Yongjiang River HSPF Model For Study Control Path Of Total Nitrogen Emiission To The Sea

In recent years,as the impact of human activities on the surface water environment has intensified,the rivers are increasingly polluted by nitrogen,and the concentration of total nitrogen has been high in recent years in the rivers entering the sea of the Yongjiang River in Ningbo City,so the Yongjiang River basin has been taken as the research object in this study,and used the historical data of water quality monitoring sections from 2016 to2021 to briefly analyze the pollution of total nitrogen in the Yongjiang River basin,has based on this,the more intensive sampling points were developed in 2022.The analysis and investigation of the current situation of total nitrogen in different water periods;Spatial and attribute data of the Yongjiang River basin was collected,the localized HSPF model of the Yongjiang River basin was established,hydrology,water quality,and influent fluxes were simulated for 2018-2021,and loads of various sources of total nitrogen entering the sea were calculated,and different scenarios were proposed for simulation and effect analysis of total nitrogen pollution in the Yongjiang River basin in 2021,based on which,a control path for total nitrogen emissions into the sea from the Yongjiang River basin was proposed.The main conclusions are as follows:(1)The total nitrogen concentration in the study area in recent 7 years is relatively high,and the total nitrogen pollution in the whole area is relatively serious,and the total nitrogen pollution in the dry season is obvious.(2)The simulated values of runoff into the sea and total nitrogen concentration in the study area fluctuated from 2018 to 2021.The simulated values of runoff into the sea was145,320,500 m~3,240,7336,100 m~3,165,9336,600 m3 and 260,435,100 m3 respectively;The simulated values of total nitrogen concentration was 3.54mg/L,3.47mg/L,2.98mg/L and 3.18mg/L,respectively.The simulated values of annual total nitrogen flux into the sea is 5100.804 tons,8353.456 tons,4944.805 tons and 8281.786 tons,respectively.(3)The total nitrogen flux into the sea from the total nitrogen pollution sources in the study area in 2021 was simulated and the total nitrogen flux into the sea was 5,771.15 tons,of which the total nitrogen flux into the sea from urban sewage plants accounted for37.25%,the total nitrogen flux from urban and rural domestic sewage accounted for31.19%and 24.56%respectively,and the total nitrogen flux from agriculture accounted for only 6.20%.The total nitrogen flux in direct discharge industry accounts for less than 1%.(4)According to the pollution situation in the study area in 2021,the total nitrogen flux into the sea of urban sewage treatment plants will be reduced by 13%according to the scenario;the total nitrogen flux into the sea will be reduced by 6.81%if the rate of urban domestic wastewater coverage in each district is increased to 95%;the total nitrogen flux into the sea will be reduced by 12%and 15.67%if the coverage rate of rural domestic wastewater facilities is increased to 95%and 100%respectively.The reduction rate of total nitrogen in the Yongjiang River basin is smaller when the land use of arable land in the Yongjiang River basin is changed,and the reduction rate of total nitrogen input to the sea was 3.22%when the arable land with slope greater than 15°was converted to forest land and the reduction rate of total nitrogen input to the sea was 3.22%when the arable land with slope greater than 15°was converted to grassland.