Global Atmospheric-Biospheric Chemistry

Volume 48 of the series Environmental Science Research pp 165-178

Terrestrial Biosphere-Atmosphere Exchange in High Latitudes

  • William S. ReeburghAffiliated withDepartment of Geosciences, University of California
  • , Nigel T. RouletAffiliated withDepartment of Geography, McGill University Montreal
  • , Bo H. SvenssonAffiliated withDepartment of Microbiology, Swedish University of Agricultural Sciences

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This paper summarizes CH4 flux measurements from high latitude tundra and wetland environments obtained during large field campaigns and a number of smaller local projects since 1986. Area-weighted time series CH4 flux measurements at fixed sites in high latitude tundra and wetland environments suggest a CH4 source strength of about 35 Tg yr-1, which agrees reasonably with atmospheric model calculations. Individual flux measurements are subject to high spatial and temporal (daily to interannual) variability, and are strongly influenced by vegetation, soil temperature, thaw depth, and water table level, which influence the balance between CH4 production and consumption. Field studies show that these subsurface parameters and CH4 fluxes are often poorly correlated. Laboratory studies on varying water table level in tundra soil columns have shown long lag times and hysteresis in the fluxes under falling and rising water table conditions. These results indicate that the soil parameters are not independent variables and that a single parameter capable of predicting CH4 flux is unlikely.

Boreal forest ecosystems appear to be a small net sink for CH4. Microbially mediated oxidation of atmospheric CH4 is the dominant process; wet bogs, fens, swamps, and beaver ponds are the only CH4 sources. Microbial CH4 oxidation is also an important modulator of tundra emission and has the potential to eliminate net CH4 emission under warmer, drier conditions.

Studies to date have emphasized CH4, but future integrated studies along boreal forest and tundra transects will include measurements of other gases and carbon dioxide fluxes for estimates of carbon fixation and storage. Field manipulation experiments aimed at determining the sensitivity of high latitude trace gas emissions to temperature and moisture variations are also planned. High latitude biosphere-atmosphere studies to date have a strong North American bias. Collaborative studies in northern European and Siberian wetlands are essential to understanding the importance of high latitude ecosystems in trace gas budgets.