干旱区生态环境知识资源中心

The Zhangye Basin, located in arid northwest China, is an important agricultural and industrial center. In recent years rapid development has created an increased demand for water, which is increasingly being fulfilled by groundwater abstraction. Detailed knowledge of the geochemical evolution of groundwater and water quality can enhance understanding of the hydrochemical system, promoting sustainable development and effective management of groundwater resources. To this end, a hydrochemical investigation was conducted in the Zhangye Basin. Types of shallow groundwater in the Zhangye Basin were found to be HCO(3)(-), HCO(3)(-)-SO(4)(2-), SO(4)(2-)-HCO(3)(-), SO(4)(2-)-Cl(-), Cl(-)-SO(4)(2-) and Cl(-). The deep aquifer groundwater type was found to be HCO(3)(-)-SO(4)(2-) throughout the entire area. Ionic ratio and saturation index calculations suggest that silicate rock weathering and evaporation deposition are the main processes that determine the ionic composition in the study area. The suitability of the groundwater for irrigation was assessed based on the US Salinity Laboratory salinity classification and the Wilcox diagram. In the study area, the compositions of the stable isotopes delta(18)O and delta D in groundwater samples were found to range from -4.00 to -9.28% and from -34.0 to -65.0%, respectively. These values indicate that precipitation is the main recharge source for the groundwater system; some local values indicate high levels of evaporation. Tritium analysis was used to estimate the ages of the different groundwaters; the tritium values of the groundwater samples varied from 3.13 to 36.62 TU. The age of the groundwater at depths of less than 30 m is about 5-10 years. The age of the groundwater at depths of 30-50 m is about 10-23 years. The age of the groundwater at depths of 50-100 m is about 12-29 years. For groundwater samples at depths of greater than 100 m, the renewal time is about 40 years.