A half-century after mine closure, metal contamination from sulfide ore mining in the headwaters continues to impair riparian vegetation and aquatic macroinvertebrates along Soda Butte Creek, Yellowstone National Park. A tailings dam failure in 1950 emplaced metal-rich sediment at high flood-plain levels, above 50 yr to 100 yr flood stages in 1996 and 1997. These large natural floods removed only a small part of the contaminated sediment through bank erosion; they also failed to lower in-channel Cu concentrations, because increased erosion of mine waste during high flows balances increased inputs of uncontaminated sediments, generating no net change in concentrations. Geomorphic processes controlling movement of contaminated sediments indicate that mine impacts will persist for centuries in Soda Butte Creek and imply long-lasting impacts in similarly affected streams worldwide.

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