4 - The role of peatlands in climate regulation

Summary

Introduction

Peatlands are the world's most important terrestrial ecosystems with respect to carbon (C) storage, and act as a source and sink for GHGs. In this chapter we outline the importance of peatlands in climate regulation and we describe the effects of drainage and restoration.

Peatlands and climate regulation

Description, status and trends

Peatlands are the largest terrestrial store of organic carbon

Peatland ecosystems (including peat and vegetation) contain much more organic carbon than other terrestrial ecosystems. In the (sub)polar zone, peatlands contain on average 3.5 times more carbon per hectare than ecosystems on mineral soil; in the boreal zone seven times more carbon; and in the humid tropics as much as 10 times more carbon (Joosten and Couwenberg 2008). While covering only 3% of the world's land area, peatlands contain 450 Gt of carbon in their peat (Joosten 2009c; Page, Rieley and Banks 2011a). Peatlands are the largest long-term carbon store in the terrestrial biosphere and among the Earth's most important stores.

The huge carbon stock of peatland ecosystems is attributable to the often thick layers of peat. Peat is a highly concentrated stockpile of carbon because it consists by definition of more than 30% (dry mass) of dead organic material that contains 48–63% of carbon. On average, the peatlands of the world hold a carbon pool in their peat of 1125 t C ha^-1 (450 Gt/400 × 10⁶ ha), which is the largest carbon density of any terrestrial ecosystem. The ecosystem with the second most carbon per hectare is the giant conifer forest in the Pacific West of North America, which, before human disturbance, reached only half the carbon density of the average peatland (Joosten and Couwenberg 2008).

Estimates of soil C stock to 1 m depth range between 1400 and 1600 Gt C (Smith 2004). Further C is stored deeper: 491 Gt C between 1–2 m depth, and 351 Gt C at 2–3 m depth (Jobbágy and Jackson 2000). The atmosphere (in 1990) contained 750 Gt C, mainly as CO₂ and CH₄ (Houghton, Jenkins and Ephraums 1990). The global terrestrial plant biomass carbon stock is estimated to be 654 Gt (IPCC 2001) with total global forest biomass holding 335–365 Gt of carbon (Shvidenko et al. 2005).