Full-cycle greenhouse gas balance of a Sphagnum paludiculture site on former bog grassland in Germany

Growing Sphagnum on rewetted bogs (=Sphagnum paludiculture) is an alternative to drainage-based land use because it retains its value as productive land while mitigating greenhouse gas (GHG) emissions. However, studies on GHG ex-change covering the full production system and cycle are missing. Here, we combined data of the establishment phase with newly recorded data of a 7-year old Sphagnum paludiculture site in Germany including partial Sphagnum harvest. GHGs were measured with closed chambers at all elements of the system (production fields, ditches, causeways). Over the full production cycle, the production fields were GHG sinks with -3.2 +/- 4.2 t ha-1 a-1 (in CO2-eq), while ditches represented sources emitting 13.8 +/- 11.5 t ha-1 a-1. New measurements on the causeway indicated that it was a stronger GHG source with 29.3 +/- 9.8 t ha-1 a-1 than previously assumed from literature values. Corrected for the area share of its elements and including the partial Sphagnum harvest (in dry mass) of-13.8 +/- 0.6 t ha-1 (=average 7-year CO2 emissions of 3.3 +/- 0.1 t ha-1 a-1), the site was a GHG source of 10.7 +/- 4.6 t ha-1 a-1, thus reducing emissions by-20 t ha-1 a-1 compared to the German emission factor for grassland on drained organic soils. Per ton harvested dry biomass, the paludiculture site emitted 9.9 +/- 4.6 t of CO2-eq. The causeways were the major contributor to the warming, calling for reducing causeway area in Sphagnum paludicultures. Future 'best -practice' could realistically comprise areal shares of 80 % production fields, 5 % ditches, 15 % causeways and a full Sphagnum harvest with the uppermost 5 cm remaining on site for recovery. In this scenario the site would emit CO2- eq emissions of 4.3 +/- 1.9 t ha-1 a-1 or 0.9 +/- 2.1 t per ton harvested dry mass.