DEVELOPMENT OF A ROAD SALT CONTAMINATION INDEX UTILIZING THECAMOEBIANS (TESTATE AMOEBAE)

Thecamoebians are testate amoebae, which have been demonstrated to be useful paleoenvironmental indicators in lacustrine settings. As they preserve well in sediments they can provide a temporal record of environmental change. We have assessed their utility as bio-indicators of road salt contamination in lakes, and applicability to development of a quantitative tool for salt monitoring that can be applied in a region with a known and significant history of road salt damage: watersheds within the Greater Toronto Area (GTA) where chloride contamination levels in lakes adjacent to roads can range up to 1200 mg/l. Road salt contamination is particularly high in a several km-wide swath adjacent to 400-series highways where on average over 220 tons per km are applied per winter in contrast to the 30 tons per 2-lane km applied to regional roads. To quantify the relationships between thecamoebian assemblages and habitat, a series of key road-salt related water property and sediment-based geochemical variables (e.g. conductivity, Na, Mg and Cl ions) were measured in selected GTA lakes where significant groundwater contamination has been sustained, and from non-impacted control sites. Detrended Canonical Analysis (DCA) and Q-R-mode cluster analysis of thecamoebian assemblages from 70 stations in 15 lakes resulted in recognition of four groupings associated with: 1) control lakes with no road salt influence; 2) salt influenced lakes with nutrient enrichment; 3) lakes with spatial salt gradients; and 4) roadside lakes primarily influenced by road salt. These preliminary results form the basis of a larger-scale study presently under way to develop a thecamoebian-derived ‘Road Salt Contamination Index’ (RSCI) that can be readily applied to lacustrine sediments in this and other regions to categorize salt damage, providing a time-averaged signal of salt contamination spanning several seasons. The larger training set will provide the basis for development of a quantitative model (transfer function) for salt contamination that can be applied to fossil thecamoebian assemblages preserved in lake sediment cores. This research will permit elucidation of the timing, scale and impacts of inferred salinity changes during the last century, and to delimit pre-disturbance conditions, which are integral for future remedial efforts.