Abstract Several biofuel cropping scenarios were evaluated with an improved version of Soil and Water Assessment Tool ( SWAT ) as part of the Cen USA Bioenergy consortium for the Boone River Watershed ( BRW ), which drains about 2,370 km 2 in north central Iowa. The adoption of corn stover removal, switchgrass, and/or Miscanthus biofuel cropping systems was simulated to assess the impact of cellulosic biofuel production on pollutant losses. The stover removal results indicate removal of 20 or 50% of corn stover in the BRW would have negligible effects on streamflow and relatively minor or negligible effects on sediment and nutrient losses, even on higher sloped cropland. Complete cropland conversion into switchgrass or Miscanthus , resulted in reductions of streamflow, sediment, nitrate, and other pollutants ranging between 23‐99%. The predicted nitrate reductions due to Miscanthus adoption were over two times greater compared to switchgrass, with the largest impacts occurring for tile‐drained cropland. Targeting of switchgrass or Miscanthus on cropland ≥2% slope or ≥7% slope revealed a disproportionate amount of sediment and sediment‐bound nutrient reductions could be obtained by protecting these relatively small areas of higher sloped cropland. Overall, the results indicate that all biofuel cropping systems could be effectively implemented in the BRW , with the most robust approach being corn stover removal adopted on tile‐drained cropland in combination with a perennial biofuel crop on higher sloped landscapes. Editor's note : This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series .
The overall goal of this project was to conduct a watershed-scale sustainability assessment of multiple species of energy crops and removal of crop residues within two watersheds (Wildcat Creek, and St. Joseph River) representative of conditions in the Upper Midwest. The sustainability assessment included bioenergy feedstock production impacts on environmental quality, economic costs of production, and ecosystem services.
The application of physics based distributed models in watershed analysis has increased in the last few decades due to increased availability special data and advanced special analysis tools. These models have the advantage of better representation of the system which produces more accurate and reliable outputs. However, they are characterized by their large parameter size, which causes lot of uncertainty in the model output. The calibration of such models is also typically complex due to the large number of parameters. Sensitivity analysis of the parameters is performed prior to calibration in order to simplify the calibration procedure; nonetheless the commonly employed sensitivity analysis methods generally do not consider the nonlinear relationship between the parameters and the output. The current study focuses on performing the nonlinear sensitivity analysis on a distributed watershed model. The method utilizes the Sobols sensitivity approach, which is based on decomposing the total variance of the model output in terms of individual parameters contribution. The parameter sampling is performed by Latin hypercube sampling in this study. The output of the analysis help ranking the parameters of the model in terms of their sensitivity towards the model output, thereby help pruning the parameters that are to be calibrated. The method is demonstrated using soil and water assessment tool (SWAT) developed for St. Joseph watershed, USA.
Nutrient recycling is fundamental to sustainable agricultural systems, but few mechanisms exist to ensure that surplus manure nutrients from animal feeding operations are transported for use on nutrient-deficient croplands. As a result, manure nutrients concentrate in locations where they can threaten environmental health and devalue manure as a fertilizer resource. This study advances the concept of the "manureshed" – the lands surrounding animal feeding operations onto which manure nutrients can be redistributed to meet environmental, production, and economic goals. Manuresheds can be managed at multiple scales, for example, on farms with both animals and crops, among animal farms and crop farms within a county, or even among animal farms and crop farms in distant counties. With a focus on redistribution among counties, we classified the 3109 counties of the contiguous United States by their capacity to either supply manure phosphorus (P) and nitrogen (N) from confined livestock production ("sources") or to assimilate and remove excess P and N via crops ("sinks"). Manure nutrient source counties were identified in 40 of the 48 states, with a substantial concentration in the southern US. Source counties for manure P greatly outnumbered source counties for manure N (390 vs. 100), and 99 of the 100 manure N source counties were also source counties for manure P. Conversely, sink counties for manure N outnumbered sink counties for manure P (2766 vs. 2317). We used the P balances of the source and sink counties to delineate four manuresheds dominated by various combinations of confined hog, poultry, dairy, and beef industries. The four manuresheds differed in the transport distances needed to assimilate excess manure P from their respective source areas (from 147 ± 51 km for a beef dominated manureshed to 368 ± 140 km for a poultry dominated manureshed), highlighting the need for systems-level strategies to promote manure nutrient recycling that operate across local, county, regional, and national scales.
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