Hydrochemical assessment of the largest desert reservoir in arid oasis area in Asia

97735 artificial reservoirs have been built in China since 1950s, which could guarantee the supply of urban water and agricultural irrigation. In arid oasis area, only the water of reservoir is available as water resource. The study of hydrochemical characteristics is the prerequisite for evaluating the water quality of domestic water and irrigation water. In the Hongyashan Reservoir, the middle of the Shiyang River Basin and the Tengger desert and Badain Jaran desert, water samples were taken at different points of the lake for about 3 years. The chemical characteristics of the lake water and their influencing factors were studied. The results of the samples for the test have shown that water of the Hongyashan Reservoir is weakly alkaline. And the main compositions of ions in the water are Ca²⁺ and (text{HCO}_{3}^{ - }), hydrochemical type is Ca–HCO₃. In terms of the seasonal variation of Hongyashan Reservoir, except for (text{NO}_{3}^{ - }), the ions in the rest of the water showed roughly the same changeable characteristics in that the composition of ion is higher in summer and autumn, but lower in winter and spring. This is consistent with the seasonal variation in runoff ions throughout the Shiyang River Basin. Ionic characteristics are consistent with the ionic values of dry lakes in the world, which are suitable for urban water and water for irrigation, but are slightly higher than the global lake background standard. Carbonate weathering products are the main source of water ions in Hongyashan Reservoir, and evaporation also affects the ion characteristics of water.