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.