Middle to Late Holocene paleoenvironments in a Great Lakes coastal wetland, Rondeau Provincial Park, Ontario, Canada

This study evaluates the factors that have constrained wetland development since the middle Holocene at a Great Lakes coastal marsh. Peat stratigraphies were examined in the two major depositional environments at the Lake Erie field site. A series of short cores from the geomorphically dynamic Rondeau spit provided a 2200-year record in which the construction of storm beach ridges, providing protected backshore environments, is a fundamental control on wetland development. Century-scale Lake Erie transgressions, however, acted to restart it episodically. Longer peat records were obtained from the head of Rondeau Bay, extending to the Nipissing Highstand 4200 radiocarbon years before present, during which time a diatom-rich Zizania marsh existed. Following the Nipissing Highstand, this community was replaced by a shrub dominated swamp at one core location and a fern dominated marsh at another, located less than 1 km to lakeward. Taken as a whole, the peat records from Rondeau show evidence for post-Nipissing Lake Erie transgressions at approximately 2200, 1300 and 750 radiocarbon years before present. Correspondence analysis is used to compare fossil and modern proxy indicator spectra and to illustrate the reduction in community diversity that has occurred since European settlement. The paleoecological records show long periods of stasis in wetland plant communities and do not contain any evidence for the autogenic processes specified in the traditional hydrosere model. The study concludes that geomorphic activity and hydrological change, controlled by climate as well as crustal movement, interact with autogenic processes that take the form of ecological community dynamics, to result in the diverse wetland complexes that have existed at the study site since the middle Holocene. The thesis also demonstrates techniques to identify pollen grains of the common wetland dominant Typha and presents data on the modern pollen rain and diatom assemblages across the study site, showing that the wettest sites dominated by Zizania aquatica are the most distinctive palynologically and in terms of diatom assemblages. A species-specific approach was used to show low pollen production relative to plant abundance in Phragmites, Sparganium and Typha. Cephalanthus and Zizania produce large amounts of pollen, which in Cephalanthus, is deposited locally.