Dynamics Of Water Quality Of East Dongting Lake And Cause Analysis

As a flood channel lake, water exchange cycle of Dongting Lake is short, which means high capacity of self-purification. However, due to the discharge of large amount of industrial wastewater, municipal sewage and agricultural non-point pollution in recent decades, plus the decrease of runoff especially from the three channels of Yangtze River after the operation of Three Gorges Dam, the capacity of purification of the lake is reduced and water quality is deteriorated. Water pollution of Dongting Lake has influenced the production and living conditions of local people and threatened the habitats of wild plants and animals. This research will study the dynamics of water quality in Xiaoxi Lake, the core area of East Dongting Lake National Nature Reserve, through monthly field monitoring, water sampling and laboratory analysis. Meanwhile, I collected hydrological data such as water level and runoff and meteorological data such as precipitation and air pressure. I discussed the association between water quality and environmental factors through correlation analysis. I expect the research could provide supporting data for alarm and management of water pollution in East Dongting Lake. Key results are as the following:1. Seasonal dynamics of water qualityThe content of dissolved oxygen (DO) is higher during Jan.-May, which varied within8.8-10.8mg/L, and is lower during June-Aug. and Oct., which is below3.0mg/L and can not satisfy the water requirement for fishery. The content of chemical oxygen demand (COD) is higher during Feb.-April and Oct.-Dec., which is over40mg/L. According to the Environmental Quality Standards for Surface Water, the content of total nitrogen (TN) in all month exceeded the standard III except in May and July. During Jan., April, Aug.-Dec., the water quality is standard V or below according to the content of TN. The content of total phosphorus (TP) exceeded the standard III during Feb., July-Oct and December. The content of each heavy metal (Mn, Fe, Cu, Pb, Cd, Hg, Cr) is below the level that can be detected in the laboratory.2. The association between water quality and environmental factors 2011is the typical low flow year. The flood was rising in mid June and receding in late August. The flooding season is less than three months, which is two months shorter than normal year. The annual precipitation is921.6mm, which is ca.30%lower than normal year. Pearson correlation analysis showed that the content of DO was negatively correlated with water level (r=-0.79, P<0.01), runoff (r=-0.65, P<0.05), and air temperature (r=-0.67, P<0.05); the content of nitrate nitrogen was positively correlated with precipitation (r=0.77, P<0.01).In summary, TN is the major pollutant all over the year. East Dongting Lake is also facing the DO deficiency in flooding season and high COD pollution in non-flooding season. Further research should strengthen the monitoring and forecasting of water pollution, and promote the study on the formation mechanisms of water pollution.