Study on Geochemical Evolution and Isotopic Characteristics of Groundwater in Arid and Semi-arid Areas

The utilization ratio of water resources is remarkably high in the Shiyang River Basin, which is a typical zone susceptible to water resources crisis in the arid area in China. Owing to the continuous deterioration of the ecological environment in the Shiyang River Basin, it is of great significance to investigate the groundwater circulation and geochemical evolution law in this area. Samples were collected from the top of the Qilian Mountains to Hongyashan Reservoir along the flow cross section. Isotopic survey and geochemical technology were employed to analyze hydrochemistry and environmental isotopes of precipitation, surface water and groundwater. Results indicated that precipitation was the provenance of water resources in the Shiyang River Basin. The groundwater runoff system accepted river leakage and irrigation water infiltration recharge constantly in the process of the runoff to the downstream, meanwhile drained through the river overflow and pumping with a primary vertical movement. The downstream of the Basin was the main groundwater discharge area. The groundwater in the northern Basin overflowed into the surface water due to the basement uplift. The TDS (Total Dissolved Solids) values were between 131 and 1750 mg/L, gradually increasing along the flow direction. The hydrochemical types showed an obvious zonation from the upper reaches to the lower, which gradually changed from bicarbonate to sulphates.