NB18 Annual greenhouse gas (GHG) emissions from degraded peatlands

Deep peat (soils having an organic layer >50 cm deep) represents a very significant carbon store, estimated at 1620 Mt C and 56% of the total soil carbon stock in Scotland (Chapman et al., 2009). Even small changes in this carbon store become comparable to other major carbon fluxes- a loss of only 1% of the carbon in Scotland’s peatland would equate to the total annual Scottish human-related emissions of greenhouse gases (Scottish Government, 2013).

The main threat for release of carbon from peatlands arises from degradation of these soils due to factors like erosion, drainage, afforestation, over-grazing, pollution and peat extraction.  While land management is often at the root of these factors, this degradation can also be a ‘natural ‘process impacted to some extent by more recent shifts in climate. Warmer and drier conditions could increase the vulnerability of vegetation communities associated with peatlands as many species are reliant upon a very high water table. Peatland with a consistently low water table will result in  the release of stored carbon, and colonisation by non-peat forming species (grasses, heather etc) which will themselves act to maintain a low water table.

This indicator uses annual GHG emissions (Emission Factors^[1]) in order to calculate the total GHG emissions in CO₂ equivalents for each peatland category (areas given in indicator “NB13 Condition of key habitats: Area of modified deep peat soils”). This will then indicate where carbon losses are coming from and in which categories this is most serious. These figures also permit calculation of the carbon benefits of restoration, or, conversely, the consequences of permitting a peatland area going into a category of greater emissions. The assumption is that restoration will eventually reduce the emissions to that of a near-natural peatland, however this cannot presently be verified experimentally as there are as yet no restoration sites that have reached a near natural vegetation or hydrological status in the UK. The GHG emissions from near-natural peatland have been assessed as -3.7 to 0.3 tCO₂e ha^-1 yr^-1(CO₂ only; Chapman et al., 2012) or -3.1 to 5.1 tCO₂e ha^-1 yr^-1 (including CH₄, N₂O and DOC; Smyth et al., 2014).

Related indicators:

NB11 Extent of key habitats: deep peat

NB13 Condition of key habitats: Area of modified deep peat soils

NB22a Peatland restoration area

Current estimates show that bare and drained land accounts for the majority of annual emissions from degraded peatlands.

Present values are based on very few relevant studies; however there is a large amount of current research which is aimed at improving the estimated emission values and reducing the associated uncertainty.

Clearly at one time peatlands were net accumulators of carbon. Most pressures are relatively recent phenomena, given that peatland formation was initiated 5,000 to 10,000 years ago. Whilst we are unable to assess past emissions from degraded peat, it is useful to consider what is known about changes in management practices that have contributed to changes in peatland degradation levels:

• Attempts to cultivate peatland were made in the eighteenth and nineteenth centuries but with little success; most of the areas now cultivated or used intensively were probably done so in the second half of the twentieth century. About this time an active programme of drainage began, funded by readily-available grants but these came to an abrupt end and there has been little further drainage (gripping) in the last thirty years.
• Management burning has probably always occurred to varying degrees in the past but took off intensively during the nineteenth century when grouse shooting became popular. This decreased considerably in the north and west of Scotland in the 1940s but continues in the south and east. Burning has also been used routinely to improve grazing, particularly for sheep, throughout the last 200 years.
• Wildfires, which can occur during drought periods and perhaps increase in frequency when drought periods coincide with the prescribed management burning period, can have significant impacts on peat condition and peatland vegetation with implications for ecosystem functionality and carbon balance.
• Afforestation of peatland began in earnest in the 1950s, particularly in south-west Scotland and continued until the 1980s, infamously in the Flow Country.
• While peat erosion is exacerbated by current land management, it may also be a ‘natural’ process, impacted to some extent by more recent shifts in climate. It is not really known when serious erosion began but there are known sites that are over 400 years old. However, many contemporary actively eroding hagg and gully systems may have been instigated by draining and burning in the recent past.
• Commercial peat extraction only took off in the early twentieth century when suitable harvesting machines were invented; however, peat cutting by hand has long been practiced, dating back to at least Roman times.

There is now considerable research on GHG fluxes from a range of peatlands within Scotland and across the UK such that we should see some reduction in uncertainties in the coming years. Effort is such that annual updates are feasible and warranted. However, there are still significant gaps where little research effort is being made currently and these will likely remain uncertainties.

The intended consequences of the drive to restore peatlands are to reduce net emissions from soils. It remains to be tested whether this can be achieved, but requires ongoing monitoring of restoration sites as these mature. Eventually we hope to be in a position to say how and where optimum restoration might be.

Our current understanding is too sparse to speculate on this. A lack of current knowledge of both inter-annual variability and successional changes in peatland ecosystems means we are unable to say how these values might have or will vary both over space and time.

The emissions data presented carry quite severe limitations. These arise as a result of the paucity of data, firstly from Scotland, secondly from the UK and similar climatic zones, and thirdly even across all non-tropical peatlands.  Because Scottish peatlands are predominantly blanket peat and this peat type is globally rare, few studies are directly applicable.

In addition, the calculation of the net emission factors is based upon adding up CO2 equivalent fluxes of the GHGs CO2, CH4, N2O, and Dissolved Organic Carbon (DOC) and, in some cases, Particulate Organic Carbon (POC). It is extremely rare that all of these components are measured at any one site and hence the calculations carry a large caveat in extrapolating data across sites with different climatic conditions and management regimes. The emission factors cover CO2, CH4, N2O fluxes and DOC losses. The latter are mainly set at the IPCC Tier 1 default value of 1.14 tCO2e ha-1 yr-1 (Smyth et al., 2014). POC losses are only likely to be significant from f) (bare peat subject to erosion). None of the emission factors are based upon whole life cycle analysis, e.g. they don’t include emissions due to on-site fuel use during drainage or tree harvesting, etc.

Lindsay,R. (2010) Peatlands and carbon: A critical synthesis.  RSPB Scotland.

http://www.rspb.org.uk/Images/Peatbogs_and_carbon_tcm9-255200.pdf

Bain, C.G., Bonn, A., Stoneman, R., Chapman, S., Coupar, A., Evans, M., Gearey, B., Howat, M., Joosten, H., Keenleyside, C., Labadz, J., Lindsay, R., Littlewood, N., Lunt, P., Miller, C., Moxey, A., Orr, H., Reed, M., Smith, P., Swales, V., Thompson, D.B.A., Thompson, P.S., Van de Noort, R., Wilson, J.D. & Worrall, F. (2011) IUCN UK Commission of Inquiry on Peatlands. Edinburgh, IUCN UK Peatland Programme.

http://www.iucn-uk-peatlandprogramme.org

Primary author of this document: Steve Chapman (James Hutton Institute)

Rebekka Artz (James Hutton Institute)