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Abstract. We analyzed the relationship between net ecosystem exchange of carbon dioxide (NEE) and irradiance (as photosynthetic photon flux density or PPFD), using published and unpublished data that have been collected during midgrowing season for carbon balance studies at seven peatlands in North America and Europe. NEE measurements included both eddy-correlation tower and clear, static chamber methods, which gave very similar results. Data were analyzed by site, as aggregated data sets by peatland type (bog, poor fen, rich fen, and all fens) and as a single aggregated data set for all peatlands. In all cases, a fit with a rectangular hyperbola

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This paper documents the performance of the organic soil version of the Canadian Land Surface Scheme (CLASS) in modelling the hydrology and energy balance of the Beverly Swamp, Southern Ontario. The hydrometeorological dataset used to assess model performance begins in the autumn of 1983 and spans 33 months, presenting the first multi-year characterization of the area. The Beverly Swamp receives approximately 900 mm of precipitation per year, of which one third is lost to net runoff, and the remainder to evaporation. Vertical drainage at this site is impeded, due to the presence of a marl layer below the highly decomposed peat soil, at approximately 1-m depth. This mixed-forest wetland is unique among surfaces used for CLASS testing to date. Within CLASS, vertical drainage at the bottom of the soil profile is set to zero to represent the marl subsurface boundary. Preliminary runs have shown that after each melt period this produced ponded water on site which persisted from year to year. The inclusion of a simple lateral drainage function in CLASS simulated actual measured lateral surface flow, and effectively reproduced seasonal differences in water table position. Comparisons between measured and modelled diurnally averaged energy budget components taken from two summers indicate that there is a marked tendency for CLASS to underestimate latent heat flux (Q E) by 29% of the observed values, the major cause of this disagreement being due to systematic error. Concurrent with this error is an overestimation of the magnitude of soil heat storage (Q G), by a factor of seven, wherein the error is dominantly systematic. Modifications made to the canopy resistance parametrization, based on site measurements, resulted in improved model estimates of Q E , reducing the underestimation to 12% of observed values, and changing the major cause of error from systematic to unsystematic in nature. The improvement in Q E corresponded with a change in the prediction of sensible heat flux (Q H). A tendency to overestimate Q H by 20% of the observed values changed to an underestimation of Q H by 14%, the error being unsystematic in each case. The modifications resulted in no significant change to either the magnitude or the nature of the error for Q G .

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