The Release of Phosphorus from Sediment to Lake Water Induced by Cyanobacterial Blooms and Phosphorus Removal by Cell Harvesting

Abstract

ABSTRACTTo investigate the influence of cyanobacterial blooms on phosphorus release across the sediment-water interface and the repair mechanisms of internal phosphorus by harvesting of cyanobacteria, a series of laboratory-based experiments were conducted. Microcystis aeruginosa was cultured in phosphorus-free BG11 medium containing sediments from different eutrophic water bodies. The culture solution was removed and the same volume of phosphorus-free BG11 medium was put into the system until the M. aeruginosa had died. Cyanobacterial density, pH and different phosphorus forms in culture solution and sediments after culturing M. aeruginosa were determined. The results showed that cyanobacterial blooms stimulated phosphorus release from the sediment to the overlying water for the sediment in the eutrophic water body. Phosphorus released from the sediment was assimilated by M. aeruginosa and no increase in water-soluble phosphorus was observed. Cyanobacterial blooms caused sharp increases in different phosphorus fractions of sediment with the exception of the phosphorite-type (Ca10-P). Cyanobacterial blooms decomposed iron minerals in the sediment yet there was no clear evidence to demonstrate a positive correlation between water-soluble phosphorus in the overlying water and iron bound phosphorus (Fe-P) in the sediment. These results indicated that harvesting of cyanobacteria might be a suitable method to eradicate cyanobacterial blooms and to limit phosphorus pollution under controlled external nutrient loads.