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The water quality target management of the control unit is a convenient and direct technology for water environment management and the development direction of water environment management in China, involving control unit division and water environment capacity calculation. Taking the Taihu Lake Basin in Jiangsu Province as an example, we propose herein the basic principle of the division of a regional control unit in a plain river network and the method of analyzing the rationality of the control unit division. On this basis, the Taihu Lake Basin in Jiangsu Province was divided into 70 control units. To calculate the water environmental capacity in the plain river network area, we established a water environmental capacity calculation framework based on multiple targets of lakes and rivers, and proposed the goal of water quality “double compliance” of the water environmental functional zone and the assessment section. For this study, we calculated the regional water environmental capacity using the mathematical model of the Taihu Lake Basin’s water environmental capacity, and the water environmental capacities of the 70 control units were allocated by the weight coefficient method, which established water area and functional division length. The research results described herein were applied to the pollution permit management of the Taihu Lake Basin in Jiangsu Province. It provides important technical support for the establishment of a pollution permit system based on the total capacity to improve environmental quality.

Lake currents have an important impact on distribution of pollutant concentrations in large shallow lakes. Taking Taihu Lake as an example, in view of the characteristics of wind-driven water flow in the lake, this paper puts forward a water environmental capacity calculation method that uses wind direction and wind speed combined frequency to provide joint correction and pollution zone control for the designed hydrological conditions. In the study, the total length of the pollution belt was controlled to be 10% of the length of the study area, and a mathematical model of two-dimensional unsteady water quantity and quality in Taihu Lake was established. By analyzing the hydrological water quality characteristics and measured data of Taihu Lake in recent years, the flow field and concentration field were simulated and verified, the mathematical model and the plausibility of the parameters were calibrated. The water environmental capacity of Taihu Lake basin was calculated by this method. The calculated results showed that the water environmental capacity of chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN) in Taihu Lake were 113,331 t·a−1, 479 t·a−1 and 6,521 t·a−1. By providing a technical basis for total pollutant control and management in Taihu Lake basin, this study is conducive to the planning and management of water environment.

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