Assessment of the effects of logging, forest fires and drought on lakes in northwestern Ontario: a 30-year paleolimnological perspective

Abstract

The frequency and intensity of large-scale watershed disturbances (e.g., clearcuts and wildfires) is increasing in northwestern Ontario. Timber harvesting and wildfires have been shown to alter water quantity and quality in stream ecosystems. Unfortunately, scientific studies of these impacts on lakes are considerably rarer. Using paleolimnological techniques, we examined the remains of scaled chrysophytes in sediment cores from four lakes that have had the majority of their watersheds clearcut, two lakes that have had large forest fires in their watersheds, and two lakes that have had minimal watershed disturbance. Lakes in this study showed minor changes in the composition of scaled chrysophytes at a temporal resolution of 2-4 years, despite removal of over 90% of the forest. Furthermore, temporal variability in the species assemblages were similar in all lakes. A gradual change in the species assemblages of all lakes suggested a regional influence may have been responsible. We hypothesize that hydrological changes brought about by a regional drought from 1970 to 1990 may have exerted an overriding influence on lakes over this time period.