Characterization of recharge processes and groundwater flow paths using isotopes in the arid Santanghu basin, Northwest China

Isotopes and hydrochemistry were used to characterize the recharge and flow of groundwater in the arid Santanghu basin in Northwest China. The results of isotopic measurement and hydrochemical facies indicate that the predominant recharge mechanism is via rivers and streams. Modern recharge only occurs in the piedmont area of Moqinwula Mountains by ephemeral rivers, and the main recharge source is precipitation in the mountain areas at an elevation of about 2,200 m above sea level. Two recharge mechanisms were identified by stable isotope methods: the ephemeral stream recharge in the piedmont with the occurrence of evaporation during recharge, and subsurface inflow recharge from the mountain regions. Diffuse recharge derived from precipitation in the basin can be ignored because of the scarcity of precipitation and intense evaporation. Groundwater in the Paleogene and Neogene confined aquifers could represent recharge during cooler climatic conditions, rather than latitude or altitude effects, signified by tritium-free samples and significant depletion of heavy stable isotopes throughout the study area. Groundwater age data suggest that central faults are controlling the flow paths of the regional groundwater flow system. Groundwater moves from the piedmont plain to the basin lowland area through lateral flow, and changes flow direction to the spring zone of Hanshuiquan Oasis because of the barrier of the central faults. A conceptual model was defined, for better understanding of the groundwater recharge and flow systems. The major findings of this study have significant implications for groundwater protection and management in arid basins.