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 reactive phosphorus (SRP) at the sediment-water interface (SWI) of Lake Kinneret were studied seasonally. The influence of pH, Eh and microbial activity on SRP nux at the SWI was investigated by manipulating the conditions in the overlying water of intact sediment cores. The calculated diffusive SRP flux out of the sediment was lower in cores sampled during winter and spring than during the period of amixis. Potential SRP release, as measured in the absence of microbial activity, was strongly enhanced upon the transition from oxic to anoxic conditions indicating P release from iron(III)-bound phosphorus. In spring and summer cores, an enhanced SRP flux from sediments at pH 7 in comparison to pH 8 indicated P release from carbonate-bound P which sedimented previously as result of high pH values during the algal spring bloom. Microbial uptake at the SWI was the most important sink for SRP and no net-flux occured under oxic conditions. The higher net-flux of P under anoxic conditions was linked to carbon limitation of the bacteria at the SWI.