Partitioning of latent heat flux at a northern peatland

The partitioning of latent heat flux (Q(E)) to vascular plant and moss surface components was assessed for a Sphagnum-dominated bog with a hummock-hollow surface having a sparse canopy of low shrubs. Results from porometry and eddy covariance measurements of Q(E) showed evaporation from the moss surface ranged from greater than 50% of total Q(E) early in the growing season to less than 20% after a dry period toward the end of the growing season. Both soil moisture and vapour pressure deficit (D-a) affected this partitioning with drier moss and peat, lower water table. and smaller D-a all reducing MOSS Q(E). Daily maximum moss Q(E) ranged from greater than 200 W m(-2) early in the growing season to less than 100 W m(-2) during a dry period. In contrast, vascular contribution to total QE increased over the season from a daily maximum of about 150 W m(-2) to 250 W m(-2) due to increase in leaf area by leaf replacement and emergence and to drying of the moss surface. Porometry results showed average daily maximum conductance from bog shrubs was near 8 mm s(-1). These conductance values were smaller than those reported for vascular plants from more nutrient-rich wetlands. The effect of increases in D-a on vascular QE were moderated by decreases in stomatal conductance. At constant available energy, vascular leaf conductance was reduced by as much as 2 mm s(-1) and moss surface conductance was enhanced by up to 3 mm s(-1) by large D-a. Considering vascular and non-vascular water transport characteristics and frequency of water table position and given the observed variations of Q(E) partitioning with water table location and moss and peat water content, it is suggested that modelling efforts focus on how dry hummocks and wet hollows each contribute to Q(E), especially as related to D-a and soil moisture dynamics. (c) 2006 Elsevier B.V. All rights reserved.