Geoscience Reference
In-Depth Information
Figure 16-28.
Shallow pond and marsh occupy a typical pothole in hummocky terrain of the Missouri Coteau
southwest of Moose Jaw, Saskatchewan, Canada. Photo by J.S. Aber.
780,000 km
2
) and including millions of
wetlands (Larsen 1991). Potholes of all sizes
and shapes may contain shallow ponds, saline
lakes, marshes, wet meadows and fens, and
their density may reach 60 per km
2
(Dugan
2005). Known as the “duck factory” of North
America, this region plays a vital role for water-
fowl breeding. Other pothole functions include
recharging ground water, storing l ood water,
absorbing nutrients, forming habitats for diverse
l ora and fauna, and providing water and forage
for domestic livestock.
Throughout much of this vast region, many
wetlands have been drained and converted for
crop agriculture. The Missouri Coteau region of
southern Saskatchewan, however, has retained
a substantial proportion of its natural habitats
(Dugan 2005). Several reasons explain the
restriction of agriculture and preservation of
coteau wetlands, including semi-arid climate
that limits soil moisture, general lack of surface
and ground water sufi cient for irrigation, and
locally hilly landscape that inhibits mechanized
cropping (Fig. 16-28). The Missouri Coteau is in
the mixed-grassland ecoregion with mean July
temperature of 19 °C, mean January temperature
about
∼
miles (
up along the edge of the coteau by glacier
advances, which created steep, hilly landscapes
(Fig. 16-29). Other conspicuous glacial land-
forms include hummocky moraine, melt-water
spillway valleys, outwash plains, and proglacial
lake basins. Wetlands are found in several geo-
morphic settings:
• Small potholes of irregular size and shape
situated between ice-shoved ridges and in
swales of hummocky moraine. These are
particularly numerous, for example in the
Dirt Hills, and vary from shallow ponds to
overgrown marshes and wet meadows (Fig.
16-30).
• Kettle holes in outwash plains. Kettle holes
mark places where blocks of stagnant glacier
ice were buried by sand and gravel depos-
ited from meltwater rivers. When the ice
later melted, deep basins were created with
steep sides. A good example is Lake Oro,
located in the outwash plain south of the
Dirt Hills (Fig. 16-31).
• Long, narrow, shallow lakes, known as
ribbon lakes, that occupy spillway valleys
such as Lake of the Rivers. This spillway
carried glacial melt water from the Dirt Hills
and Cactus Hills as well as overl ow from
the proglacial lake that occupied Old Wives
basin. Nowadays the valley contains a series
of shallow lakes and marshes during wet
years (Fig. 16-32).
• Broad, shallow lakes that occupy former
proglacial lake basins. Proglacial lakes were
dammed between the ice sheet to the north
−
13 °C, and annual water dei cit greater
than 0.5 m (Padbury and Acton 1994).
The Missouri Coteau is a prominent northeast-
facing escarpment that extends from North
Dakota across southern Saskatchewan. The
coteau is a bedrock feature resulting from pre-
glacial erosion and subsequently modii ed by
repeated glaciations (Aber and Ber 2007). In
particular, large ice-shoved ridges were thrust
