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

[摘要] Wetlands can either be net sinks or net sources of greenhouse gases (GHGs),depending on the mean annual water level and other factors like averageannual temperature, vegetation development, and land use. Whereas drained andagriculturally used peatlands tend to be carbon dioxide (CO₂) andnitrous oxide (N₂O) sources but methane (CH₄) sinks, restored (i.e.rewetted) peatlands rather incorporate CO₂, tend to be N₂O neutraland release CH₄. One of the aims of peatland restoration is to decreasetheir global warming potential (GWP) by reducing GHG emissions.

We estimated the greenhouse gas exchange of a peat bog restoration sequenceover a period of 2 yr (1 July 2007–30 June 2009) in an Atlantic raised bogin northwest Germany. We set up three study sites representing different landuse intensities: intensive grassland (deeply drained, mineral fertilizer,cattle manure and 4–5 cuts per year); extensive grassland (rewetted, nofertilizer or manure, up to 1 cutting per year); near-natural peat bog(almost no anthropogenic influence). Daily and annual greenhouse gas exchangewas estimated based on closed-chamber measurements. CH₄ and N₂Ofluxes were recorded bi-weekly, and net ecosystem exchange (NEE) measurementswere carried out every 3–4 weeks. Annual sums of CH₄ and N₂Ofluxes were estimated by linear interpolation while NEE was modelled.

Regarding GWP, the intensive grassland site emitted564 ± 255 g CO₂–C equivalents m⁻² yr⁻¹ and850 ± 238 g CO₂–C equivalents m⁻² yr⁻¹ in the first(2007/2008) and the second (2008/2009) measuring year, respectively. The GWPof the extensive grassland amounted to −129 ± 231 g CO₂–Cequivalents m⁻² yr⁻¹ and 94 ± 200 g CO₂–Cequivalents m⁻² yr⁻¹, while it added up to45 ± 117 g CO₂–C equivalents m⁻² yr⁻¹ and−101 ± 93 g CO₂–C equivalents m⁻² yr⁻¹ in 2007/08and 2008/09 for the near-natural site. In contrast, in calendar year 2008 GWPaggregated to 441 ± 201 g CO₂–C equivalentsm⁻² yr⁻¹, 14 ± 162 g CO₂–C equivalentsm⁻² yr⁻¹ and 31 ± 75 g CO₂–C equivalentsm⁻² yr⁻¹ for the intensive grassland, extensive grassland, andnear-natural site, respectively.

Despite inter-annual variability, rewetting contributes considerably tomitigating GHG emission from formerly drained peatlands. Extensively usedgrassland on moderately drained peat approaches the carbon sequestrationpotential of near-natural sites, although it may oscillate between being asmall sink and being a small source depending on inter-annual climaticvariability.

[学科分类] 地球化学与岩石