The Azimuth Project
Peatland (Rev #3)

Summary

Peatlands store more carbon per square metre than any other terrestrial ecosystem. Covering only about 3% of Earth’s land area, they hold the equivalent of half of the carbon that is in the atmosphere as CO2. This makes them important as a potential positive feedback to a warming climate.

Peat structure

Peat is about 95% water, and varies in depth up to 6m or so. See the Peatland Ecology Research Group for more details.

Distribution

Peat bogs are widely distributed in cold, temperate climes, mostly in the northern hemisphere. The world’s largest wetlands are the bogs of the Western Siberian Lowlands in Russia, which cover more than 600,000 km 2km^2. Sphagnum bogs were once widespread in northern Europe, and there are extensive bogs in Canada and Alaska (called muskeg). According to the 2007 Survey of Energy Resources, the total area of peatlands approaches 3 million km 2km^2, and the total volume of peat in situ is in the order of 3,500 to 4,000 billion m 3m^3.

Peat bogs and climate change

Carbon sink, methane source

Partially decomposed organic material accumulates as carbon-rich peat due to an imbalance between the rates of primary production and decomposition, usually because of restrictions on soil oxygen availability, temperature and nutrients. The low oxygen and nutrient levels, waterlogged conditions and cool climate support a unique, characteristic vegetation community dominated by Sphagnum moss.

The same processes of anaerobic decomposition that allow carbon to accumulate also produce the strong greenhouse gas methane (CH4). Over the time span of centuries, peatlands exert a net cooling effect on the global radiation balance, because the effect of removing long-lived atmospheric CO2 ultimately surpasses that of releasing short-lived CH4. However, should peatlands begin to degrade on a large scale, the stored carbon could be released, reducing — or even reversing — their climate cooling effect.

Threats

Climate change

Warmer air temperatures, drier summers and more frequent droughts, have been shown to cause peatlands to degrade and begin to lose, through erosion, decomposition, or fire, the carbon that they have been accumulating for hundreds or thousands of years.

Nitrogen pollution

Nitrogen pollution can cause soil acidification and nutrient enrichment. Moderate increases in nitrogen deposition from a low level may increase plant productivity without an equal increase in decomposition rates, leading to enhanced carbon accumulation. However, shifts in species composition from bryophytes (mosses) to vascular plants (higher plants) may increase the production of easily-decomposable plant material, leading to higher rates of decomposition, and reduced carbon accumulation.

Drainage

The major change to water-table behaviour occurs in the surface (acrotelm) layer only, which may become permanently emptied and result in significant ecological changes. Drainage also causes the lower layer (catotelm) of a peat bog to undergo changes including oxidation of peat carbon. Drained bogs are a substantial carbon source, losing it as gaseous emissions and in water.

Plantation forests on peat

In the short term, conifer forests grown on peat may result in a net carbon gain. In the longer term, however, plantation forests are acknowledged to result in net carbon losses because eventually the carbon gains of the forest are outweighed by losses from the bog. The tipping point, beyond which such conifer forests appear to cause net carbon losses exceeding the maximum possible long term carbon gains for the forest and its products, could be as little as 30 years.

Restoration

Peat and Repeat: Can Major Carbon Sinks Be Restored by Rewetting the World’s Drained Bogs?

In the UK

It is reasonable to assume that the majority of peatbog erosion in the UK results from human action and thus warrants restoration. Where bogs have lost their soft protective top layer, as have a large proportion of UK peat bog, their carbon stores are being lost.

From Peat bogs and carbon, The rural information network.

References

Peatland Response to Global Change, Nancy B. Dise, Science 6 November 2009: Vol. 326 no. 5954 pp. 810-811, DOI: 10.1126/science.1174268

PEATBOG, Manchester Metropolitan University, UK

Peatland Ecology Research Group (PERG)

Peatbogs and carbon: a critical synthesis to inform policy development in oceanic peat bog conservation and restoration in the context of climate change, Richard Lindsay, Environmental Research Group, University of East London.

Bog, Wikipedia

Blanket bog, Wikipedia

Peat, Wikipedia

category: biodiversity, carbon