|Benoit, George - RETIRED|
|Staricka, James - NORTH DAKOTA STATE UNIV.|
Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 25, 1999
Publication Date: N/A
Interpretive Summary: Ground water recharge in the Prairie Pothole Region primarily occurs in spring during snowmelt. We observed that frozen soil on the slopes and ridges of potholes prevented snowmelt infiltration. Instead, snowmelt runoff was channeled to the base of the pothole where it rapidly infiltrated to groundwater through seemingly large, unfrozen soil pores. Since snowmelt runoff carries both sediment and chemicals, it is likely that chemicals will enter groundwater systems from the base of potholes during spring recharge. Therefore, management methods must be adapted that will curtail snowmelt runoff and promote snowmelt infiltration on slopes and ridges within the prairie pothole landscape.
Technical Abstract: The prairie pothole is an important hydrologic component of the Prairie Pothole Region of North America. Snow cover and frozen soil affect runoff and soil water recharge, but little is known concerning their temporal and spatial characteristics across a prairie pothole. A 2 ha prairie pothole near Morris, MN was instrumented to assess snow cover, soil water, and frost depth at 11 positions across two transects that traversed the major and minor axis. Measurements were made over three winters beginning in 1990. Snow cover was deepest on the leeward side of a ridge located on the NW end of the major axis and shallowest and least variable in the bottom of the depression. Rate of decent of the freezing front in the soil approached 25 mm d**-1 while depth of soil freezing neared 1.2 m across the depression during the winter of 1990-1991. Rate of soil freezing during late fall was more rapid at locations of higher elevation and with thinner snow cover. Maximum frost penetration was deepest at locations with the least snow cover. Thawing of the soil profile was most rapid in the bottom of the depression and appeared to be accentuated by infiltration of surface water through frozen soil. Surface thaw rate approached 40 mm d**-1 during spring 1991. Thaw was more rapid at lower elevations. Soil water recharge occurred during spring snowmelt; but snow cover accounted for less than 20% of the variation in recharge. This study suggests that topographic features across a prairie pothole can influence snow cover and therefore frost depth. Thickness of snow cover, however, has little influence on soil water recharge during spring because frozen soil channels snowmelt to the bottom of the depression.