Temporal And Spatial Distribution Of Nitrogen And Phosphorus Pollution And Simulations Of Recharge By Groundwater In Dianchi Watershed

There is serious eutrophication in Dianchi Lake, and the infiltration of nutrient elements via groundwater cannot be ignored. Therefore, it is necessary to do research on the groundwater contamination from the agricultural non-point sources.To investigate the temporal and spatial distribution of groundwater nitrogen and phosphorus in the Dianchi watershed, a typical case-Dahe River was chosen as the study area, and the content of nitrogen and phosphorus in groundwater and surface water and their fluctuation trend according to time and space were studied. From September2010to December2011,446water samples were collected from20wells alongside the river and187water samples were collected from9sampling points of the river, and their concentrations of NO2--N, NH3-N, NO2--N and TP were analyzed. The result showed that the nitrogen and phosphorus pollution in Dahe watershed were serious. Among these, the most serious was the nitrate pollution in groundwater, and the mean concentration of NO3--N was34.25mg-L"1, exceeding the limits for drinking water, and was16.13times higher than the limits of eutrophication. Only10.3%of the samples were below the limits of eutrophication(2mg·L-1), and43.9%of them exceeded the criterion for serious NO3--N pollution (20mg-L-1). Moreover, the pollution of NH3-N in groundwater and TP in surface water was relatively serious.The concentrations of nitrogen and phosphorus showed the certain trends the temporal and spatial distribution. In the space, the concentrations of the three nitrogen and TP in surface water increased from upstream to downstream and the concentration of TP in groundwater has a stable trend. According to the temporal distribution, the three nitrogen concentrations of groundwater and surface water in October and November were the highest, and the concentrations in April and May were the lowest. From the time series, nitrate content in the dry season showed a clear downward trend, and showed a upward trend in the rainy season. And the concentration of TP in surface water has a stable trend.Through statistic analysis of the site of wells, precipitation, groundwater level depth, and their application of N fertilizer, the nitrogen concentration of groundwater was found to depend on the four factors. And there was a good response relationship between groundwater and surface water in Dahe watershed.In this paper, through field experiments, survey, chemical analysis and water level observation of the study area, we obtain the first-hand data of hydrogeological conditions, water level and quality changes of groundwater and surface water. Meanwhile, we study the problem of groundwater non-point source pollution by means of numerical simulation, thus, a complete groundwater flow model was established successfully. Finally, the nitrogen and phosphorus loading from the groundwater system into the surface water were calculated. The research provides basal support and quantitative basis for preventing eutrophication of Dianchi Lake, and has important significance for the research on the eutrophication of Dianchi Lake.