Drainage Ditches Contribute Considerably to the CH4 Budget of a Drained and a Rewetted Temperate Fen

Small water bodies including (former) drainage ditches can be hotspots for methane (CH 4 ) emissions from peatlands. We assessed the CH 4 emissions of a drained and a rewetted temperate fen including emissions of active and former drainage ditches over the course of 2.5 years, covering three vegetation periods. Ditch CH 4 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 CH 4 budget, despite covering only 1.5 % of the area. In the drained fen CH 4 emissions were solely made up of ditch emissions. When including CH 4 uptake by the peat soil, the CH 4 balance of the drained fen was neutral. Dissolved organic carbon concentrations likely had an enhancing effect on CH 4 emissions while nitrate and sulphate in the ditch water seem to have had an inhibitory effect. Air and water temperature controlled seasonal variability of ebullitive as well as diffusive CH 4 emissions. Ebullition contributed less than 10 % to the overall CH 4 budget in the ditches. Drainage ditches represent a hotspot of CH 4 emissions and need therefore be taken into account when assessing the success of rewetting projects of peatlands.