Learn how plants respond to higher atmospheric CO2 concentrations

How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic


Peatlands -- Summary
Global warming has been predicted by the IPCC to release long-sequestered carbon in Earth's peatlands to the atmosphere, possibly freeing enough of it at a sufficiently rapid rate to rival CO2 emissions from anthropogenic sources, with the end result of this scenario being a strong positive feedback to the ongoing rise in the air's CO2 content, which the IPCC contends will lead to further warming of the planet. But is this contention correct?

In a study that broaches this important question, Cai and Yu (2011) employed multi-proxy data derived from a sediment core they extracted from Tannersville Bog, located near the edge of the Pocono Mountains in Monroe County, Pennsylvania (USA), in order to document the Bog's historical peat accumulation pattern and rate, as well as climate variations experienced by this "temperate tree-covered poor fen" that is located at "the extreme warm end of climate space for northern peatlands."

Results indicated, in the words of the two authors, that "carbon accumulation rates increased from 13.4 to 101.2 g C/m2/year during the last 8,000 years," with a long-term average value of 27.3 g C/m2/year. This mean rate significantly exceeds the 18.6 g C/m2/year obtained for boreal, subarctic and arctic peatlands based on measurements made at 33 sites in the Northern Hemisphere (Yu et al., 2009); and this fact led the authors to conclude that their relatively high accumulation rate "was likely caused by high primary production associated with a warmer and wetter temperate climate." In light of their findings, Cai and Yu say their study implies that "northern peatlands can continue to serve as carbon sinks under a warmer and wetter climate, providing a negative feedback to climate warming."

Further illumination of the relationship between climate and carbon accumulation in peatlands, but on a much grander spatial scale, was the task of Beilman et al. (2009), who used "a network of cores from 77 peatland sites to determine controls on peat carbon content and peat carbon accumulation over the last 2000 years across Russia's West Siberian Lowland," which is the world's largest wetland region. In doing so, they discovered that carbon accumulation over the past two millennia varied significantly with mean annual air temperature, growing ever greater as air temperature rose from -9 to 0°C, with maximum carbon accumulation occurring between -1 and 0°C, which is "where air-soil temperature differences optimize net primary production relative to soil respiration, e.g., near 0°C (Swanson et al., 2000)." On average, in fact, the researchers found that "cores from non-permafrost sites have accumulated four times more peat by depth and twice as much carbon than cores from permafrost sites."

Given such findings, Beilman et al. write that the "relationship between temperature and peat carbon sequestration, and the current spatial distribution of peatland ecosystems, should be an important consideration in future attempts to anticipate the impact of climate warming on the carbon sink potential of the West Siberian Lowland region." And with respect to that impact, they opine that "permafrost thaw may promote a boost in peat carbon sequestration in affected sites," and, therefore, they state that "future warming could result in a shift northward in long-term West Siberian Lowland carbon sequestration."

Another data-based study that counters the claim that peatland ecosystems will release great quantities of previously-sequestered carbon to the atmosphere in the form of CO2 and methane as temperatures warm comes from Bao et al. (2010). Working in the Changbai mountain region that runs along the boundary between China and North Korea, this group of researchers extracted eight peat cores that they analyzed for numerous parameters, among which were those required to calculate the recent rate of carbon accumulation (RERCA) in the peatlands of that region over the past two centuries.

In describing their findings, the four researchers report that "obvious increasing trends in RERCA were observed in all peat cores," as "organic carbon content declined from the top to the substrate." What is more, they say that the temporal increase in RERCA in the upper regions of the cores -- which likely corresponded to the warmest segment of their two-century study period -- "changed to a much greater extent in recent decades than in the earlier period of peat formation."

Introducing their study of the subject, Flanagan and Syed (2011) write that "northern peatland ecosystems are consistent net carbon (C) sinks that account for between one-quarter to one-third of the global soil carbon pool (Gorham, 1991; Turunen et al., 2002)," noting that their sequestration of carbon "results from moderate rates of ecosystem photosynthesis that exceed decomposition and autotrophic plant respiration (Gorham, 1991)." Because of the IPCC-based projections that "exposure to warmer temperatures and drier conditions associated with climate change will shift the balance between ecosystem photosynthesis and respiration providing a positive feedback to atmospheric CO2 concentration," Flanagan and Syed set out to conduct a long-term experiment designed to explore this climate-alarmist contention. Specifically, they used the eddy covariance technique "to determine the sensitivity of ecosystem photosynthesis, respiration and net CO2 exchange to variations in temperature and water table depth associated with inter-annual shifts in weather over a six-year period."

Their work was conducted in "a moderately rich treed fen" -- which they described as "the most abundant peatland type in western Canada" -- at a peatland flux station northeast of Athabasca, Alberta, which was established in 2003 as part of the Fluxnet-Canada Research Network (Margolis et al., 2006), and which during 2007-2009 was part of the follow-on Canadian Carbon Program. Results indicated that "contrary to previous predictions, both ecosystem photosynthesis and respiration showed similar increases in response to warmer and drier conditions," such that "the ecosystem remained a strong net sink for CO2 with an average net ecosystem production of 189 47 gC/m2/year." And they add that these "current net CO2 uptake rates were much higher than carbon accumulation in peat determined from analyses of the relationship between peat age and cumulative carbon stock." As a result of these findings, therefore, Flanagan and Syed concluded that "in the absence of fire or other major disturbance, significant net carbon sequestration could continue for decades at this site and help to reduce the positive feedback of climate change on increasing atmospheric CO2 concentration."

Also working in Canada, Turetsky et al. (2007) explored "the influence of differing permafrost regimes (bogs with no surface permafrost, localized permafrost features with surface permafrost, and internal lawns representing areas of permafrost degradation) on rates of peat accumulation at the southernmost limit of permafrost in continental Canada." In the words of the five American researchers who conducted this study, the work revealed that "surface permafrost inhibits peat accumulation and that degradation of surface permafrost stimulates net carbon storage in peatlands." In fact, they report that "unfrozen bogs and internal lawns had net organic matter accumulation rates two-times faster [italics added] than rates of accumulation in localized permafrost features over the most recent 25-year horizon."

In discussing their findings, Turetsky et al. say their data suggest that "permafrost degradation within peatland environments, likely triggered by climate change, could serve as a negative feedback to net radiative forcing via enhanced carbon accumulation as peat." They note, however, that "increased methane emissions to the atmosphere will partially or even completely offset this enhanced peatland carbon sink for at least 70 years following permafrost degradation." Nevertheless, they say that because "internal lawns succeed relatively quickly (within 70 years) to more bog-like conditions and [since] bogs in continental Canada are associated with low methane emissions, the degradation of localized permafrost in peatlands is likely over the long-term to serve as a negative feedback to radiative forcing [italics added]."

In yet another study, Daimaru et al. (2002) dug 27 soil pits at various locations in and around the central location of a snowpatch grassland on the southeastern slope of Japan's Mt. Zarumori (~39.8°N, 140.8°E), carefully examining the peat content of the soil and determining its age based on 14C dating and tephrochronology. Results indicated that "peaty topsoils were recognized at seven soil pits in the dense grassland" where the snow melts earlier in the season and the period for plant growth is the longest. In contrast, soils located in areas where the snowmelt occurs later in the season "lacked peaty topsoil." However, Daimaru et al. note that beneath these carbon-poor topsoils was a carbon-rich layer that they were able to date back to the Medieval Warm Period, suggesting that the buried peat layers in the poor vegetation area accumulated in consequence of the warmer temperatures of that period. Consequently, as has been found to be the case with each of the other peatland studies referenced above, when it comes to real-world historical observations, the IPCC-based predictions -- in terms of the influence of Earth's peatlands on the planet's temperature -- are one hundred and eighty degrees out of phase with reality. In stark contrast, these land types provide a negative feedback to global warming, whereby when they warm, they extract more, not less, CO2 from the atmosphere, effectively applying a brake on rising temperatures, as opposed to pushing the planet past a tipping point towards a state of catastrophic runaway global warming.

At least one model-based study has come to the same conclusion. Noting that "throughout the Holocene, northern peatlands have both accumulated carbon and emitted methane," so that "their impact on climate radiative forcing has been the net of cooling (persistent CO2 uptake) and warming (persistent CH4 emission)," Frolking and Roulet (2007) developed Holocene peatland carbon flux trajectories based on estimates of contemporary CH4 flux, total accumulated peat C, and peatland initiation dates, which they used as inputs to a simple atmospheric perturbation model to calculate the net radiative impetus for surface air temperature change. In doing so, the two researchers determined that the impact on the current atmosphere of northern peatland development and carbon cycling through the Holocene is a net deficit of 40-80 Pg CO2-C (~20-40 ppm of atmospheric CO2) and a net excess of ~200-400 Tg CH4 (~75-150 ppb of atmospheric CH4).

In discussing their findings, Frolking and Roulet note that early in the Holocene, the capture of CO2 and emission of CH4 by Earth's northern peatlands is likely to have produced a net warming impetus of up to +0.1 W m-2. Over the following eight to eleven thousand years, however, they say that Earth's peatlands have been doing just the opposite, and that the current radiative forcing due to these atmospheric CO2 and CH4 perturbations represents a net cooling force on the order of -0.22 to -0.56 W m-2, further establishing the fact that the impetus for global cooling due to carbon sequestration by Earth's peatlands historically has been -- and currently is -- significantly greater than the global warming potential produced by their emissions of methane.

Lastly, in an experimental as opposed to an historical study, Fenner et al. (2007) collected intact peat monoliths -- comprised predominantly of Sphagnum (S. subnitens Russ. and Warnst.) and Festuca ovina L., with small amounts of Juncus effusus L. and Polytrichum commune Hedw. -- in perfusion systems that allowed for fine control of the water table and lateral water movements, which they maintained for approximately three years in Solardomes with atmospheric CO2 concentrations of ambient or ambient plus 235 ppm, while daily supplying the mini-ecosystems with synthetic rainwater that was comparable in volume and nutrient content to that received at the site from which the monoliths were extracted.

At the end of their 3-year experiment, the seven UK researchers say they found that "species composition showed a shift from a Sphagnum-dominated community to one in which vascular monocotyledonous species dominated," as S. subnitens cover declined by 39% under elevated CO2, whereas J. effusus cover increased, from less than 1% in the control perfusion systems to 40% in the systems exposed to elevated CO2. At the same time, they found that "aboveground plant biomass showed a substantial increase under elevated CO2 (115%, P < 0.01) as did belowground biomass (96%, P < 0.01)." What is more, they report that "J. effusus roots were observed to be particularly thick, deep, and extensive under elevated CO2."

In conclusion, and in considering all of the above findings, as the air's CO2 content continues to climb ever higher, the carbon content of the planet's peatlands will most likely also continue to rise -- and dramatically so, notwithstanding the IPCC's model-based projections to the contrary.

References
Bao, K., Yu, X., Jia, L. and Wang, G. 2010. Recent carbon accumulation in Changbai Mountain peatlands, northeast China. Mountain Research and Development 30: 33-41.

Beilman, D.W., MacDonald, G.M., Smith, L.C. and Reimer, P.J. 2009. Carbon accumulation in peatlands of West Siberia over the last 2000 years. Global Biogeochemical Cycles 23: 10.1029/2007GB003112.

Cai, S. and Yu, Z. 2011. Response of a warm temperate peatland to Holocene climate change in northeastern Pennsylvania. Quaternary Research 75: 531-540.

Daimaru, H., Ohtani, Y., Ikeda, S., Okamoto, T. and Kajimoto, T. 2002. Paleoclimatic implication of buried peat layers in a subalpine snowpatch grassland on Mt. Zarumori, northern Japan. Catena 48: 53-65.

Fenner, N., Ostle, N.J., McNamara, N., Sparks, T., Harmens, H., Reynolds, B. and Freeman, C. 2007. Elevated CO2 effects on peatland plant community carbon dynamics and DOC production. Ecosystems 10: 635-647.

Flanagan, L.B. and Syed, K.H. 2011. Stimulation of both photosynthesis and respiration in response to warmer and drier conditions in a boreal peatland ecosystem. Global Change Biology 17: 2271-2287.

Frolking, S. and Roulet, N.T. 2007. Holocene radiative forcing impact of northern peatland carbon accumulation and methane emissions. Global Change Biology 13: 1079-1088.

Gorham, E. 1991. Northern peatlands: role in the carbon cycle and probable responses to climatic warming. Ecological Applications 1: 185-192.

Margolis, H.A., Flanagan, L.B. and Amiro, B.D. 2006. The Fluxnet-Canada research network: influence of climate and disturbance on carbon cycling in forests and peatlands. Agricultural and Forest Meteorology 140: 1-5.

Swanson, D.K., Lacelle, B. and Tarnocai, C. 2000. Temperature and the boreal-subarctic maximum in soil organic carbon. Geog. Phys. Quat. 54: 157-167.

Turetsky, M.R., Wieder, R.K., Vitt, D.H., Evans, R.J. and Scott, K.D. 2007. The disappearance of relict permafrost in boreal North America: Effects on peatland carbon storage and fluxes. Global Change Biology 13: 1922-1934.

Turunen, J., Roulet, N.T., Moore, T.R. and Richard, P.J.H. 2004. Nitrogen deposition and increased carbon accumulation in ombrotrophic peatlands in eastern Canada. Global Biogeochemical Cycles 18: 10.1029/2003GB002154.

Yu, Z.C., Beilman, D.W. and Jones, M.C. 2009. Sensitivity of northern peatland carbon dynamics to Holocene climate change. In: Baird, A.J., Belyea, L.R., Comax, X., Reeve, A. and Slater, I. (Eds.). Carbon Cycling in Northern Peatlands. American Geophysical Union, Washington, DC, USA, pp. 55-69.

Last updated 1 February 2012