Arcellaceans as Pollution Indicators in Mine Tailing Contaminated Lakes near Cobalt, Ontario, Canada

Abstract

Six assemblages resulting from Q-mode cluster analysis of 27 arcellacean taxa in thirty-nine sediment-water interface samples collected from two small lakes heavily polluted by mine tailings near the town of Cobalt, northeastern Ontario, Canada, correlated well with various distinct polluted and remediated environments. Results of R-mode cluster analysis indicated that arcellacean strains within the same species often discriminate between environments, thus utilization of infraspecific categories increases resolution when studying lake microenvironments, pollutants, and rates of lake remediation. Results of this study suggest that successful lake remediation in these and similarly polluted lakes is best achieved by leaving the tailings undisturbed to be buried naturally, or to speed the process by addition of an allochthonous sediment cap. INTRODUCTION Arcellaceans (thecamoebians) are freshwater protozoans that form agglutinated tests. They occur abundantly in Holocene lacustrine sediments (Medioli and Scott 1983; Scott and Medioli 1983) and have been successfully used to reconstruct Pleistocene-Holocene lacustrine paleoenvironments (Patterson et al. 1985; McCarthy et al. 1995). Most previous investigations have been of a reconnaissance nature and primarily concerned with the determination of occurrences, and ranges in different environments (Patterson et al. 1996). However, recent research of lakes in Canada and Italy has demonstrated the use of arcellaceans as an excellent indicator of pollution levels (Collins et al. 1990; Asioli et al. 1996; Patterson et al. 1996). For example, Patterson et al. (1996) have demonstrated the relationship between the distribution of arcellacean faunal assemblages and heavy metal pollutants (arsenic and mercury) in tailings in northeastern Ontario lakes. In addition, Asioli et al. (1996) have also conducted similar studies in Italy on acidic lakes polluted with copper and ammonium sulphates. These studies indicate that different arcellacean species appear to be influenced by the metal pollutants from mine tailings and they may indicate certain environmental parameters. Although ecological stresses on various arcellacean species have not been investigated thoroughly, some have been shown under laboratory conditions to vary in their gross morphology (strain) when under environmental duress (Medioli et al. 1987). Asioli et al. (1996) confirmed these laboratory results in the field when they recognized distinct morphotypic variations within three species of arcellaceans to characterize distinct paleoenvironments. As a result of these studies, the importance of investigating the distribution of strains of different arcellacean species was realized. Cobalt, Ontario is a prime example of an area heavily contaminated by tailings and waste by-products of silver mining (Patterson et al. 1996). In 1911, when silver mining in Cobalt was at highest levels of production, annual silver production exceeded 850 metric tons per year which easily made Cobalt Camp, as it was then known, the world's largest producer of the metal (Murphy 1977). An unfortunate legacy of this exploration is the millions of tons of mine waste and tailings that were dumped into nearby lakes and streams which, in addition to being detrimental to the surrounding environment, pose a great residual health risk to the 10,000 current residents of the Cobalt area. Most problematic is the arsenic associated with the silver ore, which ended up in the tailings, and the mercury and cyanide used in the ore milling process (Dumaresq 1993). We have observed several distinctive strains within the arcellacean populations of Crosswise and Peterson lakes (text-figure 1). These strains have developed in response to different environmental stresses and stimuli, such as the presence of chemical pollutants in the substrate and low oxygen levels. These morphotypic, or infraspecific, names are not considered valid under the International Code of Zoological Nomenclature (ICZN) and thus we use them in an informal sense. To avoid confusion where possible we have derived our morphotypic names from published literature. In most cases, what we consider strains of the same species have been described at various times as separate species. The purpose of this research is to increase our understanding of arcellaceans as environmental and pollution indicators by correlating these morphotypes with the geochemical environment (affected by mine tailings), bathymetry, organic content, and bottom sediment type (Table 1).