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(70-37) Experimental study of bioturbation effects on cadmium transfers from a natural contaminated sediment. Ciutat, Aurélie*,1, Laurens, Ludovic1, Anschutz, Pierre2, Schaefer, Joerg2, Blanc, Gérard2, Boudou, Alain1, 1 LEESA, Université Bordeaux 1, Arcachon, France2 DGO, Université Bordeaux 1, Talence, France ABSTRACT- Bioturbation effects on cadmium transfers from sediment were analysed using freshwater indoor microcosms including a two-compartment biotope – natural sediment (S) collected from a contaminated site on the Lot river, SW France ([Cd] = 85.5 ± 4.7 Key words: bioturbation, Oligochaetes, cadmium, sediment |
g/g, dw) and dechlorinated tap water (W) – and two biological species: oligochaetes (tubificidae worms) as the bioturbation source via their burrowing activity in the sediment superficial layers; benthic bivalves (Corbicula fluminea), as bioindicators of Cd transfers and metal bioavailability at the interface "S/W". Within a complete experimental design, four conditions were set up, in order to investigate the direct and indirect roles of the two biological models: (system A) S + W, without organisms added (Cd diffusion processes); (system B) S + W + 4 C.fluminea; (system C) S + W + oligochaetes (780 worms/system - 1.5 ± 0.03 g, fw); (system D) S + W + 4 clams + 780 worms. During a 30 days' exposure period, turbidity, Cd concentrations in the water column (unfiltered and filtered samples), pH and dissolved oxygen were periodically measured. At time 10, 20 and 30 days, Cd bioaccumulation was quantified in bivalves and worms; sediment cores were sampled in order to measure interstitial and particulate Cd, Fe and Mn concentrations in 6 sediment layers (0-1 cm; 1-2 cm; 2-3 cm; 3-5 cm; 5-7 cm and 7-9 cm). The geochemistry of water column and sediment compartments was analysed from vertical profiles of 02, Mn and Fe using polarographic microelectrodes, jointly to mineral salts (nitrate and ammonium) determination in pore water samples. Results from these different biogeochemical approaches will be presented and discussed, notably Cd fluxes and metal bioavailability, in relation to the four experimental conditions studied.