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

Municipal water managers use copper sulfate (CuSO 4 ) to control algae, predominantly phytoplankton, in water supply reservoirs. In multiple-purpose upground reservoirs in northwestern Ohio, CuSO 4 application regimens vary from no application to over 600 µg Cu/L/year. Whereas CuSO 4  effectively suppresses phytoplankton growth, it also has documented toxicities to zooplankton, which serve as forage for stocked sport fish. Consequently, CuSO 4 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 CuSO 4 application in Ohio upground reservoirs. Copper concentrations and zooplankton community characters were measured at four upground reservoirs (n = 2 treated with CuSO 4 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 CuSO 4 applications, indirectly affecting stocked sport fish success.