LAUSR

Abstract Study region Surveys of stable isotopes of water in 50 boreal lakes were conducted during 2002–2017 as a component of Alberta’s Oil Sands acid sensitivity program in northeastern Alberta. Study focus Using an isotope mass balance approach, watershed, climatic and isotopic data were applied to estimate evaporation losses and residence time of lakes, as well as to estimate water yield from watersheds. New hydrological insights for the region Site-specific differences in water yield to 50 lakes over 16 years were found to be controlled by latitudinal gradients in climate, wetland type, lake/watershed configuration and permafrost. 19 plateau watersheds located northeast of Fort McMurray and in the Birch and Caribou Mountains which contained significant permafrost were found to have similar water yield to permafrost-poor watersheds if fen-dominated (159 mm/yr: n = 5 vs. 166 mm/yr; n = 31), and enhanced water yield (405 mm/yr; n = 14) if bog-dominated. Water yield was found to be systematically dependent on permafrost extent, yielding up to several hundred millimetres of additional runoff in bog-dominated systems. Temporal trend analysis indicates systemic momentum of change in hydrologic drivers over the 16-year period, although few are statistically significant. A new conceptual framework is proposed for classification of site-to-site permafrost thaw stage to improve water yield prediction, which is expected to influence lake water quality including observed pH increases noted previously for many lakes in the region.