Vertical Pollution Characteristics Of Lake Sediments Located In Middle Reaches Of The Yangtze River

The Basin in Yangtze River was the most densely distributed freshwater lakes in China. Due to the emissions of heavy metals and nutrients exceeded environmental Capacity, there were different degrees of water pollution and eutrophication problems in lakes, while these pollutants through a series of physical, chemical and biological reactions into the sediment. Through the research on the vertical typical lake sediment, had a good understanding of the ancient environmental climate, pollution sources and environment variation course and rule, and provided certain reference for environmental control and protection of the Yangtze river basin. According to this perspective, In this paper we selected the typical lakes of the core sediments of Lake Donghu, Wuhan, Lake Haikou and Lake Nanhu, Zhongxiang, and the surface sediments of Lake Liangzi and Lake Hong in the middle reach of Yangtze river; the research contents were as follows:(1)To reveal the variation patterns and the main sources of core sediment pollution in different types of lakes in the middle reaches of the Yangtze River, vertical distributions of total organic carbon (TOC), total nitrogen (TN) were investigated in the sediments of Lake Donghu, Wuhan, Lake Haikou and Lake Nanhu, Zhongxiang. The results showed that:the concentrations of TOC and TN showed little change between 50 to 30 cm depth, but increased largely from 30 to 10 cm, followed by decrease in 10 cm, which was consistent with the evolutionary times of each lake, which was consistent with the environmental change around the lakes. The maximum value of TOC concentration appeared in Lake Haikou, while the maximum value of TN concentration appeared in Lake Donghu, and the TOC and TN had obvious homologous relevance. Based on the organic index and organic nitrogen, we can concluded that the sediments in Lake Donghu, Lake Haikou belong to IV levels, namely serious pollution degree, and Lake Nanhu, Zhongxiang belong to III levels, namely less clean category.(2)Vertical characteristics of sediments in Lake Dong, Wuhan, Lake Haikou, Lake Nan, Zhongxiang showed that Cu, Zn and Pb in the study area were relatively influenced by humans, while Cr was from natural source; The sort order of 5 kinds of metal pollution was Lake Dong, Lake Haikou, Lake Nan, the analysis indieated that the main sources of the pollutants in core sediments of Lake Dong were mineral combustion and domestic waste-water; for Lake Haikou, the main source of pollutant was planting; while the pollutants in Lake Nan Zhongxiang mainly came from domestic waste-water. The three lakes pollution contribution rate of human was greater than natural, and problem of nutrient and Pb pollution was common; Results of nemerow and geo-accumulation pollution index(Igeo) revealed that the potential ecological risk of Ni and Cr in three lakes were slight, but the Zn, Cu and Pb had potential ecological risk in Lake Dong and Lake Haikou. While five mentals in sediments of Lake Nan Zhongxiang were no pollution.(3)The total organic carbon(TOC), total nitrogen(TN) and organic carbon and nitrogen isotopes were analyzed in suface sediments from Lake Liangzi and Lake Hong. The results showed that the contents of C/N and TN were 6.16 to 8.16 and 0.19% to 0.54%. The maximum value of ?15N concentration appeared in B, while the minimum was C. The ?13C content in Lake Liangzi was in the ranges of-30.98%o--23.09%o, with an average value of-27.19?. the contents of C/N and TN in the surface sediments of Lake Hong were 13.71 to 65.9 and 0.03% tol.19%, and the original organic-matter input was higher terrigenous plants. The ?13C content in the surface sediments of Lake Hong was in the ranges of -28.02%o?-8.31%o, with an average value of-18.96%o, demonstrating that the main source of sediment pollution was C4 plant except aquatic plant. Shore terrestrial input point was obvious, the whole lake wetland soil erosion increased risk.