Estimation of nitrogen and phosphorus non-point source pollution fluxes in basins without monitoring data based on remote sensing information
There are still many basins in China that suffer from serious non-point source pollution but lack hydrological monitoring.Estimating the non-point source pollutant fluxes into rivers in these basins is very difficult.To solve this problem,this study selected the upstream basin of Miyun Reservoir as a typical experimental area,using the EcoHAT model and remote sensing hydrological station technology to simulate the process of nitrogen and phosphorus non-point source pollution on a monthly scale from 2001 to 2022.By quantifying the filtering capacity of vegetation on the riparian to pollutants,the simulation results were corrected to complete the estimation of non-point source pollution fluxes.The results showed that:① The constructed correction model had good accuracy,with R² above 0.69 and RMSE lower than 0.07;② The accuracy of the simulation results improved significantly after correction,with the NSE range for total nitrogen inflow flux before correction ranging from 0.61 to 0.72,and the NSE range after correction increasing to 0.77 to 0.86.The NSE range for total phosphorus inflow flux before correction ranged from 0.61 to 0.75,and the NSE range after correction increased to 0.76 to 0.82;③ After correction,the total nitrogen and total phosphorus non-point source pollution inflow fluxes in the Miyun Reservoir upstream watershed from 2001 to 2022 were 25849.59 t and 682.49 t,respectively,which decreased by 35.19%and 27.04%compared to before correction.Overall,the total nitrogen and total phosphorus non-point source pollution inflow fluxes in the watershed showed a downward trend,with a total nitrogen change rate of-1.66 t·a-1 and a total phosphorus change rate of-0.07 t·a-1.
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