Nitrogen component in nonpoint source pollution models

Authors: YUAN, YONGPING - Environmental Protection Agency (EPA); Bingner, Ronald - Ron; MOMM, HENRIQUE - Middle Tennessee State University

Submitted to: Precision Conservation: Geospatial Techniques for Agricultural and Natural Resources Conservation
Publication Type: Book / Chapter
Publication Acceptance Date: 5/29/2017
Publication Date: 11/8/2018
Citation: Yuan, Y., Bingner, R.L., Momm, H. 2018. Nitrogen component in nonpoint source pollution models. Precision Conservation: Geospatial Techniques for Agricultural and Natural Resources Conservation. (59)27-64. https://doi.org/10.2134/agronmonogr59.2013.0012.
DOI: https://doi.org/10.2134/agronmonogr59.2013.0012

Interpretive Summary: The health of ecosystems is dependent on maintaining good water quality from a variety of landscape features, particularly from agricultural crop lands, conservation areas, wetlands, lakes, and streams. Agricultural management practices are used to reduce nonpoint source pollution and improve water quality, but evaluating the effectiveness of these practices is very difficult. Many simulation models have been developed as an aid in making good management decisions of selecting conservation practices that reduce pollutant loads from agricultural landscapes. This study provides an evaluation of the science and capabilities of various models to simulate nitrogen loads from agricultural systems. Although components of the nitrogen cycle included in each model varied, such as with crop nitrogen uptake, there exist a lot of similarities of the models in simulating nitrogen processes. The review of many model applications found that all models were able to make reasonable predictions of total nitrogen loading following model calibration. However, for a certain set of management applications commonly one model would perform well, but in another set of applications the same model would not perform well, regardless of the complexity of the model in representing nitrogen processes, particularly in cases associated with dissolved nitrogen. The comparison between the models suggests the capability of the current state-of-the-art models to accurately predict nitrogen losses from agro-ecosystem remains uncertain at this time.

Technical Abstract: Pollutants entering a water body can be very destructive to the health of that system. Best Management Practices (BMPs) and/or conservation practices are used to reduce these pollutants, but understanding the most effective practices is very difficult. Watershed models are an effective tool to aid in the decision making process of selecting the BMPs that are most effective in reducing the pollutant loading and are also the most cost effective. The Erosion-Productivity Index Calculator (EPIC), now the Agricultural Policy/Environmental eXtender (APEX) for application at field scale, the Annualized Agricultural Nonpoint Source pollution (AnnAGNPS) and the Soil and Water Assessment Tool (SWAT) for application at watershed scale have been developed as technological tools for evaluation of the impact of agricultural management practices on water quality and long-term soil productivity. Evaluation of model performance at various scales and locations demonstrated mixed results due to the complexity of nitrogen processes. In this book chapter, nitrogen processes simulated in each model were reviewed and compared. Furthermore, current research on nitrogen losses from agricultural fields were also reviewed. Finally, applications with those models were reviewed and selected successful and unsuccessful stories were described. Although components of the N cycle included in each model varied, there are a lot of similarities in simulating N processes. The estimation of nitrogen loss at the watershed scale is a complex problem; nonpoint source pollution models need to be further improved, and novel technology is still needed to integrate nutrient models with hydrological and erosion models.