Sources, Sinks, and Fluxes of Dissolved Organic Carbon in Subarctic 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 mgL–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.