| The deposit pollution is one of the important research contents in lake pollution, and is a worldwide prominent environmental problem. As an important component of lake ecosystem, sediment is not only the central part of lake nutrient circulation, but also the main pollutant storehouse. In the interaction process between water body and sediment, significant amount of nutrients in the deposit will be released to the water body and form the endogenous load of nutrient salts in lake after the extraneous source is under active control. Some people have done research on the aspect of deposit pollution of lake, such as, Chaohu Lake, Tai Lake, Yunnan pond, East Lake, but few researchers have done for the lakes in cold-arid regions.The horizontal and vertical distribution of nutrient salts and heavy metals were analyzed in quantity on the sediment of Wuliangsuhai Lake, which is located in semiarid north part of China. The interrelationship between nutrient salts and the heavy metals in the surficial sediment were studied using the SPSS, meanwhile, the present situation assessment of organic and heavy metal pollution were carried on. Based on the above experiment and analysis, the theory of environmental chemistry and biogeochemistry were applied to preliminary research on pollution mechanism. Through the release experiment of nitrogen, phosphorus, iron and manganese in the original columnar and mixed-disturbed deposit of Wuliangsuhai Lake, it is shown that endogenous nutrient salt release had influence on the superjacent water quality when the environmental factors (pH and DO) were changed. The results were concluded as:(1) The interrelationship among carbon, nitrogen, phosphorus in sediment and its environmental implication showed that The TOC/TN ratio reflected the organic matter originating from the aquatic organism of lake and terrigenous inputs, and the extraneous source inputs were slightly predominated, and they were significantly positive correlated. Besides, the ratio of TOC/TP is higher than the TOC/TN, and the horizontal distribution of TN/TP had similar change characteristic with that of the TOC/TP.(2) The results of organic pollution assessment in the surface deposit of Wuliangsuhai Lake indicated that the average value of organic index for the whole lake was 0.42, which was still at clean state, the average value ofω(ON) was 0.17%, which was belonged to the organic nitrogenous polluting condition.(3) The correlation analysis between nutritive elements and heavy metals indicated that heavy metal elements-Cu, Cr, Pb, Cd had significant positive correlation in pairwise. The organic matter had significant positive correlation with As and Hg, total nitrogen had significant positive correlation with Hg, while had significant negative correlation with Pb, total phosphorus only had negative correlation with As. Nine kinds of metal elements were classified into three types by R- cluster analysis. Factorial analysis was done between nutrient salts and heavy metals using the method of principal component analysis in the top deposit of Wuliangsuhai Lake, which obtained 4 factors, and the scientific connotation of various principal components were analyzed.(4) The evaluation method of potential ecological risk and index of geo-accumulation were applied to assess the present situation of heavy metal pollution for the data in winter and summer, and the results of the two methods were compared. The assessment results of the two methods were basically consistent: the pollution of Hg and As were the most serious in summer and they were relatively weaken in winter, while Cd became the main pollutant.(5) The endogenous nutrient salt release of indoor simulating experiment in the original columnar and mixed-disturbed deposit of Wuliangsuhai Lake showed that the high pH value and the low dissolved oxygen had advantageous to the release of DIP and DTP. The release of TN was quite complex as the influence of various nitrogen types, Fe and Mn were easy to be released in the condition of meta-acid and anaerobic and the effects of nutrient salts release in the mixed-disturbed deposit was inferior to the original deposit.Therefore, the distributed character, the origin, the present pollution level of the sediment of Wuliangsuhai Lake and its influence on eutrophication were discovered in order to provide scientific basis in controlling water body pollution with countermeasures. According to the above study, we could diagnose the state of health of the lake wetland ecosystem, and provide the instructions and reference comments for restoring the function of deteriorated wetlands. The research on the process of migration and transformation of sediment nutrient - water interface under the change of environmental condition were done to seek suitable reclamation technology to control the endogenous pollution and to lay the foundation for developning eutrophication model of Wuliangsuhai Lake. Meanwhile, it also had practical significance to control and manage the quality of lake water as well as the environmental ecosystem.
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