This study is aimed at precising the originns and the spatio-temporal variations of particulate matter fluxes in Lake Geneva. Sampling, using sediment traps set at depths of 60, 200 and 300 m, has been carried out for two years (1986, 1987) at SHL2, the central lake station.

The particles have several origins: autochthonous production, river inputs (Rhône and Dranse), resuspension of bottom sediments. lt is possible, thanks to major elements, to distinguish the different sources. The seasonal trend of the fluxes shows a distinct two-season pattern in which the fluxes are maximum in summer, minimum in winter. The increase of the fluxes with depth enhances the importance of lateral inputs and the role of the central basin in the focusing of sediments. Autochthonous material is dominant at 60 m in summer whereas allochthonous material prevails at greater deRths. When the dissolved oxygen content at the bottom of the lake decreases to about 4 mg.l^-1, PO₄ ^3- diffuses into the water column. The NAIP (Non Apatitic lnorganic Phosphorus) plus OP (Organic Phosphorus} flux at the sediment-water interface varies from 1.65 to 3.57 mg.m^-2.d^-1 depending on the season.