Development of a benthic invertebrate objective for mesotrophic Great Lakes waters

A biological indicator of mesotrophic conditions should (1) provide an appropriate and interpretable objective; (2) be achievable if corrective measures are taken (i.e., it should be within the expected environmental range of the system); and (3) allow measurement of progress toward the objective. Historical data from the Great Lakes suggest that population density of the burrowing mayfly, Hexagenia limbata, could provide an appropriate objective, and that the tubificid oligochaete community can be used to evaluate progress toward that objective. Finally, data from other systems show thatHexagenia can return to locations where it was formerly abundant, and therefore is an attainable objective for formerly mesotrophic ecosystems.