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AN EVALUATION OF THE FIELD-BASED AQUATIC BENCHMARK FOR SPECIFIC CONDUCTANCE FOR USE IN NORTHEASTERN MINNESOTA

We reviewed the application of the field-based aquatic benchmark for specific conductance, as originally developed for the central Appalachian Mountains, for use in northeastern Minnesota. We identified interesting issues that should be considered prior to more wide-scale application of the method. Comparing extirpation coefficients for genera common to both ecoregions showed substantially different limits for the same genera. This is an issue with the underlying premise of the conductivity benchmark that physiological limits to ion chemistry affect the distribution of benthic invertebrate taxa. Additionally, stressor-response profiles revealed different responses for common genera and highlighted the influence of low capture probability on the hazard concentration. The effects of low capture probability placed in the context of relative abundance for any one genera is not factored into the presence/absence approach used in the benchmark. This issue should be further investigated, because extirpation of a genus is largely pinned on the presence/absence of a single individual and its likelihood of being collected in a stream. We conclude that the specific conductance benchmark approach would still benefit from further investigation of these issues prior to application to other ecoregions.

Kimberly Gerlock (Primary Presenter/Author), GEI Consultants, Inc., kschott@geiconsultants.com;