15 
In this region, the use of land for permanent pasture served to reduce 
siltation, as erosion from the cultivated slopes surrounding potholes was 
considerable while erosion from pasture land was apparently slight. Siltation 
was apparently a minor factor in the potholes themselves, The dense growth 
of weeds, grasses, and moist-soil plants served to trap even the great amounts 
of soil washed from the cultivated slopes by the exceptionally heavy rain of 
July 28. At this time, silt was found as deep as 8 inches surrounding some of 
the potholes; yet it had not penetrated more than a foot into this border of 
vegetation, and only potholes Nos. 20 and 33 were found to be perceptibly 
roiled. 
Since there was a possibility that siltation was greater in other years, 
the bottoms of those potholes which were cover-mapped were rated as firm or 
soft, Suprisingly enough, most of the firm bottoms were Type Al, although 
each type was represented by at least one firm and one soft bottom. Apparently, 
neither siltation nor turbidity is an important factor. 
Disturbance of the vegetation was apparently the most important influence 
of grazing. Wherever sedge was available to livestock, it was readily consumed. 
Whitetop, with the exception of cases where it grew as sparse stands with coarse 
stems in the deeper waters, was apparently as readily eaten. Other emergent 
vegetation was not disturbed unless upland forage became scarce as in the case 
of pothole No. 25, Thus sedge and whitetop were either weakened or destroyed 
under constant grazing, 
Reeve (1949), in a study of the muskrat marshes of Manitoba, found that 
sedge (probably Carex rostrata) was able to crowd out other emergents owing to 
its extensive root system. On the Minnedosa study area, Whitetop apparently 
competed on an equal basis with sedge and, if left in an undisturbed condition, 
these two species were able to crowd out other emergents. When a pothole was 
grazed or trampled, these species were eaten by cattle and either retarded in 
their development or removed so that a bare area was created, This not only 
allowed cattail and bulrush to spread by rhizome growth, but permitted sexual 
reproduction of these species during times of low water. 
Muskrats <-- These aninals cut a fairly large amount of sedge and whitetop 
late in the summer and may have been largely responsible for the small clumps 
of cattail and bulrush growing on the Type Al potholes, They removed the 
cover at the time when the waters would normally have been receding, leaving 
bare mid flate suitable for germination of cattail and bulrush seeds, No 
seedlings of cattail or hardstem bulrush were seen during the summer of 199, 
probably because of the heavy rains in late July which raised the water levels 
and prevented the exposure of md banks. 
Mowing —- This practice as observed in 199 affected only vegetation 
growing on moist soil and did not greatly disturb the potholes, Spikerush 
and rush were able to attain temporary dominance of the mown area, but were 
soon replaced by whitetop and sedge which recovered rapidly after a single 
cutting. In drier years the entire pothole is often mown, and the effect 
might be more pronounced. 
- Since all burning observed on the study area was done in the 
fall o » this practice resulted in conditions similar to those produced 
by mowing and was not seen to affect plants growing in the water; whitetop 
and sedge became reestablished early the following spring. 
Relative Age -- All potholes on the study area were presumably formed 
within the same period and have experienced the same climatic changes since 
formation. 
