Multi-proxy paleoenvironmental record of colonial land-use change in the lower Rideau Canal system (Colonel By Lake), Ontario,Canada |
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| Authors: | E P Sonnenburg J I Boyce E G Reinhardt |
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| Institution: | (1) School of Geography and Earth Sciences, McMaster University, Hamilton, ON, L8S 4K1, Canada |
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| Abstract: | The construction of the Rideau Canal was one of the greatest engineering accomplishments of the nineteenth century, creating
a navigable waterway linking the Ottawa River with Lake Ontario. Colonel By Lake, located at the southern end of the canal
near Kingston Mills, was created by the damming of the lower Cataraqui River. The canal flooding in 1831 raised water levels
by almost 8 m, inundating former wetlands and lowland areas. European settlement in the pre-canal-era (ca. 1780s) was associated
with widespread deforestation and limited flooding of wetlands by construction of mill dams. A detailed sediment coring program
was conducted in Colonel By Lake to reconstruct the pre-canal environment and to document water level and land-use changes
associated with European settlement and canal construction. The paleoenvironmental record was obtained through analysis of
multiple environmental indicators including sediment facies, particle size, magnetic susceptibility and downcore changes in
testate amoebae (thecamoebian) diversity. The core lithostratigraphy consists of organic-rich muds overlying peaty gyttja
and a lowermost unit of fine to coarse silts. 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 high numbers of Difflugia oblonga and Cucurbitella tricuspis that indicate a shift to a deeper and more eutrophic environment. In contrast, the pre-canal environment has lower thecamoebian
abundance with assemblages characteristic of marsh environments (Centropyxis constricta, Centropyxis aculeata). The onset of canal flooding (ca. 1790s) is identified by an increase in Pontigulasia compressa (~50 cm), recording a higher water flow rate. The study shows that a multi-proxy paleoenvironmental approach can clearly
define different environmental changes due to land-use changes during colonisation and canal-era construction activities. |
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