Numerical simulation model of water quality evolution in urban rivers considering adsorption–desorption process of nitrogen and phosphorus in sediments

In order to more realistically simulate the river channel water quality considering the characteristics of sediment release, it is necessary to couple the simulation model of sediment release to the hydrology-hydrodynamics-water quality model to quantify the complexities involved in the nitrogen and phosphorus cycle in river channel sediments. However, in the existing studies, most of the water–sediment models constructed in the analysis of single pollutants such as NH3-N or BOD, but fail to consider the interaction between multiple pollutants, and the model software related to water quality simulation fails to establish complex river sediment pollution simulations, there are still challenges in the application of the existing water quality module of the MIKE simulation software to the nitrogen and phosphorus cycle of sediments. In this study, based on the new sediment nitrogen and phosphorus release mechanism, we rewrite the water quality module ECOLab of the MIKE 21 model. The laboratory test results and the measured data are applied to the calibration of the model parameters. The new water quality module considering the adsorption–desorption process of sediments was embedded into the MIKE 21 model. The new module couples the MIKE model and the SWWM model to establish a 2D water quality model of river channel hydrology-hydrodynamics-water quality-sediment release coupling. This model targeted applies in urban river channels with sediment releasion as the main pollution. The results show that the new model has significantly improved the simulation accuracy of BOD and NH3-N, and has an optimized effect on the simulation of TP. The R, NSE, and RMSE values of the model for NH3-N simulation are 0.904, 0.845, and 0.612. This model is more suitable for numerical simulation of urban river water quality where sediment release is the main cause of endogenous pollution.