oakridgenationallaboratory

Adding bioenergy to the U.S. energy portfolio requires long‐term profitability for bioenergy producers and
long‐term protection of affected ecosystems. In this study, we present steps along the path toward evaluating both sides of
the sustainability equation (production and environmental) for switchgrass (Panicum virgatum) using the Soil and Water
Assessment Tool (SWAT). We modeled production of switchgrass and river flow using SWAT for current landscapes at a
regional scale. To quantify feedstock production, we compared lowland switchgrass yields simulated by SWAT with estimates
from a model based on empirical data for the eastern U.S. The two produced similar geographic patterns. Average yields
reported in field trials tended to be higher than average SWAT‐predicted yields, which may nevertheless be more
representative of production‐scale yields. As a preliminary step toward quantifying bioenergy‐related changes in water
quality, we evaluated flow predictions by the SWAT model for the Arkansas‐White‐Red river basin. We compared monthly
SWAT flow predictions to USGS measurements from 86 subbasins across the region. Although agreement was good, we
conducted an analysis of residuals (functional validation) seeking patterns to guide future model improvements. The analysis
indicated that differences between SWAT flow predictions and field data increased in downstream subbasins and in subbasins
with higher percentage of water. Together, these analyses have moved us closer to our ultimate goal of identifying areas with
high economic and environmental potential for sustainable feedstock production.

Indicators are needed to assess environmental sustainability of bioenergy systems. Effective indicators
will help in the quantification of benefits and costs of bioenergy options and resource uses. We identify
19 measurable indicators for soil quality, water quality and quantity, greenhouse gases, biodiversity, air
quality, and productivity, building on existing knowledge and on national and international programs
that are seeking ways to assess sustainable bioenergy. Together, this suite of indicators is hypothesized
to reflect major environmental effects of diverse feedstocks, management practices, and post-production
processes. The importance of each indicator is identified. Future research relating to this indicator suite is
discussed, including field testing, target establishment, and application to particular bioenergy systems.
Coupled with such efforts, we envision that this indicator suite can serve as a basis for the practical
evaluation of environmental sustainability in a variety of bioenergy systems.

A broad-scale perspective on the nexus between climate change, land use, and energy requires consideration of interactions that were often omitted from climate change studies. While prior analyses have considered how climate change affects land use and vice versa (Dale 1997), there is growing awareness of the need to include energy within the analytical framework. A broad-scale perspective entails examining patterns and process at divers spatial and temporal resolutions.

As the US begins to integrate biomass crops and residues into its mix of energy feedstocks, tools are needed to measure the long-term sustainability of these feedstocks. Two aspects of sustainability are long-term potential for profitably producing energy and protection of ecosystems influenced by energy-related activities. The Soil and Water Assessment Tool (SWAT) is an important model used in our efforts to quantify both aspects. To quantify potential feedstock production, we used SWAT to estimate switchgrass yields at a national scale. The results from this analysis produced a map of the potential switchgrass yield along its natural eastern range. To quantify ecological protection, we are using the SWAT model to forecast changes in water quality and fish richness as result of landscape alterations due to incorporating bioenergy crops. We have implemented the SWAT model in the Arkansas-Red-White region, which drains into the Mississippi River, and we present our methods here. We identified two sub-watershed for sensitivity analysis and calibration of the water quality results, and then, explored ways to apply the calibration results to the whole region and validate the model setup. We also present an overview of our research in which results from the calibrated regional SWAT model were used to analyze potential changes in fish biodiversity. Only by evaluating the energy and environmental implications of landscape changes can we make informed decisions about bioenergy at the national scale, and the SWAT model will enable us to reach that goal.

The establishment of bioenergy crops will affect ecological processes and their interactions and thus has an influence on ecosystem services provided by the lands on which these crops are grown. The regional-scale effects of bioenergy choices on ecosystem services need special attention because they often have been neglected yet can affect the ecological, social, and economic aspects of sustainability. A regional-scale perspective provides the opportunity to maximize ecosystem services, particularly with regard to water quality and quantity issues, and also to consider other aspects of ecological, social, and economic sustainability. We give special attention to cellulosic feedstocks because of the opportunities they provide.

Developing scientific criteria and indicators should play a critical role in charting a sustainable path for the rapidly developing biofuel industry. The challenge ahead in developing such criteria and indicators is to address the limitations on data and modeling.

Country borders have been chosen as system boundaries to inventory GHG emissions under the Kyoto Protocol. The use of country boundaries is clear and allows summing over all countries. The country inventories purposefully account for where and when both fossil-fuel combustion emissions occur, and changes in the biological stocks of carbon occur. The approach can be widely adopted, but this accounting is hampered by uncertain data (1, 2) and two basic shortcomings: Not all countries are required to report, and not all biological carbon stocks are inventoried. A first step to improve inventories would be to address these issues through concerted cooperation to improve the reliability of land cover and carbon stock data and establish comprehensive accounting of current stocks.

Despite recent claims to the contrary, plant-based fuels developed in economically and environmentally sensible ways can contribute significantly to the nation’s— indeed, the world’s—energy security while providing a host of benefits for many people worldwide.

The U.S. Department of Energy Biomass Program sponsored the Land-Use Change and Bioenergy workshop in Vonore, Tennessee, from May 11 to May 14, 2009. More than 50 experts from around the world gathered to review the state of the science, identify opportunities for collaboration, and prioritize next steps for the research and data needed to address key issues regarding the land-use effects of bioenergy policies. A key outcome of the workshop was the
identification of research areas that may improve our understanding of land-use change in a bioenergy context.

IN THEIR REPORTS IN THE 29 FEBRUARY ISSUE (“LAND CLEARING AND THE BIOFUEL CARBON debt,” J. Fargione et al., p. 1235, and “Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change,” T. Searchinger et al., p. 1238), the authors do not provide adequate support for their claim that biofuels cause high emissions due to land-use change. The conclusions of both papers depend on the misleading premise that biofuel production causes forests and grasslands to be converted to agriculture. However, field research, including a meta-analysis of 152 case studies, consistently finds that land-use change and associated carbon emissions are driven by interactions among cultural, technological, biophysical, political, economic, and demographic forces within a spatial and temporal context rather than by a single crop market (1–3). Searchinger et al. assert that soybean prices accelerate clearing of rainforest based on a single citation (4) for a study not designed to identify the causal factors of land clearing. The study (4) analyzed satellite imagery from a single state in Brazil over a 4- year period and focused on land classification after deforestation. Satellite imagery can measure what changed but does little to tell us why. Similarly, Fargione et al. do not rely on primary empirical studies of causes of landuse change. Furthermore, neither fire nor soil carbon sequestration was properly considered in the Reports. Fire’s escalating contribution to global climate change is largely a result of burning in tropical savannas and forests (5, 6). Searchinger et al. postulate that 10.8 million hectares could be needed for future biofuel, a fraction of the 250 to 400 million hectares burned each year between 2000 and 2005 (5, 6). By offering enhanced employment and incomes, biofuels can help establish economic stability and thus reduce the recurring use of fire on previously cleared land as well as pressures to clear more land (7–9). Neither Searchinger et al. nor Fargione et al. consider fire as an ongoing land-management tool. In addition, deep-rooted perennial biofuel feedstocks in the tropics could enhance soil carbon storage by 0.5 to 1 metric ton per hectare per year (10). An improved understanding of the forces behind land-use change leads to more favorable conclusions regarding the potential for biofuels to reduce greenhouse gas emissions.