Papers on peatland greenhouse gas emissions

This is a list of papers on greenhouse gas emissions from peatlands. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Greenhouse gas fluxes in a drained peatland forest during spring frost-thaw event – Pihlatie et al. (2010) “Fluxes of greenhouse gases (GHG) carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) were measured during a two month campaign at a drained peatland forest in Finland by the eddy covariance (EC) technique (CO₂ and N₂O), and automatic and manual chambers (CO₂, CH₄ and N₂O). In addition, GHG concentrations and soil parameters (mineral nitrogen, temperature, moisture content) in the peat profile were measured. The aim of the measurement campaign was to quantify the GHG fluxes during freezing and thawing of the top-soil, a time period with potentially high GHG fluxes, and to compare different flux measurement methods. The forest was a net CO₂ sink during the two months and the fluxes of CO₂ dominated the GHG exchange. The peat soil was a small sink of atmospheric CH₄ and a small source of N₂O. Both CH₄ oxidation and N₂O production took place in the top-soil whereas CH₄ was produced in the deeper layers of the peat, which were unfrozen throughout the measurement period. During the frost-thaw events of the litter layer distinct peaks in CO₂ and N₂O emissions were observed. The CO₂ peak followed tightly the increase in soil temperature, whereas the N₂O peak occurred with a delay after the thawing of the litter layer. CH₄ fluxes did not respond to the thawing of the peat soil.” [Full text]

Observations and Status of Peatland Greenhouse Gas Emissions in Europe – Drösler et al. (2008) “A peatland is a type of ecosystem where carbon (C) along with nitrogen and several other elements has been accumulated as peat originating from the plant litter deposited on the site. A logical consequence of the above definition of peatlands is that they are ecosystems, which by way of nature are a sink for atmospheric carbon dioxide (CO₂). This is the case because more C is accumulated through photosynthesis than is released through respiration. As a consequence of this, organic matter accumulates as peat. The C accumulated in peatlands is equivalent to almost half the total atmospheric content, and a hypothetical sudden release would result in an instantaneous 50% increase in atmospheric CO₂. While this scenario is unrealistic, it nevertheless highlights the central role of peatlands where huge amounts of CO₂ have almost entirely been “consumed” since the last glacial maximum, but could respond differently as a result of future changes in climatic conditions. Peatlands have, hence, over the last 10,000 years helped to remove significant amounts of CO₂ from the atmosphere. A complicating factor in this respect is that in terms of the major greenhouse gases (GHGs), peatlands are not just acting as a sink for CO₂. The wet conditions that lead to the slow decomposition of organic material and enable peat accumulation to occur, also cause significant amounts of the powerful GHG methane (CH₄) to be formed. Indeed global wetlands (predominantly peatlands) are considered to be the largest single source of atmospheric CH₄ also when considering all anthropogenic emissions. Peatlands are, therefore, also a key player in the atmospheric CH₄ budget and as a result also influence the global climate.”

Decadal vegetation changes in a northern peatland, greenhouse gas fluxes and net radiative forcing – Johansson et al. (2006) “This study provides an analysis of how permafrost thawing and subsequent vegetation changes in a sub-Arctic Swedish mire have changed the net exchange of greenhouse gases, carbon dioxide (CO₂) and CH₄ over the past three decades. Images of the mire (ca. 17 ha) and surroundings taken with film sensitive in the visible and the near infrared portion of the spectrum, [i.e. colour infrared (CIR) aerial photographs from 1970 and 2000] were used. The results show that during this period the area covered by hummock vegetation decreased by more than 11% and became replaced by wet-growing plant communities. The overall net uptake of C in the vegetation and the release of C by heterotrophic respiration might have increased resulting in increases in both the growing season atmospheric CO₂ sink function with about 16% and the CH₄ emissions with 22%. Calculating the flux as CO₂ equivalents show that the mire in 2000 has a 47% greater radiative forcing on the atmosphere using a 100-year time horizon. Northern peatlands in areas with thawing sporadic or discontinuous permafrost are likely to act as larger greenhouse gas sources over the growing season today than a few decades ago because of increased CH₄ emissions.” [Full text]

Greenhouse Gas Emissions from Canadian Peat Extraction, 1990–2000: A Life-cycle Analysis – Cleary et al. (2005) “This study uses life-cycle analysis to examine the net greenhouse gas (GHG) emissions from the Canadian peat industry for the period 1990–2000. GHG exchange is estimated for land-use change, peat extraction and processing, transport to market, and the in situ decomposition of extracted peat. The estimates, based on an additive GHG accounting model, show that the peat extraction life cycle emitted 0.54 × 10⁶ t of GHG in 1990, increasing to 0.89 × 10⁶ t in 2000 (expressed as CO₂ equivalents using a 100-y time horizon). Peat decomposition associated with end use was the largest source of GHGs, comprising 71% of total emissions during this 11-y period. Land use change resulted in a switch of the peatlands from a GHG sink to a source and contributed an additional 15%. Peat transportation was responsible for 10% of total GHG emissions, and extraction and processing contributed 4%. It would take approximately 2000 y to restore the carbon pool to its original size if peatland restoration is successful and the cutover peatland once again becomes a net carbon sink.” [Full text]

Siberian Peatlands a Net Carbon Sink and Global Methane Source Since the Early Holocene – Smith et al. (2004) “Interpolar methane gradient (IPG) data from ice cores suggest the “switching on” of a major Northern Hemisphere methane source in the early Holocene. Extensive data from Russia’s West Siberian Lowland show (i) explosive, widespread peatland establishment between 11.5 and 9 thousand years ago, predating comparable development in North America and synchronous with increased atmospheric methane concentrations and IPGs, (ii) larger carbon stocks than previously thought (70.2 Petagrams, up to 26% of all terrestrial carbon accumulated since the Last Glacial Maximum), and (iii) little evidence for catastrophic oxidation, suggesting the region represents a long-term carbon dioxide sink and global methane source since the early Holocene.”

Exchange of greenhouse gases between soil and atmosphere: interactions of soil physical factors and biological processes – Smith et al. (2003) A review article. “This review examines the interactions between soil physical factors and the biological processes responsible for the production and consumption in soils of greenhouse gases. The release of CO₂ by aerobic respiration is a non-linear function of temperature over a wide range of soil water contents, but becomes a function of water content as a soil dries out. Some of the reported variation in the temperature response may be attributable simply to measurement procedures. Lowering the water table in organic soils by drainage increases the release of soil carbon as CO₂ in some but not all environments, and reduces the quantity of CH₄ emitted to the atmosphere. Ebullition and diffusion through the aerenchyma of rice and plants in natural wetlands both contribute substantially to the emission of CH₄; the proportion of the emissions taking place by each pathway varies seasonally. Aerated soils are a sink for atmospheric CH₄, through microbial oxidation. The main control on oxidation rate is gas diffusivity, and the temperature response is small. Nitrous oxide is the third greenhouse gas produced in soils, together with NO, a precursor of tropospheric ozone (a short-lived greenhouse gas). Emission of N₂O increases markedly with increasing temperature, and this is attributed to increases in the anaerobic volume fraction, brought about by an increased respiratory sink for O₂. Increases in water-filled pore space also result in increased anaerobic volume; again, the outcome is an exponential increase in N₂O emission.” [Full text]

Carbon balance and radiative forcing of Finnish peatlands 1900–2100 – the impact of forestry drainage – Minkkinen et al. (2002) “In this paper, changes in peat and tree stand C stores, GHG fluxes and the consequent RF of Finnish undisturbed and forestry-drained peatlands are estimated for 1900–2100. The C store in peat is estimated at 5.5 Pg in 1950. The rate of C sequestration into peat has increased from 2.2 Tg a^-1 in 1900, when all peatlands were undrained, to 3.6 Tg a^-1 at present, when c. 60% of peatlands have been drained for forestry. The C store in tree stands has increased from 60 to 170 Tg during the 20th century. Methane emissions have decreased from an estimated 1.0–0.5 Tg CH₄–C a^-1, while those of N2O have increased from 0.0003 to 0.005 Tg N₂O–N a^-1. The altered exchange rates of GHG gases since 1900 have decreased the RF of peatlands in Finland by about 3 mW m^-2 from the predrainage situation. This result contradicts the common hypothesis that drainage results in increased C emissions and therefore increased RF of peatlands. The negative radiative forcing due to drainage is caused by increases in CO₂ sequestration in peat (–0.5 mW m^-2), tree stands and wood products (–0.8 mW m^-2), decreases in CH₄ emissions from peat to the atmosphere (–1.6 mW m^-2), and only a small increase in N₂O emissions (+0.1 mW m^-2). Although the calculations presented include many uncertainties, the above results are considered qualitatively reliable and may be expected to be valid also for Scandinavian countries and Russia, where most forestry-drained peatlands occur outside Finland.”

Peatlands, carbon storage, greenhouse gases, and the Kyoto Protocol: Prospects and significance for Canada – Roulet (2000) “Natural peatlands are presently a relatively small sink for CO₂ and a large source of CH₄: globally, they store between 400 and 500 Gt C. There are large variations among peatlands, but when the “global warming potential” of CH₄ is factored in, many peatlands are neither sinks nor sources of GHGs. Some land-use changes may result in peatlands acting as net sinks for GHGs by reducing CH₄ emissions and/or increasing CO₂ sequestration (e.g., forest drainage), while other land uses may result in large losses of CO₂, CH₄, and N₂O (e.g., agriculture on organic soils, flooding for hydroelectric generation). Other land uses, such as peatland creation and restoration, produce no net change if they are replacing or restoring a previous level of GHG exchange.”

CO₂ Fluxes from Peat in Boreal Mires under Varying Temperature and Moisture Conditions – Silvola et al. (1996) “CO₂ emissions in boreal peatlands were measured during two seasons on various mire site types representing different nutrient statuses and water tables. In order to examine the long term effects of water table draw-down on the CO₂ fluxes, the sites also included 25-50-year-old drainages. On virgin sites the lowest CO₂ fluxes were measured at ombrotrophic sites dominated by Sphagnum fuscum (78-127 mg CO₂ m super(-2) h super(-1) at 12 degree C, 60-200 g CO sub(2)-C m super(-2) year super(-1)) and the highest CO₂ fluxes were at ombrotrophic sites with abundant under-storey vegetation (183-259 mg CO₂ m super(-2) h super(-1) at 12 degree C, 290-340 g CO₂-C m super(-2) year super(-1)). Lowering of the water table by 1 cm increased CO₂ fluxes by an average of 7.1 mg CO₂ m super(-2) h super(-1) at 12 degree C and 9.5 g CO₂-C m super(-2) year super(-1). In some cases the effect of ditches on the water table, and correspondingly on CO₂ fluxes, was small. However, effective draining caused approximately 100% increase in CO₂ fluxes. Drainages had higher CO₂ fluxes compared with virgin subsites at the same temperature and water table. The effect of temperature on CO₂ fluxes depended on the water table, the average Q sub(10) value being 2.9 with water tables of 0-20 cm and 2.0 with water tables below 20 cm. CO₂ fluxes are compared with primary production figures, and peat carbon stores and the carbon balance in changing climate are discussed.”

Impact on the Greenhouse Effect of Peat Mining and Combustion – Rodhe & Svensson (1995) “Combustion of peat leads to emission of carbon dioxide (CO₂) to the atmosphere. In addition, mining of the peat alters the environment such that the natural fluxes of CO₂ and other greenhouse gases are modified. Of particular interest is a reduction in the emission of methane (CH₄) in the drained parts of the mires. We estimate the total impact on the greenhouse effect of these processes. The results indicate that the decreased emission of methane from the drained mires compensates for about 15% of the CO₂ emission during the combustion of the peat. It follows that, in a time perspective of less than several hundred years, peat is comparable to a fossil fuel, as far as the contribution to the greenhouse effect is concerned.”

The influence of temperature and water table position on carbon dioxide and methane emissions from laboratory columns of peatland soils – Moore & Dalva (1993) “Laboratory columns (80 cm long, 10 cm diameter) of peat were constructed from samples collected from a subarctic fen, a temperate bog and a temperate swamp. Temperature and water table position were manipulated to establish their influence on emissions of CO₂ and CH₄ from the columns. A factorial design experiment revealed significant (P < 0.05) differences in emission of these gases related to peat type, temperature and water table position, as well as an interaction between temperature and water table. Emissions of CO₂ and CH₄ at 23°C were an average of 2.4 and 6.6 times larger, respectively, than those at 10°C. Compared to emissions when the columns were saturated, water table at a depth of 40 cm increased CO₂ fluxes by an average of 4.3 times and decreased CH₄ emissions by an average of 5.0 times. There were significant temporal variations in gas emissions during the 6-week experiment, presumably related to variations in microbial populations and substrate availability. Using columns with static water table depths of 0, 10, 20, 40 and 60 cm, CO₂ emissions showed a positive, linear relation with depth, whereas CH₄ emissions revealed a negative, logarithmic relation with depth. Lowering and then raising the water table from the peat surface to a depth of 50 cm revealed weak evidence of hysteresis in CO₂ emissions between the falling and rising water table limbs. Hysteresis (falling > rising limb) was very pronounced for CH₄ emissions, attributed to a release of CH₄ stored in porewater and a lag in the development of anaerobic conditions and methanogenesis on the rising limb. Decreases in atmospheric pressure were correlated with abnormally large emissions of CO₂ and CH₄ on the falling limb. Peat slurries incubated in flasks revealed few differences between the three peat types in the rates of CO₂ production under aerobic and anaerobic conditions. There were, however, major differences between peat types in the rates of CH₄ consumption under aerobic incubation conditions and CH₄ production under anaerobic conditions (bog > fen > swamp), which explain the differences in response of the peat types in the column experiment.”

Effect of a lowered water table on nitrous oxide fluxes from northern peatlands – Martikainen et al. (1993) “Here we present a comparison of present-day N₂O fluxes from virgin peatlands in Finland with those from sites in the same regions that were drained by ditching 30 and 50 years ago. The lowered water table had no effect on N₂O emissions from nutrient-poor peat but enhanced those from nutrient-rich peat. We estimate that equivalent drying caused by climate change would increase the total emissions of N₂O from northern peatlands by 0.03–0.1 teragrams of nitrogen per year, which is just 0.3–1% of the present global annual emissions. Thus northern peatlands are unlikely to exert a significant climate feedback from N₂O emissions.”

Fluxes of CO₂, CH₄ and N₂O from a Welsh peatland following simulation of water table draw-down: Potential feedback to climatic change – Freeman et al. (1992) “A potential effect of climatic change was simulated by manipulating the water table height within intact peat monoliths. The treatment decreased methane flux (maximum –80%) and increased both carbon dioxide flux (maximum 146%) and nitrous oxide flux maximum 936%). Returning the water table height to its original level caused both nitrous oxide and carbon dioxide flux to rapidly return to control levels. However, methane flux remained at its experimentally induced low levels.”

Northern Peatlands: Role in the Carbon Cycle and Probable Responses to Climatic Warming – Gorham (1991) “Boreal and subarctic peatlands comprise a carbon pool of 455 Pg that has accumulated during the postglacial period at an average net rate of 0.096 Pg/yr (1 Pg = 10¹⁵g). Using Clymo’s (1984) model, the current rate is estimated at 0.076 Pg/yr. Longterm drainage of these peatlands is estimated to be causing the oxidation to CO₂ of a little more than 0.0085 Pg/yr, with conbustion of fuel peat adding °0.026 Pg/yr. Emissions of CH₄ are estimated to release ° 0.046 Pg of carbon annually. Uncertainties beset estimates of both stocks and fluxes, particularly with regard to Soviet peatlands.” [Full text]