Recent and present sedimentary fluxes of heavy metals and radionuclides in oligotrophic Lake Annecy, France

Abstract

The present study focuses on two aspects of heavy metals and radionuclide fluxes to lake Annecy: a long term. secular evolution by analysing dated sediment cores, and a short term, seasonal evolution through the analysis of settling particles collected by sediment traps. Compared to background values prior to 1900, sediment cores reveal a two-fold (Cd, Cu, Zn) to a four-fold (Pb) increase in heavy metal concentration after the 40s, and a smaller decrease after the 70s except for Cu, which does not decrease. Sediment traps moored from April 1998 to November 2000 record strong variations of particles (range: 0.5 - 6.1 g m(-2) d(-1)), organic matter (range 0.03 - 0.27 g m(-2) d(-1)) and carbonate fluxes (range: 0.2 - 4.9 g m(-2) d(-1)). The maximum fluxes are observed at the end of spring and summer, related to increased phytoplankton production. Mean annual heavy metal fluxes (0.014 mug.cm(-2).y(-1) for Cd, 1 mug.cm(-2). y(-1) for Ph and Cu and 2.8 mug.cm(-2).y(-1) for Zn) are lower than those recorded in the surface layers of the sediment cores. No relation has been observed between fluxes of heavy metal and of particles. Comparison of heavy metal fluxes in Lake Annecy with two other peri-alpine lakes show that this lake receive more Cu and Ph of anthropogenic origin, in spite of the sewage collector built around the lake.