Isotopic Assessment of Hydrologic Variability in the Oil Sands Region of Alberta and Implications for Risk of Acidification

An isotope mass balance technique is applied to quantify water yield variations and is used for the first time to refine a steady-state critical acid loadings assessment for a network of fifty lakes in hydrologically complex, wetland-rich terrain of northeastern Alberta. The approach uses readily obtainable physical and climatological data combined with site-specific measurements of evaporative isotopic enrichment of deuterium and oxygen-18 in lakewater as a means for quantifying throughflow, lake residency and ungaged runoff to lakes. Comparison of the method with Water Survey of Canada hydrometric data suggests very similar water yields, a favourable result, in moderate to large-sized watersheds, although isotope-based estimates appear to capture a different, and potentially improved view of water balance variability for small, low-yield drainages apparently disconnected from the landscape, and high-yield drainages that appear to be fed by regional groundwater flow systems. The isotope mass balance method is of practical interest owing to its potential for broad incorporation into water quality networks, and capability for characterizing hydrologic variability across regions and among specifically targeted study basins. For aquatic ecosystems of northeastern Alberta, an area expected to be affected by acid deposition from regional oil sands development, the critical loadings results are preliminary and subject to further refinement. Nevertheless, they serve to demonstrate the sensitivity of the approach to hydrological setting, and emphasize the inherently low threshold to acidification of lakes with low water yield, due to reduced fluxes of watershed-derived base cations.