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Increased mercury and reduced insect diversity in linked stream-riparian food webs downstream of a historical mercury mine

April 11, 2022

Historical mining left a legacy of abandoned mines and waste rock in remote headwaters of major river systems in the western United States. Understanding the influence of these legacy mines on culturally and ecological important downstream ecosystems is not always straight-forward because of elevated natural levels of mineralization in mining-impacted watersheds. To test the ecological effects of historic mining in the headwaters of the upper Salmon River watershed (USA), we measured multiple community and chemical endpoints in downstream linked aquatic-terrestrial food webs. Mining inputs impacted downstream food webs through increased mercury accumulation and decreased insect biodiversity. Total mercury (THg) in seston, aquatic insect larvae, adult aquatic insects, riparian spiders, and fish at sites up to 7.6 km downstream of mining was in much higher concentrations (1.3 to 11.3-fold) and isotopically distinct compared with sites immediately upstream of mining inputs. Methylmercury (MeHg) concentrations in bull trout and riparian spiders were sufficiently high (732 – 918 and 347 – 1,140 ng MeHg g-1dw) to affect humans, birds, and piscivorous fish. Furthermore, the alpha-diversity of benthic insects was locally depressed by 12-20% within 4.3 to 5.7 km downstream of from the mine. However, because total insect biomass was not affected by mine inputs, the mass of mercury in benthic insects at a site (i.e., ng Hg m-2) was extremely elevated downstream (10 – 1,778-fold) compared with directly upstream of mining inputs. Downstream adult aquatic insect-mediated fluxes of total mercury were also high (~16 ng THg m-2d-1). Abandoned mines can have ecologically important effects on downstream communities, including reduced biodiversity and increased mercury flux to higher order consumers, including fish, birds, and humans.

Publication Year 2022
Title Increased mercury and reduced insect diversity in linked stream-riparian food webs downstream of a historical mercury mine
DOI 10.1002/etc.5342
Authors Johanna M. Kraus, JoAnn Holloway, Michael Pribil, Ben N. Mcgee, Craig A. Stricker, Danny Rutherford, Andrew S. Todd
Publication Type Article
Publication Subtype Journal Article
Series Title Environmental Toxicology and Chemistry
Index ID 70231327
Record Source USGS Publications Warehouse
USGS Organization Columbia Environmental Research Center