Phosphorus fractions in surface sediment and their contributions to water in a southern sub-tropical shallow lake

The forms of phosphorus in the surface sediments of a typical southern sub-tropical shallow lake-Xinghu Lake were investigated by sequential chemical extraction and determinated.The results showed that the contents of total phosphorus(TP) forms in the surfaces sediments ranged from 352.32 mg/kg to 710.33 mg/kg in Xinghu Lake with an average of 505.82 mg/kg for all sediment sample.The concentration of TP in sediment of Xinghu Lake followed the order:Bohai LakeQinglian LakeXiannv LakeZhongxin Lake.The contribution of bio-available phosphorus(BAP) to total sedimentary phosphorus ranged from 39.12% to 52.59%.The total sediment phosphorus consisted mainly of metal oxides bound phosphorus(NaOH-P),organic phosphorus(Org-P) and calcium bound phosphorus(HCl-P),and also contained small amounts of reducible phosphorus(BD-P)and loosely absorbed phosphorus(NH4Cl-P).The rank order according to the mean concentration of P-fraction in Xinghu Lake was Org-PNaOH-PHCl-PBD-PNH4Cl-P.There was a gradient of the soluble reactive phosphorus(SRP)at sediment-water interface,which indicated that the potential SRP could diffuse from sediment into the overlying water for algae's growth.