Long-term agroecosystem research in the central Mississippi River Basin: SWAT simulation of flow and water quality in the Goodwater Creek Experimental Watershed

Authors: Baffaut, Claire; Sadler, Edward; Ghidey, Fessehaie; ANDERSON, STEPHEN - University Of Missouri

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2014
Publication Date: 1/8/2015
Publication URL: http://handle.nal.usda.gov/10113/60606
Citation: Baffaut, C., Sadler, E.J., Ghidey, F., Anderson, S.H. 2015. Long-term agroecosystem research in the central Mississippi River Basin: SWAT simulation of flow and water quality in the Goodwater Creek Experimental Watershed. Journal of Environmental Quality. 44:84-96. DOI: 10.2134/jeq2014.02.0068.

Interpretive Summary: A good watershed model integrates all we know about flow, soils, topography, and human activities in the watershed. Data have been collected since 1971 in the Goodwater Creek Experimental Watershed, which is part of the Central Mississippi River Basin Long-Term Agricultural Research site. An existing hydrologic simulation model, the Soil and Water Assessment Tool, was modified to better simulate how water moves through a very dense layer of clay that restricts infiltration in the middle of the soil profile. It was also modified to take into account the variations in timing of atrazine application throughout the watershed. These two modifications were needed to reproduce measured data. The model can be used to estimate the impact of other drivers, e.g., changing aspects of climate, land use, cropping systems, tillage, or management practices. As an example, it was used to assess the effects of atrazine incorporation after application and atrazine rates reduction. Incorporation resulted in a 17% simulated reduction in atrazine load when achieved by field cultivation, without significant increase in sediment yields. Reducing atrazine rates produced proportional atrazine transport reductions. The changes relative to water infiltration will be useful to scientists and planners who work with soils that have a similar restrictive layer. The process used to take into account operation timing can be applied to any watershed model and will benefit scientists and resource managers concerned with the interaction of management practices and water quality at watershed scale.

Technical Abstract: A good watershed model integrates all that is known about the bio-physical characteristics of and human activities in that watershed to simulate flow and pollutant transport. Starting in 1971, hydrologic, climatologic, and social data have been collected in the Goodwater Creek Experimental Watershed, which is part of the Central Mississippi River Basin Long-Term Agricultural Research site. The Soil and Water Assessment Tool was calibrated and validated over 1993-2010 for flow, sediment, atrazine and dissolved phosphorus. Specific changes were introduced in the model to: 1) better simulate percolation through and saturation above the claypan, and 2), simulate the spatial and temporal variations of field management operations throughout the watershed. The resulting model was used to assess atrazine incorporation after application and atrazine rates reduction. Model calibration was achieved at the daily time step for flow and at a monthly time step for water quality constituents. The new percolation routines ensured correct balance between surface runoff and groundwater. The temporal heterogeneity of atrazine application ensured correct frequency of daily atrazine loads. Incorporation resulted in a 17% simulated reduction in atrazine load when achieved by field cultivation, without significant increase in sediment yields. Reducing atrazine rates produced proportional atrazine transport reductions. We describe the remaining challenges with simulating flow and pollutant transport in watersheds dominated by claypan soils. The model can be used to estimate the impact of other drivers, e.g., changing aspects of climate, land use, cropping systems, tillage, or management practices.