Quantifying the Farmland Application of Compost to Help Meet California's Organic Waste Diversion Law.

California's landmark waste diversion law, SB 1383, mandates the diversion of 75% of organic waste entering landfills by 2025. Much of this organic waste will likely be composted and applied to farms. However, compost is expensive and energy intensive to transport, which limits the distance that compost can be shipped. Though the diversion of organic waste from landfills in California has the potential to significantly reduce methane emissions, it is unclear if enough farmland exists in close proximity to each city for the distribution of compost. To address this knowledge gap, we develop the Compost Allocation Network (CAN), a geospatial model that simulates the production and transport of waste for all California cities and farms across a range of scenarios for per capita waste production, compost application rate, and composting conversion rate. We applied this model to answer two questions: how much farmland can be applied with municipal compost and what percentage of the diverted organic waste can be used to supplement local farmland. The results suggest that a composting system that recycles nutrients between cities and local farms has the potential to play a major role in helping California meet SB 1383 while reducing state emissions by -6.3 ± 10.1 MMT CO2e annually.

Global bioenergy potential from high-lignin agricultural residue.

Almost one-quarter of the world's population has basic energy needs that are not being met. Efforts to increase renewable energy resources in developing countries where per capita energy availability is low are needed. Herein, we examine integrated dual use farming for sustained food security and agro-bioenergy development. Many nonedible crop residues are used for animal feed or reincorporated into the soil to maintain fertility. By contrast, drupe endocarp biomass represents a high-lignin feedstock that is a waste stream from food crops, such as coconut (Cocos nucifera) shell, which is nonedible, not of use for livestock feed, and not reintegrated into soil in an agricultural setting. Because of high-lignin content, endocarp biomass has optimal energy-to-weight returns, applicable to small-scale gasification for bioelectricity. Using spatial datasets for 12 principal drupe commodity groups that have notable endocarp byproduct, we examine both their potential energy contribution by decentralized gasification and relationship to regions of energy poverty. Globally, between 24 million and 31 million tons of drupe endocarp biomass is available per year, primarily driven by coconut production. Endocarp biomass used in small-scale decentralized gasification systems (15-40% efficiency) could contribute to the total energy requirement of several countries, the highest being Sri Lanka (8-30%) followed by Philippines (7-25%), Indonesia (4-13%), and India (1-3%). While representing a modest gain in global energy resources, mitigating energy poverty via decentralized renewable energy sources is proposed for rural communities in developing countries, where the greatest disparity between societal allowances exist.

Role of soil health in maintaining environmental sustainability of surface coal mining.

Mountaintop coal mining (MCM) in the Southern Appalachian forest region greatly impacts both soil and aquatic ecosystems. Policy and practice currently in place emphasize water quality and soil stability but do not consider upland soil health. Here we report soil organic carbon (SOC) measurements and other soil quality indicators for reclaimed soils in the Southern Appalachian forest region to quantify the health of the soil ecosystem. The SOC sequestration rate of the MCM soils was 1.3 MgC ha(-1) yr(-1) and stocks ranged from 1.3 ± 0.9 to 20.9 ± 5.9 Mg ha(-1) and contained only 11% of the SOC of surrounding forest soils. Comparable reclaimed mining soils reported in the literature that are supportive of soil ecosystem health had SOC stocks 2.5-5 times greater than the MCM soils and sequestration rates were also 1.6-3 times greater. The high compaction associated with reclamation in this region greatly reduces both the vegetative rooting depth and infiltration of the soil and increases surface runoff, thus bypassing the ability of soil to naturally filter groundwater. In the context of environmental sustainability of MCM, it is proposed that the entire watershed ecosystem be assessed and that a revision of current policy be conducted to reflect the health of both water and soil.

Production of biodiesel and biogas from algae: a review of process train options.

Algae are an attractive biofuel feedstock because of their fast growth rates and improved land use efficiency when compared with terrestrial crops. Process train components needed to produce algal biofuels include (1) cultivation, (2) harvesting, and (3) conversion into usable fuel. This paper compares various process train options and identifies knowledge gaps presently restricting the production of algal biodiesel and algae-derived biogas. This analysis identified energy-intensive processing and the inability to cultivate large quantities of lipid-rich algal biomass as major obstacles inhibiting algal biodiesel production. Anaerobic digestion of algal biomass requires fewer process train components and occurs regardless of lipid content. In either scenario, the use of wastewater effluent as a cultivation medium seems necessary to reduce greenhouse gas emissions and maximize water use efficiency. Furthermore, anaerobically digesting algal biomass generated from low-technology wastewater treatment processes represents an appropriate technology approach to algal biofuels that is poorly investigated. Coupling these processes can improve global health by improving sanitation, while providing a cleaner burning biogas alternative to indoor biomass cooking systems typical of less-developed areas.

Response to Comments on "Recent global decline of CO2 fertilization effects on vegetation photosynthesis".

Our study suggests that the global CO2 fertilization effect (CFE) on vegetation photosynthesis has declined during the past four decades. The Comments suggest that the temporal inconsistency in AVHRR data and the attribution method undermine the results' robustness. Here, we provide additional evidence that these arguments did not affect our finding and that the global decline in CFE is robust.

Comparison of regression coefficient and GIS-based methodologies for regional estimates of forest soil carbon stocks.

Estimates of forest soil organic carbon (SOC) have applications in carbon science, soil quality studies, carbon sequestration technologies, and carbon trading. Forest SOC has been modeled using a regression coefficient methodology that applies mean SOC densities (mass/area) to broad forest regions. A higher resolution model is based on an approach that employs a geographic information system (GIS) with soil databases and satellite-derived landcover images. Despite this advancement, the regression approach remains the basis of current state and federal level greenhouse gas inventories. Both approaches are analyzed in detail for Wisconsin forest soils from 1983 to 2001, applying rigorous error-fixing algorithms to soil databases. Resulting SOC stock estimates are 20% larger when determined using the GIS method rather than the regression approach. Average annual rates of increase in SOC stocks are 3.6 and 1.0 million metric tons of carbon per year for the GIS and regression approaches respectively.

Estimating the health benefits from natural gas use in transport and heating in Santiago, Chile.

Chilean law requires the assessment of air pollution control strategies for their costs and benefits. Here we employ an online weather and chemical transport model, WRF-Chem, and a gridded population density map, LANDSCAN, to estimate changes in fine particle pollution exposure, health benefits, and economic valuation for two emission reduction strategies based on increasing the use of compressed natural gas (CNG) in Santiago, Chile. The first scenario, switching to a CNG public transportation system, would reduce urban PM2.5 emissions by 229 t/year. The second scenario would reduce wood burning emissions by 671 t/year, with unique hourly emission reductions distributed from daily heating demand. The CNG bus scenario reduces annual PM2.5 by 0.33 µg/m³ and up to 2 µg/m³ during winter months, while the residential heating scenario reduces annual PM2.5 by 2.07 µg/m³, with peaks exceeding 8 µg/m³ during strong air pollution episodes in winter months. These ambient pollution reductions lead to 36 avoided premature mortalities for the CNG bus scenario, and 229 for the CNG heating scenario. Both policies are shown to be cost-effective ways of reducing air pollution, as they target high-emitting area pollution sources and reduce concentrations over densely populated urban areas as well as less dense areas outside the city limits. Unlike the concentration rollback methods commonly used in public policy analyses, which assume homogeneous reductions across a whole city (including homogeneous population densities), and without accounting for the seasonality of certain emissions, this approach accounts for both seasonality and diurnal emission profiles for both the transportation and residential heating sectors.

Terrestrial carbon disturbance from mountaintop mining increases lifecycle emissions for clean coal.

The Southern Appalachian forest region of the U.S.--a region responsible for 23% of U.S. coal production--has 24 billion metric tons of high quality coal remaining of which mountaintop coal mining (MCM) will be the primary extraction method. Here we consider greenhouse gas emissions associated with MCM terrestrial disturbance in the life-cycle of coal energy production. We estimate disturbed forest carbon, including terrestrial soil and nonsoil carbon using published U.S. Environmental Protection Agency data of the forest floor removed and U.S. Department of Agriculture--Forest Service inventory data. We estimate the amount of previously buried geogenic organic carbon brought to the soil surface during MCM using published measurements of total organic carbon and carbon isotope data for reclaimed soils, soil organic matter and coal fragments. Contrary to conventional wisdom, the life-cycle emissions of coal production for MCM methods were found to be quite significant when considering the potential terrestrial source. Including terrestrial disturbance in coal life-cycle assessment indicates that indirect emissions are at least 7 and 70% of power plant emissions for conventional and CO(2) capture and sequestration power plants, respectively. To further constrain these estimates, we suggest that the fate of soil carbon and geogenic carbon at MCM sites be explored more widely.

Biomass energy: the scale of the potential resource.

Increased production of biomass for energy has the potential to offset substantial use of fossil fuels, but it also has the potential to threaten conservation areas, pollute water resources and decrease food security. The net effect of biomass energy agriculture on climate could be either cooling or warming, depending on the crop, the technology for converting biomass into useable energy, and the difference in carbon stocks and reflectance of solar radiation between the biomass crop and the pre-existing vegetation. The area with the greatest potential for yielding biomass energy that reduces net warming and avoids competition with food production is land that was previously used for agriculture or pasture but that has been abandoned and not converted to forest or urban areas. At the global scale, potential above-ground plant growth on these abandoned lands has an energy content representing approximately 5% of world primary energy consumption in 2006. The global potential for biomass energy production is large in absolute terms, but it is not enough to replace more than a few percent of current fossil fuel usage. Increasing biomass energy production beyond this level would probably reduce food security and exacerbate forcing of climate change.

The global potential of bioenergy on abandoned agriculture lands.

Converting forest lands into bioenergy agriculture could accelerate climate change by emitting carbon stored in forests, while converting food agriculture lands into bioenergy agriculture could threaten food security. Both problems are potentially avoided by using abandoned agriculture lands for bioenergy agriculture. Here we show the global potential for bioenergy on abandoned agriculture lands to be less than 8% of current primary energy demand, based on historical land use data, satellite-derived land cover data, and global ecosystem modeling. The estimated global area of abandoned agriculture is 385-472 million hectares, or 66-110% of the areas reported in previous preliminary assessments. The area-weighted mean production of above-ground biomass is 4.3 tons ha(-1) y(-1), in contrast to estimates of up to 10 tons ha(-1) y(-1) in previous assessments. The energy content of potential biomass grown on 100% of abandoned agriculture lands is less than 10% of primary energy demand for most nations in North America, Europe, and Asia, but it represents many times the energy demand in some African nations where grasslands are relatively productive and current energy demand is low.