[Contribution Analysis of External Source Pollution Load and Environmental Capacity Estimation of Reservoirs in...

To explore the source of the pollution load and its contribution rate in the upper reaches of the plateau reservoir and to analyze the water environment capacity of the reservoir, we selected the Chaishitan Reservoir in the Yunnan Plateau as the research object, applied the pollutant discharge coefficient method to estimate the source of external pollution in the upstream basin of the reservoir, used the simultaneous monitoring data of hydrology and water quality to calculate pollution load into the reservoir, and used the eutrophication model to calculate the maximum capacity of TN and TP in the reservoir under different water quality target scenarios. The results showed that:① the main characteristic pollutants in Chaishitan Reservoir and the above basin were TN and TP. ② COD and TP in the upper reaches of the reservoir mainly came from rural non-point source pollution, with contribution rates of 49.40% and 50.11%, respectively; NH₄⁺-N and TN mainly came from urban domestic pollution sources, with contribution rates of 45.76% and 33.77%, respectively. Among the contributions of rural non-point source pollution, the contribution rates of COD and TP in Luliang District were 34.82% and 36.82%, respectively. The contributions of COD, NH₄⁺-N, TN, and TP to urban domestic pollution were the highest in Qilin District, all of which were up to 65%. ③ The inflows of COD, NH₄⁺-N, TN, and TP were 28050.90, 2465.16, 4680.54, and 870.93 t·a^-1, respectively. The inflow of TN and TP pollution load was 4637.80 t·a^-1 and 125.04 t·a^-1, respectively. ④ When the target of water quality was Class Ⅲ, and the requirements of the Water Function Zoning of Yunnan province were met, the environmental capacities of TN and TP were 1102.62 t·a^-1 and 54.85 t·a^-1, respectively. Rural non-point source pollution and urban domestic pollution sources were the main sources of pollution in the upper reaches of Chaishitan Reservoir, which were priority control sources. These research results can provide a scientific theoretical basis for pollution source treatment in the plateau reservoir basin.