Siliceous microfossil changes in impact and reference lakes in the uranium mining region of the Athabasca basin in northern Saskatchewan

Uranium mining activities can lead to the release and accumulation of highly toxic elements into adjacent aquatic ecosystems resulting in potential impacts on the biota of the lakes. Lakes adjacent to uranium mines in the eastern margin of the Athabasca basin in northern Saskatchewan were assessed for any detectable change in siliceous microfossils contemporaneous with documented metal enrichment. Analysis of similarities (ANOSIM) was used to determine if pre- and post-mining assemblages of five dated sediment cores within ~5 km of the mines were significantly different. These records were then compared to five sediment records from lakes ~20 km west and northwest of the mining activities to assess any regional trends in variation in siliceous microfossils in the absence of mining activities in their watersheds. Significant changes in diatom species assemblages between pre- and post-mining samples were evident in three of the five lakes adjacent to mining, however, significant differences were also evident between pre- and post-mining time periods in all but one of the five reference lakes. Variability in the pre-mining diatom assemblages of both the reference and adjacent lakes indicates that any analyses of change must be lake specific. Benthic Fragilariaceae were a common component of most lakes and were often identified through analysis of similarity percentages (SIMPER) as being amongst the highest contributors to the changes in the diatom composition, however, each lake also had other unique taxa changes contributing to the differences. The significant changes in specific diatom taxa from pre-mining to post-mining assemblages were not consistent across the impact lakes, nor were they consistent in the reference lakes. Teratological counts in the lakes adjacent to mining did not indicate any increases of deformed diatoms in the post-mining samples. The assessment of siliceous microfossil changes in the five lakes adjacent to mining operations with documented uranium enrichment, often accompanied by other elemental enrichments, suggests little influence on diatom assemblages can be linked to the uranium mining activities. This is supported by the significant changes also recorded in the siliceous component of the sediment record in the five reference sites.