Hydrological and hydrochemical investigations in a glacial lake catchment: Implications for organochlorine transport

Previous observations have indicated that fish from glacially fed alpine lakes contain elevated levels of organochlorine (OC) contaminants. Trout from Bow Lake, Banff National Park, Alberta, had the highest contaminant concentrations of all the lakes surveyed in western Canada (Donald et al., 1993). Subsequent investigations showed that the elevated levels of contaminants in fish from Bow Lake could not be explained by biomagnification (Campbell et al., 2000), as has been found in similar studies of lakes at lower elevations (Kidd et al., 1995). It was determined that glacial runoff was the dominant source of OC inputs to Bow Lake, and that most OCs from this source were in the dissolved phase and hence were highly bioavailable (Blais et al., 2001a; Braekevelt, 2001). This study was conducted to determine why glacial runoff is a major source of OC contaminants. The research focuses on the roles of water sources and flow routing in adjacent glacial and non-glacial watersheds in controlling the delivery of OCs to the lake. The conclusions are based on a combination of hydrological and hydrochemical analyses of runoff.; A combination of low forest and soil cover in the glacial catchment, and lower DOC concentrations in runoff likely contribute to high deposition, efficient delivery, and high bioavailability of OCs in glacial runoff. The presence of forests appears to reduce the total accumulation of OCs (and snow) relative to barren/sparsely vegetated areas. Thus, the lack of/limited forest cover in glacial catchments may contribute to higher OC deposition in glacial catchments relative to environments with more forest cover. DOC and solute chemistry indicate that there is likely lower retention of OC contaminants in glacial catchments due to the limited presence of organic soils and vegetation, and the limited contact between glacial runoff and these sources of organic carbon. The lower DOC concentrations and less aromatic nature of DOC in glacial runoff could enhance the bioavailability of OC contaminants relative to snowmelt fed catchments where the flushing of soils during snowmelt provides higher concentrations of more aromatic DOC. High contributions of OCs from glacial runoff in years with extensive melt may result from multi-year storage of OCs in firn or glacier ice and/or from flushing of OCs stored within the firn aquifer during low ablation years.