Sources Identification Of Surface Water And Shallow Groundwater Nitrate-N On Typical Urban And Agricultural Regions

Nitrogen which was one of the essential elements in organisms is the primary element contributing to water eutrophicate. Water nitrate nitrogen contamination is becoming an environmental problem in many regions of the world with the rapid development of agriculture and increasing population intensity. Chemical fertilizer, organisms, domestic sewage, soil organic matters, nitrogen deposition were all the important water nitrate nitrogen pollution sources. Therefore, identification of water nitrate nitrogen pollution sources has a significance to water environmental quality management and ecosystem sustainable development.Nitrogen and oxygen isotopic tracing method is a well established method of detecting the nitrate sources and quantitative research of nitrate sources. The objects of this project was to analyze the pollution level and seasonal variation of water nitrate nitrogen and indentify it’s pollution sources in Beijing urban ecosystem and Qianyanzhou songtang basin using nitrogen and oxygen isotope method and hydro-chemical method. The proceed of this project was based on the monitoring data of Chinese Ecosystem Research Network(CERN) from2004to2009. Findings from this study will provide key information that will be useful in landscape construction in Beijing urban ecosystem and sustainable development of agricultural ecosystem in Qianyanzhou songtang basin.The main conclusitions in this study are as follows:(1) The average surface water nitrate nitrogen concentrations in Beijing urban ecosystem ranged from0.74to7.58mg-L-1with relatively higher values occurred in Dongbianmen and Tonghuihe. The nitrate nitrogen concentrations of Dongbianmen and Tonghuihe were significant higher than those of the other8sampling sites indicating that there could be pollution sources near these two sampling sites. The examination of seasonal variation showed that there was a significant inverse relationship between nitrate nitrogen concentrations and precipitation, and that nitrate nitrogen concentrations peaked in the dry seasons.(2) Overall, the δ15N,δ18O values of surface water in urban Beijing ranged from-1.3to28.9‰,-0.093-14.898‰with the average values of11.5‰(n=54),7.531‰(n=22) respectively. Combined with the information from hydro-chemical analysis, nitrate nitrogen concentration and the values of δ15Nnitrate, δ18Onitrate we concluded that sewage effluent mainly control nitrate distribution in Beijing urban surface water with some possible influence of atmospheric NO3-and soil nitrogen, especially in Dongbianmen ang Tonghuihe.(3) The average nitrate nitrogen concentrations of water in Qianyanzhou songtang bansin were lower than0.3mg·L-1, while0.1mg·L-1and lmg·L-1for NH4+-N and TN. The nitrate nitrogen concentration of groundwater was significantly higher than those of other three types of sampling site. The examination of seasonal variation showed that the nitrate nitrogen concentrations peaked in the summer seasons and lower in spring and autumn, but no obviously seasonal change in ammonium nitrogen and total nitrogen.(4) In the natural pond and Jiazhu river water of Qianyanzhou songtang basin, the δ15N,δ18O values ranged from5.6‰to10.7‰,1.207‰-9.083‰and11.7‰to29.4‰,0.033‰～14.898‰in the fishponds and shallow groundwater (including drinking wells and monitoring wells in the paddy field). The results indicated that nitrate nitrogen was most likely to have come from the organic sources (e.g. manure, domestic sewage, and septic systems). but it could also have originated from soil.(5) The comparison of nitrate nitrogen concentrations between the two ecosystems showed that the nitrate nitrogen was more serious in Beijing urban ecosystem surface which was significantly affected by sewage effluent. The nitrate nitrogen concentrations were about ten times higher than those of Qianyanzhou songtang basin. The seasonal variations of nitrate nitrogen were also different to each other with urban ecosystem peaking in spring and autumn but summer for Qianyanzhou songtan basin. This was mainly attributed to the differences in nitrate nitrogen sources and seasonal distribution of precipitation. The nitrate nitrogen sources were different due to the variation of dominate landscape. The nitrogen sources in urban surface water mainly controlled by point nitrogen pollution which was come from sewage effluent and surface runoff. In Qianyznhou songtang basin, however, agricultural non-point pollution has advantages over other nitrogen pollution sorces with the nitrate nitrogen primaryly derivered from the organic sources (e.g. manure and domestic sewage).