Long-Term Limnological Dynamics in Multiple-Stressor Systems in the Athabasca Oil Sands Region, Canada
Lakes in the Athabasca Oil Sands Region (AOSR) are threatened by multiple environmental stressors linked to industrial development of the local hydrocarbon deposits and climate change. Waterbodies are vulnerable to changes in water quality and quantity, as well as shifts in ecosystem structure and function. Due to insufficient monitoring prior to industrial development, little is known about the long-term changes in AOSR lakes and the effects of multiple stressors in the region. This thesis uses paleolimnological approaches to determine baseline conditions, track biotic changes through time, and investigate the relative effects of industrial pollution (i.e., contaminants and nutrients) and climate change on the environmental trajectories of the region’s shallow lakes. A multiproxy study of a shallow, isolated lake receiving substantial industrial contamination assessed how multiple trophic levels of a typical AOSR lake have changed over the past ~75 years. While there was no evidence of a threshold-type response to industrial pollution, biotic assemblages from multiple trophic levels suggest the benthic environment increased in complexity, consistent with the warming climate. Spectrally-inferred sedimentary chlorophyll-a profiles from 23 lakes and bioavailable nutrient deposition maps were used to investigate the extent, timing, and causes of increased primary production. Widespread, asynchronous increases in primary production and correlations to observed air temperatures suggest climate change as the main driver of elevated primary production, rather than bioavailable nutrients from industry. Finally, a “top-bottom” paleolimnological analysis comparing pre-disturbance (~1850) and present-day subfossil diatom assemblages from 18 shallow lakes was completed to survey the region’s biotic changes and investigate which environmental variables structured the diatom communities. While diatom assemblages in some lakes changed markedly, most AOSR lakes demonstrated resiliency to the region’s stressors. There were no apparent biological responses to industrial airborne pollution, including deposition of bioavailable nutrients. Instead, most diatom community shifts were consistent with known responses to climate change, and were likely mediated by lake-specific characteristics. Collectively, this research concludes that anthropogenic climate change is the main driver of overall muted community change and marked primary production increases in the shallow lakes of the AOSR. Yet, future changes are possible given the expected continuation of the region’s industrial development.