Study Concludes That Use of Cellulosic Feedstocks to Meet US Biofuel Requirements Will Still Likely Result in Expansion of the Gulf Dead Zone

Posted on September 11, 2009. Filed under: Cellulosic | Tags: , , , |

Study Concludes That Use of Cellulosic Feedstocks to Meet US Biofuel Requirements Will Still Likely Result in Expansion of the Gulf Dead Zone

Green Car Congress

10 September 2009

Nitrate output within the MARB (colored bars, lefthand y-axis) and mean areal extent of hypoxia in the NGOM with “No Buffer” and “50% Buffer” (gray scale bars, righthand y-axis). Nitrate output columns represent mean values and the 80% credible intervals from modeling. Credit: ACS, Costello et. al. Click to enlarge.

A study by researchers at Carnegie Mellon University and the University of Pittsburgh found that while moving from corn to cellulosics to meet the biofuel goals specified by the Energy Independence and Security Act of 2007 (EISA 2007) for ethanol production may result in a 20% decrease (based on mean values) in NO3 (nitrate) output from the Mississippi and Atchafalaya River Basin (MARB) relative to corn, this will still result in increased nitrate loadings, contributing to the expansion of the hypoxic “Dead Zone” in the Northern Gulf of Mexico (NGOM). (Earlier post.)

The findings suggest that an aggressive nutrient management strategy will be needed to reach the goal of a 5,000 km2 areal extent of hypoxia set forth by the Mississippi River/Gulf of Mexico Watershed Nutrient Task Force even in the absence of biofuels, given current production to meet food, feed, and other industrial needs. Their paper was published online 13 August in the ACS journal Environmental Science & Technology.

Nitrogen and phosphorus from agricultural fertilizer have been found to promote excess growth of algae in water bodies—a problem that’s common across North America and in many areas of the world. In some cases, decomposition of algae consumes much of the oxygen in the water. Fertilizer applied to cornfields in the central US—including states such as Illinois, Iowa, Nebraska and Wisconsin—is the primary source of nitrogen pollution in the Mississippi River system, which drains into the Gulf of Mexico.

Each summer, the export of nitrogen from the MARB creates a large NGOM “Dead Zone”—a region of oxygen-deprived waters that are unable to support aquatic life. Marine species either die or flee the hypoxic zone, so the spread of hypoxia reduces the available habitat for marine species which are important for the ecosystem as well as commercial and recreational fishing in the Gulf.

A 2008 study by Simon Donner of the University of British Columbia and Chris Kucharik of the University of Wisconsin concluded that ramping up the production of corn ethanol to meet the targets set by the new US Renewable Fuel Standard (RFS) would worsen pollution in the Gulf of Mexico, increasing the growing hypoxic region. (Earlier post.)

In the current study, Christine Costello, W. Michael Griffin and H. Scott Matthews of CMU and Amy E. Landis of the University of Pittsburgh took a system-wide approach in considering the NO3 output and the relative areal extent of hypoxia in the NGOM due to the introduction of additional crops for biofuel production. They stochastically estimated nitrate loading to the NGOM and used these results to approximate the areal extent of hypoxia for scenarios that meet the EISA 2007 biofuel goals for 2015 and 2022. Crops for ethanol include corn, corn stover, and switchgrass; all biodiesel was assumed to be from soybeans.

The 2007 Energy Independence and Security Act (EISA) calls for the production of 36 billion gallons (Bgal) of biofuels by 2022 of which 15 Bgal is corn ethanol and 21 Bgal is “advanced biofuel”. Advanced biofuels are assumed to be 20 Bgal of ethanol that is derived from switchgrass or stover and one Bgal of biodiesel derived from soybeans. Achieving these goals may result in a significant increase in demand for agricultural products. Simultaneously as populations increase so will demand for food/feed products. A pressing question to answer is how will an increase in agricultural activity impact nutrient loading to the NGOM and ultimately the size of the hypoxic zone.

—Costello et al. 2009

The team modeled in two scenarios for the use of vegetative buffer strips (VBS) to reduce run-off: one at a 100% level and one at a 50% level. The authors note that 100% interception of runoff by buffers from agricultural fields is unlikely; they included this idealized scenario to illustrate the need for aggressive nutrient management within the MARB.

They found that NO3 output for corn-derived ethanol will be higher on average than output for switchgrass- or stover-derived ethanol. While use of cellulosics result in lower NO3output on a per unit basis compared to corn (e.g., one gallon ethanol or one acre), the decrease is insufficient to reduce the hypoxic zone below the EPA’s 5000 km2 target.



In summary, the results of modeling hypoxic area indicates that meeting the biofuel goals set forth by EISA will likely increase the occurrence of hypoxia in the NGOM, regardless of the selection of crops. This work also suggests that aggressive nutrient management is needed even in the absence of energy crops or stover use. There are a number of options to consider for mitigating nitrogen loading from agricultural activities, including wetland construction, vegetative buffers, tillage management, and precision fertilizer application.

…The results presented here suggest that only when all of the nitrogen runoff associated with the production of corn, soy, and switchgrass is reduced will the EPA goal be met. This is an oversimplification since the approximation of the areal extent of the hypoxic zone includes unmitigated output from all other N sources within the MARB, i.e., other agricultural crops, wastewater treatment facilities, etc. Any aggressive management strategy aimed at reducing nutrient sources within the MARB will likely target these other sources as well.

…The presented results demonstrate that using cellulosic crops for biofuel production will decrease TN [total nitrogen] loading to the NGOM relative to corn but overall TN loading will still increase as the goals of the EISA are met, adding to the need for aggressive nitrogen mitigation strategies.

—Costello et al. 2009


  • Christine Costello, W. Michael Griffin, Amy E. Landis and H. Scott Matthew (2009) Impact of Biofuel Crop Production on the Formation of Hypoxia in the Gulf of Mexico. Environ. Sci. Technol., Article ASAP doi: 10.1021/es9011433

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    Renergie created “field-to-pump," a unique strategy to locally produce and market advanced biofuel (“non-corn fuel ethanol”) via a network of small advanced biofuel manufacturing facilities. The purpose of “field-to-pump” is to maximize rural development and job creation while minimizing feedstock supply risk and the burden on local water supplies.


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