Design of Studies in Evaluating Effects of Mining on Aquatic Ecosystems

The effects of land-disposed mine tailings at an abandoned gold mine in British Columbia, Canada, were assessed in a multidisciplinary study. During heavy rains and spring snowmelt, the tailings became severely eroded with subsequent transport of As, Pb, Cu, and Zn into adjacent lake. The locations of the sampling stations in the multidisciplinary study were selected with respect to the location of anticipated point-sources of the trace elements and to the studies of individual components of the lake’s ecosystem (Figure 1). It was found that Pb in the tailings was mainly associated with particles 23 urn (up to 2,000 ug/g As). The association of Pb and As with different particle size in the tailings affected the distribution of Pb and As in bottom sediments in the lake. The concentrations of Pb in the sediments were similar within the lake due to the transport of the fine-grained particles across the lake. However, the concentrations of As were considerably greater in the sediments along the shore with the land-disposed tailings. The results of the study showed that the bioavailability of some trace elements in the sediments was greatest along this shore than in the remainder of the lake. There was evidence that the tailings inhibited a variety of microbial activities including enzyme functions, CO2 production, etc. The degree of inhibition of the microbial activity increased with the abundance of bioavailable Cu and Pb in the sediments. No effects on the benthic community in the lake were observed during the study. There was some indication of reduced overall numbers of benthic species along the shore with the disposed tailings. The results of the study indicated the heterogeneity of sediment geochemistry in the 1.5-km2 large lake, and suggested the importance of proper sampling design and control areas in studies involving point-sources of contaminants, such as in studies of effects of mining (and, most likely, other industries) on aquatic ecosystems.