Showing papers on "Atmospheric carbon cycle published in 2005"

Young organic matter as a source of carbon dioxide outgassing from Amazonian rivers

Abstract: Rivers are generally supersaturated with respect to carbon dioxide, resulting in large gas evasion fluxes that can be a significant component of regional net carbon budgets 1,2 Amazonian rivers were recently shown to outgas more than ten times the amount of carbon exported to the ocean in the form of total organic carbon or dissolved inorganic carbon 1 High carbon dioxide concentrations in rivers originate largely from in situ respiration of organic carbon 1‐3 , but little agreement exists about the sources or turnover times of this carbon 2,4,5 Here we present results of an extensive survey of the carbon isotope composition ( 13 C and 14 C) of dissolved inorganic carbon and three size-fractions of organic carbon across the Amazonian river system We find that respiration of contemporary organic matter (less than five years old) originating on land and near rivers is the dominant source of excess carbon dioxide that drives outgassing in medium to large rivers, although we find that bulk organic carbon fractions transported by these rivers range from tens to thousands of years in age We therefore suggest that a small, rapidly cycling pool of organic carbon is responsible for the large carbon fluxes from land to water to atmosphere in the humid tropics Riverine CO2 concentrations in Amazonian lowlands are 5–30 times supersaturated with respect to atmospheric equilibrium 1 ; such conditions may be prevalent throughout the humid tropics In situ respiration is the primary source of CO2 sustaining supersaturation in rivers, although inputs from groundwater supersaturated by soil respiration can be important in small systems and from submerged root respiration in floodplain-influenced systems 1–3,6–8 Although air–water gas exchange is a bi-directional process, atmospheric CO2 invasion has a negligible role compared to the large CO2 evasion fluxes, except at low supersaturation 2,3,6,7 13 C and 14 C isotopes can provide constraints on sources and turnover times of organic carbon fuelling river respiration, but no previous tropical study has used a dual-isotope approach to address these questions Studies in temperate eastern USA provide contrasting findings In the Hudson River, up to 70% of the centuries-old terrestrial organic carbon entering the river is respired in transit, and the average age of riverine organic carbon decreases downstream 2 However, the youngest components of dissolved organic carbon (DOC) are preferentially respired in the York River 5 , and modern dissolved inorganic carbon (DIC) in the Parker River may be explained by respiration of young DOC produced within the estuary 4 Documenting key patterns and controls on CO2 sources in diverse ecosystems is critical to advance our understanding of CO2 outgassing from rivers and its contribution to regional net carbon budgets To identify dominant sources and turnover times of riverine carbon throughout the Amazon basin, we analysed 14 C and 13 Co f

An appraisal of global wetland area and its organic carbon stock

Abstract: Wetlands are among the most important natural resources on earth They are the sources of cultural, economic and biological diversity With their wealth of stored carbon, wetlands provide a potential sink for atmospheric carbon, but if not managed properly could become sources of greenhouse gases (GHGs) such as carbon dioxide and methane Two important long-term uncertainties have initiated much debate in the scientific community These are global wetland area and the amount of carbon stored in it Compilation of relevant databases could be useful in setting up a long-term strategy for wetland conservation It has been difficult to estimate the net carbon sequestration potential of a wetland, because the rate of decomposition of organic matter and the abundance of methanogenic micro-organisms and fluxes from the sediment are extremely complex, and there are often gaps in relevant scientific knowledge The present discussion on density distribution of soil organic C in global wetlands could well be instrumental in formulating efficient strategies related to carbon sequestration and reduction of GHG emissions in wetland ecosystems Effective assessment of wetlands will only take place when the available information becomes accessible and usable for all stakeholders

Methanotrophic symbionts provide carbon for photosynthesis in peat bogs

Abstract: Wetlands are the largest natural source of atmospheric methane, the second most important greenhouse gas. Methane flux to the atmosphere depends strongly on the climate; however, by far the largest part of the methane formed in wetland ecosystems is recycled and does not reach the atmosphere. The biogeochemical controls on the efficient oxidation of methane are still poorly understood. Here we show that submerged Sphagnum mosses, the dominant plants in some of these habitats, consume methane through symbiosis with partly endophytic methanotrophic bacteria, leading to highly effective in situ methane recycling. Molecular probes revealed the presence of the bacteria in the hyaline cells of the plant and on stem leaves. Incubationwith 13C-methane showed rapid in situ oxidation by these bacteria to carbon dioxide, which was subsequently fixed by Sphagnum, as shown by incorporation of 13C-methane into plant sterols. In this way, methane acts as a significant (10–15%) carbon source for Sphagnum. The symbiosis explains both the efficient recycling of methane and the high organic carbon burial in these wetland ecosystems.

Peatland hydrology and carbon release: why small-scale process matters

Abstract: Peatlands cover over 400 million hectares of the Earth's surface and store between one-third and one-half of the world's soil carbon pool. The long-term ability of peatlands to absorb carbon dioxide from the atmosphere means that they play a major role in moderating global climate. Peatlands can also either attenuate or accentuate flooding. Changing climate or management can alter peatland hydrological processes and pathways for water movement across and below the peat surface. It is the movement of water in peats that drives carbon storage and flux. These small-scale processes can have global impacts through exacerbated terrestrial carbon release. This paper will describe advances in understanding environmental processes operating in peatlands. Recent (and future) advances in high-resolution topographic data collection and hydrological modelling provide an insight into the spatial impacts of land management and climate change in peatlands. Nevertheless, there are still some major challenges for future research. These include the problem that impacts of disturbance in peat can be irreversible, at least on human time-scales. This has implications for the perceived success and understanding of peatland restoration strategies. In some circumstances, peatland restoration may lead to exacerbated carbon loss. This will also be important if we decide to start to create peatlands in order to counter the threat from enhanced atmospheric carbon.

hydrology and carbon release: why small-scale process matters

Abstract: Peatlands cover over 400 million hectares of the Earths surface and store between one- third and one-half of the worlds soil carbon pool. The long-term ability of peatlands to absorb carbon dioxide from the atmosphere means that they play a major role in moderating global climate. Peatlands can also either attenuate or accentuate flooding. Changing climate or management can alter peatland hydrological processes and pathways for water movement across and below the peat surface. It is the movement of water in peats that drives carbon storage and flux. These small-scale processes can have global impacts through exacerbated terrestrial carbon release. This paper will describe advances in understanding environmental processes operating in peatlands. Recent (and future) advances in high-resolution topographic data collection and hydrological modelling provide an insight into the spatial impacts of land management and climate change in peatlands. Nevertheless, there are still some major challenges for future research. These include the problem that impacts of disturbance in peat can be irreversible, at least on human time-scales. This has implications for the perceived success and understanding of peatland restoration strategies. In some circumstances, peatland restoration may lead to exacerbated carbon loss. This will also be important if we decide to start to create peatlands in order to counter the threat from enhanced atmospheric carbon.

An Assessment of Carbon Pools, Storage, and Wood Products Market Substitution Using Life-Cycle Analysis Results

Abstract: The study utilized the results from a life-cycle assessment (LCA) of housing construction to analyze forest products' role in energy displacement and carbon cycling. It analyzed the behavior of three carbon pools associated with forest products: the forest, forest products, and fossil fuel displaced by forest products in end-use markets. The LCA provided data that allowed us to create an accounting system that tracked carbon from sequestration to substitution in forest product end-use markets. The accounts are time-dependent since the size of the carbon pools is influenced by harvest timing; hence the size of each pool is estimated under alternative harvesting scenarios and presented over time. The analysis of the alternative harvesting scenarios resulted in shorter harvest cycles and provided the largest carbon pools when all three pools were considered together. The study concluded that forest products led to a significant reduction in atmospheric carbon by displacing more fossil fuel-intensive products in housing construction. The result has important policy implications since any incentive to manage forest lands to produce a greater amount of forest products would likely increase the share of lands positively contributing to a reduction of carbon dioxide in the atmosphere.

Rising Atmospheric CO2 Reduces Sequestration of Root-Derived Soil Carbon

Abstract: Forests have a key role as carbon sinks, which could potentially mitigate the continuing increase in atmospheric carbon dioxide concentration and associated climate change. We show that carbon dioxide enrichment, although causing short-term growth stimulation in a range of European tree species, also leads to an increase in soil microbial respiration and a marked decline in sequestration of root-derived carbon in the soil. These findings indicate that, should similar processes operate in forest ecosystems, the size of the annual terrestrial carbon sink may be substantially reduced, resulting in a positive feedback on the rate of increase in atmospheric carbon dioxide concentration.

Carbon Dioxide and Methane Emissions from Estuaries

Abstract: Carbon dioxide and methane emissions from estuaries are reviewed in relation with biogeochemical processes and carbon cycling. In estuaries, carbon dioxide and methane emissions show a large spatial and temporal variability, which results from a complex interaction of river carbon inputs, sedimentation and resuspension processes, microbial processes in waters and sediments, tidal exchanges with marshes and flats and gas exchange with the atmosphere. The net mineralization of land- and marsh-derived organic carbon leads to high CO2 atmospheric emissions (10–1000 mmol·m−2·d−1 i.e. 44–44 000 mg·m−2·d−1) from inner estuarine waters and tidal flats and marsh sediments. Estuarine plumes at sea are sites of intense primary production and show large seasonal variations of pCO2 from undersaturation to oversaturation; on an annual basis, some plumes behave as net sinks of atmospheric CO2 and some others as net sources; CO2 atmospheric fluxes in plumes are usually one order of magnitude lower than in inner estuaries. Methane emissions to the atmosphere are moderate in estuaries (0.02–0.5 mmol·m−2·d−1 i.e. 0.32–8 mg·m−2·d−1), except in vegetated tidal flats and marshes, particularly those at freshwater sites, where sediments may be CH4-saturated. CH4 emissions from subtidal estuarine waters are the result of lateral inputs from river and marshes followed by physical ventilation, rather than intense in-situ production in the sediments, where oxic and suboxic conditions dominate. Microbial oxidation significantly reduces the CH4 emissions at low salinity (<10) only.

A Robust Strategy for Sustainable Energy

Abstract: The known energy resource base is more than sufficient to provide a growing world population with energy on the scale to which the industrial countries have grown accustomed and to which the developing countries aspire. Environmental constraints exist but have promising solutions, provided farsighted policies are adopted in timely fashion. We illustrate the scale of the problem using a simple numerical scenario of world energy demand over the next century and calculating the implied increase in carbon emissions and atmospheric carbon concentrations. We conclude that action is needed soon to keep carbon concentrations below 500 parts per million as of 2050 and that the cost of mitigation will be less than 1 percent of gross world product as of 2050, assuming today’s promising technologies prove successful, but also that additional novel mitigation technologies will need to be developed and adopted after 2050.

The carbon balance of forest soils: detectability of changes in soil carbon stocks in temperate and Boreal forests.

Abstract: Estimating soil carbon content as the product of mean carbon concentration and bulk density can result in considerable overestimation. Carbon concentration and soil mass need to be measured on the same sample and carbon contents calculated for each individual sample before averaging. The effect of this bias is likely to be smaller (but still greater than zero) when the primary objective is to determine stock changes over time. Variance and mean carbon content are significantly and positively related to each other, although some sites showed much higher variability than predicted by this relationship, as a likely consequence of their particular site history, forest management, and micro-topography. Because of the proportionality between mean and variance, the number of samples required to detect a fixed change in soil carbon stocks varied directly with the site mean carbon content from less than 10 to several thousands across the range of carbon stocks normally encountered in temperate and Boreal forests. This raises important questions about how to derive an optimal sampling strategy across such a varied range of conditions so as to achieve the aims of the Kyoto Protocol. Overall, on carbon-poor forest sites with little or no disturbance to the soil profile, it is possible to detect changes in total soil organic carbon over time of the order of 0.5 kg (C) m(-2) with manageable sample sizes even using simple random sampling (i.e., about 50 samples per sampling point). More efficient strategies will reveal even smaller differences. On disturbed forest sites (ploughed, windthrow) this is no longer possible (required sample sizes are much larger than 100). Soils developed on coarse aeolian sediments (sand dunes), or where buried logs or harvest residues of the previous rotation are present, can also exhibit large spatial variability in soil carbon. Generally, carbon-rich soils will always require larger numbers of samples. On these sites, simple random sampling is unlikely to be the preferred method, because of its inherent inefficiency. More sophisticated approaches, such as paired re-sampling inside relatively small plots (see, for example, Ellert et al., 2001) are likely to reduce sample size significantly and lead to detection of smaller differences in carbon stocks over time. However, it remains to be shown that at these sites the application of efficient sampling designs will result in the detection of differences relevant for the objectives of the Kyoto Protocol (cf., Conant et al., 2003). Finally, it should also be noted that, compared to the accuracy with which changes in atmospheric carbon content can be detected (less than 1 p.p.m. CO2), changes in soil carbon stocks are very uncertain. A release of 0.5 kg (C) from 1 m2 of soil surface is equivalent to an increase in CO, concentration of about 125 p.p.m. in the air column above the same area.

Multicentury Changes to the Global Climate and Carbon Cycle: Results from a Coupled Climate and Carbon Cycle Model

Abstract: In this paper, we use a coupled climate and carbon cycle model to investigate the global climate and carbon cycle changes out to year 2300 that would occur if CO2 emissions from all the currently estimated fossil fuel resources were released to the atmosphere. By year 2300, the global climate warms by about 8 K and atmospheric CO2 reaches 1423 ppmv. In our simulation, the prescribed cumulative emission since pre-industrial period is about 5400 Gt-C by the end of 23rd century. At year 2300, nearly 45 % of cumulative emissions remain in the atmosphere. In our simulations both soils and living biomass are net carbon sinks throughout the simulation. Despite having relatively low climate sensitivity and strong carbon uptake by the land biosphere, our model projections suggest severe long-term consequences for global climate if all the fossil-fuel carbon is ultimately released to the atmosphere.

CO2 air–sea exchange due to calcium carbonate and organic matter storage, and its implications for the global carbon cycle

Abstract: Release of CO2 from surface ocean water owing to precipitation of CaCO3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface water to sedimentary storage was studied by means of a quotient θ = (CO2 flux to the atmosphere)/(CaCO3 precipitated). θ depends not only on water temperature and atmospheric CO2 concentration but also on the CaCO3 and organic carbon masses formed. In CO2 generation by CaCO3 precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric CO2 concentration (195–375 ppmv), and increasing CaCO3 precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic carbon counteracts the CO2 production by carbonate precipitation and it results in lower CO2 emissions from the surface layer. When atmospheric CO2 increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO2 transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric CO2. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon from land, the calculated CO2 flux to the atmosphere is a function of the CaCO3 and Corg net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO2 flux near the Last Glacial Maximum is 17 to 7×1012 mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time it is 38–42×1012 mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic emissions of CO2 to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total alkalinity owing to the CaCO3 storage and consequent emission of CO2. These results are in agreement with the conclusions of a number of other investigators. As the CO2 uptake in mineral weathering is a major flux in the global carbon cycle, the CO2 weathering pathway that originates in the CO2 produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large imbalances of the atmosphere and land organic reservoir at 102–104-year time scales.

Greenhouse Gas Emissions from Hydroelectric Reservoirs

Abstract: The presence of certain trace gases (e.g., CO2 and CH4) in the atmosphere is related to human activity (fossil fuel combustion, deforestation, and intensive agriculture), and to the biogeochemical processes that occur in natural environments (tropical and boreal forests and tundra). For many years now, scientists have been trying to determine the importance of natural environments as sinks for or sources of these trace gases (1, 2, 3). The terrestrial biosphere constitutes a major carbon sink (4); more than a third of the anthropic CO2 emissions are fixed there (5). However, certain changes in land use (e.g., deforestation and the draining of marshes for agriculture) can lead to changes in the way greenhouse gases (GHGs) are produced or fixed by modifying the physicochemical characteristics of these soils. In the medium and long term, these changes are likely to invert the carbon sink capacity that has been attributed until now to certain natural environments (e.g., boreal regions). This article examines how one of these land-use changes, the creation of hydroelectric reservoirs, significantly modifies the carbon cycle in natural environments. Keywords: hydroelectric; greenhouse gas (carbon dioxide and methane); boreal reservoirs; tropical reservoirs; flooded soil

Centennial-scale interactions between the carbon cycle and anthropogenic climate change using a dynamic Earth system model

Abstract: [1] A complex Earth system model including atmosphere, ocean, ice sheets, marine carbon cycle and terrestrial vegetation was used to study the long-term response (100–1000 yrs) of the climate to different increased atmospheric CO2 concentrations. A 3.2 K global mean surface temperature increase is simulated for a 3xCO2 experiment. The freshwater input by melting of the Greenland Ice Sheet due to global warming is of minor importance compared to hydrological changes in the atmosphere. Increased equatorial upwelling enhances the tropical outgassing of CO2 from the oceans, lowering the total marine carbon uptake by 16–22%. On land, carbon release due to increase in soil temperature reduces the anthropogenic carbon uptake from CO2 fertilization up to 43%. Thus, we show that both marine and terrestrial carbon cycle have a positive feedback on climate, which has to be considered for future carbon emission scenarios.

Human Health and Ecological Effects of Carbon Dioxide Exposure

Abstract: This chapter focuses on the CO 2 storage in the context of the global carbon cycle, reviews information on human health effects and ecosystem impacts from exposure to high concentrations of CO 2 , and reviews industrial uses of CO 2 and describes the regulations put in place to protect workers and the public. Carbon dioxide is ubiquitous in the natural world. It undergoes an endless cycle of exchange among the atmosphere, living systems, soil, rocks, and water. Volcanic outgassing, the respiration of living things from humans to microbes, mineral weathering, and the combustion or decomposition of organic materials all release CO 2 into the atmosphere. Atmospheric CO 2 is then cycled back into plants, the oceans, and minerals through photosynthesis, dissolution, precipitation, and other chemical processes. Biotic and abiotic processes of the carbon cycle on land, in the atmosphere, and in the sea are connected through the atmospheric reservoir of CO 2 .

Sensitivity of global-scale climate change attribution results to inclusion of fossil fuel black carbon aerosol - article no. L14701

Abstract: It is likely that greenhouse gas emissions caused most of the global mean warming observed during the 20th century, and that sulphate aerosols counteracted this warming to some extent, by reflecting solar radiation to space and thereby cooling the planet. However, the importance of another aerosol, namely black carbon, could be underestimated. Here we include fossil fuel black carbon aerosol in a detection and attribution analysis with greenhouse gas and sulphate aerosols. We find that most of the warming of the 20th Century is attributable to changes in greenhouse gases offset by net aerosol cooling. However the pattern of temperature change due to black carbon is currently indistinguishable from the sulphate aerosol pattern of temperature change. The attribution of temperature change due to greenhouse gases is not sensitive to the inclusion of black carbon. We can be confident about the overall attribution of total aerosols, but less so about the contributions of black carbon emissions to 20th century climate change. This work presents no evidence that black carbon aerosol forcing outweighed the cooling due to sulphate aerosol.

The Interaction of Climate Change and the Carbon Dioxide Cycle

Abstract: The flow of carbon dioxide through the atmosphere is a complex system because it consists of several cycles; e.g., through the biosphere which produces and consumes it, and through the Earth's water surfaces which absorb and emit it. These processes are dependent on temperature but their reactions to temperature have different signs. Temperature rise promotes both the consumption and the production of carbon dioxide by the biosphere but liberates carbon dioxide from water surfaces. This paper offers a comprehensive review of the behaviour of these processes. It considers these flows and assesses observations of the movement of carbon dioxide to and from the atmosphere. The disturbance of the natural cycle by current anthropogenic emissions is used as an instrument to throw light on what is actually happening to cause alteration to atmospheric carbon dioxide concentration. Also, these considerations are used in attempts to model the processes with mathematical equations derived from physics and biology. It...

Limited Increase of Agricultural Soil Carbon and Nitrogen Stocks Due to Increased Atmospheric CO2 Concentrations

Abstract: SUMMARY Increased atmospheric concentrations of CO2 may lead to increases in agricultural soil carbon and nitrogen storage, but the impact is likely to be small and is uncertain due to limitations in other resources (e.g., nutrients, water) and interactions with climatic changes. Since only a small percentage of carbon added to the soil becomes stabilised, the impact of CO2 fertilisation of crops is considered to be very small compared to deliberate efforts to increase soil carbon by improved agricultural management. Even if agricultural soil carbon stocks are increased, carbon credits cannot be claimed under the Kyoto Protocol since the increases are not directly human-induced, a condition which must be met in order for any carbon sink to be included in emission reduction targets.

Growing season carbon dioxide exchange of two contrasting peatland ecosystems

Abstract: The CO2 flux of two peatlands in northern Alberta was examined during the 2004 growing season using eddy covariance measurements of net ecosystem exchange (NEE), chamber measurements of total ecosystem respiration, and empirical models driven by meteorological inputs. The two ecosystems, a poor fen and an extreme-rich fen, differed significantly in plant species composition, leaf area index, aboveground biomass and surface water chemistry. The mean diurnal pattern of NEE at the peak of the season was similar between the sites, however, the extreme-rich fen had a higher photo synthetic and respiratory capacity than the poor fen. Over the 6 month study, the poor fen was shown to accumulate between 2 to 3 times more carbon than the extreme-rich fen despite having a lower photosynthetic capacity. The evergreen nature of the poor fen site allowed for a longer season of net CO2 uptake than the deciduous species that dominated the extreme-rich fen.

The importance and place of the photosynthetic carbon sequestration in the organic branch of its global cycle

Abstract: Results of comparative analysis of turnover times and the capacity of major global pools of organic carbon are presented; the place of photosynthetic carbon sequestration is defined; concept of its catalytic role in the regulation of the organic branch of the global carbon cycle is ground. Concept of reservoir-flux model of photosynthetic carbon sequestration and of the net photosynthetic production at the territory of Northern Eurasia is suggested.

Agricultural sinks in the developing world: Different disciplines and different perspectives

Abstract: Agriculture is historically a source of atmospheric carbon. With the best management practices, this could be partly reversed, with a potential increase in size of the soil carbon pool that would have significant impact as a measure to mitigate climate change. This might benefit farmers twice over, as the carbon has a cash value, while the soil organic matter that contains it will assist productivity. There is therefore a business opportunity in carbon payments for farmers in the developed world. However, this article considers whether such payments might alleviate rural poverty and fund agricultural development in low-income countries. They might do so, but badly designed projects could lead to emission rather than sequestration, accompanied by productivity losses. Prevention of such perverse outcomes requires a multidisciplinary approach and an awareness of the political ecology context of sinks projects. An appropriate methodology is needed for the evaluation of soil carbon projects in developing count...

Implications of Carbon Sequestration for Landowners

Abstract: Carbon sequestration on agricultural lands might become an important instrument of the U.S. policy for reduction of atmospheric carbon, which is believed to be a major contributing factor to recent climatic change. Herein, we examine the near term income enhancing prospects of carbon sequestration for landowners. Based on a review of current U.S. policies, sequestration cost, and recent developments in the carbon market, we show that presently the prospects may be limited.

Atmospheric Carbon Dioxide and Climate: Historical-Geological Aspects

Abstract: Insignificant role of anthropogenic carbon dioxide in the total balance of this gas in the atmosphere is shown. Relationship of the atmospheric CO2 content with climate in geological history of the Earth and history of mankind is ambiguous. It is assumed that the influence of greenhouse effect on global climate was less significant than was thought previously. Its impact is governed by complex relationship of cosmic and terrestrial factors, including the position of continental massifs.