Identification of nitrogen pollution sources and the fate of nitrogen in groundwater in the Weihe River Basin
Nitrogen pollution in groundwater has significant implications for human health,therefore identifying the nitrogen pollution sources is crucial for effective groundwater pollution control.This study collected Groundwater samples from the Weihe River Basin during the summer and winter seasons.Hydrochemical methods and environmental stable isotope techniques were applied to investigate the spatio-temporal distribution characteristics,migration and transformation processes,and sources of nitrogen pollution in groundwater.The SIAR isotope mixing model was utilized to quantitaty the contribution rates of different sources to groundwater nitrogen.Results showed that nitrate is the primary form of nitrogen pollution in groundwater.There were no significant differences in the concentration of nitrate nitrogen(NO3--N)and ammonium nitrogen(NH4+-N)between summer and winter(p>0.05).However,nitrite nitrogen(NO2--N)concentrations were significantly higher in winter than in summer(p<0.01).Spatially,There were no significant differences in NO3--N concentrations.NO2--N concentrations were higher downstream compared to upstream and midstream(p<0.01),while ammonium nitrogen concentrations were higher midstream than upstream and downstream(p<0.01).The nitrate nitrogen concentrations of groundwater samples collected from Baoji City and Xingping City in winter and from Baoji City,Meixian County,and Xingping City in summer exceeded the drinking water standard limit of 10 mg·L-1(GB 5749-2022),with exceeding rates of 20%and 30%,respectively.The δ15N values of the samples ranged from+1.33%to+14.36%.The main sources of groundwater nitrate were identified as manure and sewage(42.73%in winter,40.34%in summer),fertilizers(22.99%in winter,36.97%in summer),and soil organic nitrogen(21.84%in winter,18.02%in summer).The contribution of atmospheric deposition to groundwater nitrogen pollution was found to be minimal both in summer and winter.The nitrification and dissimilatory nitrate reduction to ammonium(DNRA)are main nitrogen transformation processes in winter,while nitrification was dominant process in summer.Enhancing domestic sewage collection efficiency,improving septic tank management,promoting the use of organic fertilizers,and increasing the efficiency of nitrogen utilization in fertilizers and soil are crucial measures to reduce groundwater nitrate nitrogen in the Weihe River Basin.
groundwaternitrogen pollutionnitrogen oxygen isotopesmigration and transformationseasonal variation
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