Mercury and selenium accumulation in the Colorado River food web, Grand Canyon, USA.
Mercury (Hg) and selenium (Se) biomagnify in aquatic food webs and are toxic to fish and wildlife. The authors measured Hg and Se in organic matter, invertebrates, and fishes in the Colorado River food web at sites spanning 387 river km downstream of Glen Canyon Dam (AZ, USA). Concentrations were relatively high among sites compared with other large rivers (mean wet wt for 6 fishes was 0.17-1.59 μg g(-1) Hg and 1.35-2.65 μg g(-1) Se), but consistent longitudinal patterns in Hg or Se concentrations relative to the dam were lacking. Mercury increased (slope = 0.147) with δ(15) N, a metric of trophic position, indicating biomagnification similar to that observed in other freshwater systems. Organisms regularly exceeded exposure risk thresholds for wildlife and humans (6-100% and 56-100% of samples for Hg and Se, respectfully, among risk thresholds). In the Colorado River, Grand Canyon, Hg and Se concentrations pose exposure risks for fish, wildlife, and humans, and the findings of the present study add to a growing body of evidence showing that remote ecosystems are vulnerable to long-range transport and subsequent bioaccumulation of contaminants. Management of exposure risks in Grand Canyon will remain a challenge, as sources and transport mechanisms of Hg and Se extend far beyond park boundaries.
US Geological Survey, Fort Collins Science Center, Fort Collins, Colorado, USA.
David M
DM
Walters
Cary Institute of Ecosystem Studies, Millbrook, New York, USA.
Emma
E
Rosi-Marshall
US Geological Survey, Southwest Biological Science Center, Grand Canyon Monitoring and Research Center, Flagstaff, Arizona, USA.
Theodore A
TA
Kennedy
Department of Ecology, Montana State University, Bozeman, Montana, USA.
Wyatt F
WF
Cross
Department of Biological Sciences, Idaho State University, Pocatello, Idaho, USA.
Colden V
CV
Baxter
D000818:Animals; D001130:Arizona; D003120:Colorado; D004784:Environmental Monitoring; D020387:Food Chain; D005843:Geography; D006801:Humans; D008628:Mercury / Q000032:analysis*; D012307:Risk Factors; D045483:Rivers / Q000737:chemistry*; D012643:Selenium / Q000032:analysis*
D008628:Mercury; D012643:Selenium
Bioaccumulation; Food web; Large rivers; Mercury; Selenium