Annual emissions of CO2, CH4 and N2O from a temperate peat bog: Comparison of an undrained and four drained sites under permanent grass and arable crop rotations with cereals and potato

Peatlands drained for agriculture are sources of atmospheric carbon dioxide (CO2) and nitrous oxide (N2O). Resulting emissions may depend on land-use, often as grassland or cropland, but few studies have directly compared the effects of land-uses. Here, we measured annual emissions of CO2, N2O and methane (CH4) from five sites in a temperate bog, representing an undrained natural bog (NB) site, and four drained sites used as permanent grassland (PG) and croplands with rotations of oat-potato, oat-spring barley and potato-spring barley (PO:SB) in the study year. Gas fluxes were measured at 1-2 week intervals using static chambers, and auxiliary data were obtained, such as temperature, depth of water table, ratio-vegetation index, pH and soil mineral N. Annual CO2 emissions were derived from empirical modelling, whereas CH4 and N2O emissions were linearly interpolated between measurement dates by bootstrapping. Soil respiration was lower at the NB site (1.8 Mg CO2-C ha(-1) yr(-1)) than at the drained sites where emissions were in the range of 5.0-8.8 Mg CO2-C ha(-1) yr(-1). The N2O emission was negligible at NB (0.3 kg N2O ha(-1) yr(-1)), low at three of the drained sites (1.5-3.7 kg N2O ha(-1) yr(-1)), but high at PO:SB (37.7 kg N2O ha(-1) yr(-1)). The CH4 emission was high at NB (172 kg CH4 ha(-1) yr(-1)), but negligible at the drained sites (-1.5 to 1.5 kg CH4 ha(-1) yr(-1)). The soil respiration at the drained sites indicated that peat losses were rather similar among the different cropping systems and depended mostly on drainage status, although soil respiration and peat mineralization may not scale directly. The pattern of N2O emissions suggested an increased risk of N2O emission from potato cultivation before and after the period of potato growth, likely due to microbial availability of NO3- outside the growing season. For initiatives aiming at reduction of greenhouse gas emissions from agricultural peat soils, this means that, e.g., conversion from cropland to permanent grassland should preferably be accompanied by measures of rewetting, whereas for potato cropping, N availability outside the growing season should be minimized.