The Characteristics Of Nitrogen And Water Quality Assessment In East Water-source Of Chaohu Lake

As an environment element with various valence states, nitrogen is the constituent of a series of organic and inorganic compounds, but excessive nitrogen input may result in eutrophication and algal bloom. Study on the conversion of nitrogen and influential factors in the water bodies of Chaohu Lake, as well as the accumulation rule of nitrogen is of great significance for the control and management of eutrophication in this area.Chaohu Lake is one of the five largest freshwater lakes in China. In the past two decades, Chaohu Lake experienced frequent occurrences of algal bloom, and serious eutrophication. The east concentrated water resource conservation area of Chaohu Lake is the only water resource for Chaohu County. Based on the on-site monitoring results, we analyzed the spatial and temporal variations of nitrogen speciation in east water-source and inflow rivers of Chaohu Lake, examined their effects and possible sources in order to provide basic data and theoretical basis for the control and management of eutrophication in Chaohu Lake. By nitrogen chemical analysis, the results of experimental are as follows:(1) The contents of NH3-N, NO3--N and NO2--N are0.14-6.71mg·L-1,0.08-7.58mg·L-1,1.30-220.00μg·L-1, respectively, showing obvious seasonal changes. The contents of NH3-N and NO2--N are higher in flood season than in non-flood season, while the contents of NO3--N are higher in non-flood season than in flood season.(2) Shuangqiao River and Xiaozhegao River have relatively high three nitrogen compounds contents. The dissolvable inorganic nitrogen (DIN) is dominated by NO3--N, accounting for27.92%-84.14%of DIN. In most regions, DIN presents significant positive correlation with NO3--N, indicating that DIN content of nitrate nitrogen.(3) DIN in Zhegao estuary and Xiaozhegao estuary are caused by sewage and industrial tail water pollution; the lake region suffers the same degree of point source and nonpoint source pollution; surface runoff and pollution from ships contribute the most for the DIN in Shuangqiao estuary. The NH3-N pollution source in Shuangqiao estuary is mainly nonpoint source; while the other regions show similar degree of point source and non-point source pollution.Evaluating the water quality of east water-source and inflow rivers of Chaohu Lake with Single-factor Index method, Nemerow Index method, Comprehensive Water Quality Index method.The object of the study is to assess water quality with major parameters (e.g. DO, COD, Permanganate index, NH3-N, TP, BOD5). Making comparative analysis of the advantages and disadvantages of these methods, the results are as follows:Single-factor Index method is conservative, but the calculation is simple and convenient. Nemerow Index method considering the maximum concentration and average concentration, which compared with the Single-factor Index method, the result is more objective.The evaluation results of Comprehensive Water Quality Index method is more reasonable and easy to put into practice.The traditional Comprehensive Water Quality Index method is improved by introducing concept of weighting value.Weight applies exceeding standard multiple method. It found that the assessment conclusion by improved Comprehensive Water Quality Index method was more scientific and reasonable, which are applicable to east water-source of Chaohu Lake.