Producing renewable fuel from dedicated energy crops, such as switchgrass, has the potential to generate localized environmental benefits. This study uses high-resolution spatial data for west Tennessee to quantify the effects of producing switchgrass for cellulosic ethanol on the grey water footprint (GWF), or the amount of freshwater needed to dilute nitrate leachate to a safe level, relative to existing agricultural production. In addition, the estimated cost and GWF are incorporated in a mixed-integer multi-objective optimization model to derive the efficient frontier of the feedstock supply chain and determine a switchgrass supply chain that achieves the greatest reduction in GWF at the lowest cost. Results suggest that background nitrate concentration in ambient water and the types of agricultural land converted to switchgrass production influence the extent of the GWF. The average GWF of switchgrass in the study area ranges between 131.8 L L−1 and 145.9 L L−1 of ethanol, which falls into the range of estimated GWF of other lignocellulosic biomass feedstock in the literature. Also, the average cost of reducing GWF from the feedstock supply chain identified by the compromise solution method is $0.94 m−3 in the region. A tradeoff between biofuel production costs and reduced nitrate loading in groundwater is driven by differences in the agricultural land converted to feedstock production. Our findings illustrate the energy-water-food nexus in the development of a local bioenergy sector and provide a management strategy associated with land use choices for the supply of energy crops. However, the water quality improvements associated with displacing crop with feedstock production in one region could be offset by expanded or more intensive agricultural production in other regions.
Switchgrass (Panicum virgatum L.), a native of the North American prairies, has been selected for bioenergy research. With a focus on biomass yield improvement, this study aim (i) to estimate the genetic variation in biomass yield and important agronomic traits in ‘Alamo’, (ii) to determine correlations between biomass yield and agronomic traits, and (iii) to compare efficiency of phenotypic selection from a sward plot and advanced cycle half-sibs (ACHS) on the basis of space-plant performance. Sixty-two Alamo half-sib families (AHS) from a 4-yr-old Alamo sward and 20 advanced cycle half-sib families (ACHS) were evaluated in replicated field trials under simulated swards in Knoxville and Crossville, TN. Results showed significant variation (P < 0.05) among AHS for biomass yield, tillering ability, and spring vigor, suggesting the importance of additive genetic variation in these traits. Overall mean biomass yield of AHS was not different from the Alamo control, demonstrating the inefficiency of phenotypic selection from swards. Mean biomass yield of ACHS was 15 and 20% less than that of the control and AHS, respectively. Such results could be attributable to the influence of environment and genotype × environment interaction. However, results showed great potential for biomass yield improvement through selection on the basis of family performance. Using 10% selection intensity, parental control of two, and a narrow-sense heritability estimate of 0.11, gain per cycle selection from half-sib family selection is estimated to be 23%. Spring vigor showed potential use for indirect selection due to its high genetic correlation (rG = 0.75) with biomass yield. However, it is impeded by the low heritability estimate (h2 = 0.34).
on environment friendly and socio-economically sustainable renewable energy sources. However, commercial production of bioenergy is constrained by biomass supply uncertainty and associated costs. This study presents an integrated approach to determining the optimal biofuel supply chain considering biomass yield uncertainty. A two-stage stochastic mixed integer linear programming is utilized to minimize the expected system cost while incorporating yield uncertainty in the strategic level decisions related to biomass production and biorefinery investment.
Despite of the key role that short rotation woody crops (SRWC) play in supporting bioenergy and the bioeconomy, questions arise about the sustainability of bioenergy. Is it net energy efficient? Is bioenergy carbon neutral? Do SRWC plantations adversely affect food security by competing for land with agriculture? How will SRWC affect biodiversity and provision of environmental services? Answers are elusive and definitive answers require considering specific technology applied at a specific location. Thus, identifying where dedicated SRWC plantations would be viable in terms of biological productivity and economic attractiveness is a necessary first step in order to begin assessing their sustainability. We present a modeling framework using a process-based growth model, 3PG, and geographic information system technology to begin to answer sustainability questions about bioenergy plantations in the southern United States. We assessed potential profitability of four candidate SRWC species, Pinus taeda, Populus deltoides, Eucalyptus grandis, and Eucalyptus benthamii. Estimated yield (mean annual increment) was evaluated as internal rate of return on investment and land expectation value at the 5-digit ZIP code tabulation area level for 13 southern states. The 3PG model incorporates data on weather, soil, and species specific parameters to estimate potential volume production. This approach can be used for as a coarse filter for bioenergy projects that are under construction, in operation, proposed, or where due-diligence is required and to guide more detailed investigations in bioenergy siting-decision support systems. This approach will be most useful for choosing species to plant on former farmland or where landowners may be willing to change species on cutover forestland. The flexibility of the 3PG model allows for different climate scenarios to be developed and to assess risk of failure or lowered yields from extreme events such as drought, as well as altered future climate effects on sustainability. The silvicultural regime used in the model represents current and emerging practice; however, many feasible management regimes and site adaptations have been proposed. For example, the well-developed value chain for loblolly pine in the southern US provide opportunities for diverse silvicultural systems that could incorporate other biomass/bioenergy components, in addition to dedicated SRWC. The yield estimates can be used for further research on sustainability of carbon sequestration. The approach is useful generally as long as sufficient information on species traits is available to model productivity, silvicultural information to estimate management costs, and spatially explicit data on climate, environmental, and growing site conditions exists.
Perennial grasses are touted as sustainable feedstocks for energy production. Such benefits, however, may be offset if excessive nitrogen (N) fertilization leads to economic and environmental issues. Furthermore, as yields respond to changes in climate, nutrient requirements will change, and thus guidance on minimal N inputs is necessary to ensure sustainable bioenergy production. Here, a pairwise meta-analysis was conducted to investigate the effects of N fertilization (amount and duration) and climate on the above-ground biomass yields of miscanthus (Miscanthus x giganteus) and switchgrass (Panicum virgatum L.). Both regression models and meta-analyses showed that switchgrass was more responsive to N than miscanthus, although both showed significant and positive N effects. Meta-analysis further showed that the positive growth response of miscanthus to N application increased with N addition rates of 60–300 kg N ha−1 year−1, but the magnitude of the response decreased with the number of years of fertilization (duration). N effects on switchgrass biomass increased and peaked at rates of 120–160 kg N ha−1 year−1 and 5–6 years of N inputs, but diminished for rates >300 kg N ha−1 year−1 and >7 years. Meta-analysis further revealed that the influences of N on switchgrass increased with both mean annual temperature and precipitation. Miscanthus yields were less responsive to climate than switchgrass yields. This meta-analysis helps fill a gap in estimation of biofeedstock yields based on N fertilization and could help better estimate minimum N requirements and soil management strategies for miscanthus and switchgrass cultivation across climatic conditions, thereby improving the efficiency and sustainability of bioenergy cropping systems.
Sustainable production of algae will depend on understanding trade-offs at the energy-water nexus. Algal biofuels promise to improve the environmental sustainability profile of renewable energy along most dimensions. In this assessment of potential US freshwater production, we assumed sustainable production along the carbon dimension by simulating placement of open ponds away from high-carbon-stock lands (forest, grassland, and wetland) and near sources of waste CO 2 . Along the water dimension, we quantified trade-offs between water scarcity and production for an ‘upstream’ indicator (measuring minimum water supply) and a ‘downstream’ indicator (measuring impacts on rivers). For the upstream indicator, we developed a visualization tool to evaluate algae production for different thresholds for water surplus. We hypothesized that maintaining a minimum seasonal water surplus would also protect river habitat for aquatic biota. Our study confirmed that ensuring surplus water also reduced the duration of low-flow events, but only above a threshold. We also observed a trade-off between algal production and the duration of low-flow events in streams. These results can help to guide the choice of basin-specific sustainability targets to avoid conflicts with competing water users at this energy-water nexus. Where conflicts emerge, alternative water sources or enclosed photobioreactors may be needed for algae cultivation.
Practicing agriculture decreases downstream water quality when compared to non-agricultural lands. Agricultural watersheds that also grow perennial biofuel feedstocks can be designed to improve water quality compared to agricultural watersheds without perennials. The question then becomes which conservation practices should be employed and where in the landscape should they be situated to achieve water quality objectives when growing biofuel feedstocks. In this review, we focused on four types of spatial decisions in a bioenergy landscape: decisions about placement of vegetated strips, artificial drainage, wetlands, and residue removal. The appropriate tools for addressing spatial design questions are optimizations that seek to minimize losses of sediment and nutrients, reduce water temperature, and maximize farmer income. To accomplish these objectives through placing conservation practices, both field-scale and watershed-scale cost and benefits should be considered, as many biophysical processes are scale dependent. We developed decision trees that consider water quality objectives and landscape characteristics when determining the optimal locations of management practices. These decision trees summarize various rules for placing practices and can be used by farmers and others growing biofuels. Additionally, we examined interactions between conservation practices applied to bioenergy landscapes to highlight synergistic effects and to comprehensively address the question of conservation practice usage and placement. We found that combining conservation practices and accounting for their interactive effects can significantly improve water quality outcomes. Based on our review, we determine that by making spatial decisions on conservation practices, bioenergy landscapes can be designed to improve water quality and enhance other ecosystem services.
New domestic, renewable energy resources must be considered to increase energy security in the U.S. Ethanol production through second-generation (cellulosic) feedstocks will help the U.S. meet the legislative Renewable Fuel Standard, which mandates 36 billion gallons of renewable fuels by 2022. However, conversion of cropland to meet the cellulosic feedstock production goals may have unforeseen environmental consequences. Using Soil Water Assessment Tool (SWAT) outputs and National Agricultural Statistics Service (USDA NASS) economic data, we conducted a spatial optimization of bioenergy feedstock introduction into the Arkansas White-Red River Basin based on water quality and economic objectives, subject to constraints on total land conversion. Results displayed tradeoffs between bioenergy yield for three crops (switchgrass, sorghum and poplar) and land rent objectives. Optimal solutions tended to prioritize conversion of land in eastern AWR subbasins where yield and water quality objective improvements were greatest. A small number of subbasins contributed to basin-wide water quality improvements, whereas subbasins contributing to economic benefits were more spatially dispersed, indicating that water quality responses are more likely to constrain feedstock placement. Biomass production targets can be met vianumerous spatial arrangements, whereas marginal improvement in water quality objectives can best be achieved by selectively siting perennial feedstocks in the eastern half of the region.
The biobased economy is playing an increasingly important role in the American economy.
Through innovations in renewable energies and the emergence of a new generation of biobased products, the sectors that drive the biobased economy are providing job creation and economic growth. To further understand and analyze trends in the biobased economy, this report compares 2011 and 2016 report data.
Advanced biomass feedstocks tend to provide more non-fuel ecosystem goods and services (ES) than 1st-generation alternatives. We explore the idea that payment for non-fuel ES could facilitate market penetration of advanced biofuels by closing the profitability gap. As a specific example, we discuss the Mississippi-Atchafalaya River Basin (MARB), where 1st-generation bioenergy feedstocks (e.g., corn-grain) have been integrated into the agricultural landscape. Downstream, the MARB drains to the Gulf of Mexico, where the most-valuable fishery in the US is impacted by annual formation of a large hypoxic “Dead zone.” We suggest that advanced biomass production systems in the MARB can increase and stabilize the provision of ES derived from the coastal and marine ecosystems of the Gulf-of-Mexico. Upstream, we suggest that choosing feedstocks based on their resistance or resilience to disturbance (e.g., perennials, diverse feedstocks) can increase reliability in ES provision over time. Direct feedbacks to incentivize producers of advanced feedstocks are currently lacking. Perhaps a shift from first-generation biofuels to perennial-based fuels and other advanced bioenergy systems (e.g., algal diesel, biogas from animal wastes) can be encouraged by bringing downstream environmental externalities into the market for upstream producers. In future, we can create such feedbacks through payments for ES, but significant research is needed to pave the way.