Water environment carrying capacity in Bosten Lake basin

By combining a system dynamics (SD) model and an analytic hierarchy process (AHP), an evaluation index system for water environment carrying capacity (WECC) in the Bosten Lake basin was developed that considers mutual interactions among six subsystems of industry, agriculture, population, water supply, water ecology, and water pollution. The model was tested with data including water level, surface area, water volume, chemical oxygen demand (COD) concentration, total nitrogen (TN) concentration, and salinity concentration observed for 2002–2010. In addition, the model was applied to study and compare the trend of WECC under seven scenarios from 2002 to 2024. The results indicated that the WECC trends of industrial water consumption drop 0.5% each year (Scenario 2) and water transport from Bosten Lake to the Tarim River of 0.5 billion m³ each year (Scenario 6) were the same as Scenario 1 (present mode), which means that Scenario 2 and Scenario 6 cannot improve the WECC of Bosten Lake. As for the other four scenarios, the effects on the WECC of Bosten Lake were in the order of increase ground water exploitation (Scenario 7) > water-saving irrigation investment (Scenario 4) > increase reed area (Scenario 5) > increase industrial water reutilization rate (Scenario 3). Although the four scenarios can improve the WECC of Bosten Lake, only Scenario 7, i.e. increasing ground water exploitation rate by 3%, can turn the carrying status of WECC from poor to good. In addition, population and concentrations of COD, TN, and salinity will improve in the improved scheme compared to the present mode. The sensitivity of three parameters including the growth rate of water demand per 10⁴ USD, growth of reutilization rate in industrial water, and ecological water transport were analyzed. The results indicated that both growth rate of water demand per 10⁴ USD and growth of reutilization rate in industrial water increased the WECC of Bosten Lake. Moreover, the WECC of Bosten Lake will be negatively affected when the water quantity of ecological water transport from Bosten Lake to the Tarim River exceeds 1 billion m³. The results provide a scientific basis for a reasonable development pattern in protecting the WECC of Bosten Lake.