Drainage ditches contribute considerably to the CH₄ budget of a drained and a rewetted temperate fen

Small water bodies including drainage ditches can be hotspots for methane (CH₄) emissions from peatlands. We assessed the CH₄ emissions of a drained and a rewetted temperate fen including emissions of managed and unmanaged drainage ditches over the course of 2.5 years, covering three vegetation periods. Ditch CH₄ emissions in the rewetted fen were significantly higher than in the drained fen. In the rewetted fen ditches contributed up to 91% of the annual CH₄ budget, despite covering only 1.5% of the area. In the drained fen CH₄ emissions were solely made up of ditch emissions. When including CH₄ uptake by the peat soil, the CH₄ balance of the drained fen was neutral. Dissolved organic carbon concentrations likely had an enhancing effect on CH₄ emissions while nitrate and sulfate in the ditch water seem to have had an inhibitory effect. Air and water temperature controlled seasonal variability of ebullitive as well as diffusive CH₄ emissions. Ebullition contributed less than 10% to the overall CH₄ budget in the ditches. Drainage ditches represent a hotspot of CH₄ emissions and need therefore be taken into account when assessing the success of rewetting projects of peatlands.