Abstracts for the 5th International GAME Conf.

3-5 October 2001

Aichi Trade Center

Nagoya Japan

Seasonal Variation of Water Vapor Flux and Its Controlling Factors over the West Siberian Bog

Kou SHIMOYAMA (1), Yoshihiro FUKUSHIMA (2), Tetsuya HIYAMA (3), Gen INOUE (4)

Seasonal variation of water vapor flux was measured using eddy correlation method in boreal bog located in southwest region of west Siberian lowland (56.8N, 83.5E) near Plotnikovo. Measurements were made at 2.0 m height above the moss surface using 3-dimensional sonic anemometer-thermometer and open-path infrared hygrometer. Continuous measurements were made from early April to middle October in 1999. Energy balance closure rate was estimated in summer period with two different values of soil heat flux, calculated with profile method and from a trigonometric function of surface temperature, due to estimate horizontal variability. The closure rates were 96 % and 98 % respectively and systematic under estimation was not observed. The probable error due to horizontal surface variability and uncertainty of water content were within }10%. The maximum latent heat flux was observed in late May, approximately 120 W/m2 (4.2 mm/d), which was almost equal to the value measured in other boreal wetlands. Measured evapotranspiration (E) was compared with the potential evapotranspiration (Ep) . The ratio E/Ep ranged from 0.3 to 0.9 during the observation period and tended to increase in summer, however it was not directly dependent on both LAI and water level, respectively. Seasonal variation of the surface parameter in bulk transfer equation, bulk transfer coefficient CH and surface moisture availability , were computed using atmospheric turbulent data measured with the eddy-correlation system. The CH ranged from 0.004 to 0.012 for reference height at 2.0 m during snow free season. A significant relationship between CH and LAI was observed during growing season. The CH value in non-growing season was relatively large compared to other non-vegetated surface because withered leaf hummock found in the bog partially and irregular sphagnum surface affects as the surface roughness.gradually declined through the season ranged from 0.1 to 0.5. When the water level was high and the bog was flooded, however, the was rather low compared with the value for water surface. This is because withered leaf hummock which was also shown in this season above the open water surface partially played a role to increase the bulk surface temperature, and therefore the tends to less than the value for water surface. A noticeable relationship was observed between and water level, while no relationship was observed between and LAI. This result indicates that evaporation is likely to be the dominant factor for latent heat flux. Bulk transfer coefficient for latent heat, CE, was computed and the significant relationship was observed between CE and E/Ep. As a result, the seasonal variation of the water vapor flux was controlled by evapotranspiration requirement of atmosphere, changes of the water level and the canopy structure through the vegetation growing.

Submittal Information

Name : Date :
    Kou SHIMOYAMA
    30-May-01-13:43:13
Organization : Theme :
    Graduate School of Science, Nagoya University
    Theme 2
Address : Presentation :
    Chikusa-ku, Nagoya 464-8601
    Poster or oral
Country : Abstract ID :
    Japan
    T2KS30May01134313
Phone : Fax :
    +81-52-789-3474
    +81-52-789-3436
E-mail :
    simoyama@ihan.nagoya-u.ac.jp