Modeling Runoff Water Quality to Improve Phosphorus Loss Assessment in the Mississippi Delta

Ramirez-Avila, J. J., Bolster, C., Locke, M., McAnally, W. H., Oldham, L., Ortega-Achury, S. L., Osmond, D., & Radcliffe, D. (2017). Modeling Runoff Water Quality to Improve Phosphorus Loss Assessment in the Mississippi Delta. 2017 World Environmental and Water Resources Congress. Sacramento, CA.

nalytical tools to explore actions and policy alternatives for managing pollutants loads from agricultural fields has been promoted by the lack of information regarding water quality monitoring and associated costs. A study was conducted i) to predict the effect of changing land use and management practice scenarios on runoff quantity/quality from an 11.3 ha agricultural subwatershed in the Mississippi Delta region; and ii) to assess the potential for phosphorus (P) in runoff from reference and simulated agricultural management scenarios. The Agricultural Policy Environmental Extender (APEX) model was used to predict changes on runoff quality/quantity, while the Mississippi P-Index was the used for a P risk assessment analysis. APEX was calibrated and validated by comparing predicted results over four years of monitoring information for event based runoff volumes, sediment and P loads and crop productivity changes under reduced tillage and the establishment of cover crops after the crop season. Water quality/quantity changes were predicted with APEX for proposed land management scenarios, which considered the use of conventional or reduced tillage, cover crops, and nutrient management plan. Model outputs were used to rank the risk of P contribution to surface water for each scenario. Results demonstrated the MS P-Index did not adequately identify relative water quality; a further sensitivity analysis needs to be performed to identify the importance of individual input factors on final P-Index ratings in order to update and modify the MS P-Index.