Groundwater recharge and evolution in the Dunhuang Basin, northwestern China

摘要

Groundwater recharge and evolution in the Quaternary aquifer beneath the Dunhuang Basin was investigated using chemical indicators, stable isotopes, and radiocarbon data to provide guidance for regional water management. The quality of groundwater and surface water is generally good with low salinity and it is unpolluted. The dissolution of halite and sylvite from fine-grained sediments controls concentrations of Na~+ and K~+ in the groundwater, but Na~+/Cl~- molar ratios >1 in all samples are also indicative of weathering of feldspar contributing to excess Na~+. The dissolution of carbonate minerals yields Ca~(2+) to the groundwater, thereby exerting a strong influence on groundwater salinity. The δ~(18)O and δ~2H values in unconfined groundwater are enriched along the groundwater flow path from SW to NE. In contrast, confined groundwater was depleted in heavy isotopes, with mean values of -10.4‰ δ~(18)O and -74.4‰ δ~2H. Compared with the precipitation values, all of the groundwater samples were strongly depleted in heavy isotopes, indicating that modern direct recharge to the groundwater aquifers in the plains area is quite limited. The unconfined water is generally young with radiocarbon values of 64.9-79.6 pmc. In the northern basin, radiocarbon content in the confined groundwater is less than 15 pmc and an uncorrected age of ～15ka, indicates that this groundwater was recharged during a humid climatic phases of the late Pleistocence or early Holocene. The results have important implications for inter-basin water allocation programmes and groundwater management in the Dunhuang Basin.