Runoff generation in a hypermaritime bog–forest upland

Shallow hillslope groundwater is shown to be a dominant source of streamflow in sloping bog-forest uplands of the North Coast Forest District, British Columbia, based on a three-component isotope hydrograph-separation analysis conducted in July 1998. At peak discharge during a mid-summer rainfall event, new water contributions accounted for only 12% of streamflow, whereas shallow groundwater accounted for 85% of streamflow and bog groundwater and deep hillslope groundwater accounted for the remaining 3% of streamflow. Mean residence time of water is estimated to be about 2 months, and soil storage capacity is roughly 400 mm based on the analysis of the baseflow discharge and isotopic response. Systematic seasonal shifts in deuterium excess of rainfall in the Prince Rupert area are shown to be useful for labelling shallow and deep groundwaters based on their residence time signatures. The potential for using dissolved organic carbon and deuterium excess as hydrological tracers is also discussed.