Phosphate removal in acidified and limed lake water

Biotic and abiotic removal of phosphate from lake water from the acidified Lake Gårdsjön as well as immediate changes in these processes upon liming were tested in laboratory experiments. Phosphate was added and analyses of particulate material from both sterilized and nonsterilized series permitted determinations of biotic uptake as the difference between the series. In the original lake water (pH 4.7) biotic uptake largely dominated phosphate removal and abiotic precipitation was of minor importance.In the limed series at pH 7.2 the results had changed and abiotic precipitation dominated the phosphate removal and biotic uptake was strongly reduced. Of the analysed metals, Ca, Mn, Fe and Al, only Fe and Al occurred in the particulate material. The coprecipitation of phosphate and iron was probably due to adsorption on iron hydroxide at both pH values. The nature of phosphorus-aluminium precipitates is largely unknown but different possible complexes are discussed as well as the relative importance of iron and aluminium precipitates.Application of the results in relation to the ongoing lake liming and phosphorus fertilization are discussed.