Disproportionately High Contribution of Ditches to Landscape Greenhouse Gas Emissions in Drained Peatlands

Abstract Drained peatlands are a significant source of greenhouse gas (GHG) emissions; however, research has predominantly focused on terrestrial areas, with much less attention given to drainage ditches. Despite their small surface area, ditches can substantially affect the peatland GHG balance owing to conditions that favour GHG production. We conducted monthly field campaigns in five ditches across two agricultural polders in the Netherlands using floating chambers to measure daytime diffusive emissions of carbon dioxide (CO 2 ), diffusive and ebullitive methane (CH 4 ), and nitrous oxide (N 2 O), and bubble traps to measure CH 4 ebullition. We compared ditch emissions to landscape-scale emissions obtained via eddy covariance (EC) and automated terrestrial chamber measurements during the same period, and explored key drivers and spatial variation in ditch GHG emissions. Mean ditch emission ranged from 8.9 to 22.8 g CO 2 -eq m −2 day −1 (based on a 100-year global warming potential). CH 4 contributed 44–94% of total emissions, averaging 62%. Although ditches occupied only 8% and 19% of the landscape in polder Zegveld and Langeweide, respectively, they contributed disproportionally to the total landscape GHG emissions, accounting for 25% in Zegveld and 33% in Langeweide. We argue that this a conservative estimate as we lacked night-time CO 2 emissions from the ditches, which tend to be higher. Our findings suggest that while manual chamber-based measurements and eddy covariance estimates of ditch emissions roughly align, significant discrepancies persist. A combined approach that uses both methods offers the most robust and representative estimates of GHG emissions from ditches.