Recolonization and recovery of an Arctic benthic community subject to mine-tailings deposits

Summary

Deposition of large volumes of mine tailings takes place in several Norwegian fjords, but the impacts on marine ecosystems have received relatively little scientific attention. At a 40 + −year old tailing deposition area for a copper mine in the Arctic fjord Repparfjorden, we investigated both short-term colonization of mine tailings-contaminated sediments through a field experiment, and the present faunal state in the old deposit area. Copper-concentrations at the old deposition site were still high (up to 291 mg/kg dry weight (dw)), and exceeded the Norwegian environmental-quality threshold (84 mg/kg dw). Furthermore, copper was identified as a significant structuring factor for the fauna in the fjord, although faunal diversity was relatively high and the community not severely disturbed. In the colonization experiment, experimental boxes filled with defaunated sediment capped with mine tailings were subject to colonization for 15 months. Benthic macrofaunal communities were successfully established in all boxes, but the boxes with tailings showed lower species richness, abundance and biomass than the controls. Mine tailings continue to have local impacts on seafloor communities decades after deposition, and even low levels of metal-rich sediments can affect faunal recruitment. These results have implications for submarine deposition of mining waste and the impacts they have on coastal ecosystems.