FRACTIONAL COMPOSITION, ADSORPTION AND RELEASE OF SEDIMENT PHOSPHORUS IN THE KIS-BALATON RESERVOIR

First part of the Kis-Balaton reservoir was opened in 1985 in order to reduce phosphorus loading of Lake Balaton. Adsorption and release of sediment-phosphorus which significantly affect the efficiency of this eutrophication management measure, were studied at five stations in the Kis-Balaton reservoir under different pH and redox conditions. Release experiments were combined with pre- and postfractionations of sediment phosphorus. The adsorption/desorption concentration limit (L(A/D)) and cumulative phosphate release followed the same pattern, i.e. pH = 7.9 < pH = 7.9 N-2 < pH = 8.8 < pH = 8.8 N-2. Both L(A/D) and release increased with the initial ''iron- and aluminium'' phosphorus (NaOH-RP) contents of the sediments. The NaOH-RP fraction was highly saturated with phosphate near the inflow of the Zala River, while in the downstream areas it was not. Sediments with high humic contents adsorbed phosphate efficiently, and released only small amounts of phosphate under any conditions. Internal phosphorus loading of the reservoir may be enhanced by high pH in the water and anaerobic conditions both in the sediments and bottom water during the period of intense algal production. It was estimated that the internal P loading may be similar to external loading under these conditions.