Simulation Study On Water Environment Carrying Capacity Based On ArcSWAT

At present,the water environment carrying capacity is mostly characterized by the water environment capacity,that is,the water environment carrying capacity is the maximum value of pollutants that a certain water body can bear under a specific environmental objective.So it is necessary to analyze the water environment carrying capacity from the water pollution mechanism.Pollution sources are mainly divided into point source pollution and non-point source pollution,as point source pollution in China has been controlled to some extent in recent years,non-point source pollution has become an important factor affecting the carrying capacity of the water environment,and nitrogen and phosphorus nutrients are the main pollutants causing non-point source pollution.The traditional method of evaluating the carrying capacity of water environment has many parameters and is complicated to calculate.With the SWAT model,the Tieling section of Liaohe River basin was selected as the study area,and the sub-basin was used as the basic calculation unit to evaluate whether the total amount of nitrogen and phosphorus lost from each sub-basin exceeds the maximum water environment carrying capacity of the sub-basin in a certain period of time through the minimum access standard of Class IV water.Finally,different scenarios were set to evaluate the effect of different management measures on pollutant reduction in the overload sub-watershed.The main results are as follows:(1)The spatial data and attribute data of Tieling section of Liaohe River basin were collected to construct the SWAT model,and then the sensitivity of the parameters was analyzed as well as the hydrological and water quality data of the model were rate determined and verified respectively.The results showed that R~2 was greater than 0.7and NS was greater than 0.65,indicating that the simulation results had little difference with the measured results,and the simulation effect was good.The SWAT model can be used to simulate the water environmental carrying capacity in Tieling section of Liaohe River Basin.(2)The data of total nitrogen and total phosphorus simulated by the SWAT model were analyzed for spatial and temporal distribution characteristics.It can be found that,in terms of time,the multi-year monthly average load of total nitrogen and total phosphorus in the flood season had the highest share of the annual load in August,and the peak loss of total nitrogen and total phosphorus in a year was mainly concentrated in May to August.Spatially,the average annual loss of total nitrogen in the upper sub-basins such as 26,32,35 and 37 was within 40 kg/km~2,the average annual loss of total phosphorus was within 10 kg/km~2.The average annual loss of total nitrogen in sub-basins 51,67,69 and 73 of the downstream was more than 115 kg/km~2,and the average annual loss of total phosphorus was more than 20 kg/km~2,and the loss of total nitrogen and total phosphorus increased gradually from top to bottom of the Liaohe River main stream.(3)The maximum water environment carrying capacity of each sub-basin was calculated by combining the requirements for total nitrogen and total phosphorus concentration in the minimum water quality standard(Class IV)of Liaohe River,and compared with the actual annual average total nitrogen and total phosphorus loss of each sub-watershed.Total nitrogen and total phosphorus in sub-basins 9,11,67,69 and73 were found to exceed the water environment carrying capacity of the sub-basins in which they are located.Finally,the pollutant reduction effects of these five sub-basins were evaluated by setting different measures and comparing the total nitrogen and total phosphorus reduction rates under various scenarios to find the most effective combination of measures.