Master of Science
Environment and Sustainability
Moser, Katrina A.
Submerged macrophyte communities are an important component of lake ecosystems that can be altered by anthropogenic disturbances. In the absence of direct monitoring, it is difficult to know how these communities respond to such disturbance. This thesis investigated the potential of epiphytic diatoms preserved in lake sediments to record submerged macrophyte community composition. Epiphytic diatoms from Chara sp., Myriophyllum spicatum and Potamogeton robbinsii were sampled from Gilmour Bay, Ontario, Canada to assess whether submerged macrophyte species were characterized by distinct diatom communities. Principal components analysis indicated overlap, but analysis of similarity suggested there were differences in diatom community composition. A tool was developed and applied to Gilmour Bay nearshore sediment samples to reconstruct past submerged macrophyte community composition, but reconstruction was hindered by abundant in situ epipelic and epipsammic diatoms. This research shows that differences in epiphytic diatom communities offer new opportunities for paleolimnological reconstructions.
Summary for Lay Audience
Aquatic plants are important in lakes, helping to maintain clear water and reduce algal abundance by uptake of nutrients. Invasive aquatic plants (i.e., those that do not naturally occur in the lake) can be introduced from boat traffic or household aquariums and potentially replace native plants causing a shift in the aquatic plant community. Changes in the aquatic plant community can affect nutrient availability (i.e., nitrogen and phosphorus) in the lake since not all plants use nutrients the same way. Knowing how the aquatic plant community has changed over time can therefore help to understand changes in nutrient availability and consequential changes that occur in lake ecosystems. Unfortunately, direct long-term monitoring of aquatic plants is rare. One way to solve this problem is to study sediment (i.e., mud) records collected from the bottom of lakes. New sediment is deposited on top of older sediment, creating an archive that can span thousands of years. Preserved in sediment are fossils of organisms that inhabited the lake when the sediment was deposited, acting as a snapshot of environmental conditions from that time. Some of these fossils are potential indicators of aquatic plant communities.
This research explored how diatoms (a type of microscopic algae found in almost all lakes and well preserved in lake sediments) that live on aquatic plants could be used to track changes in aquatic plants over time. Samples from three aquatic plants, including one invasive species, were collected from Gilmour Bay, Ontario, Canada, and their diatom communities studied. The results identified that the diatom community living on different aquatic plants can be differentiated, although there is overlap among plants. Using this knowledge, an attempt was made to identify the historic aquatic plant community from diatoms preserved in sediment using key diatoms associated with specific aquatic plants. Unfortunately, in the sediment samples collected, diatoms living directly on the sediment overwhelmed the diatoms from aquatic plants, making it difficult to assess the historic aquatic plant community. However, the technique showed promise, and this research provides the foundation for future research aimed at using fossil diatoms to track changes in aquatic plant communities.
Zilkey, David Rawn, "An Investigation of Epiphytic Diatom Substrate Specificity and Its Use in Paleolimnology" (2021). Electronic Thesis and Dissertation Repository. 7618.
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Available for download on Sunday, January 01, 2023