Drainage-constrained field-scale modelling of rewetting and regional CO2 ̶ CH4 emissions in lowland peatlands.

Drained peatlands are major sources of greenhouse gas (GHG) emissions. Reducing these is essential for achieving climate mitigation targets and agricultural net-zero goals. Water table depth (WTD) strongly influences emissions, yet national assessments often overlook the role of drain water levels within complex lowland drainage networks in controlling WTD. The objective of this study was to test a drainage-constrained field-scale modelling framework for estimating how raised ditch-water levels alter water-table dynamics and modelled CO₂-CH₄ emissions across managed lowland peat fields. LiDAR-derived hydrological data were integrated with a physically based daily water table model to generate a spatially explicit assessment of field-scale carbon dioxide (CO₂) and methane (CH₄) emissions from drained lowland peat soils in Eastern England. Emissions were estimated under baseline drainage conditions and a set of rewetting scenarios that progressively raised drain water levels while maintaining hydrological connectivity. Results indicate that raising drain water levels reduced modelled landscape GHG emissions by up to 58% relative to baseline. Most mitigation benefits were achieved in the initial stages of rewetting, with successive scenarios delivering progressively smaller gains (mean modelled GHG emissions decreases by ∼5.3 tCO₂eq/ha/yr between baseline and scenario 3, but by only ∼0.01 tCO₂eq/ha/yr between scenario 10 and scenario 13, indicating a near-plateau with negligible additional mitigation). Beyond moderate increases in water level, further reductions in CO₂ emissions were offset by rising CH₄ emissions, highlighting a clear trade-off between reduced CO₂ losses and enhanced CH₄ release. By explicitly resolving fine-scale hydrological variability, we demonstrate the importance of spatially detailed modelling for capturing the variability in the drivers of modelled peatland GHG emissions and guiding mitigation strategies. Realising the full benefits of rewetting will require sustained summer water supplies, modifications to drainage infrastructure to improve field-level water management, and economic mechanisms that reward rewetting.