Holocene paleovegetation and paleohydrology of a prairie
pothole in southern Saskatchewan, Canada
Catherine Yansa
The Andrews site represents one of countless prairie potholes
found in areas of hummocky moraine on the northern Great Plains. Sediments
from a depth of 5.8 to 3.1 m at this “kettle-fill” site in the Missouri Coteau
upland of southern Saskatchewan, Canada, provides a record of vegetation,
climate, and hydrologic changes within a small, ca. 30 m diameter, closed-drainage
basin from ca. 10.2 to 5.8 ka. Plant macrofossil analyses of 67 samples,
6 14C ages, and stratigraphy were used to identify 5 zones, representing
the paleohydrological changes that followed deglaciation in southern Saskatchewan.
Results of this study indicate that with the melting of
residual stagnant ice a pond (> 2 m deep) with abundant aquatic, emergent,
and shoreline plants developed in the basin at ca. 10.2 ka and persisted
until at least ca. 8.8 ka. During this time there was a shift in upland
vegetation from a white spruce forest (Zone II) to a deciduous parkland at
ca. 10 ka (Zone III). As climate warmed, brackish and alkaline conditions
developed coincident with shallowing of the pond at the end of Zone III.
The perennial water phase ended at ca. 8.8 ka and was followed by a low-water
stand lasting ca. 1100 years. Prairie fires and slopewash from unstable
slopes were dominant sedimentological processes until ca. 7.7 ka (Zone IV).
Water levels began to rise and between ca. 7.7 and 5.8 ka a semi-permanent
pond was established in a grassland setting (Zone V). After ca. 5.8
ka this prairie pothole wetland became ephemeral, to the point that plant
macrofossils could not be preserved, a situation continuing today.
Interactions between climate change, variability in local groundwater supply,
and sedimentological processes likely account for the paleohydrologic events
reconstructed at the Andrews site.