Impacts of historical gold mining on chironomid assemblages in lake Thomas, Nova Scotia.

Abstract

Gold mining operations were one of the predominant economic activities in the Waverley Gold District between the 1860s and 1940s. The mine tailings produced were transported into the local environment and likely contributed to pollution of the Shubenacadie Canal drainage basin. In this study, I used paleolimnological approaches to understand the long-term ecological effects of historical gold mining operations on benthic invertebrates in Lake Thomas. Sedimentary concentrations of total arsenic (As) and total mercury (Hg) were measured from a dated sediment core to track pollution history. Subfossil chironomid remains were analyzed to examine biological effects of mining pollution on the benthos. Sedimentary As and Hg levels were low prior to gold mining activities; however, during the mining era concentrations of both elements increased. Chironomid production declined by half from the pre-mining period and suggests biological impacts from historical mining pollution. Chironomid assemblage compositions between pre-mining and post-mining periods were significantly different (p<0.003). Recent sediments showed mining-related contaminants were higher than national sediment quality guidelines by ~12x for As and ~11x for Hg. Although the Waverley Gold District was closed to mining eight decades ago, elevated contaminant levels from historical mining may still be affecting the composition and production of aquatic biota associated with the benthic habitat. My research contributes to the growing number of environmental assessments that aim to understand the long-term ecological consequences of mining operations on aquatic ecosystems.