Characteristics and sources of nitrate pollution in groundwater of lower reaches and tributaries of Ganjiang River under extreme drought climate

In order to study the influence of extreme drought climate on the characteristics and sources of nitrate pollution in groundwater, the groundwater chemical characteristics, spatial distribution and sources of nitrate were compared before and during extreme drought in the lower reaches of Ganjiang River Basin and its tributaries. The results showed that the \mathrmNO_3^- content of groundwater in the study area in the extreme drought year of 2022 was 0-73.89 mg/L, with an average value of 6.58 mg/L, which was generally lower than that in the normal year (2021). In the study area in 2021 and 2022, the groundwater types were mainly HCO₃-Ca type and a small amount of Cl-Ca·Mg type in the wet and dry seasons. The hydrochemical components in the normal year and the extreme drought year were mainly affected by rock weathering, and the points with high nitrate values tended to be in the atmospheric precipitation region, indicating that the nitrate changes were mainly directly influenced by the outside world. The spatial distribution of nitrate in the wet and dry seasons in the extreme drought year was lower than in the normal year in terms of high-value area and degree. Long-term drought resulted in the reduction of groundwater recharge sources. The nitrate content was affected by rock salt leaching, excretion and denitrification, with increased contribution from human and animal feces and domestic sewage.