Using diatoms to track road-salt seepage into small, shallow, softwater Ontario lakes

Abstract

Since the 1950s, the widespread application of road salt for winter road maintenance and safety in cold regions has led to increased conductivity levels in many freshwater systems. Salting practices have adversely affected freshwater biota; however, the magnitude of ecological impacts may vary by species and ecosystem. Here, we examine diatom assemblage changes during the past ~200 years from sedimentary records from five impacted lakes (measured specific conductance values of 149 – 350 S/cm) and a reference lake (15 S/cm) located in the Muskoka River Watershed, south-central Ontario, Canada. Diatom compositional changes in the road-salt impacted sites were consistent with increasing conductivity and increased diatom-inferred conductivity was evident during the latter half of the 20th century, concurrent with known road salt application. The strongest predictor of DI-conductivity changes among the six lakes was the km equivalents of roads within the watershed (i.e. km of road x # of lanes). Similar to changes observed in a previous study focussing on cladoceran assemblages, we conclude that even modest applications of road salt have affected diatom assemblages in softwater lakes in south-central Ontario.