Modelling the effect of water-table management on CO2 and CH4 fluxes from peat soils

Drainage of peatlands for agriculture causes an increase of CO2 flux from peat decomposition, contributing to national CO2 emission. The reverse process, i.e. for re-creation of wetlands, reduces the CO2 flux, but increases the CH4 flux. We developed a process model (PEATLAND) to simulate these fluxes from peat soils subject to different water-table management scenarios. The model combines primary production, aerobic decomposition of soil organic matter (including the soil-parent material, peat), CH4 formation, oxidation, and transport. Model input requires specification of water table and air temperature data sets, vegetation parameters such as primary production and parameters related to gas transport, and basic soil physical data. Validation using closed flux-chamber measurements Of CO2 and CH4 from five different sites in the western Netherlands shows that seasonal changes in fluxes Of CO2 and CH4 are correctly modelled. However, the CO2 submodel underestimates peat decomposition when peat decomposition rates obtained from laboratory incubation experiments are used as input. Field decomposition rates are considerably higher. This is attributed to enhancement of decomposition by the addition of easily decomposable material from root exudation ('priming effect'). Model experiments indicate that 1) drainage increases the CO2 production from peat decomposition strongly; 2) restoring a high water table may decrease the total greenhouse gas flux by a small amount although the CH4 flux increases strongly; 3) a warmer climate may cause higher greenhouse gas fluxes from peat soils resulting in a positive feedback to climate warming, and 4) high vegetation productivity in fen meadows may stimulate peat decomposition by the priming effect.