Distribution characteristics and influencing factors of iron-rich groundwater in Xining City

Groundwater is an important water supply source in Xining City. Previous works have found that iron-rich groundwater limits water development and utilization. However, few studies focus on the distribution characteristics and mechanism of iron-rich groundwater in different types of aquifers in Xining City. Based on the hydrochemical data of 144 groundwater samples, combined with the geological and hydrogeological conditions, the distribution characteristics and influencing factors of iron content in groundwater in different aquifers were analyzed by methods of statistics and geostatistics. The results show that the exceeding standard ratio of iron in groundwater of unconsolidated sediments aquifer (Area Ⅰ) is 27. 85%, which is 1. 6 times and 2. 7 times higher than that of clastic rocks fissure-pore aquifer (Area Ⅱ) and bedrock aquifer (Area Ⅲ), respectively. The proportion of iron-rich groundwater (concentration greater than 0. 3 mg/L) in construction land area is significantly higher than in areas with other land use types. The redox environment and human activities (such as industrial wastewater, domestic sewage, and infiltration of iron-rich river water) may be the main factors affecting the increase of iron content in groundwater in Area I. In addition to the redox environment, Agricultural nitrogen fertilizer use and domestic sewage discharge are also important factors affecting iron-rich groundwater in Area Ⅱ. The iron-rich groundwater in Area Ⅲ is mainly controlled by redox conditions. On the regional scale, the distribution of iron-rich groundwater presents in bands or spots along the river. The iron deposits releasing in the primary strata and human activities (industrial wastewater) are the main source of iron ions in the shallow groundwater in the study area. The migration and enrichment of iron in groundwater are mainly controlled by redox conditions, and affected by the runoff condition, without relation to pH and salt effect. This study can provide scientific basis for urban water environment management in Xining City and similar arid and semi-arid areas.