Postimpoundment Time Course of Increased Mercury Concentrations in Fish in Hydroelectric Reservoirs of Northern Manitoba, Canada

Abstract

Mercury (Hg) concentrations in fish in boreal reservoirs have been shown to be increased for up to 3 decades after impoundment. However, the time course of increased concentrations is not well known. The purpose of this study was to determine the evolution of Hg concentrations in fish in the boreal reservoirs of northern Manitoba, Canada, and its relationship with severity of flooding. We determined total Hg concentrations in three species of fish for up to 35 years after impoundment in 14 lakes and lake basins. Postimpoundment trends depended on fish species and reservoir. In the benthivorous lake whitefish (Coregonus clupeaformis), Hg concentrations increased after flooding to between 0.2 and 0.4 microg g(-1) wet weight compared with preimpoundment concentrations between 0.06 and 0.14 microg g(-1) and concentrations in natural lakes between 0.03 and 0.06 microg g(-1). Hg concentrations in lake whitefish were usually highest within 6 years after lake impoundment and took 10 to 20 years after impoundment to decrease to background concentrations in most reservoirs. Hg concentrations in predatory northern pike (Esox lucius) and walleye (Sander vitreus) were highest 2 to 8 years after flooding at 0.7 to 2.6 microg g(-1) compared with preimpoundment concentrations of 0.19 to 0.47 microg g(-1) and concentrations in natural lakes of 0.35 to 0.47 microg g(-1). Hg concentrations in these predatory species decreased consistently in subsequent years and required 10 to 23 years to return to background levels. Thus, results demonstrate the effect of trophic level on Hg concentrations (biomagnification). Peak Hg concentrations depended on the amount of flooding (relative increase in lake surface area). Asymptotic concentrations of approximately 0.25 microg g(-1) for lake whitefish and 1.6 microg g(-1) for both walleye and northern pike were reached at approximately 100% flooding. Downstream effects were apparent because many reservoirs downstream of other impoundments had higher Hg concentrations in fish than would be expected on the basis of flooding amount.

Mercury bioaccumulation in the food web of Three Gorges Reservoir (China): Tempo-spatial patterns and effect of reservoir management

“…Elevated Hg concentrations in fish were found in hydropower reservoirs of North America and northern Europe in the late 1970s and early 1980s (Abernathy and Cumbie, 1977;Lodenius et al, 1983). Typically, several-fold increases in fish Hg concentration were detected at the first 5-10 years after the filling of reservoirs (Verdon et al, 1991;Bodaly et al, 2007). The sampling in this study was conducted just two years after TGR reached its maximum depth of impoundment and the "reservoir effect" of Hg contamination in TGR was not significant.…”

Recent advances in the study of mercury methylation in aquatic systems

“…Increases in MeHg concentrations in flooded environments result from the stimulation of microbial methylators by organic material supplied via decaying vegetation and soils (Bodaly et al 1984;Kelly et al 1997;Hall et al , 2005, resulting in elevated fish Hg concentrations 10-20 years post impoundment (Bodaly et al 2007). Revisiting the sites of inundated terrestrial areas nine years after initial flooding has shown that MeHg concentrations in the once flooded soils remain elevated (Rolfhus et al 2015).…”

Mercury and methylmercury concentrations in two newly constructed reservoirs in the Wujiang River, Guizhou, China

“…It is widely reported that Hg concentrations in predatory fish in newly constructed reservoirs in North America and Europe exceeded 1.0 mg/kg [2][3][4][5][6][7][8], the consumption limit of MeHg in fish recommended by the Joint Food and Agriculture Organization of the United Nations/World Health Organization Expert Committee on Food Additives [9]. The high levels of MeHg persist for decades after initial flooding [10,11]. The decomposition of organic matter (OM) from flooded soils and increased microbial methylation of inorganic Hg II to MeHg species after flooding are believed to be responsible for the elevation of MeHg in fish [12][13][14][15].…”