The Study On Distribution Characteristics And Regional Diversities Of Nitrogen Nutrients In Taihu Lake

Eutrophication is a worldwide environmental problem and has become the research focus nowadays. Taihu Lake is a typical large-scale shallow lake, located in the middle and lower reaches of Yangtze River Delt in Eastern China, which has made significant contributions to the rapid economic development, but with the rapid development of industrialization and urbanization, the Taihu water quality is deteriorated sharply, and the eutrophication levels are worsen, blue algae blooms are outbreaking frequently, which has been a serious threat to people's normal work and life.Nitrogen in the aquatic ecosystem is as one of the most important nutrients elements, directly participates in the nitrogen cycles of the aquatic ecosystems, and plays an essential role in the algal growth and the biological productivity of aquatic ecosystems. Whereas superfluous nitrogen and phosphorus nutrients, causing abnormal increase of algae and other aquatic biology, and water quality seriously deteriorate, arises eutrophication of lake. Therefore, investigates the forms of nitrogen, nitrogen contents, and distribution characterics, plays important roles in comprehensive studying the the nitrogen cycles, process of transferation and transformation and the mechanisms of the eutrophication.This paper was founded by the National Basic Research Program of China (973 Program) "The characteristics of regional diversities in the lake water quality" (2008CB418201). Selecting the typical eutrophication lake——Taihu Lake as the research object, analysing the forms of nitrogen nutrients and concentrations in the Lake water, pore-water and sediments, different regions of Taihu Lake, and illustrating the spatial and temporal distributions, variation trends and regional diversties, in order to providing references for the preventing and controling eutrophication, and constituting basical criterion of the lake water.The main research results and conclusions are as follows:(1) The concentrations of TN in Taihu water is different in spring and autumn, and TN in spring is obviously higher than in autumn, whereas there are little difference in vertical distribution. Choosing TN as the single evaluation factor, Taihu water quality is GradeⅣorⅤ, and some regions are even wore than GradeⅤ. (2) DON is the main forms in Taihu water, accounting 65%～80%proportion of TN, which much higher than PN, and concentration of different forms of DON is NO3--N> DON> NH4+-N. While NH4+-N and NO2--N are main forms in pore-water, especially NH4+-N, accounting 36.84%～73.98% of TDN, which is reverse to Taihu water. And in sediments, ON is the main forms and much higher than the other nitrogen forms.(3) Analysing the vertical distribution of sediments core, in the pore-water the NH4+-N increases with depth, while DON and NO3--N showed a slowly decreased trend with depth. And TN, ON are tortuous decrease with depth in sediments, while NO3--N increases first and then decreases with depth.(4) The spatial distribution of TN, TDN, PN, NO3--N and NH4+-N in Taihu water shows a trends of higher in northwest and lower in southeast, especially the Zhushan Bar, Meiliang Bar and Taihu northwest coastal belt, the concentrations in these regions are higher than the Eastern Taihu. And in pore-water, TDN and NH4+-N are decreas along North regions to southwest regions and along the Eastern Taihu to southwest regions, while NO2--N and NO3-N shows a trends of higher in northesat and lower in southwest, and the regional diversity of DON is distinct at different depths. Whereas each nitrogens in sediments shows distinct regional distribution characteristics in vertical levels, TN and ON are similar in different depth of lcm, 10cm and 20cm, which much higher in Zhushan Bar, northwest coastal belt and Xuhu Bar, and lower in southwest coastal belt; NH4+-N shows a trend of higher in northwest lower in southeast, while the spatial distribution of NO3--N is distinct obviously in different depth.From the above analysis, we come to conclusion that Taihu Lake was already at the eutrophic state, especially the regions of Zhushan Bar, Meiliang Bar, Taihu northwest coastal belt and Gonghu Bar, nitrogen nutrients excessively overloads. Consequently, we should strengthen environmental monitoring and scientific research in these regions, and take some useful measures of biology, chemistry and physics, preventing and controling the eutrophication of Taihu Lake.