Dissolved organic carbon fluxes in a discontinuous permafrost subarctic alpine catchment



The sources and fluxes of dissolved organic carbon (DOC) were investigated within a subarctic catchment with discontinuous permafrost (Granger Basin, Yukon) from 23 June 2001 to 22 June 2002. During spring freshet, stream DOC increased rapidly on the rising limb of the hydrograph, peaked prior to maximum discharge, then declined exponentially to pre-baseflow levels while flows remained high. During summer storms, a similar pattern was observed whereby DOC increased on the ascending hydrograph limbs and peaked prior to maximum flows. Suction lysimeter and well data indicate that most of the DOC was mobilized from within near-surface organic soils. Comparisons between permafrost and seasonal frost slopes indicate that permafrost slopes are a greater source of DOC due to their thicker organic soils and wetter antecedent conditions that promote lateral flow in the shallower soil layers of the active layer. In contrast, slopes with seasonal frost encourage percolation and sorption of DOC in deeper mineral layers. Mass balance estimates of DOC export using actual and extrapolated data from regressions of DOC versus discharge indicate that 1.64 g C m−2 was exported from Granger Basin during the study year, 69% of this occurred during the 13 May to 22 June snowmelt period. Copyright © 2003 John Wiley & Sons, Ltd.