ALGAL MICROFOSSILS PROVIDE HIGH TEMPORAL RESOLUTION OF ENVIRONMENTAL TRENDS

Sedimentary chrysophytes and diatoms from Baby Lake (Sudbury, Canada) were analyzed to assess lakewater trends associated with (i) the commencement of metal mining and smelting activity at the Coniston Smelter in 1913, and (ii) the closure of the smelter in 1972. We reconstructed several environmental variables (i.e. pH, total [Al], and [Ni]) by applying weighted-averaging regression and calibration models to our paleolimnological data. As a result of emissions from the Coniston Smelter, the lake started to acidify from a high pH of about 6.5 in 1940 to a low pH of 4.2 in 1975. During this period, inferred lakewater [Al] and [Ni] also increased dramatically. Following the closure of the smelter in 1972, inferred lakewater pH and metal concentrations recovered close to pre-industrial levels. The inferred pH recovery corresponds closely to the known lakewater pH recovery (a difference of about 0.4 and 0.6 of a pH unit was observed between measured pH, and chrysophyte and diatom-inferred pH, respectively). Our study demonstrates that algal microfossils can provide high resolution inferences of past environmental trends. This approach holds great potential for documenting a lake's response to decreased loadings of sulphate and metals, and in helping to establish and implement emission standards.