| Summary: | Measurements of net ecosystem carbon dioxide fluxes were made over a sedge fen, Churchill, Manitoba during the summertime period, 1994. This period, when compared to 50 year records (1943 to 1993), was warm and dry. The mean daily temperature was 2 "C warmer than normal. Total precipitation for the summertime period was 45% less than normal, with 56% of the events occurring during the month of August. The water table was generally 0.30 m below the surface and periodically as deep as 0.44 m. The active layer reached a depth of 1.12 m by the end of the measurement period. The growing season for sedge extended from June 23 to August 8. Using atmospheric gradient techniques, the total net ecosystem flux of carbon dioxide over the measurement period was determined. The total summertime flux was positive indicating that the tundra is losing more carbon dioxide through respiration than it is gaining via photosynthesis. There is still a substantial loss during the period of active photosynthesis. In fact, almost one half of the total carbon dioxide efflux occurred during the period of active growth. It is hypothesized that warmer soil temperatures and better aerated soil conditions are more conducive to decomposition, therefore resulting in a larger absolute respiration flux relative to photosynthesis. This is in accordance with several other high latitude studies. Master of Science (MS)
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