| dc.description.abstract | Anthropogenic stressors such as urban development, agricultural practices and industrial activities are a growing concern throughout the Muskoka River watershed of Ontario, Canada, because they can alter physical, chemical and biological conditions of aquatic ecosystems. Cumulative effects of multiple stressors are often difficult to anticipate based on what is known about the individual effects of each stressor acting in isolation; thus, it is important to track cumulative effects on ecological integrity of our aquatic resources. Periphytic diatoms have potential to serve as an early indicator of ecological degradation in aquatic systems. Within the Muskoka River watershed there is a need to maintain the perceived naturalness of the region as it is a key driver of the tourism based economy. This thesis examines relations between diatom community composition, water chemistry and the abundance of anthropogenic stressors within the Muskoka River watershed and uses these relations to develop a bioassessment framework for tracking changes in biological integrity within lakes of the South Muskoka River Watershed. To do this, 86 lakes were examined to assess relations between diatom community composition, water chemistry and measures of nine anthropogenic stressors based on analyses by GIS. These relations were assessed using a combination of univariate and mulitvariate statistical methods. Composition of periphytic diatom communities was found to be associated with the concentration of ions from anthropogenic sources (i..e, application of road salt and dust suppressants), but relations became weaker at sites with a low abundance of anthropogenic stressors due to confounding influence of lake-water pH.
Relations between periphytic diatom community composition and anthropogenic stressors were sufficiently strong to permit development of bioassessment indices for the evaluation of ecological degradation at a watershed-scale. Multiple variations of two primary indices (Eastern Canadian Diatom Index (IDEC), Index of Biological Integrity (IBI)) were developed and assessed to identify the best index for evaluating biological integrity of lakes. To reduce the cofounding influence of pH at low levels of stressors, the indices were developed separately for acidified lakes (pH 5.23-6.45) and circumneutral lakes (pH 6.52-7.47). IBI-3-Acidified and IBI-3-Circumneutral, which are based on a continuous IBI method, were found to be the best indices to assess lakes across the watershed. However, IBIs make use of only a small number of ‘indicator’ taxa, and as a result, may encounter no-analogue situations when applied to some lakes. Consequently, use of IBI-3-Acidified and IBI-3-Circumneutral is recommended for assessment of lakes within the Muskoka River watershed. But we suggest that the IDEC also be included as a backup in lakes where the IBI-3 index encounters no-analogue situations. Advantages of the use of periphytic diatom-based bioassessment protocols are presented in the thesis. By increasing ecological monitoring capacity, management agencies will be better prepared to avoid or mitigate cumulative effects of ever-evolving stressors. | en |
