Indirect effects of copper sulfate addition on zooplankton communities in Ohio upground reservoirs

Abstract

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 fsh. Consequently, CuSO4 application promotes one upground reservoir benefcial use (water supply) while potentially negatively a?ecting another use (sport fshing). We compared copper concentrations ([Cu]) in dissolved and particulate fractions with corresponding zooplankton community composition and abundance both before and after CuSO4application 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 percent 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 percent post-treatment. Post-application zooplankton communities shifted from a mixed community that included larger cladocerans to dominance by small copepod nauplii, which represent a less-suitable food source for stocked juvenile yellow perch Perca?avescens. Thus, short-term negative effects to the zooplankton community may result from CuSO4 applications, indirectly a?ecting stocked sportfsh success.