干旱区生态环境知识资源中心

On basis of hydrogeology of the study area, the characteristics of chemistry of river water and groundwater were analyzed. Analysis results of three river water samples (B(3), B(4) and B(5)) collected in the middle section of Dousitu River show the TDS increases from B(3) to B(4) and decreases from B(4) to B(5). The concentrations of Cl(-), Na(+), K(+), Mg(2+) and HCO(3)(-) have a similar change with TDS, but the concentrations of Ca(2+) and SO(4)(2-) increase steadily along flow path. The chemical types of the river water change from HCO(3)center dot Cl-Na to Cl center dot SO(4)center dot HCO(3)-Na, and finally to SO(4)center dot Cl-Na. The causes of these changes are analyzed and studied in depth using various methods. Results indicate river water evaporation, dissolution/precipitation of minerals, cation exchange and mixing of different waters all play important roles in the formation of the river water chemistry. But in different sections of the river, the main processes are different. The study shows that when a reservoir is built in arid areas, the loss of water resources due to evaporation is huge, which can lead to the degradation of water qualities. Hence, great care should be taken to build a reservoir in arid or semi-arid regions.