Fate and forms of Cu in a reservoir ecosystem following copper sulfate treatment (Saint Germain les Belles, France)

Abstract

Copper sulfate (CuSO 4 ) addition to freshwater for phytoplankton control has been practiced for decades, and remains the most effective algicidal treatment for numerous managed water bodies. A reservoir in the centre of France was the site for an investigation of copper distribution in aquatic systems after a copper sulfate treatment. Results of copper monitoring showed a rapid conversion of dissolved Cu to particulate forms, with significant accumulation in the sediments (83% of total copper added). Total sediment Cu content increased from approximately 37.7 to 45.4 μg/g dry weight after the first treatment. Sequential extraction suggested that a significant portion of the sediment-borne Cu was associated with the organic fraction which may release Cu to the water column, although significant release would occur only under extreme changes in water chemistry. Based upon measured Cu concentrations, flows at the down-stream water, and known mass applied during treatment, mass balance calculations indicated that approximately 17% of the Cu was exported from the reservoir over a 70 day period following a 196 μg/L Cu 2+ (as CuSO 4 .5H 2 O) treatment. The largest amount of copper was probably adsorbed on downstream sediment or lost in running water. Copper bioaccumulation by a moss, Fontinalis antipyretica, in the down-stream water showed that it was possible to distinguish between a treated and an untreated area. The impact of copper treatment in the down-stream reservoir could be followed using mosses. The bioaccumulation data further showed that there is a distance effect which could be exploited to determine potential copper impact on receiving water bodies. Thirty days after copper sulfate addition, Fontinalis still indicated copper exposure.