Abstract
AbstractThe 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 withTHMB, a hydrology model capable of simulating streamflow andDINexport. Simulations were conducted at varying fertilizer application rates (0–200 kg N ha−1) and fractional replacement (5–25%) of current row crops with miscanthus or switchgrass across theMARB. The analysis also includes two scenarios where miscanthus and switchgrass (MRXandMRS, 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 theMARB, with the largest differences (ca. 6%) occurring for miscanthus at the highest fractional replacement scenarios in drier portions of the region. However, differences in totalMARBdischarge at the basin outlet were less than 1.5% even in theMRXscenario. Reductions inDINexport were much larger on a percentage basis than reductions in runoff, with the highest replacement scenarios decreasing long‐term meanDINexport by ca. 15% and 20% for switchgrass and miscanthus, respectively. Fertilization scenarios show that significant reductions inDINleaching are possible even with application rates of 100 and 150 kg N ha−1for 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 ofDIN, while avoiding hydrologic impacts of reduced streamflow.
Highlights
To meet the cellulosic targets set in place by the US 2007 Energy Independence and Security Act (EISA), the Mississippi–Atchafalaya River Basins (MARB) may require significant land use change
With respect to the management of perennial feedstocks, there is significant uncertainty surrounding the most likely application rates of fertilizer in the management of switchgrass and miscanthus, a series of simulations were conducted at varying fertilizer levels (Table 1)
The results presented here support anticipations 1 and 2 by showing that increasing the production of the cellulosic feedstocks miscanthus and switchgrass will reduce both the runoff of water and leaching of dissolved inorganic nitrogen (DIN), with proportional reductions in streamflow and the export of DIN in the MARB
Summary
To meet the cellulosic targets set in place by the US 2007 Energy Independence and Security Act (EISA), the Mississippi–Atchafalaya River Basins (MARB) may require significant land use change. Numerous studies implementing a wide range of statistical, empirical and numerical techniques have indicated that the leaching of excess nitrogen (N) fertilizer in the form of dissolved inorganic nitrogen (DIN) under current row crop production is a major driver of the Gulf of Mexico hypoxic zone or ‘dead zone’ (Rabalais et al, 1996; Goolsby et al, 2000, 2001; Donner et al, 2004a; Royer et al, 2006; Alexander et al, 2008; David et al, 2010; Turner et al, 2012; Deb et al, 2015) A potential option to meet the mandated cellulosic production without increasing nutrient inputs while reducing the size of the hypoxic zone is to convert a portion of the land in the MARB to produce dedicated perennial cellulosic feedstocks such as switchgrass and miscanthus (Heaton et al, 2008; Somerville et al, 2010; Deb et al, 2015; Hudiburg et al, 2016)
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