COPRECIPITATION OF PHOSPHATE WITH CALCIUM-CARBONATE IN LAKE VELUWE

Coprecipitation of dissolved phosphate with calcite (CaCO3) has been o bserved in many lakes. In 1979/1980 white flocks occurred in Lake Velu we after the inlet of water with a high calcium content. A high oversa turation with respect to calcite occurred at that time, presently (198 5-1987) the oversaturation is much smaller. The intense photosynthesis decreased and maximum summer pH values came down from 10.0 to about 8 .5. In laboratory experiments the coprecipitation of phosphate with ca lcite occurred only when the crystalization was initiated by adding se eds of calcite. Literature and this research show that the incorporati on efficiency of phosphate decreases at lower phosphate concentrations . Literature data for the incorporation of P in CaCO3 in mg P [g Ca](- 1) are fitted as 10.9 x [P](0.5) with r(2)=0.50. The coprecipitation a t the actual low phosphate concentration in Lake Veluwe (1993) is not as efficient as in the period 1985-1987.