Hydrochemical characteristics and water quality assessment of surface water in the northeast Tibetan plateau of China

The Tibetan Plateau is very important as it provides water resources for about 40% of the world's population and the runoff-yield area of the Yellow rivers. In this paper, the water quality in Xiahe County, located in the northeast Tibetan Plateau, was investigated. Six parameters (chloride, chemical oxygen demand, ammonia nitrogen, nitrate, fluoride, sulfate) were selected to assess the quality and health status of surface water in Xiahe County. The main types of hydrochemical in the surface water were considered to be Mg2+-Ca2+-HCO3--Cl- and Mg2+-Ca2+-HCO3-. The cations and anions were mainly from weathering and dissolution of carbonate rock. Fuzzy comprehensive evaluation (FCE) results showed that the water quality in all 69 sampling sites was all class I. The integrated health status was higher than 0.95 and the health rate was 100%. Although ammonia nitrogen was recognized as the main contaminant, it had little effect on the entire body of water. Overall, the surface water qualities of most samples in Xiahe County were found to be in good condition.