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Title: Assessing the potential to decrease the Gulf of Mexico hypoxic zone with Midwest US perennial cellulosic feedstock production

item VAN LOOCKE, ANDY - Iowa State University
item TWINE, TRACY - University Of Minnesota
item KUCHARIK, CHRISTOPHER - University Of Wisconsin
item Bernacchi, Carl

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2016
Publication Date: 7/1/2016
Citation: VanLoocke, A., Twine, T., Kucharik, C., Bernacchi, C.J. 2016. Assessing the potential to decrease the Gulf of Mexico hypoxic zone with Midwest US perennial cellulosic feedstock production. Global Change Biology Bioenergy. doi:10.1111/gcbb/12385.

Interpretive Summary: Perennial bioenergy feedstocks are predicted to provide more renewable energy than current annual bioenergy feedstocks. However, this increase in fuel production is linked with an increase in the amount of water that these ecosystems will need. More water moving from the soil to the atmosphere through the plants means less water flowing through streams and water ways. Perennial bioenergy feedstocks also require much less fertilizer than annual row crops that they will replace and they are more efficient at taking up fertilizer from the soil. Less fertilizer, and improved fertilizer uptake efficiency means that water quality may improve due to less nutrient run-off into streams and water ways. This research investigates, through ecosystem and hydrological models, the impact of different perennial grass establishment rates on stream/river flows and water quality through the Mississippi River Basin and into the Gulf of Mexico. The research focuses on two key perennial bioenergy feedstocks – miscanthus and switchgrass- compared with existing row crops – maize and soybean. The results show that higher fraction of planting of miscanthus and switchgrass has a small (2-3% effect) on the amount of water flowing through streams and rivers but has a relatively large (15-20% effect) improvement on water quality. This research suggests that in addition to the climate benefits of incorporating perennial grasses into the Midwestern US, there exists the potential for drastic improvements in water quality with little impact on water quantity.

Technical Abstract: The goal of this research is to determine the changes in streamflow, dissolved inorganic nitrogen (DIN) leaching and export to the Gulf of Mexico associated with a range of large-scale dedicated perennial cellulosic bioenergy production scenarios within in the Mississippi-Atchafalaya River Basin (MARB). To achieve this goal, we used a vegetation model capable of simulating the biogeochemistry of row crops, miscanthus and switchgrass, coupled with a hydrology model capable of simulating streamflow and DIN export. Simulations were conducted at varying fertilizer application rates (0 to 200 kg N ha-1) and fractional replacement (5 to 25%) of current row crops with miscanthus or switchgrass across the MARB. The analysis also includes two scenarios where miscanthus and switchgrass (MRX and MRS respectively) each replace the ca. 40% of maize production currently devoted to ethanol. Across the scenarios, there were minor reductions in runoff and streamflow throughout the MARB, with the largest differences (ca. 6%) occurring for miscanthus at the highest fractional replacement scenarios in drier portions of the region. However, differences in total MARB discharge at the basin outlet were less than 1.5% even in the MRX scenario. Reductions in DIN export were much larger on a percentage basis than reductions in runoff, with the highest replacement scenarios decreasing long-term mean DIN export by ca. 15 and 20% for switchgrass and miscanthus, respectively. Fertilization scenarios show that significant reductions in DIN leaching are possible even with application rates of 100 and 150 kg N ha-1 for switchgrass and miscanthus respectively. These results indicate that, given targeted management strategies, there is potential for miscanthus and switchgrass to provide key ecosystem services by reducing theexport of DIN, while avoiding hydrologic impacts of reduced streamflow.