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Ecosystem services of peatlands

Climate change mitigation: Peatlands as carbon reservoir and GHG source

Peatlands act as a carbon sink, absorbing 150 to 250 million tonnes of carbon dioxide (CO2) from the atmosphere each year worldwide. Carbon absorbed by plants during their growth remains in peat when they die. Over many millennia, peatlands have thus evolved into a gigantic carbon reservoir. Although they cover only three percent of the land area, they store in their peat layers one-third of all global carbon – about twice as much as is stored in the biomass of all forests worldwide (Parish et al. 2008).

Organic peat soils in boreal regions of Russia contain about seven times as much carbon as is held in surface forest biomass. Peat in tropical peatland forests even stores about ten times as much carbon as tropical forests on mineral soils. The degraded peatlands of Sumatra and Borneo alone emit over 400 million tonnes of CO2 a year (Wibisono et al. 2011).

For Germany, it is estimated that peatlands store just as much carbon as is held in forests – that is about a third of the total stock of carbon – although peatlands cover only about four percent of the German land surface and forests about 30 percent.


Net gas exchange in natural, drained and renaturalised peatlands
Figure modified from Freibauer et al. 2009: Net gas exchange in natural, drained and renaturalised peatlands

A chart based on Freibauer et al. 2009 (modified) gives a qualitative overview of net gas exchange in natural peatlands, peatlands drained to differing degrees, and renaturalised peatlands.

Even in intact peatlands, peat is broken down by bacteria in anaerobic conditions. This gives rise to climate-damaging methane (CH4), which escapes from the peat into the atmosphere. Despite this, the carbon balance of natural peatlands remains positive.

If peatlands are drained for use, air enters the peat layers and the peat mineralises. This results in the escape not only of vast quantities of the previously stored CO2, but also nitrous oxide (N2O), which has a far greater (some 300 times greater) climate impact than CO2. Drained peatlands are thus vulnerable in terms of their function as carbon reservoirs, they turn into greenhouse gas sources and are a major factor in climate change. In Germany, peat soils emit about 2.5 to 5 percent of total annual emissions (CO2 equivalent) due to non-appropriate exploitation. Peatlands ploughed and fertilised for arable use account for a particularly large share of emissions. A critical trend in this connection is the increasing cultivation of maize as a biomass to energy crop. This practice ultimately has both a negative greenhouse gas balance (Freibauer et al. 2009) and a negative energy balance (Wichmann et al. 2010).

Dry peat in drained peatlands is also easily set alight. Peatland fires like those seen in Russia in 2010 spread under the surface and can burn for a very long time and release the stored carbon extremely rapidly.


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Landscape hydrology

Near-natural peatlands can store large quantities of water thanks to the sponginess of peat and the buoyancy of the vegetation. Heavy rains are initially absorbed and released only slowly over a period of several days.

By influencing the timing of run-off in this way, peatlands are able to regulate landscape hydrology. They serve as a natural retention area and are thus important in the control of flood peaks. In contrast to intact bogs, which store 90 percent of rainwater in this way, on drained peat grassland 70 percent of rainwater runs off (Zollner & Cronauer 2004). This rain retention function can mostly be restored by renaturalisation, however.

Vicious circle of draining and subsidence

“Whereas peat-accumulating mires continue to grow, drainage results in surface subsidence. Mineralisation of the organic matter results in continuous loss of surface height, and water levels gradually rise towards the surface. To keep such land under cultivation, farming practice is to re-drain the land at varying intervals. This vicious circle of draining and subsidence is relevant in the climate change debate, especially in relation to peatlands whose surface is close to sea level. With rising sea levels and loss of land surface height, the effort and expense of draining increases. As an adaptation strategy to rising sea levels, it is thus additionally necessary to minimise subsidence-induced loss of surface height at elevations at or close to sea level” (Trepel 2008).

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Nutrient balance

Peatlands not only regulate hydrology, they also influence water quality. They are able to capture and permanently store both nutrients and pollutants from percolating groundwater and surface water. They thus act as a water filter and sink.

Substances captured from the water are stored in the growing peat layers. Their sink function is not limited to carbon, but also extends to nutrients such as nitrogen and phosphorus compounds, and to trace elements such as lead, copper and manganese, which are pollutants at high concentrations and would otherwise make their way into the groundwater and surface waters.

Thanks to these natural processes, peatlands not only regulate the nutrient balance, but also contribute significantly in ensuring water quality (purity). Peatlands are consequently sometimes known as the ‘kidneys of the landscape’, as they release only filtered, nutrient-free water to downstream groundwater levels, lakes, rivers and streams.

When drained, peatlands become a nutrient source, as the stored nutrients are extracted with the water.


Mesoclimate

The large water storage capacity of peatlands has a balancing effect on the local climate. The peatland water body moderates extremes and thus acts as a temperature buffer. The continuous evaporation of water, particularly in warm and dry weather conditions, also helps cool the atmosphere (Solantie 1999).

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Recreational function

Peatlands have trans-regional importance in terms of recreation and experiencing nature. The rarity and uniqueness of near-natural peatlands in today’s cultural landscape, the peace they offer with little disturbance from farming or infrastructure, and their great biodiversity make them highly attractive for holidaymakers. In many cases, exploration trails in peatland reserves enhance visitors’ experience of nature. Boardwalks lead visitors alongside varied habitat complexes, with information boards to learn about rare species and about renaturalisation work that has been carried out.

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Economic value of ecosystem services

Peatland conservation and revitalisation can be a cost-effective way of cutting greenhouse emissions. Targeted re-wetting of a peatland site can reduce greenhouse gas emissions by between four and 15.5 tonnes of CO2 equivalent per hectare per year (Drösler et al. 2012). Fostering the natural development of and re-wetting peat soils can also play an outstanding part in the attainment of current mitigation targets for greenhouse gases. In connection with EU climate targets in particular (under the Kyoto Protocol and the Framework Convention on Climate Change), the climate change mitigation services of peatlands can be assigned a monetary value and incorporated into emission trading by determining the greenhouse gas avoidance costs of peatland revitalisation.

The effort and expense involved in reducing the climate impact of peatlands is relatively small. Greenhouse gas avoidance costs vary significantly according to land use and region, however, and this complicates monetary valuation. Even before taking any macroeconomic utility into account, the costs are lower than the CO2 avoidance costs attainable, for example, with biogas installations (Drösler et al. 2009).

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