Habitat Availability and Benthic Invertebrate Population Changes Following Alum Treatment and Hypolimnetic Oxygenation in Newman Lake, Washington

Abstract

Abstract Changes in benthic macroinvertebrate population density and diversity were studied in a mesotrophic lake with seasonal hypoxia/anoxia prior to and following aluminum sulfate (alum) treatment and hypolimnetic oxygenation. Historically, low oxygen concentrations created a benthic zone with reduced fish predation pressures which allowed chaoborids to flourish. Population densities of chironomids and oligochaetes were suppressed by prolonged periods of summer anoxia Benthic macroinvertebrate community diversity values were indicative of poor water quality and/or habitat quality. Following alum treatment and prior to hypolimnetic oxygenation, chaoborid densities doubled. This was due, in part, to changes in trophic structure which provided an abundant food source for early instar chaoborids. In addition, Newman Lake was stocked with fewer trout in 1990 and 1991 resulting in reduced predation on the invertebrate community. Alum treatment had no effect on chironomid or oligochaete populations. Hypolimne...