Direct human impacts on the peatland carbon sink
Northern peatlands occupy over 3 million km2 globally and contain the largest carbon (C) pool (typically >100 kg C m-2) among terrestrial ecosystems. Agriculture, forestry, and peat harvesting are the principal human-induced activities that alter the peatland and hence the distribution and flux of carbon. As a prerequisite to those uses, the peatland is usually drained, which has long-term effects on the site hydrology and corresponding direct linkages to changes in C dynamics in the vegetation and soils. Soil organic matter decomposition is stimulated following drainage, typically reported as increased CO2 emissions and peat subsidence. The vegetation also changes following drainage, regardless of cropping or harvesting practices, and this change influences the net ecosystem C exchange rate. Peatland drainage tends to reduce CH4 emissions, as a result of a greater aerated surface soil volume. The net global effect of active management of northern peatlands has been to reduce the C pool, because agricultural use is dominant. There remain considerable uncertainties in estimating the C pools, fluxes, and responses to management in peatlands; the issues span inadequate inventories to sampling and measurements in complex settings.