| Nitrogen nutrient is one of the important nutrient elements of the lake ecosystem, and is the key factor in the process of Lake eutrophication. If outer-originated pollution can be controlled, the release of internal nutrient will keep relatively high concentration of nitrogen in the water, which plays an essential role in the algal and other aquatic organisms growth.This paper selected the typical eutrophication urban shallow lake-Dianchi Lake as the research object, studying the forms of nitrogen nutrients and concentrations in the lake water, the pore water of surface sediments in different regions of Dianchi Lake, and characteristics of different forms of nitrogen in the surface sediments of Dianchi Lake were analyzed by chemical sequential extraction methods.Then explained the spatial and temporal distributions, variation trends, regional diversities and the functions in recycling of nitrogen with different forms in sediment-water interface, in order to providing references for the preventing and controlling eutrophication of the lake water.The main research results and conclusions are as follows:(1) The distributions of N in Caohai for lake water and the pore water of surface sediments, which were higher than that in Waihai, and the highest concentration area of N was northwest area in Waihai.So it is with different forms of TF-N in surface sediments.(2) There was no discrepancy between the distributions of N in surface, middle and overlaying water, it showed that lake water was moved dramatically and fixed completely. But the concentrations of NH4+-N,TN in pore water of surface sediments were fourteen times and six times higher than the concentrations in overlaying water of Waihai respectively, and they formed a remarkable concentration gradient.However the concentrations of NO3--N in pore water of surface sediments were almost the same with those in overlaying water of Waihai. In the pore water of surface sediments, N was mainly consisted of NH4+-N, and the concentrations of which was much higher than that of NO3--N, thus there was the trend of N release from sediment to watef, and it was a potential threat of eutrophication in Dianchi Lake.(3) The content of TF-N in natural grain size surface sediments of Dianchi Lake was much higher than other waters. On average, the content of TF-N was 1825.45μg/g, and TF-N accounted for 44.79% of TN. Consequently, the internal pollution sources were more likely to maintain the persistent eutrophic status in Dianchi Lake. The SOEF-N contents (733.68μg/g) were the highest among the four forms of nitrogen; and the contents of IEF-N (501.76μg/g) were lower than those of SOEF-N, while were the highest among the inorganic nitrogen; the contents of WAEF-N (392.09μg/g) were lower than those of IEF-N and higher than those of SAEF-N(197.93μg/g).(4)Analysis of TF-N and their functions in sediment-water exchange showed that absolute contributions of different nitrogen forms in nitrogen recycling were consistent with their contents in sediment, which had the sequence SOEF-N(40.19%)>IEF-N(27.49%)>WAEF-N(21.48%)>SAEF-N(10.84%). Compared with other waters, the absolute contributions of SOEF-N were lower.(5)The results showed that there was remarkable relativity between the concentrations of N in pore water of surface sediments and the water body. Meanwhile, the analysis on correlation indicated that very close correlations existed between the distributing characteristics of TF-N in Surface sediments and that of different forms nitrogen in overlaying water and the pore water from the surface sediments. Especially, IEF-N was highly and positively correlated to them. There were the results that the different forms of nitrogen in sediment-water interface and the nitrogen cycling in Dianchi Lake were found interaction. |
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