Peatlands and the carbon cycle: from local processes to global implications – a synthesis

Abstract

Abstract. Peatlands cover only 3% of the Earth's land surface but boreal and subarctic peatlands store about 15-30% of the world's soil carbon (C) as peat. Despite their potential for large positive feedbacks to the climate system through sequestration and emission of greenhouse gases, peatlands are not explicitly included in global climate models and therefore in predictions of future climate change. In April 2007 a symposium was held in Wageningen, the Netherlands, to advance our understanding of peatland C cycling. This paper synthesizes the main findings of the symposium, focusing on (i) small-scale processes, (ii) C fluxes at the landscape scale, and (iii) peatlands in the context of climate change.The main drivers controlling C fluxes are largely scale dependent and most are related to some aspects of hydrology. Despite high spatial and annual variability in Net Ecosystem Exchange (NEE), the differences in cumulative annual NEE are more a function of broad scale geographic location and physical setting than internal factors, suggesting the existence of strong feedbacks. In contrast, trace gas emissions seem mainly controlled by local factors.Key uncertainties remain concerning the existence of perturbation thresholds, the relative strengths of the CO 2 and CH 4 feedback, the links among peatland surface climate, hydrology, ecosystem structure and function, and trace gas biogeochemistry as well as the similarity of process rates across peatland types and climatic zones. Progress on these research areas can only be realized by stronger co-operation between disciplines that address different spatial and temporal scales.

The carbon stock of alpine peatlands on the Qinghai–Tibetan Plateau during the Holocene and their future fate

“…Though covering only 3% of the Earth's land surface, peatlands stores 15e30% of the total world soil carbon pool (Gorham, 1991;Turunen et al, 2002;Limpens et al, 2008), accumulating more than 600 Pg carbon since the Last Glacial Maximum (Yu et al, 2010). Undisturbed peatlands are presently a consistent sink of carbon dioxide (CO 2 ) (Roulet, 2000), a source of methane (CH 4 ), approximately 10% of the global CH 4 sources (Roulet, 2000;Mikaloff Fletcher et al, 2004) and at the same time sources of particulate and dissolved organic carbon to the nearby watershed landscape (Billett et al, 2004(Billett et al, , 2011(Billett et al, , 2012.…”

“…As a result, though peatlands have contributed to global cooling for millennia (Roulet et al, 2007), it is uncertain whether their cooling function will continue or even shift to warming. The cooling or warming role of peatlands depends on their carbon balance under intensified global change and anthropogenic activities (Moore et al, 1998;Limpens et al, 2008). For a very long time most of studies about carbon dynamics have been focused on boreal and subarctic peatlands (Gorham, 1991;Moore et al, 1998;Turunen et al, 2002;Roulet et al, 2007;Billett et al, 2011;Yu, 2012), though during the last decade carbon dynamics of tropical peatlands have also become an issue of global importance (Page et al, 2002(Page et al, , 2011Jauhiainen et al, 2012;Lähteenoja et al, 2012).…”

A water-table dependent reservoir model to investigate the effect of drought and vascular plant invasion on peatland hydrology

“…Their response to global change is uncertain as positive or negative feedback can be triggered (Lashof et al, 1997). This uncertainty creates the need to better assess and predict their C source or sink functioning to be able ultimately to take the peatland contribution into account in the global climate model (Limpens et al, 2008). In the carbon cycle, hydrological functioning controls the physical, chemical and biological processes (Weiss et al, 2006) and hence is one of the most important factors regulating carbon fluxes.…”

Biogeochemical processes along a nutrient gradient in a tropical ombrotrophic peatland

“…However, they are under increasing threat from changes in land use and climate (Chimner and Ewel 2004;Day et alThe inaccessible nature of tropical peatlands has meant that few detailed investigations have been carried out on their formation, ecology, and function (but see Phillips et al 1997;Page et al 1999). This limits our ability to predict the consequences of increased direct and indirect anthropogenic pressures upon them (Phillips 1998;Limpens et al 2008;Langner and Siegert 2009).…”