To uncover the biotic influence of the internal phosphorus release in the sediment of Lake Xuanwu, colony-counting method of flat-panel culture was used to analysis the amount and categories of phosphorus-degrading microorganism. The result showed that there were phosphorus-degrading microorganisms in the sediments of the Lake Xuanwu and most them were inorganic phosphorus-degrading microorganisms, the number was 5.25 × 104 cfu each gram sediment, while the organic phosphorus-degrading microorganism was few. The internal phosphorus release contrast experiments were done with the sediment with microorganism and without microorganism. The result showed that the microorganism absorbed more phosphorus but degraded few due to the aerobic interface of the sediment, so the microorganisms in the sediment inhibited the internal phosphorus release from the sediment. In Alkaline water condition, the internal phosphorus release more than in the neutral water condition, which infer that the chemical release process was that insoluble Ca3(PO4)2, Fe3(PO4)2 transformed into insoluble Ca(OH)2 and Fe(OH) 3 and resulted the PO43- dissolved into the overlying water.
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