Water environment capacity in arid area: A case study of the Yongding River in Zhangjiakou City

The deterioration of water quality in the watersheds of arid regions has become an issue that cannot be ignored. The salient features of such deterioration are small water volume and high levels of pollution, and the task of improvement is very difficult.This report focusses on the upper reaches of Yongding River in Zhangjiakou City. According to the current water pollution status, the chemical oxygen demand (COD), ammonia nitrogen and total phosphorus are factors that affect capacity, and the improved coefficient formula method suitable for arid areas was applied to study the water environmental capacity and rational allocation of the upper reaches of the Yongding River in Zhangjiakou City.The results showed that the water environmental capacity of COD, ammonia nitrogen, and total phosphorus were 16 264.44, 789.15 and 183.64 t·a^–1, respectively. The COD reductions for the industry, urban life, rural life, agricultural sources, livestock and poultry farming and tourism sectors were 317.05, 3 108.66, 318.10, 67.14, 130.19, and 207.57 t·a^–1, respectively; the ammonia nitrogen reductions were 72.83, 1 212.64, 238.95, 45.48, 237.37, and 97.89 t·a^–1; and the total phosphorus reductions were 2.23, 61.48, 12.35, 4.49, 10.87, and 3.39 t·a^–1, respectively. The water environmental capacities measured in Zhangjiakou area on the upper reaches of Yongding River are scientifically sound and within reasonable expectations, and provide a scientific basis for the relevant administrative departments of the city to carry out water environment management and to formulate discharge limits for key enterprises, which has a practical significance.