ausblenden:
Schlagwörter:
WATER-VAPOR; INTERANNUAL VARIABILITY; SIBERIAN BOG; HEAT FLUXES;
EVAPOTRANSPIRATION; WETLAND; CARBON; EVAPORATION; EXCHANGE; VEGETATIONEnergy balance; Evaporation; Boreal peatland; Fen; Russia; Eddy
covariance;
Zusammenfassung:
Boreal peatland energy balances using the eddy covariance technique have previously been made in Alaska, Canada, Scandinavia, and Western Siberia, but not in the European portion of the Russian Federation. European Russia contains approximately 200,000 km(2) of peatlands and has a boreal (subarctic), continental climate influencing the region's energy balance. To help fill this research gap, the surface energy balance was determined for a boreal peatland fen in the Komi Republic of Russia for an 11-month period in 2008-2009 using the eddy covariance method. The total measurement period's cumulative energy balance closure rate was 86%, with higher closure during the critical summer growing season. Similar to other boreal peatland sites, the mid-summer shortwave radiation demonstrated albedo between 0.13 and 0.19 as calculated on a cumulative monthly basis, whereas monthly albedo was >0.9 during the months with greatest snow (January, February 2009). Mid-summer Bowen ratios averaged 0.20-0.25 on a cumulative basis, with monthly averaged mid-day values in the range 0.35-0.53 during the growing season. Latent energy (LE) fluxes exceeded 70% of net radiation and 60% of potential evapotranspiration. During the study period, total evapotranspiration (406 mm) was slightly greater than rainfall (389 mm), with later snowfalls creating excess moisture in the atmospheric water budget. These characteristics together point to a peatland whose energy balance behavior is generally consistent with data from other boreal fens. The LE fluxes were dominantly controlled by net radiation, with less canopy resistance than at other northern fens and a lighter role for vapor pressure deficit to play in the energy balance. The aerodynamic and canopy conductance terms were of similar magnitude, both through the season and through any given diurnal cycle. The consequently high decoupling coefficient (0.65 +/- 0.16 in the growing season) allows further modeling of fens in this region with reduced effects from the uncertainties of parameterizing surface conductance terms and their responses to water table and vapor pressure deficit changes. The Priestley-Taylor method provides a reasonable approach to modeling evapotranspiration, given some assumptions about the site's energy balance closure. This understanding of the local drivers on the energy and water budgets has important implications for peatland ecology and growth, regional carbon dynamics, and downstream hydrology. (C) 2014 The Authors. Published by Elsevier B.V.
