Paleolimnological Assessment of Past Hydro-ecological Variation at a Shallow Hardwater Lake in the Athabasca Oil Sands Region Before Potential Onset of Industrial Development

Effective environmental monitoring requires knowledge of inherent natural variation.
In the absence of pre-development monitoring of aquatic ecosystems, paleolimnological approaches have been championed as a scientifically rigorous method to define pre-development conditions. Motivated by regulatory processes and absence of pre-development data, we conducted a comprehensive paleolimnological study at McClelland Lake to determine an appropriate timeframe for defining natural ranges of variation (NRVs) in hydroecological variables before
potential onset of mining within its catchment.
New hydrological insights for the region: During the past ~325 years, five distinctive intervals of hydroecological conditions were identified. The first phase (ca. 1695–1750) coincided with the Little Ice Age (LIA), when arid conditions supported lake levels 2.6–3.5 m below present. Phase II (ca. 1750–1840) encompassed subsequent warming, lake-level rise to 1.2–2.6 m below present and increased aquatic productivity. Phase III included frequent natural disturbance by wildfires
(ca. 1840–1900). During Phase IV (ca. 1900–1970), the lake deepened and algal communities diversified. Phase V (post–1970) captured influence of regional industrial development, climate warming and lake-level decline, and wildfires. We propose quantitative definitions of NRVs for McClelland Lake be derived from paleolimnological indicators since 1750, which provide a conservative and relevant range of hydroecological conditions, and explore merits and drawbacks of shorter-duration NRV definition for monitoring change.