Hydrogeochemical characteristics and nitrate distribution of groundwater in Weibei Plain, Northern China

Nitrate pollution in groundwater has become an issue that cannot be overlooked, specifically in areas where there is intense agricultural groundwater extraction. This study focuses on the Weibei Plain, where 46 shallow groundwater monitoring wells were selected for sampling during the dry and wet seasons in 2016 and 2021. The purpose of this study was to analyze the regional groundwater hydrogeochemistry and investigate the temporal or spatial variation of nitrate content. The results demonstrated that the groundwater in the study area had a weakly alkaline nature. The hydrochemical composition of the groundwater shifted from being dominated by HCO 3 -Ca-Mg in 2016 to HCO 3 -Na and SO 4 -Cl-Ca-Mg in 2021. The hydrochemical characteristics were predominantly impacted by both rock weathering and cation exchange. The average concentration of nitrate in the 184 samples was 25.93 mg/L, surpassing the drinking water limit of 20 mg/L. A significant correlation was observed between NO 3 − and Cl − as well as SO 4 2− . The areas with high nitrate concentrations were predominantly located in the groundwater depression cone and regions with intensive agricultural activities, indicating that human activities were the main contributors to nitrate pollution. Furthermore, the nitrate concentration was significantly higher during the wet season compared to the dry season. This could be attributed to rainfall intensifying the infiltration of nitrate from the soil into the groundwater. Furthermore, there was a substantial increase in nitrate concentration in 2021 compared to 2016. This increase was primarily ascribed to the excessive exploitation of groundwater for irrigated agriculture, leading to a considerable influx of nitrate into the groundwater.