半干旱草原地下水硝酸盐来源转化与健康风险OA

Nitrate(NO3−-N)pollution has become an important environmental problem in several regions world-wide.However,its environmental behavior and fate in the groundwater of semiarid pastoral grasslands remain poorly understood.Herein,the distribution patterns,transformation processes,sources,and human health risks of nitrate in the groundwater of the Xilingol grassland were studied based on dual nitrate isotopes(δ15N-NO3− and δ18O-NO3−).Nitrate was the dominant dissolved nitrogen species,with NO3−-N concentrations ranging from 0.44 to 7.71 mg·L-1.The observed coupled enrichment of δ15N-NO3− and δ18O-NO3− as well as the results of Keeling plots indi-cate considerable denitrification within the aquifer.Nevertheless,its attenuation capacity is insufficient to offset the nitrate accumulation due to persistent external inputs.Principal component analysis revealed a considerable positive correlation between NO3−-N and grazing intensity.The Bayesian isotope mixing model identified manure and sewage as the dominant nitrate sources,contributing 25.91%±2.26%,followed by soil organic nitrogen(21.33%±0.81%)and ammonium fertilizers(20.79%±1.30%).Health risk assessment suggests that noncarcino-genic risks for adults and children are still below the threshold.However,children exhibit higher risks than adults,showing a clustered spatial pattern.These findings advance the mechanistic understanding and risk-orient-ed management of nitrate contamination in pastoral grassland groundwater.They also provide scientific basis for sustainable groundwater resource management in semiarid regions.