Role of organic matter in copper mobility in a polymictic lake following copper sulfate treatment (Courtille Lake, France).

Lake Courtille is a shallow eutrophic polymictic lake treated with copper sulphate for four years. Water column monitoring and laboratory experiments have shown that dissolved copper (CuD) behaviour correlates well with Dissolved Organic Carbon (DOC). Sequential extraction indicates that a significant fraction of the sediment-borne Cu is associated with the organic fraction (50% to 88% of total copper). This fraction of copper could be released into the water column depending on environmental conditions. Laboratory resuspension experiments have shown that significant short term release of Cu was not possible under circumneutral pH and the oxygenated conditions of the lake (less than 3% of the total copper sediment was released). Nevertheless over the long term, a fraction of the copper bound to the sediment could be released depending on the organic matter mineralization which could explain the presence of copper in the water column one year after the last copper addition.