Historical and Contemporary Patterns of Mercury in a Hydroelectric Reservoir and Downstream Fishery: Concentration Decline in Water and Fishes.
Mercury (Hg) contamination can pose risks to human and animal health as well as commercial fisheries. Reservoir construction in riverine systems produces flooded conditions amenable to Hg(II)-methylating bacteria, which can transform this relatively benign environmental contaminant into the bioaccumulative, environmentally relevant, and neurotoxic methyl-Hg (MeHg). Hg concentrations ([Hg]) in fishes from reservoirs can take decades to decrease to pre-dam levels, but less is known about Hg exported downstream and its dynamics within downstream fish populations. We examined and compared the multidecadal rates of biotic [Hg] decrease and contemporary factors affecting [Hg] in fish collected from a hydroelectric reservoir (Tobin Lake) and a related downstream fishery (Cumberland Lake) along the Saskatchewan River, Canada. Rates of [Hg] decrease were considered in four species-northern pike (Esox lucius), sauger (Sander canadensis), goldeye (Hiodon alosoides), and walleye (S. vitreus)-all of which showed a significant decrease over time (p < 0.001) and are now lower than Health Canada consumption guidelines (0.5 μg/g). Rates of decrease ranged from 0.5 to 3.9 %/year and were similar between sites in the cases of northern pike and sauger. Contemporary factors affecting [Hg] in walleye collected downstream include fish length (p < 0.001), fish age (p < 0.001), and trophic magnification through the food web (p < 0.001), and relationships between [Hg] and trophic level in predatory and prey fish are now similar to those found in non-Hg-inundated systems at a similar latitude. Together, these results suggest connected contamination between the two sites and delineate the timeline during which [Hg] in a variety of fish species decreased to nontoxic levels in both locations.
Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK, S7N 5B3, Canada. d.green@usask.ca.|Toxicology Graduate Program, University of Saskatchewan, Saskatoon, SK, Canada. d.green@usask.ca.
Derek J
DJ
Green
Fisheries Unit, Saskatchewan Ministry of Environment, La Ronge, SK, Canada.
Mark
M
Duffy
Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK, S7N 5B3, Canada.|Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, SK, S7N 5B3, Canada.
David M
DM
Janz
Compliance and Field Services, Saskatchewan Ministry of Environment, Regina, SK, Canada.
Kevin
K
McCullum
Cumberland House Fisherman's Coop, Cumberland House, SK, Canada.
Gary
G
Carrière
Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, SK, S7N 5B3, Canada.|School of Environment and Sustainability, University of Saskatchewan, Saskatoon, SK, Canada.
Timothy D
TD
Jardine
D000818:Animals; D004784:Environmental Monitoring; D005398:Fisheries / Q000706:statistics & numerical data; D005399:Fishes / Q000378:metabolism*; D008628:Mercury / Q000032:analysis* / Q000378:metabolism; D011210:Power Plants; D045483:Rivers / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000378:metabolism; D014877:Water Pollution, Chemical / Q000706:statistics & numerical data*
D014874:Water Pollutants, Chemical; D008628:Mercury