Study On The Characteristics Of The Nitrogen Pollution In The Main Rivers Inflowing Into Weishan Lake And The Nitrogen Release Control Technology Of Sediments

Nitrogen is the restrictive elements for lake eutrophication. Usually sediment is the sink of nitrogen, but the nitrogen in sediments would release when the environment of lake changes, then become an important nitrogen loading for lake. Release of nitrogen from sediments deponds on its chemical forms and is closely related with the environment factors. Weishan Lake is an important lake which would effect the water quality of the South to North Water Diversion Project directly. However, the reaserch on the status of nitrogen pollution of the rivers inflowing into Weishan Lake and the nitrogen release of sediments is rare, therefore, it is necessary to do research on the sediments of Weishan Lake.This dissertation aims to study the characteristics of the nitrogen pollution, the rule of release and its ecological control technology of sediments of the rivers inflowing into Weishan Lake. This dissertation includes the following components:(1) In order to present status of nitrogen pollution of the three important rivers inflowing into Weishan Lake. The distributions of nitrogen in overlying water, organic matter and nitrogen in soil and sediments are analyzed. The results show that:â‘ The concentrations of organic matter and nitrogen in soil and sediments show obvious increasing trend from upstream to downstream in the Xinxue River. The content of nitrogen in Zhuangli and organic matter in Xiaoyandian are highest. The highest concentrations of TN, NO3--N, NH4+-N and NO2--N are produced in Zhonghonglin, Quanli, and Zhuangli respectively while the lowest concentrations are in Yangzhuang. As a whole, the upper basin nitrogen loading of Xinxue River is higher than the lower basin.â‘¡The concentrations of organic matter and nitrogen in soil and sediments, the nitrogen in water are higher in Jianxi and Xiqubo along Dasha River. The concentrations of the nitrogen in water are the lowest in Buling. The concentrations of organic matter and nitrogen in soil and sediments are lower in Xixubo and Dasha River inlet which is the highest in Buling.â‘¢The concentrations of organic matter and nitrogen in soil and sediments are the lowest in Xinxue City along Xiaosha River while the concentrations of TN and NO3--N in water are the highest in this site. The concentrations of organic matter and nitrogen in soil and sediments in Xiaosha River inlet which the concentrations of the nitrogen in water are the lowest along the river are higher than in Xinxue City because of domestic sewage. Compare with the lower basin, the pollution level of the upper basin is higher, especially in Buling which the content of organic matter and nitrogen in soil and sediment and the content of the nitrogen in water are the highest which is affected by industrial enterprises. Therefore, in Buling it is critical to control the point source pollution into the river.(2) The nitrogen release rule of sediments from different river inlet sites is studied in laboratory. The results show that:â‘ The rank order of organic matter and nitrogen in sediments in Dasha River inlet and Xiaosha River inlet is (5-10cm)> (15-25cm)>(10-15cm)>(2-5cm)>(0-2cm); The rank order of organic matter and nitrogen in sediments in Xinxue River inlet is (0-2cm)>(2-5cm)>(5-10cm)> (10-15cm)>(15-25cm). The rank order of organic matter in different sites is Xiaosha River inlet> Dasha River inlet> Xinxue River inlet.â‘¡The nitrogen status of overlying water can affect the release of nitrogen from sediments. The release of nitrogen compounds from sediment becomes easier when the drinking water with low nitrogen concentration is the supplement water, while it became difficult when the lake water is the supplement water. Therefore, when the water from the upstream of the river with low nitrogen concentration flowing into the lake, it can induce the rapid release of nitrogen from sediments, This situation is more significant during water diversion process, the nitrogen concentration of the overlying water even increase in some sample site.â‘¢The effect of environment factors on the release of nitrogen from sediments show that:DO effect TN releasing in lesser degree, the release of NO3--N,NH4+-N,NO2--N in aerobic condition can be inhabited. Acidity and alkalinity enhance the release of nitrogen from sediments compare with neutral state. High temperature is disbennifit to control TN,NH4+-N,NO2--N release from sediments, and restraining the concentrations of NO3--N in comparison to low temperature.(3) The research on ecological control technology in sediments show that:â‘ The submerged plants play an important role in inhibiting the release of nitrogen from sediments. The three studied submerged plants can control the release of total nitrogen effectively.â‘¡The rank of removal rate of NO3--N of the three studied submerged plants in different planting densities is:high planting density>middle planting density>low planting density. The effect of the release NO3--N from sediments is more important than the removal effect of the submerged plants.â‘¢The rank of removal rate of NH4+-N of the three studied submerged plants in different planting densities is:middle planting density>high planting density>low planting density. The removal effect of Potamogeton crispus is the best than the others while Hydrilla verticillata is the worst.â‘£The submerged plants is an effective method to control the release of NO2--N. The concentration of NO2--N can keep lying below 0.02mg/L.