Effects of Multiphase Restoration, Particularly Aluminum Sulfate Application, on the Zooplankton Community of a Eutrophic Lake in Eastern Washington

ABSTRACT

Zooplankton populations of Liberty Lake, Washington were investigated over a span of four years to determine the short-term effects of a series of multiphase lake restoration measures on lake zooplankton. The effects of the treatments, particularly of suction dredging of lake bottom sediments and of a two stage whole-lake aluminum sulfate application, were assessed by analyzing population density and biomass fluctuations of Rotifera, Cladocera, and Eucopepoda for several years before and after the treatments were completed. Suction dredging had no apparent effect upon the zooplankton in Liberty Lake. The gross effects of aluminum sulfate applications on the zooplankton population were also minimal. A sharp decline in numbers was observed in all major groups immediately following each alum application, but recovery was evident in the maintenance of typical seasonal growth patterns. The Eucopepoda exhibited rapid recovery following both alum treatments, responding most favorably to the short term oligotrophic-like conditions apparently created by the treatments. Similarities in zooplankton response to the alum application and to the May 1980 Mt. St. Helens ashfall are briefly discussed.