Abstract:

Land-use disturbances such as forestry can affect mercury (Hg) dynamics in boreal stream food webs by influencing the availability and methylation of Hg and by altering dietary exposure to Hg through changes in basal resources. This study aimed to quantify differences in consumer Hg concentrations ([Hg]) and Hg biomagnification rates 1) pre- (2019), during- (2020), and post-harvest (2021) within Boreal streams, 2) and across harvested and non-harvested landscapes. Streams were sampled for basal food sources (aquatic and terrestrial), invertebrate primary and secondary consumers, and top predators (fish). To determine differences in consumer [Hg] and Hg biomagnification rates across years and landscapes, samples were analyzed for [Hg], and carbon and nitrogen stable isotopes. Overall, we detected variable effects of forestry on consumer [Hg] and biomagnification rates pre-and post-harvest, likely due to differences in best management practices across sites. Further, when comparisons were made across harvested and non-harvested landscapes, we detected significantly higher consumer [Hg] in harvested landscapes, but no difference in biomagnification rates. On-going analyses comparing the diversity of basal resources within stream food webs pre- and post- harvest will help elucidate effects of forest harvesting on Hg uptake. Ultimately, this work will advance our understanding about Hg cycling in impacted boreal streams and may assist in the development of forestry guidelines that will minimize Hg risk to aquatic systems.