Water chemistry and phytoplankton recovery of metal-contaminated and acidified lakes in the Sudbury Region, Canada

The recovery of water quality and phytoplankton of two previously acidified and metal contaminated lakes located in the Sudbury Region, Canada was examined. Despite acidic deposition these lakes are able to buffer inputs and remain circumneutral. The rate of recovery for Ni and Cu has slowed since the mid 1980s, however, lake water concentrations for these metals are still decreasing. Toxicity of lake water, as measured by algal bioassay, has also decreased. Phytoplankton assemblages have similar biomass but fewer species than non-polluted lakes in the region. These assemblages were dominated by two different species in 1992 and a single species in 1995. Algal isolates from one of the lakes showed varying degrees of tolerance to Ni and Cu. Analysis revealed that both lakes possess a substantial pool of Cu and Ni in their sediments. Despite major improvements in water quality the recovery of the phytoplankton in these lakes remains delayed.