Implementation of regenerative ditch borders in Dutch peat meadows: effects on soil CO₂ fluxes and potential carbon trade-offs

Abstract. Drained peatlands account for 3 % of the Dutch national greenhouse gas (GHG) emissions. Topsoil removal (TSR; which leads to removal of built-up nutrients and labile soil carbon) in combination with rewetting (groundwater table management) in drained peatlands is often proposed as a restoration measure effective in reducing carbon dioxide (CO₂) emissions, yet often politically challenging to implement. TSR is however currently applied at a smaller scale during the implementation of regenerative ditch borders (RDBs), but its effectiveness in reducing CO₂ remains uncertain. We investigated the effects of RDBs on soil CO₂ emissions in comparison to conventional borders (CDBs) in a year-round field survey (June 2023 – March 2024) in a lowland peat agroecosystem. Soil respiration was measured at four distances from the water’s edge (40, 80, 360 and 640 cm) over a ten-month period and used to fit statistical models with the predictors soil temperature, soil moisture content and exposed carbon (a variable integrating profile soil carbon density and groundwater level). The resulting model was used to calculate annual soil respiration, and to estimate the payback time (no. of years for net negative effects on cumulative CO₂ emissions) of the removed carbon. Spatiotemporal variation in soil respiration was mostly explained by exposed carbon and soil temperature (32 % and 30 %, respectively). Soil respiration peaked at 65 % soil moisture content. At distances 40 and 80 cm reduced soil respiration in RDBs in spring and summer was driven by lower amounts of exposed carbon, while at 360 and 640 cm in RDBs higher soil temperatures and soil moisture content mostly counteracted this effect. Model-based annual soil respiration was 17 % lower in RDBs in comparison to CDBs. If it is assumed that all soil carbon removed during RDB construction is mineralized, the payback time can exceed 100 years. While RDBs can promote reductions in soil CO₂ emissions and therefore more sustainable peatland-adapted agriculture, potential emissions from excavated carbon should be accounted for.