Decoupling natural and anthropogenic change at Alta Lake, Whistler, British Columbia: Implications for management


Small, recreationally important lakes are economically critical to communities across Canada. Currently the development of management practices to prevent the deterioration of water quality in these lakes is based on 1-2 year limnological assessments that are only able to provide short-term characterizations of water quality variability. Using carbon-dated sediment cores from Alta Lake, Whistler, British Columbia, this study reconstructed long-term changes in water quality using C/N stable isotopes, metals, and historical records. Evidence was found for large-scale landscape destabilization ca. AD 1650 and the rerouting of Twenty-one mile creek from Alta Lake to the Green Lake watershed by alluvial fan dynamics ca. AD 1770. Changes in productivity indicators (δ^13^C and δ^15^N) coincident with anthropogenic metal deposition (AD 1900 – present) were not similar to changes in productivity indicators associated with landscape destabilization and watershed dynamics, indicating human-induced nutrient loading and increased productivity. Traditional assessments of Alta Lake concluded that Alta Lake is an oligotrophic, clear-water lake with excellent water quality. This study confirmed these data but suggested that nutrient loading and increased productivity on Alta Lake is a result of human activity. These changes are subtle but indicate that a comprehensive assessment of nutrient input is necessary to prevent the future deterioration of water quality. Collectively these data confirm that a long-term perspective on water quality variability is critical for the development of effective management practices for Alta Lake and other small, recreationally important lakes across Canada.

Ontario-Québec Paleolimnology Symposium
Dewey Dunnington
Geoscientist, Programmer, Educator