Effects of glacier retreat on proglacial streams and riparian zones in the Coast and North Cascade Mountains

• Main Author: Cowie, Natasha Michel
• Language: English
• Published: University of British Columbia 2011
• Online Access: http://hdl.handle.net/2429/38623

This study examined the trajectories of proglacial channel evolution in coastal British Columbia and Washington. Reach morphologies were identified by field surveys of 70 headwater reaches in ten catchments in the Coast and North Cascade Mountains. Riparian vegetation development and potential fish habitat were characterized in an additional 22 catchments using GIS analysis and satellite image interpretation. The study focused on reaches exposed by post-Little Ice Age (LIA) glacier retreat. Channel morphologies were predominantly governed by slope. The predominance of slope as a morphological control is a reflection of the landscape template imposed by the Quaternary glaciation, which appears to override most of the modern effects of the LIA. However, high sediment yield induced by post-LIA deglaciation influences channel form by providing large amounts of readily mobile sediment. Logistic regression models of riparian vegetation and forest development indicate that vegetation presence and maturity are positively correlated with reach age and negatively correlated with reach elevation. The timeline for riparian development is longer than that reported for other proglacial streams, suggesting that post-LIA instability and sediment inputs delay the establishment of riparian vegetation. A gradient-based classification tree model of potential fish presence in post-LIA channels suggests that fish may be able to access the majority of recently deglaciated headwaters, and that low-gradient, glacially carved hanging valleys may present habitat opportunities. The ability of fish to colonize proglacial streams will become increasingly important as climatic warming shifts thermal barriers for cold water species further upstream. Estimates of maximum weekly average stream temperature (MWAT) indicate that, at present, the majority of proglacial streams are thermally suitable for cold water fish. However, future projections of MWAT without basin ice cover show a 30% decline in cold water species habitat within the study basins. The work presented here contributes to the understanding of recently deglaciated headwaters by identifying first-order controls on proglacial stream morphology and riparian vegetation, which influence habitat and govern channel change in new streams.