SEDIMENT RESUSPENSION IN A MONOMICTIC EUTROPHIC RESERVOIR

During the mixing period sediment traps were placed at 9 different levels of the water column in La Concepcion reservoir (Malaga-Spain). During the exposure time a benthic nepheloid layer with high suspended matter was detected. Seston vertical flux profile shows an exponential increase with depth, suggesting that a large fraction of the collected particulate matter comes from bottom resuspension, due to an intermittent complete mixing process. It was estimated that resuspension 1 m above the bottom increased the fluxes of seston, particulate organic carbon, particulate nitrogen and particulate phosphorus by factors of 4.1, 1.5, 2.1 and 4.8 respectively. The fitting to an exponential function allowed us to obtain a resuspension coefficient and the scale vertical length for this event, 36 m, which is higher than those estimated for other aquatic environments. From the above results the calculated vertical eddy diffusivity, suggesting a high turbulence in the water reservoir during the turnover period. Resuspension is considered important in order to estimate net downward fluxes and to understand different processes such as redistribution of sediment and fertilization of the water column.