Hydrology of a morainic landscape near St. Denis, Saskatchewan, in relation to the genesis, classification and distribution of soils

Abstract

The purpose of this study was to ascertain the relationship between groundwater flow, soil moisture regimes, and soil genesis and distribution in a hummocky morainal landscape. In addition, the color criteria used to classify soils affected by saturation and reduction were examined on soils that were monitored for soil moisture and redox potential. The results of this study indicate that the genesis of soils in a given landscape position can be related to certain groundwater flow conditions, as based on piezometers and observation wells. Non-saline and non-carbonated soils in upland depressions can be attributed to "depression-focused" recharge by snow and snowmelt runoff in the spring, as evidenced by groundwater mounds and strong recharge conditions. The upper surface of the water table in the spring resembles a "mirror-image" of the ground surface and extensive leaching occurs under the upland sloughs. Non-saline and carbonated soils around upland depressional fringes, on lower slope positions, are found to be associated with local discharge in the spring via the adjacent groundwater mound, as well as upward flow in the summer when phreatophytic consumption by willows created a water table depression around the slough fringes. Normally, a shallow water table would be expected to dominate these soils in the spring, as evident by carbonates at the soil surface. However, the two dry years of this study resulted in a much deeper water table in the spring. Saline and carbonated soils at low elevations in the study area can be associated with a shallow and rather stable water table, and local discharge fran surrounding higher elevations. The relatively short length of the local flow systems and high salinity of the soil extracts in this area, indicates that the soluble salt content of the glacial till is a factor in increasing soil salinity at discharge ends of local flow systems. Generally, carbonated or non-carbonated, and non-saline soils on mid and upper slope positions can be related to a deep water table with mainly recharge or lateral flow occurring in the saturated zone. Highly permeable gravel and sand lenses in the till deposits channel flow laterally, and determine to a large extent flow direction, within the less permeable glacial till. Upland soil types are more dependent on slope position and infiltration than the depth to water table or groundwater flow. Electrical conductivity and soluble salt distribution of soil extracts reveal that upland depression infiltration of surface runoff water is the dominant factor in influencing distribution of soluble salts in this hummocky landscape. Low quantities of soluble salts under the upland depressions and higher values in adjacent upslope soils suggest lateral flow is not a major water redistribution process. The dominance of magnesium sulphate salts throughout the area indicates that relatively short local flow systems prevailed in this area. Soils in a given landscape position exhibit similar chemical characteristics as evident by dithionite-, oxalate- and pyrophosphate-extractable iron, electrical conductivity values, Mg++/Ca++ ratios of water-soluble soil extracts, and the presence or absence of Mg-bearing calcites in the upper Ck or Cca horizons. Humic Luvic Gleysols exhibit the greatest reduction as exemplified by matrix chromas of 1 or less. Other Gleysols are less strongly gleyed, having moderately low matrix chramas and mottles.Mottle contrast may be too specific at the present time to correctly classify soils affected by saturation and reduction. Most Cca horizons near the soil surface in Gleysolic soils have rusty mottles, indicating that these horizons were once reduced. Four soils in upland depressions and three soils on lower slopes were monitored for extent of saturation and redox potential. The two soils occupying the middle of the sloughs, which had the wettest moisture regime in the spring, exhibit reducing conditions. It is doubtful whether soil moisture and redox conditions recorded were representative of actual conditions during soil development, due to the two abnormally dry years of this study. Color criteria fail to satisfactorily identify some gleyed intergrades and well-drained soils on mid and upper slope positions.