Environmental Controls on Aquatic Ecosystem Sensitivity to Metal Bioaccumulation

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Metals occur naturally in the environment; however, human activities have altered the biogeochemical cycles of these elements and increased their release to air, soils, and water. Metal pollution from point source emissions can have both local and long-range impacts (through atmospheric transport) on ecosystem and human health. There is currently insufficient information on how environmental conditions control the fate of metals deposited in Canada's North. Recent evidence from my research program indicates that Arctic lakes are more sensitive to metal bioaccumulation (specifically mercury) compared with lakes at temperate latitudes. New research is needed to identify how climate related factors affect the bioaccumulation of metals and their transfer in food chains in order to evaluate and mitigate impacts of metal pollution on these vast water resources. The environmental processes involved are complex and occur at multiple scales. At the ecosystem scale, unproductive lakes (i.e. having lower organic matter production) at higher latitudes may accumulate more metals at the base of the food chain because the contaminant mass taken up from water is “concentrated” in less microbial biomass. At the organism scale, colder temperatures and low food availability alter the physiology of consumers that may enhance their metal levels. In particular, slower growth rates may lead to higher metal levels in Arctic aquatic organisms. Over the next five years, this research program will focus on the role of two key climate-related factors - temperature and productivity - in controlling the sensitivity of northern aquatic ecosystems to bioaccumulation and food chain transfer of mercury and arsenic. Mercury is a priority contaminant due to its long-range atmospheric transport, and little information is available on arsenic accumulation in Arctic lakes despite releases from northern resource developments. Laboratory and field experiments will investigate how cold, unproductive environments enhance organism accumulation of metals and their transfer through the food chain. Because these factors are correlated in the environment, experimental approaches under controlled conditions are needed to separate potential independent and interactive effects. This research program will provide process-based predictions for future climate-change impacts on metal pollution, improve our ability to determine the fate of metal deposition, and support the management and protection of vast water resources still widely used by northerners for subsistence fisheries.