Greenhouse Gas Exchange of a NW German Peatland, 18 Years After Rewetting

Undisturbed peatlands are usually a sink of greenhouse gases (GHG), but turn to a GHG source when drained. While rewetting and restoration of drained peatlands play an important role in efforts to mitigate global warming, high uncertainties exist concerning the time period it takes after the start of rewetting until the point when the peatland becomes a GHG net sink. We investigated a site within the "Uchter Moor", NW Germany. It is an oligotrophic raised bog, which was never used for agriculture, but was drained in 1950 for peat mining. In 1999, restoration began; now the ecosystem is in transition back to a typical raised bog vegetation with Eriophorum vaginatum, Molinia caerulea and Eriophorum angustifolium being the dominant species. Sphagnum cuspidatum appears in patches. From June 2016 to January 2018, an eddy covariance (EC) tower measured the fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The flux of ozone (O-3) was also measured for 6 months by EC and modeled for the remaining experimental period. Using the sustained global warming potential for a 100-year time horizon, the balance of CO2, CH4, and N2O in 2017 was +500 +/- 120 g CO2-equiv m(-2) a(-1). The plus sign indicates a net emission of GHG into the atmosphere. Methane contributed 78% to this flux. The inclusion of O-3 into the balance yielded a somewhat smaller total flux of +430 +/- 120 g CO2-equiv m(-2) a(-1). Overall, the peatland is still a source of GHG, 18 years after re-wetting.