[Distribution and Emission Flux Estimation of Phosphorus in the Sediment and Interstitial Water of Xiangxi River].

The distribution and vertical variation of phosphorus forms in sediments along Xiangxi River were analyzed with Hedley classification method, meanwhile the influences of physical and chemical properties of overlying and interstitial water on the release of phosphorus in sediment were discussed. The major findings showed that the pH values in the overlying and interstitial water increased from 4.72 to 8.55, and were slightly acidic in summer, while weak alkaline in other seasons. The redox potential of sediment was in the reduction state overall. The annual variation range of total phosphorus (TP) content in the overlying and interstitial water, and that in the sediment was 0.02-0.48 mg·L and 0.48-1.45 g·kg, respectively. The distribution features of TP content in the sediment were the same with those in the interstitial water along the Xiangxi River. It was interesting that the content of TP in the interstitial water in spring and summer was higher than that in autumn and winter, but that in the sediment of Xiangxi River was opposite. The content of different phosphorus (P) forms decreased successively:HCl-P (HCl extracted phosphorus)> Res-P (residual phosphorus)> NaOH-P (NaOH extracted phosphorus)> NaHCO-P (NaHCO extracted phosphorus)> HO-P (water-soluable phosphorus). The reductive environment of the interface between sediment and overlying water, and pH of water in spring (weak alkaline) and summer (slightly acidic), were conducive to phosphorus release from sediment into overlying water, increasing the eutrophication risk. TP content in the interstitial water was closely related to that in sediment. The PO-P in 4 sampling areas diffused from the interstitial water into the overlying water with diffusive fluxes in the range of 0.01-0.04 mg·(m·d). All of these findings indicated that sediments is an important source of nutrient for the overlying water.