This study applied the use of a stable isotope mass-balance model to calculate water throughflow, residency and water-yield and to assess acid-sensitivity for 50 lakes in the Athabasca Oil Sands region of northeastern Alberta. The research project was aimed at improving existing regional hydrologic estimates, based on coarse-scale runoff values derived from river gauging stations. Regional isotopic variations measured for components of the water cycle indicated a wide range of hydrologic conditions prevail, from throughflow, high water-yield lakes (186 mm.yr-1) to evaporative, low water-yield systems (23 mm•yr-1). Notably, hydrology is shown to be a controlling factor on acid-sensitivity and may be altering acid-sensitivity via such processes as water flow through peatland dominated catchments or convergence with acidic neutralizing soils, geology or ground waters. At the throughflow end of the hydrologic spectrum at low levels of isotopic enrichment, isotopes in precipitation were sensitive up to 30%. Relative humidity, on the other hand, is sensitive at high levels of enrichment at the evaporative end of the scale on the order of 25%.
This application, in conjunction with landscape and chemical analysis, highlighted the over-riding hydrologic processes occurring at lowland and upland systems of the Boreal Plain that may lead to increased acid-sensitivity or buffering capacity. This thesis documents the first ever demonstration of an isotope mass-balance model to estimate water-yields and subsequently assess critical acid loadings in North America. The results of this research project will allow for improved predictive ability and management of acid-sensitive aquatic ecosystems within future planning frameworks.