ABSTRACT:

This resource contains the SWAT-MODFLOW model for the Santa Fe River of North Central Florida used in the Floridan Aquifer Collaborative Engagement for Sustainability (FACETS) project. The FACETS project was funded by the USDA National Institute of Food and Agriculture (Award Number: 2017-68007-26319) to promote the economic sustainability of agriculture and silviculture in North Florida and South Georgia while protecting water quantity, quality, and habitat in the Upper Floridan Aquifer and the springs and rivers it feeds (https://floridanwater.research.ufl.edu/). SWAT-MODFLOW couples the Soil and Water Assessment Tool (SWAT) to the U.S. Geological Survey modular finite-difference flow model (MODFLOW) to produce an integrated surface-groundwater model (https://swat.tamu.edu/software/swat-modflow/). Within SWAT-MODFLOW, SWAT handles most surface and soil processes, MODFLOW handles groundwater processes, and both models interact to simulate stream flows.

The SWAT portion of this model was developed using USGS digital elevation models, the 2017 Statewide Land Use / Land Cover map of the Florida Department of Environmental Protection (FDEP), Florida Department of Health septic tank data, STATSGO soil maps, the Public Land Survey System, and NLDAS weather data. Agricultural and silvicultural production land uses and management practices implemented within SWAT were co-developed with stakeholders in a participatory modeling process (PMP) and included row crops (corn-peanut and corn-carrot-peanut rotations) forage crops (bermudagrass hay and pasture), and production forestry (slash pine). Additional land uses implemented in SWAT included urban, low-density residential, septic tanks, rapid infiltration basins, fertilized lawns, natural grass, wetlands, and open water. The MODFLOW portion of the model was developed from the larger North Florida Southeast Georgia (NFSEG) MODFLOW model (version 1.0) as developed by the St John’s River and Suwannee River Water Management Districts. A detailed description of the complete model development process can be found in a document within this resource.

Calibration of the model was conducted using a Bayesian Sample-Importance-Resample method. Data used in the model calibration included: 1) USGS discharge data (Stations 02322500, 02322700, 02322800, and 02321500); 2) USGS operational Simplified Surface Energy Balance (SSEBop) actual evapotranspiration; and 3) Upper Floridan Aquifer potentiometric surfaces from FDEP. The calibration period of the model was 2010-2018 and the validation period was 1980-2009.

ABSTRACT:

The Upper Floridan aquifer underlying the Suwannee River Basin in Florida has experienced increased groundwater pumping and nitrate leaching over the last half century resulting in violation of water quantity and quality standards, largely due to row crop production. Increasingly carrot is being added as a winter cash crop to the traditional corn-peanut rotation in the region which may further increase pumping and nitrogen leaching. Establishing carrot nitrogen and irrigation best management practices is therefore critical to help growers meet yield goals while minimizing groundwater quantity and quality impacts. In this study, a carrot cultivation field experiment was conducted to evaluate the effects of a range of irrigation and nitrogen fertilizer practices on irrigation demand, nitrogen uptake and carrot crop growth and yield. Results showed that soil moisture sensor-based irrigation reduced the amount of water used for carrot cultivation by approximately 30% over the calendar-based irrigation without statistically significant reductions in yield, and fertilization rates above 224 kg ha-1 showed no statistically significant increase in yield. A field-scale SWAT carrot model was calibrated using the field experiment data and validated using previously published experimental results. The carrot parameters were then incorporated into a watershed-scale SWAT model of the Santa Fe River Basin, a tributary of the Suwannee River, and used to assess groundwater recharge and nitrate leaching impacts of adding carrot into corn-peanut rotations across all row crop lands in the watershed. Modeling results showed that adding carrot cultivation to the rotation will increase irrigation by 32-43% and decrease net groundwater recharge from row crop land by 9-28%. Moreover, it will increase nitrate leaching from row crop land by 60-100%. These results indicate that adding carrot cultivation to the conventional corn-peanut rotation will make water quantity and quality standards in the region more difficult to achieve.

ABSTRACT:

The Soil and Water Assessment Tool (SWAT) was used to simulate crop yields and nitrate leaching for corn-peanut rotations under a variety of nutrient and irrigation management practices in the Suwannee River Basin (Florida), where groundwater feeds springs that are protected by a federally mandated nutrient criteria of 0.35 mg/L Nitrate-Nitrogen (NO3-N). Data from a field experiment of nine irrigation and nitrogen (N) management treatments were used to calibrate SWAT, with good to excellent results (Nash Sutcliffe Efficiencies from 0.72 to 0.97 for soil moisture, 0.85–0.96 for crop yield, 0.48–0.96 for crop N uptake, and 0.15–0.82 for soil nitrate). The calibrated model was then used to quantify differences in crop yields, irrigation applied and nitrate leaching among practices over a range of historical weather. Soil moisture sensor-based irrigation with 246 kg N/ha for corn and 0 kg N/ha for peanut showed no statistical difference in yields compared to common practices in the region (calendar-based irrigation, fertilization of 336 kg N/ha corn and 17 kg N/ha peanut), while reducing N leaching by 40% and irrigation applied by 45% (reductions of ~70 kg N/ha/ yr and ~300 mm/year, respectively). Planting a rye cover crop during the fallow season reduced leaching by an additional ~50 N/ha/yr for all treatments. These results show the potential for widespread adoption of nutrient and water conservation practices to achieve the reductions in NO3-N load needed to meet environmental and regulatory goals without impacting crop yields.

This work is published in Rath S. , M. Zamora-Re, W. Graham, M. Dukes, and D. Kaplan, Quantifying nitrate leaching to groundwater from a corn-peanut rotation under a variety of irrigation and nutrient management practices in the Suwannee River Basin, Florida, Agricultural Water Management. https://doi.org/10.1016/j.agwat.2020.106634 , 2021.

Experimental data used to calibrate and validate the model is archived at Zamora-Re, M., J. Merrick, M. Dukes (2021). Floridan Aquifer Collaborative Engagement for Sustainability (FACETS) – Field trial data from Live Oak, Florida. Ag Data Commons. https://doi.org/10.15482/USDA.ADC/1521079.