Drainage ditches are year‐round greenhouse gas hotlines in temperate peat landscapes

Abstract

Abstract Greenhouse gas (GHG) emissions from drained peatlands have been studied extensively. Considerably less attention has been paid to the emissions from the ditches used to drain peatlands. High within‐ditch GHG production and lateral inflow of GHGs may lead to ditches emitting considerable amounts of GHGs on the landscape scale. We quantified annual emissions of ebullitive and diffusive methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) in 10 drainage ditches in intensively used temperate peatlands used for dairy farming, in The Netherlands. Additionally, we assessed water and sediment quality to determine proxies for emissions via the two emission pathways. The mean annual emissions from the studied ditches varied between 3.57 and 60.1 g CO2‐eq. m−2 day−1 (based on a global warming potential over a 100‐year timeframe), where CO2 contributed on average 43% (ranging between 1.9 and 22.0 g CO2 m−2 day−1) and diffusive CH4 contributed 16% (0.1–16.5 g CO2‐eq. m−2 day−1) to the total GHG emission. Ebullition of CH4 made up nearly half of the total GHG emission (40%, 1.3–40.9 g CO2‐eq. m−2 day−1). N2O emissions were mostly low. CO2 emissions were higher in winter months, while CH4 ebullition was higher during spring and summer. Diffusive CH4 emissions did not show a seasonal pattern. The mean emission factor, the estimate of average emissions per unit area (EF), for CH4 was 2144 kg CH4 ha−1 year−1, which is two times higher than the tier 1 EF reported by the IPCC (with underrepresented ebullition data), underlining the high variability of ditch emissions. Ditch emissions were also higher than the EF used for the surrounding drained peatlands indicating that ditch emissions can be important on the landscape scale and should be considered to be included in national greenhouse gas reporting.