A Catchment-Scale Hydro-Biogeochemical Model for Simulating Watershed Nitrogen Process and Key Factors in Modeling Denitrification

Abstract:

Nitrogen non-point source (NPS) pollution is a great concern to the society for its widely presence and negative impact on aquatic environment and public health. Denitrification is a key process as it removes excessive nitrogen in the ambient environment, controlling nitrogen export from watershed affected by agricultural activity.

Distributed environmental models, like SWAT, have been a useful tool for investigating denitrification process and its effect in agricultural watersheds, but their simple model structures introduce uncertainty on the predicted results, especially for total denitrification amount and its spatial patterns. Despite recent development, it is still unclear to what extent limitations in representing realistic landscape connectivity in these models would affect nitrogen process simulations. To answer this question, a new coupled model is developed in which nitrogen-related processes involved in SWAT are coupled into a fully distributed hydrological model (DHSVM) which features connection and interaction among neighboring spatial units. In this work, the new model, called DHSVM-N, is compared to SWAT, which has no spatial connectivity among its spatial units for nitrogen transport, to investigate impacts of hydrological processes simulation and model structure on denitrification process modeling result.

Results confirms the important role of soil moisture and hydrological process in denitrification simulation. Results also show model structure affects both the magnitude and spatial pattern of simulated denitrification. Simple model structure may risk underestimating watershed denitrification potential and contribution of denitrification “hot spots”. A more realistic model structure incorporated in the model as is done here more accurately pinpoints denitrification “hot spots” and provides better and more accurate picture for agricultural management decision making. The new DHSVM-N model is further applied to investigate how different wetland conditions and placements could affect watershed denitrification and nitrogen exports under various designed scenarios.