Offset CO2 Emissions Research Articles

Ecosystem carbon dynamics differ between tundra shrub types in the western Canadian Arctic

Shrub expansion at high latitudes has been implicated in driving vegetation ‘greening’ trends and may partially offset CO2 emissions from warming soils. However, we do not yet know how Arctic shrub expansion will impact ecosystem carbon (C) cycling and this limits our ability to forecast changes in net C storage and resulting climate feedbacks. Here we quantify the allocation of photosynthate between different ecosystem components for two common deciduous Arctic shrubs, both of which are increasing in abundance in the study region; green alder (Alnus viridis (Chaix) DC.) and dwarf birch (Betula glandulosa Michx., B.). Using 13C isotopic labelling, we show that carbon use efficiency (i.e. the fraction of gross photosynthesis remaining after subtracting respiration) in peak growing season is similar between the two shrubs (56 ± 12% for A. viridis, 59 ± 6% for B. glandulosa), but that biomass production efficiency (plant C uptake allocated to biomass production, per unit gross photosynthesis) is 56 ± 14% for A. viridis, versus 31 ± 2% for B. glandulosa. A significantly greater proportion of recent photosynthate is allocated to woody biomass in A. viridis dominated plots (27 ± 5%), compared to plots dominated by B. glandulosa (4 ± 1%). Allocation of C to belowground pools also differs significantly; after 2.5 weeks we recovered 28 ± 6% of recent photosynthate in root-free soil under B. glandulosa, but under A. viridis we were unable to detect recent photosynthate in the soil. We provide the first evidence that the impact of shrub expansion on Arctic C cycling will be species dependant. Where Betula dominates, ~1/3 of recently photosynthesised C will be rapidly allocated belowground to soil and microbial pools. Where Alnus dominates, more recently fixed C will be allocated to woody biomass. We conclude that models driven by remotely-sensed aboveground canopy characteristics alone (i.e. greenness) will be unable to accurately represent the impact of vegetation change on Arctic C storage.

Fine resolution map of top- and subsoil carbon sequestration potential in France

Although soils have a high potential to offset CO2 emissions through its conversion into soil organic carbon (SOC) with long turnover time, it is widely accepted that there is an upper limit of soil stable C storage, which is referred to SOC saturation. In this study we estimate SOC saturation in French topsoil (0–30cm) and subsoil (30–50cm), using the Hassink equation and calculate the additional SOC sequestration potential (SOCsp) by the difference between SOC saturation and fine fraction C on an unbiased sampling set of sites covering whole mainland France. We then map with fine resolution the geographical distribution of SOCsp over the French territory using a regression Kriging approach with environmental covariates. Results show that the controlling factors of SOCsp differ from topsoil and subsoil. The main controlling factor of SOCsp in topsoils is land use. Nearly half of forest topsoils are over-saturated with a SOCsp close to 0 (mean and standard error at 0.19±0.12) whereas cropland, vineyard and orchard soils are largely unsaturated with degrees of C saturation deficit at 36.45±0.68% and 57.10±1.64%, respectively. The determinant of C sequestration potential in subsoils is related to parent material. There is a large additional SOCsp in subsoil for all land uses with degrees of C saturation deficit between 48.52±4.83% and 68.68±0.42%. Overall the SOCsp for French soils appears to be very large (1008Mt C for topsoil and 1360Mt C for subsoil) when compared to previous total SOC stocks estimates of about 3.5Gt in French topsoil. Our results also show that overall, 176Mt C exceed C saturation in French topsoil and might thus be very sensitive to land use change.

Carbon storage in a wolfberry plantation chronosequence established on a secondary saline land in an arid irrigated area of Gansu Province, China

Carbon (C) storage has received significant attention for its relevance to agricultural security and climate change. Afforestation can increase C storage in terrestrial ecosystems, and has been recognized as an important measure to offset CO2 emissions. In order to analyze the C benefits of planting wolfberry (Lycium barbarum L.) on the secondary saline lands in arid areas, we conducted a case study on the dynamics of biomass carbon (BC) storage and soil organic carbon (SOC) storage in different-aged wolfberry plantations (4-, 7- and 11-year-old) established on a secondary saline land as well as on the influence of wolfberry plantations on C storage in the plant-soil system in an arid irrigated area (Jingtai County) of Gansu Province, China. The C sequestration and its potential in the wolfberry plantations of Gansu Province were also evaluated. An intact secondary saline land was selected as control. Results show that wolfberry planting could decrease soil salinity, and increase BC, SOC and litter C storage of the secondary saline land significantly, especially in the first 4 years after planting. The aboveground and belowground BC storage values in the intact secondary saline land (control) accounted for only 1.0% and 1.2% of those in the wolfberry plantations, respectively. Compared to the intact secondary saline land, the SOC storage values in the 4-, 7- and 11-year-old wolfberry plantations increased by 36.4%, 37.3% and 43.3%, respectively, and the SOC storage in the wolfberry plantations occupied more than 92% of the ecosystem C storage. The average BC and SOC sequestration rates of the wolfberry plantations for the age group of 0–11 years were 0.73 and 3.30 Mg C/(hm2•a), respectively. There were no significant difference in BC and SOC storage between the 7-year-old and 11-year-old wolfberry plantations, which may be due in part to the large amounts of C offtakes in new branches and fruits. In Gansu Province, the C storage in the wolfberry plantations has reached up to 3.574 Tg in 2013, and the C sequestration potential of the existing wolfberry plantations was 0.134 Tg C/a. These results indicate that wolfberry planting is an ideal agricultural model to restore the degraded saline lands and increase the C sequestration capacity of agricultural lands in arid areas.

Creation of Zero CO2 Emission Plants Due to Energy Use: A Case Study in Crete, Greece

Creation of zero CO2 emission enterprises due to energy use in Crete, Greece has been examined with reference to an orange juice producing plant (Viochym). Energy intensity at Viochym has been estimated at 1.66 KWh per € of annual sales. Oil used for heat generation has been replaced with solid biomass produced locally in Crete and resulting in zero CO2 emissions due to the use of heat. Offsetting CO2 emissions due to grid electricity use has been proposed with two options. The first includes the installation of a solar photovoltaic system with nominal power of 417 KWp, according to net metering regulations, generating annually 625 MWh equal to annual grid electricity consumption in the plant. Its capital cost has been estimated at 0.5 mil € which corresponds to 1.07 € per kg of CO2 saved annually.The second option includes the creation of a tree plantation in an area of 107 hectare resulting in carbon sequestration equal to carbon emissions in the plant due to electricity use. Both options for offsetting CO2 emissions in Viochym have various advantages and drawbacks and they are considered realistic and feasible, resulting in the elimination of its carbon emissions due to energy use. Improvement of the energy intensity of various processes in Viochym could result in lower CO2 emissions and smaller sizing of the required renewable energy systems for eliminating them.

Pattern changes in determinants of Chinese emissions

The Chinese economy has been recovering slowly from the global financial crisis, but it cannot achieve the same rapid development of the pre-recession period. Instead, the country has entered a new phase of economic development—a ‘new normal’. We use a structural decomposition analysis and environmental input–output analysis to estimate the determinants of China’s carbon emission changes during 2005–2012. China’s imports are linked to a global multi-regional input–output model based on the Global Trade and Analysis Project database to calculate the embodied CO2 emissions in imports. We find that the global financial crisis has affected the drivers of China’s carbon emission growth. From 2007 to 2010, the CO2 emissions induced by China’s exports dropped, whereas emissions induced by capital formation grew rapidly. In the ‘new normal’, the strongest factors that offset CO2 emissions have shifted from efficiency gains to structural upgrading. Efficiency was the strongest factor offsetting China’s CO2 emissions before 2010 but drove a 1.4% increase in emissions in the period 2010–2012. By contrast, production structure and consumption patterns caused a 2.6% and 1.3% decrease, respectively, in China’s carbon emissions from 2010 to 2012. In addition, China tends to shift gradually from an investment to a consumption-driven economy. The proportion of CO2 emissions induced by consumption had a declining trend before 2010 but grew from 28.6%–29.1% during 2010–2012.

Development of a pricing mechanism for valuing ancillary, transportation and environmental services offered by a power to gas energy system

Power to gas is a novel energy storage concept that can help in providing energy storage and offer sustainable and efficient alternative ways to utilize the surplus electricity generated by the provincial grid of Ontario, Canada. This situation of ‘surplus electricity’ also exists elsewhere as there in increasing intermittent renewable power on various grids. The ability of the power to gas energy hubs to utilize the existing natural gas distribution and storage network (within the province) to distribute and store the electrolytic hydrogen produced is one of its major advantages. In this study an optimization model of a power to gas energy hub having a hydrogen production module capacity of 2 MW has been developed. The goal of the optimization study is to carry out an economic feasibility of the energy hub under existing pricing mechanisms for the three primary services that it provides, namely: 1) Offsetting CO2 emissions at natural gas end users by providing hydrogen enriched natural gas; 2) Providing demand response when directed by the Independent Electricity System Operator of the province, and 3) Providing pure hydrogen to a fuel cell vehicle refueling station. It is observed that current pricing mechanisms are not valued high enough for the power to gas energy hub to be economically feasible and payback periods longer than the project lifetime (20 years) have been observed. Therefore, through a post-processing economic calculation, the additional monetary incentive required for the energy hub to achieve a NPV equal to zero for shorter project lifetimes of 8, 9 and 10 years have been calculated. The required additional monetary incentives (for the new project lifetimes) have then been split proportionally to the share of the revenues earned by the energy hub while providing each of the three services. Through this, the existing pricing mechanisms have been scaled up and a new pricing mechanism has been developed that highlights the monetary requirements of a power to gas energy hub to be economically feasible. It is seen that the required increase in the pricing of the three different services offered by the energy hub are reasonable and lie within the ranges proposed for them in coming years.

International Aviation Emissions Under International Civil Aviation Organization’s Global Market Based Measure: Ready for Offsetting?

In a landmark decision on 7 October 2016, the International Civil Aviation Organization (ICAO) General Assembly adopted a resolution for the establishment of a Global Market Based Measure (Global MBM) to offset CO2 emissions from international aviation. After the Paris Agreement, this is not only the first ever global solution to curb emissions of a whole industry sector, but it is also a fundamental step as ICAO has been wrestling to come up with an international solution to address the issue of climate change of aviation over the last years. The Global MBM delivers the basis for the future climate regime in international aviation. This article outlines the key features of the new Global MBM and provides a first evaluation of the adopted approach and its implications with the EU Emissions Trading Scheme (EU ETS).

The Carbon Holdings of Northern Ecuador's Mangrove Forests

Within a geographic information systems environment, we combine field measures of mangrove tree diameter, mangrove species distribution, and mangrove tree density with remotely sensed measures of mangrove location and mangrove canopy cover to estimate the mangrove carbon holdings of northern Ecuador. We find that the four northern estuaries of Ecuador contain approximately 7,742,999 t (±15.47 percent) of standing carbon. Of particularly high carbon holdings are the Rhizophora mangle–dominated mangrove stands found in and around the Cayapas-Mataje Ecological Reserve in northern Esmeraldas Province, Ecuador, and certain stands of Rhizophora mangle in and around the Isla Corazón y Fragata Wildlife Refuge in central Manabí Province, Ecuador. Our field-driven mangrove carbon estimate is higher than all but one of the comparison models evaluated. We find that basic latitudinal mangrove carbon models performed at least as well, if not better, than the more complex species-based allometric models in predicting standing carbon levels. In addition, we find that improved results occur when multiple models are combined as opposed to relying on any one single model for mangrove carbon estimates. The high level of carbon contained in these mangrove forests, combined with the future atmospheric carbon sequestration potential they offer, makes it a necessity that they are included in any future payment for ecosystem services strategy aimed at using forest systems to offset CO2 emissions and mitigate predicted CO2-driven temperature increases.

Current European policies are unlikely to jointly foster carbon sequestration and protect biodiversity

The extension of forest area is a globally accepted tool to offset CO2 emissions from deforestation and the combustion of fossil fuels. The common assumption is that in addition to the perceived climate benefits increasing forest area will also support biodiversity, thus making afforestation a “win-win scenario”. Based on the existing scientific evidences, we show that joined climate and biodiversity benefits are strongly context-dependent and that the outcome of afforestation is often highly questionable. In Europe, grasslands managed at low intensity contribute substantially to biodiversity conservation and carbon storage. However, many of these grasslands have been lost due to abandonment and subsequent spontaneous succession towards woody vegetation, or due to land use intensification. Moreover, grasslands are the ecosystems most often deliberately afforested in the context of EU carbon-centered policies that may thus counteract biodiversity conservation programmes. By reviewing the main EU policies targeting forests and grasslands, we found a striking ambivalence between policies and funding schemes addressing grassland conservation on the one hand (e.g. Habitats Directive, green payments within the Common Agricultural Policy) and those supporting afforestation on the other (e.g. rural development funds). We suggest three measures towards a better harmonization of the European Union policies that target forest and grassland ecosystems: (1) promoting the alignment of the decisions taken across different policy sectors; (2) focusing on the whole range of ecosystem services and biodiversity issues rather than on carbon management only; (3) valuing systems managed at low-intensity for their multifunctionality.

The role of short rotation coppice technology in fuelwood supply in Rungwe district, Tanzania

The roles of Short Rotation Coppice (SRC) Technology in fuelwood supply and offsetting CO2 emissions in the Tanzania and most African countries remain poorly understood. This study was carried in Rungwe District, Mbeya region in Tanzania, to determine trends, extent and drivers of adoption of SRC; identify various sources of household energy and assess the contribution of SRC to the total household fuelwood needs, and trees and shrub species used as sources of fuelwood. Data were collected using reconnaissance, field and social surveys and was analyzed using the Statistical Package for Social Sciences (SPSS). Results revealed that, 97.5% of local community adopted the SRC technology since 1960s. Eucalyptus spp. are mostly planted in woodlots and field boundaries while Persea americana and Leucaena leucocephala are intercropped in farmlands. The survey indicated that out of 176 tons of fuelwood used annually, 73% comes from SRC technology, 25% from non-SRC technology, and only 2% is purchased to supplement household fuelwood shortage. Local communities depend heavily on biomass energy from woodlots and farmlands where tree species like Eucalyptus spp. plays a key role in meeting the energy demand. This study demonstrates that SRC technologies like woodlots, boundary planting, and intercropping in farmland hold high promise to meet the household energy demand. If promoted and backed with strong policies and supportive land tenure, these technologies may reduce the harvesting pressure on native forests for energy demand and contribute to climate change mitigation and adaptation.Int. J. Agril. Res. Innov. & Tech. 6 (1): 41-46, June, 2016

Thermodynamic and mass transfer modeling of carbon dioxide absorption into aqueous 2-piperidineethanol

Amine scrubbing is a necessary technology to offset CO2 emissions from fossil-fuel power plants. Of the many solvents studied, hindered amines are of particular interest for their marriage of the capacity of tertiary amines with rates a hundredfold greater than tertiary amines. The relatively rapid rates of hindered amines have not been adequately explained, despite their extensive use in commercial solvents. This work seeks to explain the rapid rate of mass transfer of 2-piperidineethanol (2PE) and uses this rationale to draw general conclusions on hindered amines.Quantitative 13C NMR data were collected to determine the equilibrium of carbamate in 30wt% 2PE. Using these data along with VLE and pKa data, a rigorous thermodynamic model of 8 molal 2PE was built with electrolyte-NRTL and activity-based kinetics. Wetted-wall column flux data were fit to create the activity-based mass transfer model. Using this comprehensive model, the mass transfer rate was examined through sensitivity studies and Brønsted correlations.This work shows that 2PE forms a more stable carbamate than 2-amino-2-methyl-1-propanol. The carbamate reaction is the most significant component of mass transfer at 40°C. The Brønsted correlation for carbamate reactions of unhindered amines predicts the rate of carbamate reaction of 2PE, but the Brønsted correlation for bicarbonate underpredicts the regressed rate. The CO2 solubility is fit with five parameters with an ARD of 0.84%. The kinetics are fit with a carbamate- and a bicarbonate-forming reaction with an ARD of 7.03%.The chief conclusions are (1) that the rapid mass transfer of hindered amines is due to the formation of carbamate and the high pKa of the amine, (2) the carbamate formation rate appears unimpeded by steric hindrance and is predicted by a Brønsted correlation, suggesting that hindered amines react in the same manner as unhindered amines.

Role of ephemeral vegetation of emerging river bottoms in modulating CO2 exchanges across a temperate large lowland river stretch

Rivers and marginal wetlands contribute significantly to the carbon (C) exchange rate per unit area compared to adjacent terrestrial ecosystems, due to high C inputs, metabolic activity and CO2 supersaturation. Within riverscapes, the contribution of emerging bottoms (i.e. parafluvial zones) and ephemeral vegetation (i.e. microphytobenthos or annual vascular plant communities) to the C metabolism is understudied. The aim of this study was to evaluate the CO2 exchange rates at the water- and emergent sand bar-atmosphere interfaces within a lowland large temperate river stretch. CO2 fluxes were measured seasonally, in summer (August 2007) and winter (March 2008) via static closed chambers, together with the primary producers’ biomass (microphytobenthos and vascular macrophytes). Our results showed that the river was a CO2 source (between 0.2 and 7.6 mmol CO2 m−2 day−1), whilst the vegetated parafluvial zones acted as a net sink, with assimilation rates peaking at 623.4 mmol CO2 m−2 day−1. Emerging bare sediments were on the contrary net emitting CO2 systems (2.7–60.1 mmol CO2 m−2 day−1). Within lotic environments, seasonally emergent vegetated sand bars may represent important C fixation hot spots, with summer primary production particularly contributing to offsetting CO2 emissions and counterbalancing the heterotrophic metabolism of the saturated zones. Based on these outcomes, we suggest that studies addressing the strictly aquatic fluvial environment, which is generally a CO2 emitter, should be linked to those from transitional areas in order to better integrate terrestrial and aquatic C budgets.

Microbiological indicators of soil quality and degradation following conversion of native forests to continuous croplands

Deforestation resulting from forest conversion to agricultural land use is an important issue worldwide. This phenomenon is known to influence the activity and size of soil microbial community due to changes in environmental conditions with subsequent losses of soil organic matter (SOM) and soil quality degradation. The objective of this study was to investigate the relationship between soil organic carbon (SOC) losses and enzyme activities following land use conversion from native forests to continuous croplands. The amount of soil microbial biomass carbon (SMBC) and the activity of five soil enzymes (i.e., urease, invertase, alkaline phosphatase, acid phosphatase and arylsulfatase) were measured in croplands derived from forests and adjacent natural forests all on similar soil type at Gorgan site located in Northeast Iran. The content of SMBC decreased (47–83%) with deforestation at both soil sampling depths (0–20 and 20–40cm). With the exception of phosphatases, the absolute activities of soil enzymes (activity on a soil mass basis) tended to decrease significantly (15–35%) with continuous cultivation. However, the specific enzyme activities expressed either per unit of SOC or SMBC tended to increase (about 1.5–5.5 times) with conversion of forestlands to croplands. The significant positive correlation between enzyme activity per SMBC and C turnover rate may imply that a faster C cycle and loss due to deforestation is related to a greater enzymatic activity by a smaller size of microbial biomass in cropland soils. In brief, the specific activities of soil enzymes could be used to reveal SOM losses and soil degradation in natural forest ecosystems, and to identify changes in soil quality and fertility following deforestation. Changes or improvements in soil management such as cessation of cultivation or implementing agricultural practices that stop or minimize soil disturbance are most likely needed to stop further soil degradation, restore soil quality and rebuild SOC stocks to offset CO2 emissions in these ecosystems.

A new baseline of organic carbon stock in European agricultural soils using a modelling approach

Proposed European policy in the agricultural sector will place higher emphasis on soil organic carbon (SOC), both as an indicator of soil quality and as a means to offset CO2 emissions through soil carbon (C) sequestration. Despite detailed national SOC data sets in several European Union (EU) Member States, a consistent C stock estimation at EU scale remains problematic. Data are often not directly comparable, different methods have been used to obtain values (e.g. sampling, laboratory analysis) and access may be restricted. Therefore, any evolution of EU policies on C accounting and sequestration may be constrained by a lack of an accurate SOC estimation and the availability of tools to carry out scenario analysis, especially for agricultural soils. In this context, a comprehensive model platform was established at a pan-European scale (EU+Serbia, Bosnia and Herzegovina, Croatia, Montenegro, Albania, Former Yugoslav Republic of Macedonia and Norway) using the agro-ecosystem SOC model CENTURY. Almost 164000 combinations of soil-climate-land use were computed, including the main arable crops, orchards and pasture. The model was implemented with the main management practices (e.g. irrigation, mineral and organic fertilization, tillage) derived from official statistics. The model results were tested against inventories from the European Environment and Observation Network (EIONET) and approximately 20000 soil samples from the 2009 LUCAS survey, a monitoring project aiming at producing the first coherent, comprehensive and harmonized top-soil data set of the EU based on harmonized sampling and analytical methods. The CENTURY model estimation of the current 0-30cm SOC stock of agricultural soils was 17.63Gt; the model uncertainty estimation was below 36% in half of the NUTS2 regions considered. The model predicted an overall increase of this pool according to different climate-emission scenarios up to 2100, with C loss in the south and east of the area (involving 30% of the whole simulated agricultural land) compensated by a gain in central and northern regions. Generally, higher soil respiration was offset by higher C input as a consequence of increased CO2 atmospheric concentration and favourable crop growing conditions, especially in northern Europe. Considering the importance of SOC in future EU policies, this platform of simulation appears to be a very promising tool to orient future policymaking decisions.

Multi-season eddy covariance observations of energy, water and carbon fluxes over a suburban area in Swindon, UK

Abstract. Eddy covariance measurements of the turbulent sensible heat, latent heat and carbon dioxide fluxes for 12 months (2011–2012) are reported for the first time for a suburban area in the UK. The results from Swindon are comparable to suburban studies of similar surface cover elsewhere but reveal large seasonal variability. Energy partitioning favours turbulent sensible heat during summer (midday Bowen ratio 1.4–1.6) and latent heat in winter (0.05–0.7). A significant proportion of energy is stored (and released) by the urban fabric and the estimated anthropogenic heat flux is small but non-negligible (0.5–0.9 MJ m−2 day−1). The sensible heat flux is negative at night and for much of winter daytimes, reflecting the suburban nature of the site (44% vegetation) and relatively low built fraction (16%). Latent heat fluxes appear to be water limited during a dry spring in both 2011 and 2012, when the response of the surface to moisture availability can be seen on a daily timescale. Energy and other factors are more relevant controls at other times; at night the wind speed is important. On average, surface conductance follows a smooth, asymmetrical diurnal course peaking at around 6–9 mm s−1, but values are larger and highly variable in wet conditions. The combination of natural (vegetative) and anthropogenic (emission) processes is most evident in the temporal variation of the carbon flux: significant photosynthetic uptake is seen during summer, whilst traffic and building emissions explain peak release in winter (9.5 g C m−2 day−1). The area is a net source of CO2 annually. Analysis by wind direction highlights the role of urban vegetation in promoting evapotranspiration and offsetting CO2 emissions, especially when contrasted against peak traffic emissions from sectors with more roads. Given the extent of suburban land use, these results have important implications for understanding urban energy, water and carbon dynamics.

Biomass carbon pools of Cunninghamia lanceolata (Lamb.) Hook. forests in subtropical China: Characteristics and potential

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) is one of the most important indigenous tree species in China. Owing to their rapid growth, good timber quality and short rotation time, increasing numbers of plantations are being established with successive rotations. Numerous competing hypotheses have been described to explain the decline in yield that occurs with successive rotations of the plantations. In addition, there are some uncertainties regarding the changes and characteristics of biomass carbon pools in Chinese fir forests in subtropical China, and information is lacking regarding how to improve carbon sequestration by this biomass sink. The total biomass carbon stock of the Chinese fir forest in China increased from 91.57 Tg C in 1977–1981 to 238.50 Tg C in 2004–2008, accounting for 2.48–4.32% of the national forest biomass carbon in the corresponding period. Due to the decreased yield during successive rotation for Chinese fir plantations before the 1990s, the biomass carbon stock of Chinese fir forests decreased in several regions in China during the 1980s and 1990s, and increased in the 2000s when several silvicultural measures were implemented to improving the quality of Chinese fir plantations. When compared with the age-based volume to biomass (V–B) method of determining biomass carbon stock in Chinese fir forests in Jiangxi Province, the site specific-based and the mixed forests-based scenarios would both help offset CO2 emissions by sequestrating more CO2 from the atmosphere.

Dynamics of soil carbon following destruction of tropical rainforest and the subsequent establishment of Imperata grassland in Indonesian Borneo using stable carbon isotopes

AbstractSoutheast Asia has the highest rate of tropical rainforest deforestation worldwide, and large deforested areas have been replaced ultimately by the highly invasive grass Imperata cylindrica. However, information on the carbon (C) budget with such land transition is very scarce. This study presents the dynamics of soil C following rainforest destruction and the subsequent establishment of Imperata grassland in the lowland humid tropics of Indonesian Borneo using stable C isotopes. To evaluate the relative contribution of organic matter originating from primary forest (C3) and grasslands (C4), we compared soil C stock and natural 13C abundance from six sites to a depth of 100 cm using samples with a wide range of soil textures. Twelve years after the first soil sampling in the grasslands, we re‐sampled to examine temporal changes in soil organic matter. The grassland topsoil (0–5 cm) is an active layer with rapid decomposition and incorporation of fresh C (mean residence time: 7.5 year) and a substantial proportion of the stable C pool (37%). The decline in forest‐derived C was slight, even at 5–10 cm depths, and subsoil (20–100 cm depth) forest‐derived C did not change along the forest‐to‐grassland chronosequence. Grassland‐derived C stock increased significantly in the subsurface and subsoils (5–100 cm). Simulation indicated that total soil C stock (0–100 cm) increased by 18.6 Mg ha−1 from initial primary forest (58.0 Mg ha−1) to a new equilibrium state of the grassland (76.6 Mg ha−1) after 30–50 years of grassland establishment. This research indicates that the soil did not function as a CO2 source when the deforested area was replaced by Imperata grassland on the Ultisols of the Asian humid tropics. Instead, increased soil C stocks offset CO2 emissions, with the C offset accounting for 6.6–7.4% of the loss of biomass C stock.

Side effects and accounting aspects of hypothetical large-scale Southern Ocean iron fertilization

Abstract. Recent suggestions to slow down the increase in atmospheric carbon dioxide have included ocean fertilization by addition of the micronutrient iron to Southern Ocean surface waters, where a number of natural and artificial iron fertilization experiments have shown that low ambient iron concentrations limit phytoplankton growth. Using a coupled carbon-climate model with the marine biology's response to iron addition calibrated against data from natural iron fertilization experiments, we examine biogeochemical side effects of a hypothetical large-scale Southern Ocean Iron Fertilization (OIF) that need to be considered when attempting to account for possible OIF-induced carbon offsets. In agreement with earlier studies our model simulates an OIF-induced increase in local air-sea CO2 fluxes by about 73 GtC over a 100-year period, which amounts to about 48% of the OIF-induced increase in organic carbon export out of the fertilized area. Offsetting CO2 return fluxes outside the region and after stopping the fertilization at 1, 7, 10, 50, and 100 years are quantified for a typical accounting period of 100 years. For continuous Southern Ocean iron fertilization, the CO2 return flux outside the fertilized area cancels about 20% of the fertilization-induced CO2 air-sea flux within the fertilized area on a 100-yr timescale. This "leakage" effect has a radiative impact more than twice as large as the simulated enhancement of marine N2O emissions. Other side effects not yet discussed in terms of accounting schemes include a decrease in Southern Ocean oxygen levels and a simultaneous shrinking of tropical suboxic areas, and accelerated ocean acidification in the entire water column in the Southern Ocean at the expense of reduced globally-averaged surface-water acidification. A prudent approach to account for the OIF-induced carbon sequestration would account for global air-sea CO2 fluxes rather than for local fluxes into the fertilized area only. However, according to our model, this would underestimate the potential for offsetting CO2 emissions by about 20% on a 100 year accounting timescale. We suggest that a fair accounting scheme applicable to both terrestrial and marine carbon sequestration has to be based on emission offsets rather than on changes in individual carbon pools.

Counting carbon on the farm: Reaping the benefits of carbon offset programs

R educing anthropogenic greenhouse gas (GHG) emissions is the greatest environmental challenge facing society over the coming decades (NAS 2005). Although the largest global source of emission stems from the use of fossil fuels, land use, including agriculture, is the second greatest contributor to increasing GHG concentrations in the atmosphere, accounting for about 30% of total net emissions (IPCC 2007). The majority of these land use emissions are associated with deforestation and land conversion, mainly in the tropics; however, in the United States, agriculture contributes around 7% of total emissions (EPA 2007). The three main GHGs of concern—carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O)—are all emitted through various agricultural activities, with the CH4 and N2O dominating agricultural emissions in the United States. However, agriculture has the capacity to not only significantly reduce its own emissions, but also to offset CO2 emissions from other sectors of the economy via carbon sequestration (CAST 2004; Paustian et al. 2006). By employing practices that increase organic matter content (about half of which is carbon) of soils, it is estimated that as much as 50 to 200 million t C per year of carbon offsets could be produced by US agriculture (Lal et al.…

Sequestration of organic carbon in West African soils byAménagement en Courbes de Niveau

A recent Intergovernmental Panel on Climate Change (IPPC) report concludes that global warming, while already a global crisis, is likely to become even more devastating. The scientific consensus is that global warming is caused by increases in greenhouse gases including carbon dioxide. The Sahel of West Africa seems to be more adversely affected by such climate changes, leading to reduced and more sporadic rainfall. In addition, food security in the region is tenuous and fragile, due to adverse climate change, but also due to the historical mining of nutrients and carbon. With the adoption of the Kyoto accords, at least by some countries, sequestered carbon (C) has become a tradable commodity. This provides a double incentive to increase soil organic carbon in the C-depleted and degraded soils of West Africa — return C to improve soil quality and assist in removing CO2 from the atmosphere to assist in mitigating climate change. A challenge, however, remains to determine which agricultural systems can actually sequester C. The technology called Amenagement en courbes de niveau (ACN), which can be roughly translated as ‘Ridge-tillage’, has given crop yield increases of 30 to 50%. To date, there has only been anecdotal evidence suggesting that Amenagement en courbes de niveau leads to increased soil organic C. The objectives of the study reported here were to determine whether the technology has the potential to sequester C in West African soils, and, if so, how much. In this study, soil organic C was measured by combustion methods in soils sampled at 0–20 and 20–40 cm depths in a series of experiments in Mali, Senegal and The Gambia. Soil organic C was measured in three very different types of experiments, all including Amenagement en courbes de niveau technology, resulting in three methods of measuring C sequestration. Our results indicate that the Amenagement en courbes de niveau technology significantly increased maize yields by 24% by weight in the Gambia experiment while soil organic C was increased by 26% in The Gambia, by 12% in Siguidolo, Mali, and by 14% in peanut systems of Nioro, Senegal. These increases in soil organic C are likely due to three factors: (1) reduced erosion and movement of soil, (2) increased crop growth resulting from the greater capture of rainfall, and (3) increased growth and density of shrubs and trees resulting from the increased subsoil water, resulting in turn from the increased capture of rainfall, and reduced runoff. Measuring soil C on fields that were successively placed under Amenagement en courbes de niveau management and the use of replicated experimental plots appear to be the best methods to quantify the C sequestration potential of the practice. These results indicate that this soil and water conservation technology not only harvests water and increases food production, but also increases soil organic carbon. This technology thus is a successful technique to sequester C in soils and if carried out in a large region may both offset CO2 emissions and help mitigate climate change.