Relation between phosphorus forms in the sediments and lake eutrophication.

The forms of phosphorus in the surface sediments were extracted and determined sequentially with ethylene dinitrilo tetracetic acid (EDTA) technique in Lake Taihu, Lake Chaohu and Lake Longganhu in the middle and lower reaches of the Yangtze River. In the surface sediments of these 3 lakes, the contents of calcium-bound phosphate were similar relatively with occupation of about 30% of total phosphorus. The percentage contents of iron bound phosphate in Lake Taihu and Lake Chaohu were higher than that of Lake Longganhu, while the related content of organic phosphorus in Longganhu was higher, reaching 40%~50%. The forms of organic phosphorus in the sediments of these three lakes differed markedly. The organic phosphorus existed mainly in the form of acid extractable phosphorus in Lake Taihu sediments and the acid extractable organic phosphorus occupied 50% of total organic phosphorus in Lake Chaohu sediments; while the major organic phosphorus combined with humic acid in Lake Longganhu. The release of acid extractable organic phosphate in sediment might be an important process leading lake eutrophication except iron-bound phosphorus.