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Multiple isotopic and hydrogeochemical tracers were utilized to understand the limits to recharge from Tibetan plateau to Gobi desert. The average direct recharge rate according to chloride mass balance is between 0.9-2.5 mm yr(-1) based on an annual rainfall of 120 mm yr(-1), indicating that this has negligible impact on groundwater. The groundwater shows markedly depleted stable isotopic composition compared to modern rainfall. The signature of groundwaters (around -10.4 parts per thousand to -9.6 parts per thousand delta O-18 in several wells) from Dajing and South Lake playa differ clearly from that of the alluvial fan and modern rainfall, and has lower or undetected tritium activity, implying that the aquifer in the desert is maintained by palaeowater. This groundwater has an estimated C-14 age of similar to 4 kyr, with a recharge temperature of 7.3 degrees C. At current hydraulic head gradients, transit time from the recharge zone (Wuwei-Gulang alluvial fan) to South lake is approximately 2200-3500 yrs, indicating that groundwater flow is relatively slow and that the water resources are non-renewable.

The geochemical information is comparable to the isotopic results of limit recharge sources of groundwater from Tibetan plateau to the Gobi desert. The buildup of dissolved solids through evaporation is a major control on groundwater composition, and the dominant anion species change systematically from HCO3-, SO42- to Cl-, but the dissolved ions from albite, calcite, dolomite and gypsum also have a significant contribution. It is advised to re-consider seriously the immigration policy of South lake to meet the groundwater management in the mountain front to Gobi desert. (C) 2008 Elsevier B.V. All rights reserved.