A hydrological and biogeochemical study was undertaken at the Mer Bleue bog, Ottawa, Ontario, Canada from May 22, 1998 to May 21, 1999. Basin runoff was generated by groundwater discharge at the peatland margin, and groundwater discharge was controlled by hydraulic gradients and horizontal hydraulic conductivities (Kh). Flux of dissolved organic carbon (DOC) measured at the basin outflow was 8.3 g C m-2 yr-1 and compared to within 23% of DOC flux estimated using a Dupuit approximation of seepage during the ice-free season. Annual DOC flux was 11% of the annual carbon sink. / Flownet analysis showed that seasonal patterns of groundwater flow were controlled by boundary condition changes that resulted from precipitation and evapotranspiration events. A pattern of recharge was most common over the hydrological year, but a discharge pattern was observed during a 40 day groundwater flow reversal. Evaluation of the peatland recharge-discharge function using in situ sodium concentrations and a diffusion model revealed that the peatland is a long-term recharge system. It is hypothesized that peatland biogeochemical function is controlled by long-term recharge despite annual occurrence of groundwater flow reversals.

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