Sampling method and season influence selenium dynamics at the base of a boreal lake food chain

Few studies have investigated the potential influence of sampling method and season on Se bioaccumulation at the base of the aquatic food chain. In particular, the effects of low water temperature associated with prolonged ice-cover periods on Se uptake by periphyton and further transfer to benthic macroinvertebrates (BMI) have been overlooked. Such information is crucial to help improve Se modelling and risk assessment at sites receiving continuous Se inputs. To date, this seems to be the first study to address these research questions. Here, we examined potential differences related to sampling methods (artificial substrates vs. grab samples) and seasons (summer vs. winter) on Se dynamics in the benthic food chain of a boreal lake (McClean Lake) receiving continuous low-level Se input from a Saskatchewan uranium milling operation. During summer 2019, water, sediment grab samples and artificial substrates were sampled from 8 sites with varying mill-treated effluent exposure. In winter 2021, water and sediment grab samples were sampled at 4 locations in McClean Lake. Water, sediment, and biological samples were subsequently analyzed for total Se concentrations. Enrichment functions (EF) in periphyton and trophic transfer factors (TTF) in BMI were calculated for both sampling methods and seasons. Periphyton collected with artificial substrates (Hester-Dendy samplers and glass plates) exhibited significantly higher mean Se concentrations (2.4 ± 1.5 μg/g d.w) than periphyton collected from the surface of sediment grab samples (1.1 ± 1.3 μg/g d.w). Selenium concentrations in periphyton sampled in winter (3.5 ± 1.0 μg/g d.w) were significantly greater than summer (1.1 ± 1.3 μg/g d.w). Nevertheless, Se bioaccumulation in BMI was similar between seasons, possibly suggesting that invertebrates are not actively feeding in winter. Further investigations are necessary to verify if peak Se bioaccumulation in BMI takes place in spring, coinciding with the reproductive and developmental windows of some fish species.