Chemical Characteristics and Evolution Simulation of Shallow Groundwater in the Taklimakan Desert

The chemistry data of shallow groundwater round was obtained through positional observation section at Luntai-Tazhong-Minfeng in the Taklimakan desert and the main chemistry indicators of groundwater were carried out system analysis. The relationship between the major ions and TDS in the desert shallow groundwater was clarified by using descriptive statistical methods and correlation coefficient methods. The spatial distribution characteristics of the groundwater TDS and pH were discussed by using the graphical method. The cross-section groundwater chemistry types and their spatial distribution were also studied by using Piper graphical method. the hydrogeochemistry simulation was carried out by using hydrogeochemical NETPATH interactive program, and the process of chemical evolution of desert shallow groundwater and its laws were also discussed. The results were shown that the TDS in desert shallow groundwater was relatively high, its value ranged between 30.246 ~ 3.093 g/L. The spatial distribution characteristics were high in the north and lower in the south, and the south was slightly higher than central region. Groundwater chemical type was mainly Na-Mg-Cl-SO₄ and Na-Cl-SO₄ type. NETPATH simulation results showed that with the diminishing sources of minerals, there was a decreasing trend of the amount of Water rock reaction products from upstream to downstream of ground water flow, the increased ion concentration in the downstream was due to the continual influence of leaching and evaporation factors. Rock salt in groundwater was always in solution, but the calcite was always in precipitation state, so that decreased the concentration of HCO₃^-, the mirabilite was dissolved to provide enough SO₄^2-; the amount of orthoclase that took part in the reaction was very small, while muscovite mainly generated precipitation, thus the content of K⁺ in the groundwater is extremely low. These proc- sses could make the groundwater ultimately evolve into the Na-Cl-SO₄ type, and gradually formed the hypersalinity salt groundwater in the downstream region.