Evaluating runoff generation during summer using hydrometric, stable isotope and hydrochemical methods in a discontinuous permafrost alpine catchment

Research on runoff generation in catchments with discontinuous permafrost has focused primarily upon the role of surface organic layers and frozen soils (both permanent and seasonal). Much of this work has been hydrometric, with isotope and hydrochemical methods receiving only limited application in delineating old and new water contributions and chemically inferred hydrological pathways. In a small subarctic alpine catchment within the Wolf Creek Research Basin, Yukon, runoff generation processes were studied in the summer of 2001 using a mixed method approach to evaluate the mechanisms and pathways of flow from the hillslopes to the stream during rainfall events. Two storms had delta(18)O isotopic ratios that differed significantly from baseflow and water within hillslopes, allowing for two-component hydrograph separation to infer new and old water contributions. Event water contributions ranged between 7 and 9%, exhibiting little variability despite the large differences in event water and stormflow volume. Utilizing delta(18)O-dissolved organic carbon and delta(18)O-specific conductance data, two tracer three-component hydrograph separations were attempted to isolate rainfall, water within the organic layer and mineral layer contributions to stormflow. Three-component separations suggest that water from the mineral soil dominates the stormflow hydrograph, yet the contribution of organic-layer water varies greatly depending upon the choice of tracers. Hydrometric data indicate that slopes with permafrost likely supply much of the stormflow water due to near-surface water tables and transmissive organic soils. However, this signal was not clearly discernable in the streamflow hydrochemistry. More integrated studies are required to establish a greater understanding of hillslope processes in mountainous discontinuous permafrost catchments. Copyright (C) 2005 John Wiley Sons, Ltd.