Groundwater Chemistry in the Badain Jaran Desert Region of China

The comparative chemistry of surface and subsurface waters and their geographical distribution in the Badain Jaran Desert of northwestern China, was assessed through field sampling. The chemical properties of the phreatic water fraction showed the recharge from atmospheric precipitation to be significant; however, the temporary runoff can only recharge groundwater in the desert margins. While montane bedrock fissure water plays an important role in recharging groundwater in the piedmont alluvial-diluvial layers, its contribution to that of the desert interior is very limited. Artesian water recharges shallow groundwater through the scuttles, particularly in interdune lands. Water quality ranges from 1.0-1.5 g L^-1 at the top of sand mountains to 1.5-2.0 g L^-1, or even above 10 g L^-1 in lakes of interdune lands. Between these locations water chemistry shifts from HCO₃ ^--SO₄ ^2--Cl^--Na⁺ to Cl^--SO₄ ^2--HCO₃ ^--Na⁺. The more soluble Cl^--Na⁺ accumulates in the topsoil layer, while insoluble bicarbonates accumulate in deeper layers, resulting in a vertical zonation. Strongly, slightly and very weakly salinized zones form at depths of 3-6 m, 10-12 m, and 15m, respectively. In the Bayinnuer area, the salinity of shallow (0.5-10 m) and deep (20-80 m) wells were 1.74 g L^-1 and 1.39 g L^-1, respectively, their water chemistries Cl^--SO₄ ^2--HCO₃ ^- and HCO₃ ^--SO₄ ^2--Cl^-, respectively, and their total hardness 32.9 German degrees for both. The existence of low salinity water or even freshwater beneath the shallower highly saline groundwater is significant in terms of the development and use of arid water resources in this arid region.