Large Carbon Sink Research Articles

Study on carbon dioxide atmospheric distribution over the Southwest Indian Ocean islands using satellite data: Part 1 – Climatology and seasonal results

The forests of the Southwest Indian Ocean (SWIO) islands States are large carbon sinks. Rapid population growth in these islands is responsible for deforestation, which in turn is the main source of carbon dioxide (CO2) emissions. This study is divided into two parts: The present study (Part 1) describes the seasonal vertical and surface spatial distribution of CO2 over the SWIO islands and the temporal variation of surface CO2 concentrations using data measured by the Tropospheric Emission Spectrometer (TES) on board the Aura Satellite. The CO2 hotspots over these islands were identified and assessed to determine if they were associated with deforestation and forest degradation anthropogenic activities. Areas of minimum or low CO2 atmospheric loading were also identified, and investigated to determine if they coincided with strong sink areas. Atmospheric CO2 concentration was building-up from summer to spring. The spatial extent of CO2 hotspots was found to increase from summer to spring. Over the study region, semi-permanent stable layers at 700 hPa and 500 hPa were shown to separate the troposphere into three layers of CO2. Furthermore, surface CO2 levels over all the study areas were found to be increasing during the period of the investigation. Part 2 of this study demonstrates the influence of meteorology and associated air transport on atmospheric CO2 distribution over the study region.

Comparing soil inventory with modelling: Carbon balance in central European forest soils varies among forest types

Forest soils represent a large carbon pool and already small changes in this pool may have an important effect on the global carbon cycle. To predict the future development of the soil organic carbon (SOC) pool, well-validated models are needed. We applied the litter and soil carbon model Yasso15 to 1838 plots of the German national forest soil inventory (NFSI) for the period between 1985 and 2014 to enables a direct comparison to the NFSI measurements. In addition, to provide data for the German Greenhouse Gas Inventory, we simulated the development of SOC with Yasso15 applying a climate projection based on the RCP8.5 scenario. The initial model-calculated SOC stocks were adjusted to the measured ones in the NFSI.On average, there were no significant differences between the simulated SOC changes (0.25 ± 0.10 Mg C ha−1 a−1) and the NFSI data (0.39 ± 0.11 Mg C ha−1 a−1). Comparing regional soil-unit-specific aggregates of the SOC changes, the correlation between both methods was significant (r2 = 0.49) although the NFSI values had a wider range and more negative values. In the majority of forest types, representing 75% of plots, both methods produced similar estimates of the SOC balance. Opposite trends were found in mountainous coniferous forests on acidic soils. These soils had lost carbon according to the NFSI (−0.89 ± 0.30 Mg C ha−1 a−1) whereas they had gained it according to Yasso15 (0.21 ± 0.10 Mg C ha−1 a−1). In oligotrophic pine forests, the NFSI indicated high SOC gains (1.36 ± 0.17 Mg C ha−1 a−1) and Yasso15 much smaller (0.29 ± 0.10 Mg C ha−1 a−1).According to our results, German forest soils are a large carbon sink. The application of the Yasso15 model supports the results of the NFSI. The sink strength differs between forest types possibly because of differences in organic matter stabilisation.

Sequestration of macroalgal carbon: the elephant in the Blue Carbon room.

Macroalgae form the most extensive and productive benthic marine vegetated habitats globally but their inclusion in Blue Carbon (BC) strategies remains controversial. We review the arguments offered to reject or include macroalgae in the BC framework, and identify the challenges that have precluded macroalgae from being incorporated so far. Evidence that macroalgae support significant carbon burial is compelling. The carbon they supply to sediment stocks in angiosperm BC habitats is already included in current assessments, so that macroalgae are de facto recognized as important donors of BC. The key challenges are (i) documenting macroalgal carbon sequestered beyond BC habitat, (ii) tracing it back to source habitats, and (iii) showing that management actions at the habitat lead to increased sequestration at the sink site. These challenges apply equally to carbon exported from BC coastal habitats. Because of the large carbon sink they support, incorporation of macroalgae into BC accounting and actions is an imperative. This requires a paradigm shift in accounting procedures as well as developing methods to enable the capacity to trace carbon from donor to sink habitats in the ocean.

Shedding Light on the Southern Ocean Carbon Sink

One of the world’s largest carbon sinks is still poorly understood.

A new estimation of China’s net ecosystem productivity based on eddy covariance measurements and a model tree ensemble approach

Accurate assessment of the strength of China’s terrestrial ecosystem carbon sink is key to understanding its regional carbon budget. However, large uncertainties in current carbon sink estimations still exist, which hinder the prediction of future climate change trajectories. In this study, we generated a high-resolution (1 km × 1 km) dataset of China’s net ecosystem productivity (NEP) in the last decade via a model tree ensemble approach combined with data from 46 flux sites in China and neighboring regions. The upscaling also included detailed information on nitrogen (N) deposition and forest age that have often been neglected in previous studies. The performance of MTE algorithm in simulating NEP at the site level is relatively high for both training (R2 = 0.81, RMSE = 0.73 gC m−2 day−1) and validation datasets (R2 = 0.76, RMSE = 0.81 gC m−2 day−1). Our data-driven estimation showed that roughly 70% of the area is a carbon sink, and the largest carbon sinks are found in the southeast and southwest monsoon regions. The total annual NEP in China in the last decade was 1.18 ± 0.05 Pg C yr−1, which is similar to the results found by another foundational global-scale study. Yet, the two studies significantly differ in the spatial distribution of carbon sink density. The seasonality of China’s NEP is characterized by region-specific kurtosis and skewness in most areas. Furthermore, ecosystem carbon use efficiency (CUE), defined as the annual NEP/GPP ratio, also showed high spatial variation. For example, the Xiaoxing’anling and Changbai Mountains in northeastern China, the eastern edge of the Tibetan Plateau, and bordering areas of the southeast and southwest monsoon regions have a larger CUE than the rest of China. On average, China’s terrestrial ecosystem CUE is approximately 0.17. Our data-driven NEP and CUE estimates provide a new tool for assessing China’s carbon dioxide flux. Our study also highlights the necessity to incorporate more environmental variables related to vegetation growth and more data derived from flux sites into NEP upscaling to reduce uncertainties in carbon budget estimations.

Effects of Land Use Change, Cultivation, and Landscape Position on Prairie Soil Organic Carbon Stocks

Temperate grassland soils are typically a sink for carbon. However, it is estimated that up to 99% of tallgrass prairies in North America have been converted to another land use. These conversions can lead to increased soil erosion and soil organic carbon (SOC) mineralization rates, turning a large carbon sink into a source. The purpose of this study was to compare by land use the retention of SOC, TSN, and fly ash on sloping landscapes with an emphasis on measuring the subsoil in addition to the surface soil. Eight paired plots were established on adjacent, sloping landscape profiles in western Iowa; one site a cropland and the other a remnant tallgrass prairie. The prairie landscape had a baseline SOC stock of 232 Mg-C ha-1. After roughly 150 years of agriculture the cropland had 52% less SOC, 39% less TSN, and 22% less fly ash which equates to annual losses of 0.55 Mg-C ha-1 yr-1, 0.04 Mg-N ha-1 yr-1, and 0.0002 Mg-fly ash ha-1 yr-1.

Coupled eco-hydrology and biogeochemistry algorithms enable the simulation of water table depth effects on boreal peatland net CO<sub>2</sub> exchange

Abstract. Water table depth (WTD) effects on net ecosystem CO2 exchange of boreal peatlands are largely mediated by hydrological effects on peat biogeochemistry and the ecophysiology of peatland vegetation. The lack of representation of these effects in carbon models currently limits our predictive capacity for changes in boreal peatland carbon deposits under potential future drier and warmer climates. We examined whether a process-level coupling of a prognostic WTD with (1) oxygen transport, which controls energy yields from microbial and root oxidation–reduction reactions, and (2) vascular and nonvascular plant water relations could explain mechanisms that control variations in net CO2 exchange of a boreal fen under contrasting WTD conditions, i.e., shallow vs. deep WTD. Such coupling of eco-hydrology and biogeochemistry algorithms in a process-based ecosystem model, ecosys, was tested against net ecosystem CO2 exchange measurements in a western Canadian boreal fen peatland over a period of drier-weather-driven gradual WTD drawdown. A May–October WTD drawdown of ∼ 0.25 m from 2004 to 2009 hastened oxygen transport to microbial and root surfaces, enabling greater microbial and root energy yields and peat and litter decomposition, which raised modeled ecosystem respiration (Re) by 0.26 µmol CO2 m−2 s−1 per 0.1 m of WTD drawdown. It also augmented nutrient mineralization, and hence root nutrient availability and uptake, which resulted in improved leaf nutrient (nitrogen) status that facilitated carboxylation and raised modeled vascular gross primary productivity (GPP) and plant growth. The increase in modeled vascular GPP exceeded declines in modeled nonvascular (moss) GPP due to greater shading from increased vascular plant growth and moss drying from near-surface peat desiccation, thereby causing a net increase in modeled growing season GPP by 0.39 µmol CO2 m−2 s−1 per 0.1 m of WTD drawdown. Similar increases in GPP and Re caused no significant WTD effects on modeled seasonal and interannual variations in net ecosystem productivity (NEP). These modeled trends were corroborated well by eddy covariance measured hourly net CO2 fluxes (modeled vs. measured: R2 ∼ 0.8, slopes ∼ 1 ± 0.1, intercepts ∼ 0.05 µmol m−2 s−1), hourly measured automated chamber net CO2 fluxes (modeled vs. measured: R2 ∼ 0.7, slopes ∼ 1 ± 0.1, intercepts ∼ 0.4 µmol m−2 s−1), and other biometric and laboratory measurements. Modeled drainage as an analog for WTD drawdown induced by climate-change-driven drying showed that this boreal peatland would switch from a large carbon sink (NEP ∼ 160 g C m−2 yr−1) to carbon neutrality (NEP ∼ 10 g C m−2 yr−1) should the water table deepen by a further ∼ 0.5 m. This decline in projected NEP indicated that a further WTD drawdown at this fen would eventually lead to a decline in GPP due to water limitation. Therefore, representing the effects of interactions among hydrology, biogeochemistry and plant physiological ecology on ecosystem carbon, water, and nutrient cycling in global carbon models would improve our predictive capacity for changes in boreal peatland carbon sequestration under changing climates.

Managing tropical wetlands for advancing global rice production: Implications for land-use management

Being fertile lands, wetlands have been managed for traditional agriculture over millennia. However, the integrity and ecosystem services of wetlands are being jeopardized by intensive land-use comprising of drainage and excessive disturbance. An adhoc and intensive use of wetlands, without preserving ecological integrity is causing ecosystem disservices and threatening conversion of a large soil organic carbon (SOC) sink into a net source. Wetlands in the tropical parts of the world are distributed unevenly and represent ∼3% of the total world land area. Due to stagnancy and even reduction in rice (Oryza sativa) yield of many agricultural regions, there is a need for additional and alternative land-uses which can raise the global rice production to ∼1 billion Mg (megagram=106g=metric ton) by 2050 from ∼497 million Mg now. Wetlands can be a viable option to advance global food security because of high soil fertility and vast geographical distribution. A ‘3-tier rice production system’ is proposed herein based on specific hydrological niche to advance global food security without degrading the ecosystem services of wetlands. In addition to increasing agronomic yield, the proposed modus operandi can also improve the livelihood security of farmers through an additional income streams by: (i) trading of SOC credits generated through adoption of conservation agriculture in littoral zones, and (ii) promoting fish and duckery culture in conjunction with deepwater rice farming. Furthermore, the proposed strategies will also set in motion the process of restoration of wetlands while enhancing C sink capacity of the ecosystems.

Net ecosystem carbon exchange of a dry temperate eucalypt forest

Abstract. Forest ecosystems play a crucial role in the global carbon cycle by sequestering a considerable fraction of anthropogenic CO2, thereby contributing to climate change mitigation. However, there is a gap in our understanding about the carbon dynamics of eucalypt (broadleaf evergreen) forests in temperate climates, which might differ from temperate evergreen coniferous or deciduous broadleaved forests given their fundamental differences in physiology, phenology and growth dynamics. To address this gap we undertook a 3-year study (2010–2012) of eddy covariance measurements in a dry temperate eucalypt forest in southeastern Australia. We determined the annual net carbon balance and investigated the temporal (seasonal and inter-annual) variability in and environmental controls of net ecosystem carbon exchange (NEE), gross primary productivity (GPP) and ecosystem respiration (ER). The forest was a large and constant carbon sink throughout the study period, even in winter, with an overall mean NEE of −1234 ± 109 (SE) g C m−2 yr−1. Estimated annual ER was similar for 2010 and 2011 but decreased in 2012 ranging from 1603 to 1346 g C m−2 yr−1, whereas GPP showed no significant inter-annual variability, with a mean annual estimate of 2728 ± 39 g C m−2 yr−1. All ecosystem carbon fluxes had a pronounced seasonality, with GPP being greatest during spring and summer and ER being highest during summer, whereas peaks in NEE occurred in early spring and again in summer. High NEE in spring was likely caused by a delayed increase in ER due to low temperatures. A strong seasonal pattern in environmental controls of daytime and night-time NEE was revealed. Daytime NEE was equally explained by incoming solar radiation and air temperature, whereas air temperature was the main environmental driver of night-time NEE. The forest experienced unusual above-average annual rainfall during the first 2 years of this 3-year period so that soil water content remained relatively high and the forest was not water limited. Our results show the potential of temperate eucalypt forests to sequester large amounts of carbon when not water limited. However, further studies using bottom-up approaches are needed to validate measurements from the eddy covariance flux tower and to account for a possible underestimation in ER due to advection fluxes.

UK macroalgae aquaculture: What are the key environmental and licensing considerations?

Macroalgae has numerous commercial uses and the potential to create large carbon sinks. The study reviewed the legal context, including environmental and social aspects, for the setting up of a seaweed farm in the UK. A lease is required to use the seabed and a Marine Licence is required from the national regulator. There is no need for new legislation, however, the existing guidance should be updated. There is a major need to clarify what level of assessment is required as part of the marine licensing process. The environmental and social considerations to licensing were also reviewed. Changes to the hydrodynamics and sediment transport are expected in and around the farm. These may lead to changes in seabed siltation and light levels. The addition of hard substrate (from the anchors) and a macroalgae canopy lead to attraction of benthic animals, fish, marine mammals and birds. These, in addition to potential changes in organic matter and nutrients reaching the seabed from exudate and detritus, could create changes in existing benthic communities on the seafloor. No reason for major population-level impacts were seen. However, numerous knowledge gaps where identified. Scale appears to be an important consideration. A small farm on its own is unlikely to have a large effect on the marine environment. However, a very large farm, or multiple small farms next to each other could have a more notable effect. Knowledge gaps were identified and recommendations were provided that can assist the development of the UK macroalgae farming industry.

Quantitative simulation of C budgets in a forest in Heilongjiang province, China

Recently, forest carbon (C) budgets have been significantly affected by climate variability, nitrogen (N) deposition, an increasing global atmospheric CO2 concentration, and disturbances (i.e., harvests, fires, and insect infestations). In this study, we quantitatively simulated the annual carbon balance of forests in Heilongjiang, China, from 1901 to 2013 using the Integrated Terrestrial Ecosystem Carbon (InTEC) model, which integrated the effects of nondisturbance (i.e., atmospheric CO2 concentration, N deposition, and climate variability) and disturbance factors. The average net primary production (NPP) of Heilongjiang was 284 g C m-2 a-1 in 1901 and increased in 1950 to 339 g C m-2 a-1; a rapid increase occurred after 1980, with an increase of 48% in 2013 compared with the NPP in 1901. The average NPP of the entire Heilongjiang region increased significantly and became more stable in 2013. However, the NPP in the northern region of the Xiaoxing’an Mountains was lower than that in the other regions. The fluctuation in average net ecosystem production (NEP) was relatively large because Heilongjiang was a carbon source for many years before the 1930s and again in the early 21st century, due to serious disturbances and intensified human activities. In recent years, NEP began to increase again, and in 2013 the forests became a large carbon sink (188 g C m-2 a-1). The spatial distribution of the average NEP was similar to that of NPP, though the largest increment in the average NEP from 1901 to 2013 was in the Changbai Mountains.

Forest cover dynamics analysis and prediction modelling using logistic regression model (case study: forest cover at Indragiri Hulu Regency, Riau Province)

Forest destruction, climate change and global warming could reduce an indirect forest benefit because forest is the largest carbon sink and it plays a very important role in global carbon cycle. To support Reducing Emissions from Deforestation and Forest Degradation (REDD +) program, people pay attention of forest cover changes as the basis for calculating carbon stock changes. This study try to explore the forest cover dynamics as well as the prediction model of forest cover in Indragiri Hulu Regency, Riau Province Indonesia. The study aims to analyse some various explanatory variables associated with forest conversion processes and predict forest cover change using logistic regression model (LRM). The main data used in this study is Land use/cover map (1990 – 2011). Performance of developed model was assessed through a comparison of the predicted model of forest cover change and the actual forest cover in 2011. The analysis result showed that forest cover has decreased continuously between 1990 and 2011, up to the loss of 165,284.82 ha (35.19 %) of forest area. The LRM successfully predicted the forest cover for the period 2010 with reasonably high accuracy (ROC = 92.97 % and 70.26 %).

Drought rapidly diminishes the large net CO2 uptake in 2011 over semi-arid Australia.

Each year, terrestrial ecosystems absorb more than a quarter of the anthropogenic carbon emissions, termed as land carbon sink. An exceptionally large land carbon sink anomaly was recorded in 2011, of which more than half was attributed to Australia. However, the persistence and spatially attribution of this carbon sink remain largely unknown. Here we conducted an observation-based study to characterize the Australian land carbon sink through the novel coupling of satellite retrievals of atmospheric CO2 and photosynthesis and in-situ flux tower measures. We show the 2010–11 carbon sink was primarily ascribed to savannas and grasslands. When all biomes were normalized by rainfall, shrublands however, were most efficient in absorbing carbon. We found the 2010–11 net CO2 uptake was highly transient with rapid dissipation through drought. The size of the 2010–11 carbon sink over Australia (0.97 Pg) was reduced to 0.48 Pg in 2011–12, and was nearly eliminated in 2012–13 (0.08 Pg). We further report evidence of an earlier 2000–01 large net CO2 uptake, demonstrating a repetitive nature of this land carbon sink. Given a significant increasing trend in extreme wet year precipitation over Australia, we suggest that carbon sink episodes will exert greater future impacts on global carbon cycle.

Seeking potential contributions to future carbon budget in conterminous US forests considering disturbances

Currently, US forests constitute a large carbon sink, comprising about 9 % of the global terrestrial carbon sink. Wildfire is the most significant disturbance influencing carbon dynamics in US forests. Our objective is to estimate impacts of climate change, CO2 concentration, and nitrogen deposition on the future net biome productivity (NBP) of US forests until the end of twenty-first century under a range of disturbance conditions. We designate three forest disturbance scenarios under one future climate scenario to evaluate factor impacts for the future period (2011–2100): (1) no wildfires occur but forests continue to age (Saging), (2) no wildfires occur and forest ages are fixed in 2010 (Sfixed_nodis), and (3) wildfires occur according to a historical pattern, consequently changing forest age (Sdis_age_change). Results indicate that US forests remain a large carbon sink in the late twenty-first century under the Sfixed_nodis scenario; however, they become a carbon source under the Saging and Sdis_age_change scenarios. During the period of 2011 to 2100, climate is projected to have a small direct effect on NBP, while atmospheric CO2 concentration and nitrogen deposition have large positive effects on NBP regardless of the future climate and disturbance scenarios. Meanwhile, responses to past disturbances under the Sfixed_nodis scenario increase NBP regardless of the future climate scenarios. Although disturbance effects on NBP under the Saging and Sdis_age_change scenarios decrease with time, both scenarios experience an increase in NBP prior to the 2050s and then a decrease in NBP until the end of the twenty-first century. This study indicates that there is potential to increase or at least maintain the carbon sink of conterminous US forests at the current level if future wildfires are reduced and age structures are maintained at a productive mix. The effects of CO2 on the future carbon sink may overwhelm effects of other factors at the end of the twenty-first century. Although our model in conjunction with multiple disturbance scenarios may not reflect the true conditions of future forests, it provides a range of potential conditions as well as a useful guide to both current and future forest carbon management.

Self-Standing Carbonaceous Sheets Composed of Micro and Nanometer Fibers Derived Bamboo and Application to PEFC and Edlc

Bamboo is a sustainable natural resource and the forests are considered to act as large carbon sinks, giving bamboo an advantage over other sustainable bioresources. However, it concerned that the rapid growth of bamboo may lead to biodiversity loss. This could be considered a serious disadvantage of bamboo in terms of its environmental impact. Bamboo has a fibrous microstructure and is composed mainly of cellulose, lignin, and hemicellulose, giving the isolation of cellulose fiber with relative ease. Owing to the unique microstructure of bamboo, we attempted to prepare self-standing carbonaceous fiber sheet by using bamboo as a starting material and have been investigated its application to polymer electrolyte fuel cells (PEFC) as the gas diffusion layer (GDL) [1].The Bamboo (Phyllostachys edulis, moso bamboo) cut in Japan was employed in this study. The basic preparation procedure of the self-standing carbonaceous bamboo fiber sheet (CBFS) was reported in [1]. In brief, CBFS was prepared viadelignification, defibration, molding, and carbonization. The bamboo fiber was obtained after the defibration process and then it was subjected to molding by using a plastic mold. After molding, the resultant fiber sheet was immersed in polyvinyl alcohol (PVA) aqueous solution for addition of PVA into the sheet. We also prepared CBFS without PVA. Finally, the sheet was subjected to carbonization under argon atmosphere. Here, the CBFS added PVA is denoted as CBFS w/ PVA. The microstructure of the CBFS was observed by field emission scanning electron microscope (FE-SEM) and was analyzed by X-ray diffraction (XRD) and Raman spectroscopy to elucidate the carbonization degree. The both of the in-plane and the through-plane of electrical conductivity were measured and the contact angle for a water droplet was measured to evaluate hydrophobicity of CBFS.A gas diffusion electrode was prepared by using CBFS, CBFS w/ PVA, the commercially available Pt-loaded carbon catalyst (Pt/C, TEC10E50E, Tanaka Kikinzoku Kogyo K. K., Japan) and Nafion ionomer solution by general manner. A single PEFC operation test was carried out by using Nafion117 membrane as the electrolyte and JARI’s standard PEFC single cell (the geometric electrode surface area was restricted to 1 cm × 1 cm).FE-SEM observation image shows CBFS is composed by aggregation of the carbonaceous fibers. The average diameter of fiber in the CBFS is ca. 6 μm irrespective to PVA addition, which is very close to that in commercially available carbon paper-based GDL as TGP-H-120 (Toray). In the case of CBFS w/ PVA, thin films derived from PVA were observed between each fibers and the surface of the fiber was seemed to be smooth, suggesting that PVA was partially covered with the bamboo fiber. The electrical conductivity was surely increased by addition of PVA.Figure 1 shows PEFC operation test results by using TGP-H-120, CBFS, and CBFS w/ PVA as GDL. The maximum power of CBFS was 135 mW cm-2, which is lower than that of TGP-H-120. On the other hand, the value was increased by addition of PVA and reached at 155 mW cm-2. Thus, the bamboo is expected as a potential GDL material. We also prepared cellulose nanofibrils (cellulose nanofibers; named as NFC or CFS) from the bamboo through chemical and physical treatments. Then, self-standing carbonaceous nanofiber sheet have been already obtained. The preparation procedure and its application to electric double layer capacitor (EDLC) will be also presented.Reference[1] T. Kinumoto et al., ACS Sustainable Chemistry & Engineering, Vol. 3(7), 1374−1380 (2015). AcknowledgementThis study was supported by The Environment Research and Technology Development Fund (ERTDF) from The Ministry of Environment, JAPAN, and the Venture Business Support Program from Oita University. The authors express gratitude to Mr. Yasuji Imahori Mr. Hideki Nakamizo, Mrs. Mayumi Nakamizo, and Mr. Yasuki Imahori of Silverloy Co. Ltd for supplying the bamboo strips. Figure 1

Carbon dynamics of China’s forests during 1901–2010: The importance of forest age

The forest ecosystem plays a significant role in long-term carbon sequestration. The magnitude of a forest carbon sink is determined by the combination of intrinsic biotic factors (i.e. forest age) and extrinsic environmental driving factors (i.e. temperature, precipitation, nitrogen deposition). The mechanism of how forest age affects the carbon balance is still unclear. Furthermore, forest age is a useful surrogate variable for analyses of the impact of disturbances on forest carbon and an important parameter for assessing carbon mitigation potential of forests at regional scale. Without considering forest age, large uncertainties exist in the simulating forest carbon cycle at regional scale. In this study, we analyzed the effect of forest age information on carbon uptake of China’s forests based on a process-based model (Integrated Terrestrial Ecosystem Carbon budget, InTEC model) in the last century, with integration of two forest age maps at 1 km spatial resolution which were derived from inventory data and remote sensing AVHRR NDVI. Inter-annual variability of net primary productivity in China’s forests during 1901–2010 based on InTEC model coupled with inventory data and remote sensing data was similar with each other. Meanwhile, the comparison approach indicated that the errors of 5 years in forest age might cause uncertainties of 25% in simulated net ecosystem productivity of China’s forests. We also discussed the significance of forest age in ecosystem process-based model and the uncertainties of carbon balance of China’s forest ecosystem during 1901–2010. Besides, the hypothesis assumed that no large-scale deforestation occurred since1950s and mature forests (and older forests) were covered the whole China. We adjusted forest age structure for different forest types and regions to simulate the effect of changes in forest age on distribution of carbon balance in China. The important finding is that the loss of carbon sink in China’s forests induced by disturbances (i.e. deforestation, afforestation or natural disturbances) is about 3.80 Pg C during last century. Based this hypothesis, China’s forests in the last two decade manifested a large carbon sink (0.23 Pg C a - 1). Currently, many process-based models are not capable of reflecting the impact of land disturbances because the explicit forest age information are lacking. Our study incorporated the forest age in models successfully and explored the effect of forest age on the simulating carbon balance of forests. The application of forest age in large-scale carbon modeling can improve the accuracy of simulated carbon dynamics and explore the uncertainties in carbon cycle models.

The global potential for carbon capture and storage from forestry.

BackgroundDiscussions about limiting anthropogenic emissions of CO_2 often focus on transition to renewable energy sources and on carbon capture and storage (CCS) of CO_2. The potential contributions from forests, forest products and other low-tech strategies are less frequently discussed. Here we develop a new simulation model to assess the global carbon content in forests and apply the model to study active annual carbon harvest 100 years into the future.ResultsThe numerical experiments show that under a hypothetical scenario of globally sustainable forestry the world’s forests could provide a large carbon sink, about one gigatonne per year, due to enhancement of carbon stock in tree biomass. In addition, a large amount of wood, 11.5 GT of carbon per year, could be extracted for reducing CO_2 emissions by substitution of wood for fossil fuels.ConclusionThe results of this study indicate that carbon harvest from forests and carbon storage in living forests have a significant potential for CCS on a global scale.

Ubiquitous Gammaproteobacteria dominate dark carbon fixation in coastal sediments.

Marine sediments are the largest carbon sink on earth. Nearly half of dark carbon fixation in the oceans occurs in coastal sediments, but the microorganisms responsible are largely unknown. By integrating the 16S rRNA approach, single-cell genomics, metagenomics and transcriptomics with (14)C-carbon assimilation experiments, we show that uncultured Gammaproteobacteria account for 70-86% of dark carbon fixation in coastal sediments. First, we surveyed the bacterial 16S rRNA gene diversity of 13 tidal and sublittoral sediments across Europe and Australia to identify ubiquitous core groups of Gammaproteobacteria mainly affiliating with sulfur-oxidizing bacteria. These also accounted for a substantial fraction of the microbial community in anoxic, 490-cm-deep subsurface sediments. We then quantified dark carbon fixation by scintillography of specific microbial populations extracted and flow-sorted from sediments that were short-term incubated with (14)C-bicarbonate. We identified three distinct gammaproteobacterial clades covering diversity ranges on family to order level (the Acidiferrobacter, JTB255 and SSr clades) that made up >50% of dark carbon fixation in a tidal sediment. Consistent with these activity measurements, environmental transcripts of sulfur oxidation and carbon fixation genes mainly affiliated with those of sulfur-oxidizing Gammaproteobacteria. The co-localization of key genes of sulfur and hydrogen oxidation pathways and their expression in genomes of uncultured Gammaproteobacteria illustrates an unknown metabolic plasticity for sulfur oxidizers in marine sediments. Given their global distribution and high abundance, we propose that a stable assemblage of metabolically flexible Gammaproteobacteria drives important parts of marine carbon and sulfur cycles.

Stability of soil organic carbon and potential carbon sequestration at eroding and deposition sites

This study aims to explore the dynamics of the factors influencing soil organic carbon (SOC) sequestration and stability at erosion and deposition sites. Thermal properties and dissolved aromatic carbon concentration along with Al, Fe concentration and soil specific surface area (SSA) were studied to 1 meter depth at two contrasting sites. Fe, Al concentrations and SSA size increased with depth and were negatively correlated with SOC concentration at the erosion site (P 30 cm deep) had a large carbon sink potential.

Spatial distribution of forest aboveground biomass in China: Estimation through combination of spaceborne lidar, optical imagery, and forest inventory data

The global forest ecosystem, which acts as a large carbon sink, plays an important role in modeling the global carbon balance. An accurate estimation of the total forest carbon stock in the aboveground biomass (AGB) is therefore necessary for improving our understanding of carbon dynamics, especially against the background of global climate change. The forest area of China is among the top five globally. However, because of limitations in forest AGB mapping methods and the availability of ground inventory data, there is still a lack in the nationwide wall-to-wall forest AGB estimation map for China. In this study, we collected over 8000 ground inventory records from published literatures, and developed an AGB mapping method using a combination of these ground inventory data, Geoscience Laser Altimeter System (GLAS)/Ice, Cloud, and Land Elevation Satellite (ICESat) data, optical imagery, climate surfaces, and topographic data. An uncertainty field model was introduced into the forest AGB mapping procedure to minimize the influence of plot location uncertainty. Our nationwide wall-to-wall forest AGB mapping results show that the forest AGB density in China is 120 Mg/ha on average, with a standard deviation of 61 Mg/ha. Evaluation with an independent ground inventory dataset showed that our proposed method can accurately map wall-to-wall forest AGB across a large landscape. The adjusted coefficient of determination ( R 2 ) and root-mean-square error between our predicted results and the validation dataset were 0.75 and 42.39 Mg/ha, respectively. This new method and the resulting nationwide wall-to-wall forest AGB map will help to improve the accuracy of carbon dynamic predictions in China. • Developed an AGB mapping method through the combination of multi-source data sets • Introduced a model to minimize the influence of plot locality uncertainty • Collected over 8000 ground inventory data across China from the literature • Mapped the wall-to-wall forest AGB of China ( R 2 = 0.75, RMSE = 42.39 Mg/ha)