FRACTIONAL COMPOSITION, ADSORPTION AND RELEASE OF SEDIMENT PHOSPHORUSIN 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 th e Kis-Balaton reservoir under different pH and redox conditions. Relea se experiments were combined with pre- and postfractionations of sedim ent 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-R P) contents of the sediments. The NaOH-RP fraction was highly saturate d with phosphate near the inflow of the Zala River, while in the downs tream areas it was not. Sediments with high humic contents adsorbed ph osphate efficiently, and released only small amounts of phosphate unde r 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 producti on. It was estimated that the internal P loading may be similar to ext ernal loading under these conditions.