Identifying Nitrogen Source Based On Nitrogen And Oxygen Isotope In Yongan River

Erhai lake basin is a highly populated area in Yunnan province,however,with the development of Farming and stockbreeding,there has been a uptrend in eutrophication in Erhai lake resulted from nitrogen and phosphonium pollution,It is estimated that about 70%lake pulltion mainly caused by the inflow river channels.Nitrogen pollution is the chief issue facing Erhai lake,therefore,in order to control pollution at source and reduce eutrophication,we need to master the source of nitrogen and its seasonal changes to take corresponding measures.The Yongan river,one of the three inflow the north of Erhai lake,is studied in this paper.It set 9 sampling points for regular water indices methods along Yongan river in 10 months.The results show that nitrogen is the main affecting factor to the water pollution.The water quality is lower than the five class standard of the surface water quality.it severely affected Erhai lake and with the temporal and spatial variation obiously,water pollution is more serious in dry season than wet season.Nitrogen and oxygen isotopic monitoring is taken at the 9 sampling points for 7 months and water sample was pretreated by using ion exchange resin method to get the statistics of?¹⁵N-NO₃^-and?¹⁸O-NO₃^-.According to the statistics,eigenvalues and on-site analysis,we give the nitrogen pollution a qualitative analysis and make a conclusion that the main source of Yongan river is caused by the animal waste,mixing chemical fertilizer with nitrogen,Rural domestic sewage and Soil Nitrogen.Meawhile,nitrogen and oxygen isotopic monitoring of?¹⁵N-NO₃^-and?¹⁸O-NO₃^-are carried in these four pollutions.By using IsoSource mixed model,regard these four sources as end members to calculate the rate of the four pollutions in the river.We found that the percentage of nitrogen source changes over time.The animal waste range is32.3%⁴9%,mixing chemical fertilizer with nitrogen is 29.8%⁴1.2%,Rural domestic sewage is 5%¹8.5%,and soil nitrogen is 8.1%¹9.4%.Above all,in situ pile and loss of animal waste is covered high proportion of 60%⁸0%which has a great influence on Yongan river.In order to better know the nitrogen pollution from countryside affacted on the Erhai lake,this paper study in the farmland sewage and river sewage.The results show that farmland sewage is main pollution in the range of 60%⁷0%and the village pollution is 30%⁴0%.Therefore,the main farmland pollution is related to the large area of crop planting.