PALEOENVIRONMENTAL RECORD OF COLONIAL LAND-USE CHANGES IN THE LOWER RIDEAU CANAL (COLONEL BY LAKE), ONTARIO, CANADA

Colonel By Lake, located near Kingston, Ontario, was artificially created during the building of the Rideau Canal between 1826-1831. The canal construction was one of the greatest engineering accomplishments of the 19th century, creating a navigable waterway linking the Ottawa River with Lake Ontario. The lake was formed by the flooding of the lower Cataraqui River valley, raising water levels by > 6 m and submerging sites of archaeological and historical interest. A detailed geophysical survey and sediment coring program was conducted in Colonel By Lake in order to reconstruct the pre-canal environment and water-level and land-use changes associated with canal construction. The paleoenvironmental record was obtained through analysis of sediment lithofacies, grain size, magnetic susceptibility and downcore changes in thecamoebian diversity.

The canal flooding surface (ca. 1831) is clearly defined by a shift to finer grain-sizes and increased magnetic susceptibility within the upper 40-60 cm. The shift is associated with an overall increase in thecamoebian abundance and diversity, and the high numbers of Difflugia oblonga and Cucurbitella tricuspis that indicate a shift to a deeper and more eutrophic environment. The pre-canal environment in contrast has lower thecamoebian abundance with assemblages characteristic of marsh environments (Centropyxis constrica, C. aculeata). The onset of deforestation prior to canal flooding (ca. 1790's) is also identified by an increase in Pontigulasia compressa (60-70 cm), recording the influx of eroded forest soils. The study shows that a multi-proxy paleoenvironmental approach can clearly define environmental changes due to canal flooding and land-use changes during colonization.