Modeling of greenhouse gas emissions from paludiculture in rewetting peatlands is improved by high frequency water table data

Abstract. Rewetting drained peatlands can reduce CO₂ emissions but prevents traditional agriculture. Crop production under rewetted conditions may continue with flood-tolerant crops in paludiculture, but its effects on greenhouse gas (GHG) emissions compared to rewetting without further management are largely unknown This study was conducted between 2021 and 2022 on a fen peatland in central Denmark. At the study site, three harvest/fertilization management treatments were implemented on Reed Canary Grass (RCG) established in 2018. Measurements of CO₂ and CH₄ emissions were conducted biweekly using a transparent manual chamber connected to a gas analyzer and manipulating light intensities with four shrouding levels. Although this was a rather wet peatland (−8 cm mean annual WTD), the site was a CO₂ source with a mean net ecosystem C balance (NECB) of 6.5 t C ha⁻¹ yr⁻¹ across treatments. Model simulation with the use of high temporal resolution water table depth (WTD) data was able to better capture ecosystem respiration (R_eco) peaks compared to the use of mean annual WTD, which underestimated R_eco. Data on pore water chemistry further improved statistical linear models of CO₂ fluxes using soil temperature (Ts), WTD, ratio vegetation indices and PAR as explanatory variables. Significant differences in CO₂ emissions and water chemistry parameters were found between studied blocks, with higher R_eco corresponding to blocks with higher pore water nutrient concentrations. Methane emissions averaged 113 kg of CH₄ ha⁻¹ yr⁻¹, equivalent to 11.3 % of the total carbon emission in CO₂ equivalents. Because of large heterogeneity among the experimental blocks no significant treatment effect was found, however, the results indicate that biomass harvest reduces GHG emission from productive rewetted peatland areas in comparison with no management, whereas on less productive areas it is beneficial to leave the biomass unmanaged.