Vertical variation of phosphorus forms in surface sediments from Wuli Bay, Taihu Lake, China

In order to investigate the cycling of phosphorus in the Taihu Lake, a sequential extraction technique was used to separate different phosphorus forms in surficial sediments from the Wuli Bay of the Taihu Lake. The concentrations of total P are high in the sediments, with an average of 2.80 mg · g-1, and a variation range between 4.02 and 2.05 mg · g-1. Total P is composed mainly of inorganic P (70% -90%), a large portion (75% - 85%) of which lies in the CDB-extractable iron oxide phase. The low Fe/P atomic ratios (2.0 - 5.3) indicate that the Fe compounds extracted with CDB have a lower proportion of relatively crystalline phases in all samples, and that the absorption between iron and phosphorus has probably reached certain equilibrium. Organic C/N atomic ratios (8.8 - 10.6) for most of the samples are lower, which suggests a lacustrine authigenic source of organic matter in the sediments. Moreover, organic C/P atomic ratios (135 - 320) are usually higher than the Redfield ratio (106: 1), showing that the organic phosphorus had been preferentially released released via organic matter degradation during the early diagenesis process.