Modeling peat thermal regime of an ombrotrophic peatland with hummock-hollow microtopography

The theory of conductive heat transfer cannot explain different attenuations of the daily amplitude of peat temperatures (Ts) in hummocks (detectable below the 20-cm depth) and hollows (disappearing above the 10cm depth). Large readily drained macropores in the upper fibric peat determine a large air permeability and hence may enhance heat transfer by air convection in porous media, driven by temperature gradients between hummock sides and interiors. In this study, the ecosys model was used to simulate a peat thermal regime at Mer Bleue peadand, Ontario, Canada. It was hypothesized that adding the air-convective heat transfer to conductive plus water-convective heat transfers would improve simulations of Ts. The results for T s ground heat fluxes, G, and sensible heat fluxes, H, modeled with and without air-convective heat transfer were tested with continuous hourly measurements from 2000 to 2004 using thermocouples, heat flux plates, and eddy covariance. Simulated air-convective heat transfer caused an average increase in G and a corresponding decrease in H of -20 W m-2 from the simulated conductive plus water-convective heat transfer. Hastened soil warming in hummocks resulted in better agreement between measured and simulated hummock Ts values with (RMSD of 2.23°C) than without air-convective heat (RMSD of 2.54°C). Enhanced hummock Ts caused an indirect increase in hollow Ts in the model with (RMSD of 1.68°C) compared to without air-convective heat (RMSD of 1.82°C). Our results suggest that air convection is probably an important mechanism of heat transfer in peat hummocks and should be included in peatland biogeochemical models