Hydrochemical and isotopic characters of surface water in agricultural oases of the Tianshan Mountains, Northwest China

Abstract

ABSTRACTFor evaluating the status of surface water in agricultural oases of the Tianshan Mountains and discussing the influences of human activities and geographical factors on hydrochemical process, we conducted hydrochemical investigations of surface water in two major agricultural oases: Manas and Yili. The δ2H and δ18O of surface water in Manas Oasis ranged from −75.4‰ to − 46.2‰ and −11.6‰ to − 5.5‰, respectively, and from −86.4‰ to − 71.8‰ and −12.5‰ to − 10.7‰ in Yili Oasis. Because rivers are mainly supplied by meltwater from ice and snow, the deuterium excess parameter is mostly positive in the oasis surface waters supplied by these rivers. Ca2+-Mg2+- is the major hydrochemical facies type in Yili and Manas oases. Surface waters of both regions are slightly saturated with carbonate minerals and undersaturated with respect to evaporite minerals, suggesting that the minerals present in the water are mainly produced by calcite and dolomite weathering. Total dissolved solids (TDS) in Manas Oasis are higher than those in Yili Oasis. The δ2H and δ18O of surface water samples in Manas Oasis are isotopically enriched, which indicates that the evaporation effect on Manas is stronger than on Yili. The relatively high salinity in Manas is also associated with local contamination by soil leaching. Agricultural activities are important to the quality of surface water. If such activity is not controlled, water salinization will be increased. Clarification of the hydrological status of these oases and their factors will be used for water management and protection of agricultural oases.