Indirect Effects of Copper Sulfate Addition on Zooplankton Communities in Ohio Upground Reservoirs

Municipal water managers use copper sulfate (CuSO4) to control algae, predominantly phytoplankton, in water supply reservoirs. In multiple-purpose upground reservoirs in northwestern Ohio, CuSO4 application regimens vary from no application to over 600 µg Cu/L/year. Whereas CuSO4 effectively suppresses phytoplankton growth, it also has documented toxicities to zooplankton, which serve as forage for stocked sport fish. Consequently, CuSO4 application benefits one upground reservoir use (water supply) while potentially negatively affecting another (sport fishing). This research sought to directly compare copper concentrations ([Cu]) in dissolved and particulate fractions with corresponding zooplankton community composition and abundance both before and after CuSO4 application in Ohio upground reservoirs. Copper concentrations and zooplankton community characters were measured at four upground reservoirs (n = 2 treated with CuSO4 and n = 2 untreated) over multiple weeks during summer 2010. Total [Cu] in treated reservoirs increased by as much as 428% from pre- (mean = 16.5 µg/L) to post-application (mean = 70.7 µg/L); concomitantly, zooplankton biomass and density decreased by as much as 93%. Post-application zooplankton communities shifted to dominance by small copepod nauplii from a mixed community that included larger cladocerans. Copepod nauplii represent a less-suitable food source for stocked juvenile yellow perch Perca flavescens. Thus, short-term negative effects to the zooplankton community may result from CuSO4 applications, indirectly affecting stocked sport fish success.