Assessing hydrologic and water quality effects of land use conversion to Brassica carinata as a winter biofuel crop in the southeastern coastal plain of Georgia, USA using the SWAT model.

Carinata (Brassica carinata) is an industrial oilseed feedstock for renewable fuels grown as a winter crop in the southeast US, which may provide a new rotation alternative and benefits for water quality. However, the effects of carinata on water quantity and quality at the watershed and local scales are unknown. In this study, we use the Soil and Water Assessment Tool (SWAT) to assess the potential influence of carinata on water balance components, nutrients and sediment loads under plausible future scenarios of land use change in the upper Suwannee River Basin in the Atlantic Coastal Plain Physiographic Region near Tifton in South‐Central Georgia. Three future scenarios are considered, including planting stand‐alone carinata in winter fallow land every third year, planting stand‐alone winter wheat in winter fallow land every third year, and carinata and winter wheat in rotation, one year of winter carinata followed by two years of winter wheat during simulation periods. The results show that under all three future scenarios, surface runoff, sediment, phosphorus, and nitrogen loadings decrease at both watershed and local scales, with higher average monthly reductions in the stand‐alone carinata scenario versus the stand‐alone winter wheat scenario. When carinata and winter wheat were planted over 36% of the total watershed area, reduction in total sediment, mineral phosphorus, and nitrate loads was ranging from 11.5% to 50.0%. However, when only 12% of the total watershed area was converted to carinata, the simulated reductions ranged from 3.8% to 14.0%. This suggests that the extent of carinata planting is crucial in assessing its hydrologic and water quality benefits. Overall, these results indicate that planting the biofuel carinata as a winter crop can reduce sediment and nutrient loading and provide water quality benefits to downstream waterbodies. [ABSTRACT FROM AUTHOR]