ABSTRACT: Determining anthropogenic impacts on kettle lakes in Southern Ontario (Canada) using a paleolimnological approach.

CGRG Bibliography of Canadian Geomorphology
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Abstract

Southern Ontario landscapes have changed due to European agriculture and deforestation (circa AD 1840), and more recent urbanization. It is uncertain how these different landscape changes have impacted aquatic ecosystems. We present high-resolution sediment records documenting the impacts of ~170 years of human disturbance on two southwestern Ontario lakes. North Pond (London Ontario) is a small (9.4 ha), deep (max depth = 20 m), urban, kettle lake and Edward Lake (Collingwood Ontario) is a larger (29.3 ha), shallow, (max depth = 5 m) lake. Two gravity cores (length ~ 50 cm) were retrieved and sub-sectioned at continuous, 0.5 cm intervals. Based on 210Pb dating each interval represents ~1 to 3 years. A minimum of 600 diatoms were enumerated and identified in each sample. Principle Components Analysis (PCA) was used to interpret the diatom data and enabled comparisons of changes in diatom community composition to instrumental temperature records. Sedimentary chlorophyll a and loss-on-ignition were also measured to track changes in in-lake primary production and erosion. Our findings suggest that diatom community compositions have changed in response to anthropogenic disturbances. In North Pond high quantities of sponge spicules and chrysophyte cysts in pre-European (before AD 1840) samples suggest clear, oligotrophic waters. A distinct increase in chlorophyll a shown at both lake sites is consistent with increased productivity following the onset of European settlement. More recent (circa AD 1970) changes are linked to increased roads due to urbanization. Despite these marked changes, preliminary evidence suggests that recent warming is also impacting these ecosystems.

Bibliography of Canadian Geomorphology