Effects of land use intensity on the full greenhouse gas balance in an Atlantic peat bog.

The assessment of emission factors for many peatlands is difficult, and reliable data on the exchange of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) between soil and atmosphere of these areas is particularly scarce. Reasons for this are the multitude of soil and land use combinations that control greenhouse gas exchange and the high effort associated with data acquisition. We investigated the greenhouse gas exchange of a peat bog restoration sequence over a period of 2 yr (July 2007-June 2009) in an Atlantic raised bog in Northwest Germany. We set up three sites representing different land use intensities: intensive grassland (mineral fertilizer, cattle manure and 4-5 cuts per year); extensive grassland (no fertilizer or manure, maximal 1 cutting per year); near-natural peat bog (almost no anthropogenic influence). We obtained seasonal and annual estimates of greenhouse gas exchange based on closed chamber measurements. CH₄ and N₂O fluxes were recorded bi-weekly, CO₂ NEE determinations were carried out 3-4 weekly. To get annual sums the CH₄ and N₂O fluxes were interpolated linearly while NEE was modelled. The intensive grassland site emitted 548±169gCO₂-Cm_-2 in the first and 817±140gCO₂-Cm_-2 in the second year. The extensive grassland site showed a slight uptake in the first year (-148 ± 143gCO₂-Cm_-2), and a small emission of 88±146gCO₂-Cm_-2 in the second year. In contrast to these agriculturally used sites, the near-natural site took up CO₂-C in both years(-8±68gCO₂-Cm_-2 and -127±53gCO₂-Cm_-2). Under consideration of N₂O and CH₄ exchange, the total average greenhouse warming potential (GWP) for 2008 amounts to 441 ±157gm_-2,14±152gm_-2 and 31 ±68gm_-2 CO₂-C-equivalent for the intensive grassland, the extensive grassland and the near-natural site, respectively. Despite inter-annual variability, rewetting contributes considerably to mitigating GHG emission from formerly drained peatlands. Already extensively used grassland on moderately drained peat approaches the carbon sequestration potential of near-natural sites, albeit it may oscillate between being a small sink and being a small source depending on interannual climatic variability. [ABSTRACT FROM AUTHOR]