Water in the Arid Zone―About Xinjian District, China―

Abstract

Turfan and Jyungar basins which have some closed salt lakes are typical closed basins in Xinjian district in western China. A research of water quality was conducted to make clear the groundwater flow in arid and semi-arid zones. The absolute quantity of ions in groundwater, river water and lake water rapidly increases as they flow into the basin and the maximum value was observed at the lake which located in the central part of the basin. The salinity also increases gradually from the foot of mountain to Ayding Lake. The dissolved substances of surface water and groundwater are composed of Ca²⁺, Mg²⁺, Na⁺ and K⁺, and gradually change from Carbonate Hardness type to Non Carbonate Alkali type according to the increase of salt content. Na⁺ and Mg²⁺ increase in accordance with the salt increase and anion changes from HCO₃^->SO₄^2->Cl^- type to SO₄^2->Cl^->HCO₃^- type as pointed out by Scholar (1959) and Langbein (1961). HCO₃^- dissolution decreases and precipitates as salt increases. NaCl and MgCl₂ increases in lake water.

The lowering of lake water level is observed in some closed lakes, such as Lake Aibir and Lake Ayding. Because of recent increase of precipitation and air temperature, it’s hard to consider that the climatological change is a element of the water level lowering. It is caused by artificial influences such as remarkable demand for irrigation and domestic use as pointed out by Yang Chuande (1993).

Limnological research on Selim Lake which is deepest lake in this area (86.9m) was carried out in August, 1997 and leads the following results. The water level dose not change largely, which is different from other salt lakes such as Ayding and Aipi Lake. And the high value in salinity is not observed like another lakes. From the view point of thermal stratification and water quality profile, the Lake Selim is classified as a holomictic and dimictic lake. The transparency is about 7-7.5 m, not so high value as an oligotrophic lake.