Distribution and genesis of high Fe and Mn groundwater in the northeast of the Jianghan Plain

The Xiaogang region is located in the northeastern Jianghan Plain, and it belongs to the contiguous poverty-stricken areas and water-scarce areas of the Dabie Mountains. The groundwater resource is relatively rare and the groundwater quality is not good. The contents of iron and manganese in the water generally exceeds the national drinking water standard. In order to find out the genesis and spatial distribution of high iron and manganese groundwater, service the development and utilization of groundwater and the problem of water supply safety in the area, we systematically collected the rock, soil, and groundwater samples to test the iron and manganese contents, analyzed the relationship between the contents of iron and manganese in groundwater and the contents of iron and manganese in aquifer sediments, the redox conditions, and pH environment of groundwater. The results show that excessive iron and manganese in groundwater is widespread in the northeastern Jianghan Plain. Among them, the over-standard rate of manganese is greater than that of iron, and the Quaternary pore phreatic groundwater is the worst, with the maximum concentrations of iron and manganese reaching 44.88 mg/L and 19.21 mg/L, respectively. Iron and manganese oxides in rock and soil in the study area, providing material sources for iron and manganese in groundwater. The weak acidity and strong reduction environment provide favorable conditions for the dissolution and release of iron and manganese in sediments. In general, from the east-west sides of the study area (recharge and runoff areas) to the Quaternary pore aquifer (discharge area) in the middle of the study area, the Eh value and pH value along the groundwater flow direction gradually decrease, and the contents of Fe and Mn gradually increase and eventually form a northward high iron-manganese groundwater zone.