Wetlands as long-term sources of metals to receiving waters in mining-impacted landscapes

• We investigate metal release from wetlands after smelter emission reductions.
• Release to outflow streams occurred primarily from SO4-related acidification events.
• Concentrations exceeded water quality guidelines by several orders of magnitude.
• Metal exports were a source to receiving lakes greater than current smelter inputs.

Wetlands are prevalent in the Sudbury, Ontario region and often operate at the interface between terrestrial and aquatic ecosystems, modifying water chemistry and potentially affecting the recovery of impacted lakes. The deposition of metals and sulphur in Sudbury in 2010–2012 was far below that reported in the 1970's, but still higher than background values. Wetlands in the area have accumulated large quantities of metals, and high concentrations of these metals in streams occurred primarily in response to SO4-related acidification events or associated with high dissolved organic carbon production in early summer. Concentrations of most metals in streams exceeded provincial guidelines and fluxes of some metals from catchments exceeded deposition inputs to lakes by as much as 12 times. The release of metals long after emissions reductions have been achieved must be considered in ecosystem recovery studies, particularly as dry conditions may become more prevalent in boreal regions affected by mining.