How to minimize greenhouse gas emissions in Sphagnum re-vegetation areas - the role of topsoil removal

Drained peatlands are major sources of greenhouse gases (GHG). To counteract this effect, drained peatlands must be rewetted. Rewetted peatlands can be left to their own devices (wilderness development/restoration) or continued to be used for agriculture (= paludiculture). Sphagnum is a key genus for bog restoration and paludiculture on bogs. For successful Sphagnum establishment on rewetted bogs formerly used as grassland, it is recommended to remove the top layer of degraded peat. However, topsoil removal will cause additional GHG emissions and therefore should be minimized. In this study, we assess the climate effects of 30 cm and less topsoil removal on former bog grassland. For this, we measured GHG emissions with closed chambers where Sphagnum has been directly applied on the rewetted, mulched grassland (“Without topsoil removal” = TSR0) or on areas with topsoil removal of 5–10 cm (TSR5) and 30 cm (TSR30) depth. Over the entire study year, TSR5 and TSR30 were GHG sinks of −5.7 ± 1.2 t ha −1 a −1 and −4.5 ± 0.6 t ha −1 a −1 (in CO 2 -eq), respectively. In contrast, TSR0 was a strong source of CH 4 resulting in a net GHG budget of 43.7 ± 7.4 t ha −1 a −1 due to the rewetted topsoil being rich in labile organic compounds. With a share of 80 % Sphagnum fields, 5 % ditches and 15 % causeways in the whole system TSR5 would emit the least GHGs of 0.9 ± 1.2 t ha −1 a −1 , because with less topsoil removal, the share of Sphagnum production fields can be increased. TSR5 would thus be the most climate-friendly and cost-effective approach for raised bog restoration and for Sphagnum paludiculture following drainage-based, agricultural use. • GHG emissions on three different top soil removal treatments were measured. • “Without topsoil removal” treatment was a strong source of CH 4 . • “5–10 cm topsoil removal” emits 0.9 ± 1.2 t ha −1 a −1 (in CO 2 -eq).