Legacy effects of historical gold mining on chironomid assemblages from Gegogan Lake, Nova Scotia

Abstract

Historical gold mining in Nova Scotia (NS), Canada, began in the 1860s, and released contaminants into the environment through tailings that were transported by wind and surface waters. I investigated the remains of benthic invertebrates and geochemical proxies archived in the sediment of a shallow lake downstream from the province’s most productive historical gold mine. Sedimentary concentrations of metal(loid)s were used to determine mining inputs of tailings as well as establish the pre-mining and post-mining time periods within the lake sediment record. Chironomid assemblages were assessed as an ecological response to long-term environmental changes. Total mercury levels peaked at six times above the sediment quality guidelines, and arsenic concentrations peaked at 165 times. Sedimentary contaminants have declined but remain above probable effect levels. There was a significant difference (p = 0.001) in assemblage compositions between the pre-mining and post-mining time periods. There were seven indicator taxa in the pre-mining and three indicator taxa in the post-mining period. In the pre-mining time period, there was an average of 1448 ± 186 chironomid head capsules per gram of sediment which declined to an average of 355 ± 257 per gram in the post-mining time period. The relative abundances of several metal(loid) tolerant chironomid taxa have increased in the post-mining period. For example, during the pre-mining period Constempellina was present at an average of 5% abundance and increased to 12% abundance post-mining. Findings from this study show that pollution from historical gold mining continues to make its way into and negatively affect the benthos of Gegogan Lake