Water table and temperature dynamics control CO2 emission estimates from peatlands under rewetting and climate change scenarios

To mitigate agricultural greenhouse gas emissions, Danish ministerial agreements have initiated a land-use transformation of historical dimensions, focusing on restoring and rewetting extensive peatland areas currently used for agriculture. In addition, a CO₂-equivalent tax on emissions from organic peatlands is scheduled to be implemented from 2028. This study informs discussions on requirements and best practices for rewetting and peatland restoration and highlights the importance of including changing climate conditions and rewetting management scenarios in future peatland management strategies.

The study integrates process-based hydrological modeling and empirical CO₂ flux modeling at a daily temporal resolution to evaluate how peatland hydrology influences CO₂ emissions under scenarios of rewetting and climate change.

Following the calibration of a three-dimensional transient distributed hydrological model for a peat-dominated catchment, daily groundwater table dynamics were simulated to represent hydrological conditions in drained peat soils. These simulations were coupled with an empirical CO₂ flux model, developed from a comprehensive daily dataset of groundwater table depth, temperature, and soil CO₂ flux measurements. The novel empirical CO₂ flux model captures a clear temperature-dependent response of soil CO₂ emissions to variations in groundwater table depth.

By applying this coupled modeling framework, we quantified CO₂ emissions at daily timescales. The results demonstrate that incorporating both temperature sensitivity and high-resolution temporal variability in water level significantly influence projections of CO₂ fluxes. In particular, high CO₂ emissions are expected in cases of co-occurrence of elevated air temperature and low groundwater tables. Using 17 different climate projections from the Euro-CORDEX regional climate modeling project, we simulated future groundwater table depth and temperature-dependent CO₂ emissions. We find increased emissions due to increased temperatures, which, however, can be counter-balanced (in the Danish case) or amplified depending on the future trend in groundwater table depth.

Our results further demonstrate that rewetting strategies that achieve near-surface groundwater tables mainly during winter result in only marginal emission reductions compared to drained conditions. Conversely, near-surface groundwater tables in summer offer more effective reductions (up to 50%).

The study illustrates the value of combining detailed hydrological simulations with emission models.