Hydrochemical characteristics, controlling factors and solute sources of groundwater within the Tarim River Basin in the extreme arid region, NW Tibetan Plateau

In the extreme arid region of the Tarim River Basin (TRB), groundwater is the most valuable resource for people's lives and regional ecology. Major ion concentrations of groundwater were analyzed to decipher hydrochemistry, temporal and spatial variations, solute sources, and controlling factors of the groundwater within the TRB. Groundwaters in this area were neutral to alkaline in nature and most of them were hard-brackish waters, dominated by Na, Ca, Mg, Cl, and SO4 ions. The total dissolved solid (TDS) varied over two orders of magnitude with a mean value of 2044 mg/L in wet season and 3091 mg/L in dry season, about 1-2 times higher than those in river water in this area. Hydrochemical types and chemical compositions of groundwaters showed zonal distribution. Mineral dissolution and evaporation were the main processes responsible for high solutes in groundwater. Ion exchange between Na on clay minerals and Ca (Mg) in groundwater increased Na+ concentrations. Groundwater was oversaturated with respect to dolomite, calcite and aragonite, and under-saturated with respect to gypsum and halite. A forward model of mass budget calculation showed that evaporite dissolution, carbonate weathering, silicate weathering, and atmospheric input contributed 58 +/- 14%, 25 +/- 12%, 13 +/- 2%, and 4 +/- 2% of the total dissolved cations on average in wet season, and 68 +/- 13%, 20 +/- 12%, 10 +/- 2%, and 2 +/- 1% in dry season for the whole basin, respectively. Spatial variations of rock weathering were significant, with higher evaporite dissolution in the southern basin, and higher carbonate weathering in the northern basin. Although anthropogenic inputs were minor, the majority of samples were not suitable for drinking with reference to TDS, F- and/or SO42-. These results can enhance the understanding of hydrochemical characteristics in desert environments and provide information for the material sources of Lop Nor. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.