Using Paleolimnology to Assess Long-Term Environmental Changes in Lakes from Killarney Provincial Park and Sudbury, Ontario, Canada

Abstract

For over a century, Sudbury in northeastern Ontario (Canada) was a major source of sulphur dioxide and other pollutants, degrading terrestrial and aquatic ecosystems in the surrounding region. In the 1970s, emissions were drastically reduced due to concerns over widespread environmental damage from smelting operations. Killarney Provincial Park (KPP), located ~60 km southwest of Sudbury, was also impacted by Sudbury smelting emissions, but little is known about how present-day conditions relate to pre-industrial conditions or the effects of climate change. I used a multi-proxy paleolimnological approach to examine ecological change in five lakes over the past ~200 years in Sudbury (Baby, Tillie, and Crooked lakes) and KPP (Ruth-Roy and Johnnie lakes). My overall goals were to: (1) infer past ecological conditions from diatom assemblages, whole-lake chlorophyll-a (Chl-a) and lakewater dissolved organic carbon (DOC) concentrations; (2) explore patterns of potential acidification recovery over the past several decades; and (3) compare my changes to recent monitoring and meteorological data. Distance from smelting operations, in combination with physical lake characteristics (i.e., water residence time, local geology), likely contributed to differences in the magnitude of change observed in the paleolimnological indicators. In general, the acidification period was characterized by declines in small circumneutral taxa (i.e., Discostella spp., Achnanthidium spp., and Aulacoseira spp.), as well as inferred chl-a and inferred DOC, concurrent with increased abundances of acidophilic diatoms (i.e., Fragilariforma acidobiontica, Eunotia spp., Tabellaria flocculosa and Asterionella ralfsii). After ~1970, only limited recovery in diatom assemblages was recorded, although inferred DOC and chl-a levels increased, indicating biological recovery is lagging chemical recovery and/or that the ecological trajectory has been influenced by large-scale environmental changes. Given the impacted nature of my study lakes, a clear climate signal in the recent diatom assemblages was not as evident as often noted in pristine Boreal Shield lakes. This study provides a thorough, up to date, multivariate analysis of selected study sites. This study further confirms the need for case-by-case consideration of lakes' status and highlights the importance of conducting multi-variate studies using long term data. While demonstrating the importance of understanding the past to better assess ecosystem recovery and future ecological trajectories.