Abstract
The chemistry of mercury in freshwater systems, particularly man-made reservoirs, has received a great deal of attention owing to the high toxicity of the most common organic form, methylmercury. Although methylmercury bioaccumulation in reservoirs and natural lakes has been extensively studied at all latitudes, the fate of the different forms of mercury (total vs. dissolved; organic vs. inorganic) along the entire river-estuary continuum is less well documented. In fact, the difficulty of integrating the numerous parameters involved in mercury speciation in such large study areas, combined with the technical difficulties in sampling and analyzing mercury, have undoubtedly hindered advances in the field. At the same time, carbocentric science has grown exponentially in the last 25 years, and the common fate of carbon and mercury in freshwater has become increasingly clear with time. This literature review, by presenting the knowledge acquired in these two fields, aims to better understand the extent of mercury export from boreal inland waters to estuaries and to investigate the possible downstream ecotoxicological impact of reservoir creation on mercury bioavailability to estuarine food webs and local communities.
Highlights
Concentrations of mercury in ambient air and water are extremely low and so do not constitute a significant source of human exposure to mercury (Clarkson 2002; Goyer and Clarkson, 2001)
The flooding of soil when hydroelectric reservoirs are impounded promotes the release of nutrients and increases bacterial activity and methylmercury bioavailability at the base of the food chain
A schematic representation of the different compartments of the river continuum attempts to summarize the main processes that come out the review (Figure 1)
Summary
Concentrations of mercury in ambient air and water are extremely low and so do not constitute a significant source of human exposure to mercury (Clarkson 2002; Goyer and Clarkson, 2001). The mercury is transferred from lower to higher trophic levels, from plankton to fish. This temporary phenomenon has been studied extensively in various regions of the world (Verta et al, 1986; Verdon et al, 1991; Porvari, 1995; Rudd, 1995; Porvari, 1998; Ikingura and Akagi, 2003; Bodaly et al, 2007; Teisserenc et al, 2014). The health risks associated with increased Hg levels in reservoir fish, which impact sport fishers and communities that rely on fish as a traditional food (Moriarity et al, 2020a), have raised concerns about the environmental footprint of hydropower.
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