Comparative ecosystem-atmosphere exchange of energy and mass in a European Russian and a central Siberian bog I. Interseasonal and interannual variability of energy and latent heat fluxes during the snowfree period

Abstract

Energy and latent heat fluxes lambdaE were measured over ombrotrophic bogs in European Russia (Fyodorovskoye) and in central Siberia (Zotino) using the eddy covariance technique, as part of the EuroSiberian Carbonflux Project. The study covered most of the snowfree periods in 1998, 1999 and 2000; in addition some data were also collected under snow in early spring and late autumn 1999 and 2000. The snowfree period in Europian Russia exceeds the snowfree period in central Siberia by nearly 10 weeks. Marked seasonal and interannual differences in temperatures and precipitation, and hence energy partitioning, were observed at both sites. At both bogs latent heat fluxes (lambdaE) exceeded sensible heat fluxes (H) during most of the snowfree period: maximum lambdaE were between 10 and 12 MJ m(-2) d(-1) while maximum H were between 3 and 5 MJ m(-2) d(-1). There was a tendency towards higher Bowen ratios at Fyodorovskoye. Net radiation was the most influential variable that regulated daily evaporation rates, with no obvious effects due to surface dryness during years with exceptionally dry summers. Total snowfree evaporation at Fyodorovskoye (320 mm) exceeded totals at Zotino (280 mm) by 15%. At the former site, evaporation was equal to or less than precipitation, contrasting the Zotino observations, where summer evaporation was distinctly higher than precipitation. During the entire observation period evaporation rates were less than 50% of their potential rate. These data suggest a strong 'mulching' effect of a rapidly drying peat surface on total evaporation, despite the substantial area of free water surfaces during parts of the year. This effect of surface dryness was also observed as close atmospheric coupling

Effects of the conversion of marshland to cropland on water and energy exchanges in northeastern China

“…It is obvious that latent heat flux was the main consumer of Rn for marshland during the peak growing season, and sensible heat flux was the main consumer of Rn in the beginning and end of growing season. These findings are similar to patterns in other wetlands (Admiral et al, 2006;Burba et al, 1999a;Kurbatova et al, 2002;Lafleur et al, 2005). Those values also led to a Bowen ratio (b = H/LE) (Bowen, 1926) less than 1 at the peak of season and more than 1 at the beginning and end of growing season.…”

“…7). This pattern was also observed in wet grasslands in Japan (peak b about 2 in non-growing season) (Li et al, 2005), in Mer Bleue bog in Canada (high b value about 1.5, and 0.2-0.5 in peak growing season) (Admiral et al, 2006), in Zotino bog (b ranging from 0 to 3, with an average of 0.4 in peak growing season) and in Fyodorovskoy bog (b ranging 0-1.6) (Kurbatova et al, 2002). Because of dry land and conditions for soybeans before July 2005, the value of b reached a maximum value (about 4) in the beginning of the 2005 growing season, and the high value (>1) persisted until early July (Fig.…”

Seasonal changes of energy fluxes in an estuarine wetland of Shanghai, China

“…We attributed the high β to the combined results of high leaf area index and high temperature. In the south fetch, the dense canopy acted as a shelter that shaded the incoming radiation that could arrive at the soil surface (Linacre et al, 1970), thus reducing the evaporation rate and making more available energy dissipated as H. While at north fetch, though soil was frequently replenished by tidal water, the quick dry-out surface soil could act as "mulch" that inhibited the evaporation from below the wet soil (Kurbatova et al, 2002), likely helping to keep the magnitude of H at high levels.…”

“…Furthurmore, the standing water could also be an important consumer of incoming radiation in some vegetated wetlands and open water area (Burba et al, 1999a;1999b;1999c;Heilman et al, 2000;Silis et al, 1989). Although meaningful explanation on the regulations of ecosystem energy fluxes have been made in peatland (Kurbatova et al, 2002;Admiral et al, 2006;Admiral and Lafleur, 2007), prairie wetland (Burba et al, 1999a;1999b;1999c), and coastal wetland (Lafleur and Rouse, 1988;Silis et al, 1989), very little is known about the energy fluxes in estuarine wetland, where tidal activities and upstream hydrology can play significant roles in regulating the magnitude and dynamics of the energy budget through horizontal transportation of mass and energy (Odum, 2000;Teal and Howes, 2000).…”

“…Generally, evapotranspiration consumed largest part of available energy during growing season in vegetated wetlands (Kurbatova et al, 2002;Admiral et al, 2006;Admiral and Lafleur, 2007). Furthurmore, the standing water could also be an important consumer of incoming radiation in some vegetated wetlands and open water area (Burba et al, 1999a;1999b;1999c;Heilman et al, 2000;Silis et al, 1989).…”