A Paleolimnological Assessment of Changes in Algal Assemblages on the St. Lawrence River at Cornwall, Ontario in Response to Local and Regional Stressors
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Authors
Moir, Katherine
Date
2024-08-07
Type
thesis
Language
eng
Keyword
paleolimnology , freshwater ecology , St. Lawrence River , diatoms , metals
Alternative Title
Abstract
The St. Lawrence River (SLR) is a large, complex fluvial system that connects the Laurentian Great Lakes to the Atlantic Ocean. A section of the SLR near Cornwall, Ontario has experienced numerous anthropogenic stressors since the mid-19th century, including pollution from waterfront industry and agricultural activity, which have impacted higher-food-web organisms. However, impacts on algal assemblages are less well understood. Recently, there has been evidence to suggest that climate-change impacts are further altering algal assemblage structure in lentic temperate, freshwater ecosystems, and it remains unclear whether similar changes are occurring large, fluvial systems. Although nutrient concentrations emanating from highly agricultural local watersheds are elevated, recent increases in cyanobacterial abundance in this section of the SLR may be attributable to a regional stressor such as the direct or indirect impacts of climate change. Additionally, other local stressors, including legacy sedimentary contamination by mercury and variations in light availability, may be influencing benthic algal community structure and need to be disentangled from potential climate signals. This thesis uses paleolimnological techniques (sediment cores, surface sediments) and spatial analyses to evaluate the impacts of sedimentary contamination, light availability, and elevated nutrient concentrations on paleolimnological proxies of algal production and assemblage structure in the SLR at Cornwall over the past century. Subfossil remains of diatoms (Class: Bacillariophyceae) were examined alongside sedimentary photosynthetic pigments and various measures of sediment geochemistry (bulk carbon and nitrogen, stable isotopes δ13C and δ15N, organic and carbonate content, and grain size) at sites along the Cornwall waterfront and in Lake St. Francis (LSF), a downstream fluvial lake. Results suggest that benthic algae on the SLR respond most strongly to changes in nutrient concentrations, although impacts of sedimentary contamination by metals are also important; climate-change impacts were not evident, though subtle site-specific effects may exist. When enough light was available to support benthic photosynthesis, variations in light availability had minimal impacts on benthic algal assemblage structure. Historical changes to industrial practices and hydrological modifications to the SLR were well recorded in the sediment cores. Overall, recent increases in cyanobacteria in LSF are likely attributable to elevated nutrient loads rather than climate-change impacts.
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Attribution-NonCommercial-NoDerivatives 4.0 International
ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.
Attribution-NonCommercial-NoDerivatives 4.0 International