Characteristics, genesis and treatment measures of NO₃ type groundwater in Xiamen, Fujian Province

Groundwater nitrate pollution is a worldwide water environment problem. The increase of nitrate concentration in groundwater causes the deterioration of water quality, while the increase of its relative contents changes the hydrochemical characteristics of groundwater. NO₃^- becomes one of the main anions in groundwater in some areas, and the name of "NO₃ type water" for this new chemical type of groundwater is gradually accepted by scholars. Based on the analysis of the distribution, characteristics and influencing factors of NO₃ type water in shallow groundwater in plain area of Xiamen City, the significance of NO₃ type water was discussed. The results show that the groundwater in Xiamen has been polluted by nitrate nitrogen. NO₃ type water comprising 36.8% of all 87 samples is mainly distributed in weathered residual plain. The eastern Xiang'an and Tong'an districts have formed a relatively large planar distribution, while the western Jimei and Haicang districts have a small distribution, and the distribution is point-like or local small area. NO₃ type water mainly exists in oxidation deposition environment with low pH, low TDS and low hardness. The weathered residual aquifer's characteristics of acid soil、slow runoff and shallow water table provide favorable environmental conditions for NO₃^- enrichment in groundwater. Human sewage, landfill leachate infiltration and agricultural fertilization are the main sources of nitrate pollution in groundwater. It is suggested to carry out research on groundwater nitrate source identification. According to different sources of pollution, measures such as improving the construction of pollution pipe network, improving toilets in rural areas and scientific fertilization should be taken to prevent and control pollution from the source.