Seasonal and interannual variation in water vapor and heat fluxes in a West Siberian continental bog

Abstract

The seasonal and interannual variation in the energy fluxes of a West Siberian continental bog were measured from April to October in 1999 and 2000 using the eddy covariance method. The energy balance closure rate (=[sensible + latent heat fluxes]/[available energy]) ranged from ∼0.8 to 0.9 and showed a better energy balance and less scattering using the soil heat flux estimated from an area‐averaged soil thermal parameter rather than from a plot‐based measurement. The net radiation ( R n ) increased drastically after snowmelt because the surface albedo ( a ) dropped from its highest value to its lowest value over the course of the snowmelt. The snowmelt water raised the water table ( z wt ) to its highest level; it then gradually decreased. The seasonal and interannual variation in a , which ranged from 0.09–0.19, depended on z wt , because surface wetness was closely related to z wt through the capillary uptake of Sphagnum moss. The seasonal variation in the latent heat flux ( lE ) was similar to that in R n . The largest lE was observed in the middle of June, and was ∼120 Wm −2 (4.2 mm d −1 ) in both years. Conversely, the sensible heat flux ( H ) did not show an obvious seasonal pattern and was lower than lE during the growing season. The Bowen ratio ( B r ) in the early growing season was 0.57 and 0.60, and the values in the peak growing season were 0.65 and 0.78, in 1999 and 2000, respectively. The lower B r was related to the higher z wt ; specifically, it was due to the wetter surface conditions. An interannual comparison of the monthly mean atmospheric water vapor deficit (δ e ) and lE showed a significant relationship with a higher lE observed in the year with a higher δ e . Therefore in the bog studied the interannual variation in the water vapor flux was controlled mainly by z wt and δ e .