Tree-Ring Inferences on Water-Level Fluctuations of Lake Athabasca

Abstract

Tree-ring data were analyzed for a long-term perspective on ecological and hydroclimatic variations on the Peace-Athabasca Delta (PAD). The ecosystem of this Ramsar Wetland of International Importance in northeastern Alberta is sensitive to fluctuations in water levels of the numerous lakes, channels and perched basins, and attention has been focused in recent decades on the possibility of deleterious effects from climatic change and regulation of the Peace River by W.A.C. Bennett Dam. A network of eight Picea glauca tree-ring chronologies was developed, time series features of growth variation were summarized, and the chronologies were applied in a regression model to reconstruct an annual time series of early summer (July 11 to 20) water levels of Lake Athabasca for the period A.D. 1801-1999. Though statistically weak (R2 = 0.36), the reconstruction verifies adequately in cross-validation and is consistent with anecdotal written records of a dramatic decline in water levels in 1879-81. Correlation of reconstructed and observed water levels improves with smoothing. Gaussian smoothing (ten years and longer) identifies a major low centred on 1890. The differential growth responses among the sites as well as evidence from other tree-ring studies suggest the 1890 low was associated primarily with diminished Peace River flows. The 20th century is unusual in a long-term context for high-amplitude multi-decadal variations in tree growth and reconstructed water levels, but the timing of these more recent fluctuations appears unrelated to the building of the W.A.C. Bennett Dam. Further research is needed to better discriminate the tree-ring signal for lake-level variation from the signal due to localized precipitation.