Name
The influence of moss surface resistance on peatland evapotranspiration estimates.
Description
Evapotranspiration is a major hydrological flux in boreal peatlands where it is often assumed to occur at or close to potential rates due to the assumed proximity of the water table to the surface, which promotes wet conditions. However, the peatland water table can fluctuate depending on the water balance between precipitation and water loss. This fluctuation is particularly apparent during the growing season, where a 5 cm drop in water table can lead to a reduction in VMC of approximately 40% in living moss layers. These living moss layers are non-stomatal and are where evaporation occurs in the peat profile. The reduction in VMC can sharply increase surface resistance to evaporation, lowering the actual evapotranspiration rate below the potential rate. By ignoring this negative feedback, models can overestimate peatland water loss via evapotranspiration, yet peatlands are typically modelled the Priestly-Taylor combination equation, which is a potential evapotranspiration estimation. Here a new conceptualization is used to quantify moss resistance and incorporate it into a Penman-Monteith combination equation framework to estimate evapotranspiration for a boreal peatland. Moss resistance was successfully integrated into the Penman-Monteith equation using an empirical relationship between the ratio of the unsaturated and saturated hydraulic conductivities and resistance. However, validation proved difficult due to a lack of dry conditions at the study site. Furthermore, the findings indicate a large degree of uncertainty remains in methods of estimating moss resistance, and that future work should attempt to reduce this uncertainty, using drier sites and higher resolution soil tension measurements.