Beavers (Castor spp.) are ecosystem engineers and important modifiers of freshwater ecosystems. They create impoundments that flood the surrounding landscape and modify the flow of materials through streams, thus potentially increasing nutrients, productivity and the availability of toxic methyl mercury (MeHg) to downstream food webs. Here we quantify food web‐available MeHg in water, periphyton, and invertebrates collected from 15 streams up‐ and down‐stream from beaver impoundments in the Rocky Mountain foothills of Western Canada. While nutrients, algal biomass, and total invertebrate standing stock were not significantly elevated below ponds, MeHg concentrations (average increase of 1.7×) and percent of total Hg that was MeHg (average increase of 1.3×) showed a trend of higher values in all compartments downstream and the difference was significant in predatory invertebrates. This suggests that beaver impoundments can increase the availability and subsequent uptake of MeHg by basal food web organisms even if their immediate influence on nutrients and resources is limited. As beaver populations continue to rebound, more research is needed to fully characterise the effects of beavers on nutrient and contaminant cycling under different biogeochemical conditions.

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Cyanobacterial blooms present challenges for water treatment, especially in regions like the Canadian prairies where poor water quality intensifies water treatment issues. Buoyant cyanobacteria that resist sedimentation present a challenge...

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