A Reconstruction of Post-Glacial Hydroclimatic Change and Mass Accumulation Rates from a Small Watershed of the Lower North American Great Lakes Region
Abstract
The effects of anthropogenic climate change have been felt globally in the form of droughts and floods, which have adverse impacts on society. Regional watersheds experience these hydrologic impacts through changes in the quantity and quality of water resources as well as geomorphic changes that modify the stability of the landscape. Records of past environmental change contained in sedimentary archives can be used to better understand the sensitivity of watersheds to changes in hydroclimate and predict responses to future changes. This study reconstructs environmental change over the late Pleistocene and Holocene epochs from Barry Lake, a small watershed in south-central Ontario, Canada.
A reconstruction of lake level from sedimentary evidence over the last ~14,700 cal years illustrates numerous fluctuations over a range of 3.5 m that reflect changing hydroclimatic conditions. Four lowstands of at least 1.5 m below the modern lake level are recorded, which were caused by some combination of reduced warm-season precipitation, reduced cold-season precipitation, and increased evaporation. Changes in seasonal moisture amounts were driven by variations in the shape and latitude of the Polar jet stream, which dictated atmospheric circulation patterns. During the late Pleistocene to early Holocene, the Laurentide Ice Sheet forced the jet stream south, resulting in reduced precipitation. Following the ice sheet collapse, declining summer insolation as well as interactions between the atmosphere and ocean basins led to variable circulation patterns and moisture conditions. Mid- to late Holocene lowstands are believed to have been caused in part by reduced summer moisture associated with the negative phase of the Pacific-North American teleconnection and/or the positive phase of the Atlantic Multidecadal Oscillation.
Reconstructions of organic, carbonate, and siliciclastic mass accumulation rates show an overall insensitivity to climate change. Primary productivity was steady throughout the post-glacial period until European settlement led to eutrophication. Similarly, catchment erosion was high following European settlement as well as during the late Pleistocene. This study demonstrates that vegetation cover buffered the catchment from the effects of climate change and that, although water quantity in Barry Lake is sensitive to hydroclimatic change, anthropogenic activity dictates water quality and overall watershed health.