LAKE THECAMOEBIANS (TESTATE AMOEBAE) AS INDICATORS OF WATERSHED DISTURBANCE: CASE STUDIES FROM THE GREATER TORONTO AREA, ONTARIO, CANADA

Thecamoebians are unicellular protozoans that are useful for paleoenvionmental reconstruction because they are sensitive to a wide variety of environmental variables. In lakes, faunal assemblages can be correlated with many environmental parameters including substrate changes associated with forest fires, de-forestation and land clearance, eutrophication, temperature change, salinity, pH and metal and organic pollutant contamination. We examined thecamoebians from 71 surface sediment samples collected from 21 lakes and stormwater management ponds in the Greater Toronto Area (GTA) and surrounding region to i) elucidate the controls on faunal distribution in lake environments; and ii) to consider the utility of thecamoebians in quantitative studies of water quality change. This area was chosen because it includes a high density of lakes that are threatened by urban development and where water quality has deteriorated as a result of contaminant inputs, particularly nutrients. Canonical Correspondence analysis (CCA) and a series of partial CCAs were used to examine species-environment relationships. Twenty-four environmental variables were considered, including water properties (e.g. pH, DO, conductivity), substrate characteristics, nutrient loading, and environmentally available metals. Thecamoebian assemblages showed a strong association with sedimentary (Olsen’s) Phosphorus (OP), reflecting the eutrophic status of many lakes. A transfer function was developed for OP using this training set based on weighted averaging with inverse deshrinking (WA Inv). The model was applied to infer past changes in OP enrichment in core samples from several lakes, including eutrophic Haynes Lake within the GTA. Thecamoebian-inferred changes in OP from a 210-Lead dated core from Haynes Lake are related to i) widespread introduction of chemical fertilizers to agricultural land in the post WWII era; ii) a steep decline in OP with a change in agricultural practices in the early 1980s; and iii) the construction of a nearby golf course in 1993. This study confirms that thecamoebians have considerable potential as quantitative indicators of eutrophication and catchment disturbance in lakes and may provide an effective tool for appraising water quality and ecological restoration initiatives in lake catchments.