PHOSPHORUS MOBILITY IN INTERSTITIAL WATERS OF SEDIMENTS IN LAKE KINNERET, ISRAEL

Monthly samples of sediment cores from maximum depth (approximately 42 m) in Lake Kinneret were taken from May 1988 until January 1989. The chemical composition of the interstitial and overlying water was investigated with respect to phosphate, Fe2+, Fe3+, Ca2+, alkalinity and electric conductivity. pH, pH2S and pe (electron-activity) were measured by microelectrodes inserted directly into the sediment core immediately after sampling. Ion activity products of vivianite, siderite, ironsulfides, Ca-P complexes and Ca-P solid phases were calculated; in addition, Ca/P ratios for the overlying and pore water were obtained by using the potential diagram technique. Despite the fact that anoxic conditions prevail for most of the year, no control of phosphate solubility by a Fe-P relationship could be found. Determination of IAPs, together with calculated molar Ca/P-ratios, suggests that hydroxyapatite as well as surface complexes like dicalcium-phosphate are the solubility-controlling species in pore water. For the overlying water a Ca3(HCO3)3PO4 surface complex is assumed to fix the phosphorus, accompanied by a subsequent transformation of the bound P into apatite.