Distribution characteristics, driving factors and risk assessment of nitrate in groundwater of the Yellow River Basin

Nitrogen fertilizers are widely used in agricultural production, and their residues can migrate to aquifers, threatening groundwater safety. As an important region for agricultural and energy production in China, the Yellow River Basin has seen the long-term application of nitrogen fertilizers. In this study, Based on the nitrate (NO₃⁻-N) data from 3116 groundwater monitoring sites collected over 2018–2022, this study investigated the occurrence and distribution characteristics of NO₃⁻-N in groundwater. Specifically, the driving factors of the migration and occurrence of NO₃⁻-N in groundwater were identified. The results show that the average concentration of NO₃⁻-N is 9.04 mg/L in the monitoring sites, and the rate of concentration exceed 10 mg/L is 24.71%. The average concentration of NO₃⁻-N gradually increases from the upstream to the downstream. The average concentration of NO₃⁻-N in groundwater decreases significantly with increasing depth, decreased from 5.75 mg/L (depth: 0-50 m) to 1.8 mg/L (depth: ≥200m). The concentration of NO₃⁻-N in phreatic water is notably higher than that in confined water. High-concentrations of NO₃⁻-N (>10 mg/L) are mainly distributed in the areas with developed agriculture and industry. Especially in the areas of phreatic aquifers with suitable temperature, abundant rainfall, intensive industrial and agricultural activities, an oxidizing, Na-Cl and Ca-Mg-Cl type groundwater environment. In some monitoring sites of phreatic aquifers with depths less than 50 m, NO₃⁻-N pose risks to human health.