| Sediments are the important reservoirs of N, P and C. Usually sediment is the "sink" of nutrients, but the nutrients in sediments would release when the environment of lake changes, then become an important nutrients loading for lake. Release of nutrients from sediments depends on its chemical forms and is closely related with the environment factors. Nansihu Lake is an important lake which would impact the water quality of the South to North Water Diversion Project directly. However, the reaserch on the distribution characters of sedimental pollution and its release rule is rare, therefore, it is necessary to do this research.Nansi Lake was chosen as the main research object, sediment pollution (N, P and OM) distribution characters were study, its release rule were analyzed, a research of submerged phytoremediation was conducted finally. This dissertation mainly includes the following several components:(1) Sedimental TN, TP and OM distribution characters of Nansi Lake showed that:①the contents of TN in Nansi Lake sediments varied greatly from 0.18 to 7.08 mg/g, with the average of 2.97 mg/g. TN content is higher in these areas:the southwest of Nanyang Lake, Dushan lake, west and central regional of Weishan Lake, and the area beside Hanzhuang.②The contents of TP in Nansi Lake sediments ranged greatly from 0.30 to 1.29 mg/g, with the average of 2.97 mg/g.③The contents of OM in Nansi Lake sediments varied from 11.4 to 106.0 mg/g, with the average of 46.1 mg/g. The higher OM areas were similar to that of TN, and they were also overlaped with aquiculture zones. The contents of TN, TP and OM were higher in the upper lake than in the lower lake, as 80%rivers were concentrated in the upper lake, mainly for domestic sewage and industrial waste water.(2) The sedimental pollution release rule of Nansi Lake showed that:①The release of TP and TN from sediments would not influence the water quality; ammonia nitrogen release in parts of Weishan Lake would have an effect on water quality (according to the grade III criteria of surface water.②The equilibrium concentration of ammonia nitrogen (CEAC) between adsorption and desorption increased from lake shore to the central, the area which had higher CWAC than 1 mg/L was composed 1/5 of whole Weishan Lake. Maximum adsorption capacity decreased from the lake shore to the central. Ammonia nitrogen would be released in the central of Weishan Lake after water transferred, and would impact water quality, should pay more attention.③The soil nutrition states of water-level-fluctuating zone beside Nansi Lake varied greatly, due to the different levels of fertilizer applied in different kinds of crops. The contents of TN, TP and OM were 1316-2016 mg/kg,443-1165 mg/kg and 77.1-140.2 mg/g respectively. Maize land had the highest contents of TN,TP and OM; reed land had the lowest TP and TN. Maize land was not only had higher TN and TP, but also easily released phosphorus. Under submerged condition, P would be released, and its quanties were-0.14,0.06,0.97 and 0.12 mg/kg, respectively.④Fish feed was rich of TN, TP and OM. Fish feed which was unutilized and metabolin would pollute water body, and increased the contents of TN,TP and OM in sediments after subside. Probably this was the reason that higher TN and OM areas were overlaped with aquiculture zones. N,P and COD would be released from fish feed under submerged condition,and DO degradagion.⑤N, P and COD would be released from decay plants, DO and pH decreased, so water quality degradation and killed fishes.(3) The research of polluted sediments restoration by submerged plants of Nansi Lake showed that:①Three kinds of plants had better effective on the reducing of N release. The peak values of ammonia nitrogen release were only 34%of blank group.②The removal efficiency of Hydrilla verticillata to ammonia nitrogen and TN were 49%and 81% respectively, and they were higher than that of Ceratophyllum demersum and Myriophyllum spicatum. Hydrilla verticillata had significant effects on the restraining of nutrition release and its remove, and should be used widely on the restoration of polluted Nansi Lake sediments.
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