Assessing the potential to decrease the Gulf of Mexico hypoxic zone with MidwestUSperennial cellulosic feedstock production

Abstract

The goal of this research was 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 Agro-IBIS, a vegetation model capable of simulating the biogeochemistry of row crops, miscanthus and switchgrass, coupled with THMB, a hydrology model capable of simulating streamflow and DIN export. Simulations were conducted at varying fertilizer application rates (0-200 kg N ha À1 ) and fractional replacement (5-25%) 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 À1for 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 the export of DIN, while avoiding hydrologic impacts of reduced streamflow.

On the Long-Term Hydroclimatic Sustainability of Perennial Bioenergy Crop Expansion over the United States

“…Fargione et al 2008;Field et al 2008;Cai et al 2011;Bagley et al 2014;Hudiburg et al 2015). Additionally, perennial bioenergy crops sequester carbon within the soil, and their use results in higher yields with lower nutrient input (e.g., reduced N 2 O) requirements relative to their annual counterparts, such as maize (Fargione et al 2008;Miguez et al 2008;Anderson-Teixeira et al 2009Dohleman and Long 2009;Smith et al 2013;Zhuang et al 2013;Gelfand et al 2013;Bagley et al 2014;Wagle and Kakani 2014;DeLucia 2015;Feng et al 2015;Oikawa et al 2015;Eichelmann et al 2016;VanLoocke et al 2016). Therefore, cultivating perennial bioenergy crops could be a more sustainable approach to meet increasing energy demand and mitigate anthropogenic climate change.…”

“…Large-scale deployment of perennial bioenergy crops, by virtue of their transition to an altered land use, modifies biogeophysical (e.g., direct impacts due to changes in the surface energy budget) processes. These changes could affect atmospheric boundary layer dynamics, mesoscale circulations, and regional climate (Weaver and Avissar 2001;Pielke 2005;Georgescu et al 2009Georgescu et al , 2011Georgescu et al , 2013Mahmood et al 2010;VanLoocke et al 2010;Levis et al 2012;Murphy et al 2012). Therefore, biogeophysical impacts associated with land-use conversion to perennial bioenergy cropping systems must be considered prior to large-scale deployment.…”

“…Recent work has examined biogeophysical impacts due to landscape conversion from annual to perennial bioenergy crops, noting changes mainly attributed to higher albedo, leaf area index (LAI), and enhanced evapotranspiration (ET) (Betts 2000;Hickman et al 2010;VanLoocke et al 2010;Georgescu et al 2009Georgescu et al , 2011Le et al 2011;Davin et al 2014;Bagley et al 2015;Eichelmann et al 2016;Wagle et al 2016;Zhu et al 2017). In addition, the importance of field-scale studies has demonstrated the significance of appropriate biogeophysical representation in process-based models that can be used to examine scenario-based environmental implications.…”

“…Studies have noted regional cooling (Georgescu et al 2011;Le et al 2011;Khanal et al 2013;Goldstein et al 2014;Feng et al 2015) and the potential for increased precipitation (Georgescu et al 2011;Khanal et al 2013Khanal et al , 2014 associated with largescale deployment of perennial bioenergy crops. These changes were attributable to enhanced ET due to the deeper and denser rooting systems extracting soil moisture from deeper soil depths (VanLoocke et al 2010;Georgescu et al 2011;Anderson et al 2013;Hallgren et al 2013;Ferchaud et al 2015).…”

“…Changes in ET and soil moisture are directly associated with and have immediate implications for the regional hydrological cycle (VanLoocke et al 2010;Seneviratne et al 2010;Georgescu et al 2011;Anderson et al 2013). Increased ET, owing to soil moisture depletion at deeper depths, can lead to decreased surface runoff (McIsaac et al 2010;Le et al 2011;Wilson et al 2011) and streamflow (Khanal et al 2014).…”