Abstract
CO2 sequestered by peatlands is accounted for and offset against national emissions. Observational and modelling studies are used to estimate emission factors that dictate the rate of CO2 emissions or removals from peatlands accounted for within the Landuse and landuse change including forestry (LULUCF) sector and often use simple Tier 1 emission factors found in the IPCC (1996) guidebook. However, the current estimates are predominately based off peatland surface fluxes measured using either chamber methods or eddy covariance techniques. These methods do not focus on sub-surface conditions while this information may prove useful in understanding efflux rates and conditions that influence them. To help assess the potential significance of subsurface dynamics in overall CO2 efflux rates from peatlands this study proposes to review the literature dealing with subsurface conditions. The review found that the production of CO2 in the sub-surface layers was often uncoupled from emissions and that on short time-scales the storage of CO2 in soil pores and dissolved in soil water may account for this. The rate of production was found to be influenced by decomposition rate, vegetation type, nutrient availability and peat depth. The review also found that the mechanism of transport of CO2 within the sub-surface was important in accounting for efflux rates. While diffusion is often assumed the most significant form of transport, the quantification and dynamics of other non-diffusive transport methods were found to also be important and further research is required to ascertain the drivers of both diffusive and non-diffusive transport.
Highlights
Peatlands play an important role in the global carbon cycle – in regulating carbon sequestration (Clymo, 1992; Zoltai and Martikainen, 1996; Clymo et al, 1998; Dean, 1999; Hilbert et al, 2000; MacDonald et al, 2006; Bhatti and Tarnocai, 2009; Beilman et al, 2009; Yu, 2011)
Many studies relating to the carbon dioxide fluxes in peatlands focus on the surface fluxes of carbon dioxide (Hommeltenberg et al, 2014; McVeigh et al, 2014, Nilsson et al.2008, Wu et al 2013., Roulet et al 2007, Olson et al 2013) but fewer studies look at the contribution of sub surface dynamics and the roles played in the production, transport and sub-surface changes in carbon dioxide concentrations
As decomposition has been found to be an important contributor to sub-surface carbon fluxes (Hoyos-Santillan et al, 2016), conditions that alter decomposition in turn; effects carbon fluxes (Tiemann and Billings, 2012.) Studies have found that decomposition rates are influenced by microbial activity in peatlands (Phillips et al, 1997; Sjögersten, et al, 2011) while in turn, microbial activity is influenced by nutrient availability (Borken and Matzner, 2009)
Summary
Peatlands play an important role in the global carbon cycle – in regulating carbon sequestration (Clymo, 1992; Zoltai and Martikainen, 1996; Clymo et al, 1998; Dean, 1999; Hilbert et al, 2000; MacDonald et al, 2006; Bhatti and Tarnocai, 2009; Beilman et al, 2009; Yu, 2011). It is becoming increasing apparent that these systems can be degraded by anthropogenic activities and climate change As a result, their normal dynamics are being disrupted which in turn diminishes the ecosystem services such as services like climate and water regulation or supporting services like habitat for biodiversity, soil formation, nutrient cycling (Rosenzweig et al.,2007; Kimmel and Mander, 2010). Peatlands ability to sequester carbon mean it is an important instrument in the mitigation of anthropogenic climate change. They have up to one third of global soil organic carbon have accumulated in peatlands (Gorham, 1991; Turunen et al, 2002) and they have potential to sequester 20–30g C m−2 yr−1. This is driven by legislative changes like the Land use and forestry regulation for 2021-2030 (Regulation (EU) 2018/841) which will require European Member States to account for and offset land use emissions by equivalent removals over the 2021-2030 period (European Commission, 2018)
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