Hydrochemical characteristics of groundwater and analysis of groundwater flow systems in Jianghan Plain

Based on increasingly serious groundwater quality problems in Jianghan Plain, the investigation of groundwater flow systems (GFSs) is vital for the sustainable management and protection of water resources. Hydrogeological conditions, hydrodynamic field and hydrogeochemistry were used to gain insight into the recharge process, water-rock interactions, and groundwater residence time in the typical area of Jianghan Plain. Because of carbonate mineral weathering, groundwater is predominantly of the HCO₃-Ca·(Mg) type. The decrease of typical ions and the depletion of isotopic distributions with depth increasing indicate that the GFSs were divided into local and regional GFSs with a depth limitation of approximately 10~20 m. The complex and independent local GFSs exhibit a pattern in which groundwater discharged into surface waters during the nonflood season. Groundwater age of local GFSs is modern according to the ³H concentrations, indicating the hydrodynamic circulation is active. Furthermore, controlled by topography, the regional GFSs flow from west or northwest to east or southeast, eventually discharging into the Yangtze River and the Han River. The evident zonations of δ¹⁸O distribution in regional GFSs are dominated by the altitude effect of recharge areas, indicating different recharge sources and flow paths. The piedmont hilly area is basically modern water. Deep into the hinterland of the plain to the discharge area of the Han River and Yangtze River, groundwater age of regional GFSs varied from hundreds of years to 6 000 years estimated by ¹⁴C isotope data, elucidating that the hydrodynamic circulation is slow to relatively stagnant. The existence of regional GFSs driven by an upward hydraulic gradient in the low-lying discharge area of Jianghan Plain, can provide a theoretical basis for researching the distribution and aggregation of primary inferior groundwater.