Study On Total Amount Control Of Water Pollutants In Ecological Conservation Area Of Xiaonhai, Songzi

The Xiaonanhai Ecological Conservation Area of Songzi City is located in the upper reaches of the Dongting Lake Basin.The water system of the conservation area is mainly Xiaonanhai Lake.The lake water flows into the Dongting Lake through the Songxi River and is an important part of the Dongting Lake Basin.Due to population growth,economic development and lake development,the water surface area and volume of Xiaonanhai Lake have been drastically reduced,lake water pollution is serious,lake functions and benefits are declining,lake protection is facing serious threats,and water pollution prevention and control forms are severe and need to be rectified.Objectively evaluate the current situation of water environment in Xiaonanhai ecological conservation area,comprehensively check the pollution source and pollution load of the basin,and carry out effective total control for the main pollutants,which is of great significance to the environmental improvement of Xiaonanhai water environment and the improvement of ecological conservation area.This paper takes Xiaonanhai Lake as the research object.According to the data of the first national pollution source survey in 2010 and the statistical data of the basin,the pollution load of the basin in 2016（the current year）and the pollution load of 2025（planning year）are analyzed and applied.MIKE21 software constructs the mathematical model of water dynamics and water quality in Xiaonanhai Lake,and simulates the movement of water movement and pollutants under dynamic hydrological conditions in Xiaonanhai Lake.Combined with local ecological and environmental protection planning,the total amount of pollutants is proposed for Xiaonanhai design.The measures for reduction measures were calculated;the water environment capacity of Xiaonanhai Lake was calculated;the effect of the total pollutant reduction measures was evaluated by the two-dimensional hydrodynamic water quality model,and the effect of total capacity control was analyzed.The main work and conclusions are as follows:1.In recent years,the water quality monitoring data of Xiaonanhai Lake shows that the water quality of Xiaonanhai Lake is poor.The water quality category is V or V.The COD of the main pollution factors is 1.6 times,the TN exceeds 1.7 times,and the TP exceeds 6.2 times.NH₃-N Exceeding the standard of 0.1 times,the pollution is serious,and it is in a state of moderate eutrophication;the water quality of the Hongqi Canal and Arthur Harbor in the lake channel is poor,and the water quality category is V or worse.2.The current annual pollution load of Xiaonanhai Lake is COD1570.1t/a,TN137.3t/a,TP25.01t/a,NH₃-N60.7t/a,sediment of various pollution sources,and aquaculture in the lake.The pollution load of the three pollution sources such as the tail water of Chengnan Wastewater Treatment Plant has the highest contribution rate,and the sum of COD,TN,NH₃-N and TP is 50%,50%,55%and 64%respectively.3.The water environment capacity of Xiaonanhai Lake under the target of Class III water quality is COD511.76t/a,TN52.27t/a,TP1.56t/a,NH₃-N24.59t/a;4.According to the relevant planning of Songzi City,the design of the total pollutant reduction measures system of“control source interception”,“water ecological restoration”and“water resources guarantee”was proposed,and the measures were reduced through the two-dimensional hydrodynamic water quality model.Simulation of the effect shows that:（1）Before the introduction of the Chengnan WWTP and the Chengnan area of the catchment into the third-grade wetland,the water diversion project from Xinhe or Songxi River must be completed to ensure the stability of the Xiaonanhai Lake inflow;（2）Regardless of the water supply from Xinhe or Songxi River to Xiaonanhai Lake,the reduction effects of COD,TN,TP and NH₃-N are basically the same.Therefore,in order to better ensure the improvement of water quantity and water quality,it is recommended to use the new water source of Xinhe and Songxi River.The water transfer plan will use Xinhe River as a conventional hydration water source.Due to the high concentration of TN in the Songxi River,the concentration of TN in Xiaonanhai may increase and the water quality deteriorates.Therefore,the Songxi River is selected as the emergency hydration water source.（3）After the implementation of the pollutant reduction measures of“control source interception,water ecological restoration（Excluding"restoration of three-dimensional aquatic plant communities in xiaonanhai lake"）and water resources protection”before2025,Xiaonanhai COD,TN and NH₃-N can reach surface water III Class level,TP can reach the level III water level of surface water river（0.2mg/L）.If TP is required to reach the level III water level of surface water lake（0.05mg/L）,“Rehabilitation Project of Stereo Aquatic Plant Community in Xiaonanhai”must be taken.5.The total amount of pollutants entering the lake in 2025 is COD1362.8t/a,TN120.6t/a,TP18.5t/a,NH₃-N51.7t/a,and the reduction of treatment measures is COD1053t/a,TN116.1t/a,TP18.4t/a,NH₃-N40.4t/a,the amount of pollutants entering the lake after reduction by treatment measures is COD309.8t/a,TN4.5t/a,TP0.1t/a,NH₃-N11.3t/a,both lower than the water environment capacity of Xiaonanhai Lake,indicating that the pollutant reduction measures are effective and feasible.