinated according to amount or intensity of urban and/or agricultural adjacent land use. We assessed composition, abundance and/or biomass of communities of emergent macrophytes (quadrats), benthic invertebrates (hand-picked from dip net samples), fish (fyke nets), amphibians and birds (visual and aural surveys) from which community-specific metrics of biological integrity were derived. Ultimately, candidate metric scales were calibrated by plotting each metric score against scores of 5 stress gradients compiled by the Great Lakes Environmental Indicator (GLEI) project for every 2nd-order or higher Great Lakes coastal watershed. Watershed-based restoration targets for the various coastal wetland community types were proposed based on discontinuities observed in the IBI - stressor score relationship. The IBIs provide simple, quantitative measures by which to summarize and communicate condition, and track changes in key communities of coastal wetlands.