Seasonal dynamics of phosphorus forms in water body and sediments of Nanhu Lake, Wuhan.

Water samples and sediment cores were taken at 5 sites of Nanhu Lake, Wuhan to investigate the seasonal dynamics of phosphorus in water body, sediments and their interstitial water, as well as the phosphorus forms in sediments. The results showed that the average concentrations of total phosphorus (TP) and orthophosphate (PO4(3-) -P) in water body were 0.240 and 0.033 mg·L^-1, respectively, with the highest concentrations of TP and PO₄^3--P in November and the lowest concentration of TP and of PO₄^3--P in February and August, respectively. The concentration of TP in sediments was averagely 1.005 mg·g^-1, being increased from April to November and becoming stable from November to February, and decreased with sedimentation depth. The concentration of PO4(3-) -P in interstitial water was 0.209 mg·L^-1 on average, being the highest in November and the lowest in February, with the same vertical distribution pattern like TP in sediments. The dominant form of phosphorus in sediments was inorganic phosphorus (IP), occupying 61.4%-77.1% of total extracted phosphorus. The concentration of bio-available phosphorus (BA-P) in sediments was very high, but decreased significantly with sedimentation depth. According to the significant correlations between phosphorus forms in sediments and PO4(3-) -P in interstitial water, the BA-P and auto-calcium bound phosphorus (ACa-P) in sediments should be the main P sources released from sediments to water body. [ABSTRACT FROM AUTHOR]