Post-glacial development of a kettle-hole peatland in southern Ontario

A kettle-hole peatland in southern Ontario was examined in a two core, multi-component paleoecological study to determine the relative importance of external and internal factors in its long-term development. Dated sediment stratigraphies, loss-on-ignition, macrofossils and diatom assemblages from two cores were used to infer hydroseral changes within the basin, while pollen assemblages from one core were used to infer surrounding forest succession. A circumneutral to slightly alkaline lake occupied the basin at 11 750 years BP after the melting of an ice block. Changes in diatom assemblages and loss-on-ignition in the early lake indicate fluctuating limnological conditions, but their exact nature is unclear. At 8200 years BP, limnological conditions in the centre of the basin stabilized to circumneutral to slightly alkaline, moderately hard waters following sediment accumulation and macrophyte growth at the edge of the basin. The water level declined 7 m by 5600 years BP, and following a return of higher water levels at around 5200 years BP, a fen mat formed around the edges of the basin, isolating the remnant lake from alkaline influences. An uncharacterized, basin-wide shift occurred at 2800 years BP, possibly as a result of a water level change. At 600 years BP, the floating fen mat advanced over the centre of the basin, and after 1830 AD, a Sphagnum-dominated floating mat was formed. Changes in basin infilling and vegetation succession coincide with regional vegetation succession, indicating that external forcing factors initiated these hydroseral chances. External factors include climate change at around 8200 years BP, 5600 years BP, 2800 years BP and 600 years BP and land clearance after 1830 AD. They appear to alter hydrological characteristics in the basin, especially water level and the resultant connection to surrounding calcareaous waters. This study demonstrates the sensitivity to external influences of these kettle-hole peatlands with floating mats. Paradigms on their development should be revised to take this sensitivity into account.