Liming of Acid and Metal Contaminated Catchments for the Improvement of Drainage Water Quality

A 38 ha near-barren experimental catchment area near an abandoned Cu and Ni smelter in Sudbury, Canada was treated with 410 tons of coarse dolomitic limestone in 1994. An additional 54 tons of pelletized fine dolomite were added to 15 wetlands within the experimental catchment in 1995. The treatments significantly increased the pH and base cation concentrations in the outlet stream. Cu and Ni concentrations initially rose after the wetland treatment, but then declined to levels below those of the reference site. Bioassay tests revealed that the toxicity of the drainage water was greatly reduced by the liming, but some localized inputs of highly toxic groundwater still posed a problem for aquatic biota. The pH of surface water in the wetlands has been maintained at >6.0 for over 4 years. The wetland liming appeared to be highly effective at neutralizing drainage water, however there may be some adverse effects on wetland plant communities as a consequence.