SOURCES, SINKS, AND FLUXES OF DISSOLVED ORGANIC-CARBON IN SUB-ARCTIC FEN CATCHMENTS

Dissolved organic carbon (DOC) concentrations and fluxes were determined over the summer in a small subarctic catchment, composed of an upland component with woodland and forest over mineral soils and a fen in the lower section. DOC concentrations were low (1-2 mg L-1) in precipitation and increased in tree throughfall and stemflow (50 and 150 mg L-1), shrub throughfall (17 mg L-1), the leachate of the surface lichens and mosses (30 mg L-1), and the soil A horizons (40 mg L-1). Concentrations decreased in the reddish-brown B horizons (17 mg L-1) and there was evidence of strong DOC adsorption by the subsoils. DOC concentrations in peat water averaged 17 mg L-1, but the stream draining the catchment contained an average of 10 mg DOC L-1, amounting to a summer export of about 1 g m-2 for the whole catchment. Summer DOC concentrations in streams draining 10 catchments ranged from 2 to 16 mg L-1 and were positively related to the proportion of the catchment occupied by peatland, illustrating the importance of subarctic fens as a source of DOC.