Assessing the Relative Influence of Nitrogen Deposition and Regional Warming on Scaled Chrysophytes in Lakes Downwind of the Athabasca Oil Sands Region, Canada
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Freshwater systems in Boreal regions are potentially threatened by a number of environmental stressors, such as point and non-point source pollutants from industrial development and climate change. In northeast Alberta, industrial activity in the Athabasca Oil Sands Region (AOSR) threatens nearby lakes, and potentially lakes downwind. In the late- 1990’s rapid annual increases in the mining of bitumen occurred, with corresponding increases in emissions of sulphur and nitrogen oxides. Recent paleolimnological studies have provided indications of increased primary production in a number of lakes in Alberta and northwest Saskatchewan. Several studies in other regions have linked deposition of reactive nitrogen (Nr) to nutrient enrichment of freshwater ecosystems, and a potential increase in primary producers. However, due to regional warming, the degree to which deposition of Nr to lakes downwind of the AOSR influences primary producers remains unknown. I investigated the relative influence of climate change and enhanced Nr deposition on scaled-chrysophyte production in northwest Saskatchewan lakes. To disentangle the influence of the two stressors, a paleolimnological assessment of 16 lakes was undertaken. Reference and impact lakes with respect to Nr deposition were chosen, and nutrient limitation was integrated into the study design to identify lake sensitivity to Nr deposition (N or P or co-limited). Scaled- chrysophyte assemblages were dominated by the taxon Mallomonas crassisquama, and little change occurred in species assemblages since ca 1900. However, recent (post ca 1980) increases in total chrysophyte abundance in cores from both reference and impact sites suggested a regional stressor (i.e. climate) as a driving factor. However, because of the low number of study lakes and small lake environmental gradient, the number of study sites was increased to 26 to further understand chrysophyte response to warming in the region. Breakpoint analysis on scale- ii to-diatom ratio time series indicated that shallower sites responded earlier than deeper sites. A canonical variate analysis also suggested that the magnitude of response is also lake specific, with low nutrient and deeper lakes showing larger increases in chrysophyte abundance. The results from this study suggest that a) widespread changes in chrysophyte populations are occurring in this region likely in response to warming and its effects on the thermal structure of lakes, and b) physical and chemical characteristics of lakes are important in modulating ecological change.