干旱区生态环境知识资源中心

In this study six sites were selected and observations of water table in one well were collected near the town of Ejina in the lower reaches of the Heihe River in northwest China. Forty-one soil samples were collected at different depths from the ground surface to the water table at each site to examine the occurrence of soluble salts and water contents in the unsaturated zone. Six groundwater samples were taken at the corresponding sites when the water table was revealed. The results indicate that concentrations of soluble ions of the soils in the unsaturated zone have a tendency to decrease with depth from the ground surface to the water table and ion contents increase at depths where root zones of the populus euphratica and the tamarisk develop. SO4 is the major anion in both the soluble ions of the soils in the unsaturated zone and in the groundwater in the saturated zone at each site. TDS in the groundwater range from about 1 g/L along the river to near 10 g/L in the middle of the Ejina Oasis. Depth to the water table varies between 2 and 4 m. The water table showed a slight decreasing trend in the past dozen of years. Decrease in the water table is believed to have an important bearing on the degradation of the ecological environment in the oasis.