[Geochemical Characteristics and Driving Factors of NO-Type Groundwater in the Rapidly Urbanizing Pearl River Delta].

In response to rapid economic development, nitrate pollution of groundwater is becoming a serious issue in many parts of China. Urbanization and industrialization are the main drivers of NO-type groundwater expansion. Focusing on the Pearl River Delta, the occurrence and driving factors of shallow nitrate groundwater are discussed. Overall, groundwater nitrate concentrations are generally high in this region. Of 1538 groundwater samples, 5.7% had nitrate concentrations higher than the groundwater quality standard(88.6 mg·L) and 18.5% were classified as NO-type waters, which are mainly distributed in the hilly and piedmont areas. Guangzhou, Dongguan, Foshan, Zhuhai and other areas show high total dissolved solid(TDS)-concentration NO-type waters, which are affected by urbanization and industrialization. In comparison, low-TDS NO-type waters are distributed in the hilly and valley areas. In the Xijiang and Dongjiang plains, the TDS concentrations on groundwater increased significantly due to inputs of industrial wastewater and saline seawater. The NO concentration in the groundwater in this area exceeded the class III water standard but did not change the hydrochemical type classification. However, industrialization has led to the frequent appearance of SO-type water in this area. The NO-type water occurs in acidic or weakly acidic environments, typically characterized by low TDS and total hardness concentrations, and high Cl, SO, and K concentrations. The formation of NO-type water is mainly affected by domestic sewage, industrial wastewater, agricultural nitrogen fertilizer, septic tank outflows, and landfill leachate leakage. Generally, the pollution loads of high-TDS NO-type waters are higher than low-TDS NO-type waters. The delineation of NO-type waters, especially the low-TDS type, is helpful for identifying groundwaters posing greater risks for human activities, and those with low nitrate concentrations but potential pollution risk, which is of great significance in the prevention and control of groundwater pollution.