Energy partitioning at an ombrotrophic bog

Energy partitioning was studied over three years (1998-2000) at the Mer Bleue peat bog near Ottawa. Sphagnum mosses blanket the undulating surface of hummocks and hollows and there is a sparse canopy (LAI = 1.2) of low shrubs (Chamaedaphne calyculata, Ledum groenlandicum, Kalmia angustifolia, and Vaccimium myrtilloids). Analysis of energy flux measurements found available energy was partitioned mostly to latent heat flux but evapotranspiration rates were often below equilibrium rates. Daily Bowen ratios decreased from values greater than unity early in the growing season when the water table was high (near or above the hollow surfaces) to values frequently less than 0.5 during midsummer when the water table was low (greater than 0.25 m below the hollow surfaces). Latent heat flux exceeded net radiation often during the late afternoon, thus energy supply for evapotranspiration was at least partly supplied by the ground heat flux. The presence of dry, warm hummocks and wetter, cooler hollows suggest possible small-scale advection occurring beneath the sparse canopy. This energy exchange between the hummocks and the canopy and hollow surfaces would be an important factor contributing to the enhancement of latent heat flux over sensible heat flux.