Influence of Incity River Sediment Dredging to Endogenous Release

The internal Qinhuai River in Nanjing City of China was selected for the research on the influence of incity river sediment dredging to endogenous release by the experiment of simulating the endogenous releases at different depths of dredging so as to analyze the correlation between the forms and the release amount of phosphorus in the sediment and the change of the phosphorus forms before and after the sediment release. The result has shown that: dredging can more or less control the release of PO₄ ^3--P in the sediment as the release rate distinctly decreases at the dredging depths of 30 cm and 40 cm, the release rate of NH₄ ⁺-N rises after dredging, the release rate of nitrogen does not change too much at different depths of dredging, and the release of CODMn can be inhibited by dredging. Exchangeable phosphorus (Ex-P), Al- and Fe-bound phosphorus (Al-P, Fe-P) are highly correlated to the concentration of total dissolved phosphorus (TDP) in the overlying water while occluded phosphorus(Oc-P), Ca-bound phosphorus(Ca-P) and organic phosphorus(Or-P) are poorly correlated. After the sediment has released, the content of Ex-P, Al-P, Fe-P and Or-P is distinctly decreased while the content of Oc-P and Ca-P is a little increased, which means that during the process of sediment releasing, there is a trend of Or-P being transformed into inorganic phosphorus, and also a trend of Al-P and Fe-P being transformed into Oc-P and Ca-P.