河套灌区不同时期地下水氮磷时空分布特征与影响因素研究OA

The Hetao Irrigation District in Inner Mongolia stands as one of China's three large-scale irrigation districts.The shallow groundwater within this region is subjected to varying degrees of nitrogen and phosphorus contamination,posing threats to both local drinking water security and sustainable agricultural development.This study focuses on the largest irrigation area within the Hetao Irrigation District—the Yichang Irrigation Area.In August and October 2024,a total of 76 monitoring points were established for field sampling.The spatiotemporal characteristics of nitrogen and phosphorus,as well as hydrochemical types,were analyzed.Additionally,hydrogen and oxygen isotopes combined with the Bayesian mixing model(MixSIAR)were used to identify recharge sources,while principal component analysis(PCA)and Pearson correlation were employed to reveal the main influencing factors.The results indicate that temporally the mean groundwater total nitrogen(TN)concentration was higher in October(14.7 mg/L)than in August(12.6 mg/L),while the mean total phosphorus(TP)concentration was lower in October(0.074 mg/L)compared to August(0.127 mg/L).Spatially,TN exhibited a punctate high-value distribution along the main drainage ditch,with high-concentration areas concentrated around large villages and breeding farms.High TP values were mainly found in the upstream sections of the main drainage channels and at sedimentation points where the channels bend.Hydrochemical analysis showed that groundwater is predominantly of the Cl-Na type.Hydrogen and oxygen isotopes,along with the MixSIAR model,indicated that recharge primarily originates from canal water infiltration(contribution rate>92%).Analysis of influencing factors revealed that agricultural fertilization,livestock manure,and rural domestic wastewater discharge are the core pollution sources.Hydrogeochemical processes(such as high Cl-competitive adsorption promoting phosphorus migration and high HCO3-facilitating phosphorus precipitation)and rainfall events collectively shape the spatiotemporal patterns of nitrogen and phosphorus pollution.These findings provide a scientific basis for groundwater pollution control and sustainable agricultural management in irrigation districts.