Arcellaceans (thecamoebians) as proxies of arsenic and mercury contamination in northeastern Ontario lakes

Abstract

Q-mode cluster analysis of arcellacean populations in three small lakes (two heavily polluted by mine tailings) near the town of Cobalt in northeastern Ontario permitted five distinct faunal assemblages to he recognized and related to ecologic tolerance. Mine waste and mill tailings were dumped into Crosswise Lake until 1970, and a leaking tailings dam continues to pollute Peterson Lake. Natural sedimentation is slowly burying the tailings in these lakes but areas of highly toxic sediments remain exposed in several areas. Levels of arsenic and mercury contamination in the substrate are as high as 7,110 ppm and 2.54 ppm, respectively, in Crosswise Lake; and 8,330 ppm and 0.77 ppm. respectively, in Peterson Lake (maximum acceptable concentrations for aquatic life are 50 ppm and 0.100 ppm, respectively). A Contaminated Substrate Assemblage (l), dominated by Centropyxis aculeata (2 = 27.5%), Centropyxis constricts (E = 13.5%), and Areella vulgaris (f = 9.7%), characterizes the most heavily polluted parts of the lakes. Centropyxids, known to be opportunistic and capable of withstanding hostile conditions, become less dominant in hiofacies found in substrates characterized by progressively less mine tailing contamination (Mine Tailings Assemblage [Z], Muddy Substrate Assemblage [3], and Diatom Mud Assemblage [4]). Unpolluted Gillies Lake was not comparable with Crosswise or Peterson lakes as a pronounced thermocline results in significantly different limnological conditions (i.e., very low bottom temperatures and oxygen concentrations) in that lake. The presence of a Cucurbitella tricuspis (i = 90.3%) dominated fauna (Transported Fauna Assemblage 1.51) in most Gillies Lake samples is enigmatic as no significant populations of Spirogyra spp., the algae with which the partially planktic Cucurbitella tricuspis has a symbiotic relationship, have been observed. We suspect that Assemblage 5 is allwhthonous. The results of this pilot study indicate that arcellaceans are useful not only to monitor environmental pollutants hut to assess rates of lake remediation.