Long-Term Agroecosystem Research in the Central Mississippi River Basin: SWAT Simulation of Flow and Water Quality in the Goodwater Creek Experimental Watershed

Abstract

Starting in 1971, stream flow and climatologic data have been collected in the Goodwater Creek Experimental Watershed, which is part of the Central Mississippi River Basin (CMRB) Long-Term Agroecosystem Research (LTAR) site. Since 1992, water quality and socio-economic data have complemented these data sets. Previous modeling efforts highlighted the challenges created by the presence of a claypan. Specific changes were introduced in the Soil and Water Assessment Tool (SWAT) (i) to better simulate percolation through and saturation above the claypan and (ii) to simulate the spatial and temporal distributions of the timing of field operations throughout the watershed. Our objectives were to document the changes introduced into the code, demonstrate that these changes improved simulation results, describe the model's parameterization, calibration, and validation, and assess atrazine [6-chloro-N-ethyl-N¢-(1-methylethyl)-1,3,5-triazine-2,4-diamine] management practices in the hydrologic context of claypan soils. Model calibration was achieved for 1993 to 2010 at a 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 the correct frequency of daily atrazine loads. Atrazine incorporation by field cultivation resulted in a 17% simulated reduction in atrazine load without a significant increase in sediment yields. Reduced atrazine rates produced proportional reductions in simulated atrazine transport. 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, in this context.

Long-Term Agroecosystem Research in the Central Mississippi River Basin: Goodwater Creek Experimental Watershed Flow Data

“…During 1997 to 2001, the common measurement period at the plot, field, and stream sites, cumulative discharge per unit area at Weir 1 was 1635 mm compared with 1335 mm at F1. The 18% difference is close to the 20% groundwater contribution to stream flow obtained by hydrograph separation on daily values from 1993 to 2010 (Baffaut et al, 2015). Maximum daily discharge per unit area was between 55 and 70 mm on the fields on 23 Aug. 2000.…”

“…Stream flow data have been used to develop pollutant exports for various catchment sizes (Baffaut et al, 2013; Lerch et al, 2015a, 2015b), which then have been used to assess temporal trends in water quality (Lerch et al, 2011b; O'Donnell, 2012; Sadler et al, 2012) and the effects of land use (Lerch et al, 2011a) on herbicide and nutrient transport. Modeling efforts included parameterization of the Root Zone Water Quality Model (RZWQM) (Ghidey et al, 1999), the Soil and Water Assessment Tool (SWAT) (Baffaut et al, 2015), and the Agricultural Policy/Environmental Extender (APEX) (Mudgal et al, 2012). These efforts confirmed that correct parameterization of the claypan layer and of the upper soil layers and good representation of the percolation processes in the soil profile are paramount to correctly simulating flows in this setting.…”

Long-Term Agroecosystem Research in the Central Mississippi River Basin: Dissolved Nitrogen and Phosphorus Transport in a High-Runoff-Potential Watershed

“…These surveys reported the proportion of each crop receiving N and P fertilizer and the average annual rates applied. The applicability of the statewide fertilizer use data to GCEW was confirmed by farmer surveys in 1992 (Rikoon et al, 1996) and 2006 (Baffaut et al, 2015a; Sadler et al, 2015a). The frequency of the National Agricultural Statistics Service (NASS) reports for Missouri was inconsistent across the four relevant crops: corn and soybean reports existed for 12 yr, winter wheat reports for 10 yr, and sorghum for only 2 yr (1992 and 2003).…”

Long-Term Agroecosystem Research in the Central Mississippi River Basin: Introduction, Establishment, and Overview

“…The next four papers (Sadler et al, 2015; Baffaut et al, 2015b; Lerch et al, 2015b, 2015c) document specific data themes of weather, flow, herbicides, and nutrients. The final four papers (Lerch et al, 2015a; Kitchen et al, 2015; Sudduth et al, 2015; Baffaut et al, 2015a) document research that used data described in the first five papers.…”