FACTORS REGULATING THE FLUX OF PHOSPHATE AT THE SEDIMENT-WATER INTERFACE OF A SUBTROPICAL CALCAREOUS LAKE - A SIMULATION STUDY WITH INTACT SEDIMENT CORES

Different factors which interactively control the flux of soluble reac tive phosphorus (SRP) at the sediment-water interface (SWI) of Lake Ki nneret were studied seasonally. The influence of pH, Eh and microbial activity on SRP nux at the SWI was investigated by manipulating the co nditions in the overlying water of intact sediment cores. The calculat ed diffusive SRP flux out of the sediment was lower in cores sampled d uring winter and spring than during the period of amixis. Potential SR P release, as measured in the absence of microbial activity, was stron gly enhanced upon the transition from oxic to anoxic conditions indica ting P release from iron(III)-bound phosphorus. In spring and summer c ores, an enhanced SRP flux from sediments at pH 7 in comparison to pH 8 indicated P release from carbonate-bound P which sedimented previous ly as result of high pH values during the algal spring bloom. Microbia l uptake at the SWI was the most important sink for SRP and no net-flu x occured under oxic conditions. The higher net-flux of P under anoxic conditions was linked to carbon limitation of the bacteria at the SWI .