A diatom-based paleolimnological survey of environmental changes since ~ 1850 in 18 shallow lakes of the Athabasca Oil Sands Region, Canada

Abstract

Aerially transported contaminants from the industrial development of the bituminous sands in the Athabasca Oil Sands Region (AOSR) of western Canada may threaten the water quality and community structure of the region’s lakes. This environmental threat is further compounded by the region’s changing climate (i.e. increased temperatures and reduced moisture). Because environmental monitoring began ~ 30 years after the initiation of the region’s bitumen-based industry (~ 1967), a paleolimnological approach is required to document pre-disturbance conditions and to determine how lakes have changed, if at all, in response to environmental stressors. Our bottom–top (before and after) study of dated sediment records compared pre-disturbance (~ 1850) and modern subfossil diatom assemblages from 18 shallow, isolated lakes (which are typical of the region), located along a spatial gradient (up to ~ 110 km) relative to the main area of local industry. Despite the region’s substantial environmental stressors, the changes in mostly benthic-dominated diatom communities were minor at 15 of the 18 lakes. We conclude that the muted biological responses may be a consequence of naturally high nutrient concentrations and/or the typically subtle nature of changes in assemblages dominated by benthic generalist taxa. At all sites, including three lakes with marked changes, we found no evidence of a diatom assemblage response to airborne inputs of contaminants (i.e. dibenzothiophenes) and nutrients (i.e. bioavailable nitrogen) from the AOSR industry. Instead, it is likely that regional warming played a role in the modest diatom assemblage changes observed in these shallow lakes, with responses mediated by lake-specific characteristics.