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The aim of the investigations was to identify the main process controlling the rather low phosphate concentration in the water of Lake Balaton. Three processes were taken into consideration: a) phosphate uptake by algae, b) coprecipitation with biogenic lime, and c ) adsorption on suspended sediment particles. A plexiglass box open a t the bottom was placed in the shallow water with its sides extending into the sediment. The water in the box was stirred. When phosphate alone was added to the water in the box, its concentration decreased very rapidly. On the other hand, if NaOCl was also added in order to kill algae and bacteria, the phosphate concentration remained constant. This proves the priority of life processes in phosphate removal. In the next experiment phosphate and EDTA-Na, were added simultaneously to the water in the box. The complexing agent prevented biogenic lime formation but did not influence the rapid phosphorus removal. This fact indicates that the main process involved in phosphate control is direct uptake by algae. The same conclusion was obtained in laboratory experiments where labelled phosphate was added to the bottles containing Lake Balaton water. It was demonstrated by the photo-oxidation technique that the phosphate removed from the water was incorporated into the organic particulate matter.

llgiil iis~:ty~ were performed on water samples taken from different sites in Lake Baluton. Selcwtstrtcni capricornuturn was used in the test to determine the primarily limiting plant nutrient. The results of siipplementary nutrient additions to the bottle tests were evaluated by cell counts. Thr tests have indicated phosphorus as growth rate limiting, and in two cases a8 biomass limiting plant nutrient, but periodic occ'urrences of nitrogen limitittion cnnnot be excluded. sis of organically bound phosphorus, making it readily available (HEALBT, 1973 ; KL~HI,, 1974; OVERBECK, 1962)..Acrordingly, the question arises of whother phosphorus litnitat ion in thc water of Lzke lialaton can be verified by an algal assay. The studies with the green alga 5618 S c e t~s~l e s m u s obtusiusculus CHOD. (FELFBLDY, 1959(FELFBLDY, , 1962 failed to prodnce the resiilta anticipated froin the chemistry of the lake water, i.c. the test algae indicatcd that 59 Int. l'.e!uc ges 1C)drobiol. VoI. 06, So. 0

The aim of the investigation was to determine the phosphorus containing minerals present in Lake Balaton sediment. Chemical, electron microscope and X-ray diffraction analysis succeeded in identifying hydroxylapatite. No proof was found for the presence of other phosphorus minerals.