Analysis Of Nitrate Pollution Sources In The Lower Reaches Of Feihe River

With the development of industry and agriculture,a large number of agricultural fertilizers,urban sewage and industrial wastewater are discharged into rivers,resulting in a concentration of NO3--N in the water body exceeding the drinking water standard of 10 mg·L-1,posing a serious threat to the human body.Therefore,screening NO3--N pollution sources in water bodies is of great significance for river pollution control and sustainable ecosystem development.In this study,the main stream of the lower reaches of the Fenhe River was used to collect water samples and water quality analysis in July and December 2018 respectively.Based on GIS and SWAT,the source of NO3--N pollution in water was analyzed.In addition,based on the analysis of the nitrification and denitrification of river water,the source of nitrate pollution in the Fcnhc River was identified by the mixed model of nitrogen and oxygen bistable isotopes and IsoSource,and the pollution ratio of pollution sources was calculated.The main contents and conclusions are as follows:(1)The correlation of inorganic nitrogen concentration and its land use types at different sampling points in July and December 2018 in the lower reaches of the Fenhe River was carried out.The research shows that the inorganic nitrogen pollution in the lower reaches of the Fenhe River is serious,the overall water quality of the river is the V-type water standard,and NO3--N is the main nitrogen pollution of the river.In the abundance and dry season,the NH4+-N concentration was higher than the V-type water standard 2.0mg L-1,and the N03--N content in the water exceeded the national water quality standard(10mg·L-1),accounting for 70%and 100%.%.The river sections with higher inorganic nitrogen concentration in the lower reaches of the Fenhe River are located in urban and agricultural land.In addition,rural and urban land plays a role of"source"for NH4+-N,while forest land plays the role of"sink".In July(beverage period),urban and rural residential land and dry land(cultivated land)are important sources of NO3--N and NH4＋-N in the lower reaches of the Fenhe River;in December(dry season),urban and rural land is downstream of the Fenhe River.An important source of NO3--N.(2)The MiSeq high-throughput sequencing of the water samples collected in July and December was used to analyze the effects of nitrification and denitrification in the waters of the lower reaches of the Fenhe River.The research shows that the water body in the lower reaches of the Fenhe River is rich in nitrification and denitrifying bacteria community structure,but the difference in dominant flora is small.Based on the main nitrification and denitrifying bacteria species and water quality data foundation,the bacteria and water bodies are inorganic.Nitrogen was subjected to principal component analysis and Spearman correlation analysis.NO2--N and NO3--N in the lower reaches of the Fenhe River are the main influencing factors of the genus Nitrobacter,and Nitroso,monas are significantly associated with inorganic nitrogen.Nitrosormonas and NO3--N in the water.The NO2--N value is positively correlated,the correlation is high(|F|>0.5),and negatively correlated with inorganic nitrogen such as NH4+-N and TN,but the correlation is low(|F|<0.45);TN in water NH4+-N,NO3--N and NO2--N are negatively correlated with denitrifying bacteria Paracocc,Rhodobacter,Pseudomomas and Thauera,and reduce inorganic nitrogen content.There is a certain promoting effect.Rhodobacter is a positive correlation with T,DO and pH in water,but the correlation is not high(|F|<0.3),and inorganic nitrogen such as NO3--N,NO2--N and TN Negative correlation,and high correlation(|F|>0.5).(3)The samples collected in July and December were subjected to nitrate nitrogen and oxygen stable isotope detection,and the source of NO3--N pollution was determined according to the range of 61 N-NO3-and δ18 O-NO3-eigenvalues.The main sources of NO3--N in the lower reaches of the Fenhe River are agrochemicals,soil organic nitrogen,manure and sewage.In July,the impact of agrochemicals was greater,and in December,manure and sewage were the main sources of NO3--N pollution.(4)Based on the results of δ15N-NO3-and δ180-NO3-analysis,the IsoSourcc model was used to quantitatively calculate the proportion of NO3--N main pollution sources in the Fenhe and dry seasons.In July,agricultural fertilizers accounted for a high level of pollution,and agricultural fertilizers at all points in the Hejin section accounted for more than 50%.In December,the contribution of feces and sewage pollution at each sampling point was higher than 40%,and the proportion of agricultural fertilizers was small,all below 30%,which was related to the winter farming period.