Mine-tailings pollution shape riverine macroinvertebrate communities: A case-study from the River Folla

Pollution from mine tailings affects water quality in several Norwegian rivers, yet its cause-and-effect relationship with riverine biodiversity remain poorly understood. This knowledge gap hinders ecological assessment of environmental conditions, leaving biodiversity and ecosystem functioning insufficiently protected. This study, conducted in the Folla River catchment in Innlandet County, Norway, examines the impacts of historical pyrite mining on riverine macroinvertebrates. Mine-tailings pollution enters the Folla through both point and diffuse pathways, introducing a harmful mixture of substances, including sulfuric acid and heavy metals such as copper, zinc, and cadmium. To assess species-specific tolerance to these pollutants, laboratory exposure studies were conducted to evaluate the survival of nine macroinvertebrate species that were exposed to varying levels of contaminated water collected from Folla. The species studied included Baetis rhodani, Ameletus inopinatus, Heptagenia dalecarlica, Ephemerella mucronata, and Ephemerella aurivillii (Ephemeroptera); Diura nanseni and Leuctra hippopus (Plecoptera); and Rhyacophila nubila and Micrasema setiferum (Trichoptera). To investigate cause-and-effect relationships at river sites, tolerance values derived from the exposure studies were applied to assess macroinvertebrate community composition along a pollution gradient in Folla. The results of this study revealed significant species-specific differences in tolerance to pollution, with the ephemeropterans exhibiting the strongest negative responses. Incorporating species-specific tolerance attributes into a Tolerance Index for bioassessment yielded promising results, with a strong linear relationship along the pollution gradient (R2 = 0.89, P ≤ 0.001). The Tolerance Index outperformed the River Acidification Macroinvertebrate Index (R2 = 0.43, P = 0.024) and Average Score Per Taxon (R2 < 0.1, P = 0.332), which are commonly used but not specifically designed for mine tailings pollution. Although this study focused on a limited number of species, the findings highlight the potential for refining bioassessment tools to enhance the usefulness of macroinvertebrates as bioindicators of mine-tailings pollution in Norwegian rivers.