Landscape evolution and soil formation: Treynor, Iowa

Agricultural Chemical Movement through a Field-Size Watershed in Iowa: Subsurface Hydrology and Distribution of Nitrate in Groundwater

“…The similarity of the precipitation and infiltration records indicates that most Groundwater movement patterns are determined by the hydraulic conductivity of the aquifer material and by the landscape position defining the gradient. As illustrated in Figure 1, both the till surface and the shallow groundwater table generally conform to the surface topography (14,15). The unsaturated zone of the loess material varies in thickness from 2 to 20 m with an average wetting-front velocity on the order of 10 -3 -10 -4 m s -1 .…”

“…Heterotrophic denitrification, with its requirement for soluble and bioavailable organic carbon, could remove nitrate from the soil pore water. However, organic carbon content in the deep loess is low, 2-3% at the surface, declining rapidly to <0.5% at 30 cm depth and to <0.1% at 150 cm depth (15). No DOC record exists for soil pore water from this field.…”

“…At both sites, the maximum concentration at the 6-8 m depth was nearly 2 times greater than that at the 2-4 m depth. The volume of water recovered in sampling was 60% less at the 7 m lysimeter depth versus shallower placements, indicating a zone of restricted conductivity due to a Sangamon paleosol unit (15). The high concentration of nitrate at the 6-8 depth in the unsaturated loess of the ridge top suggests that substantial leaching occurs beneath these landscape positions.…”

Soil parent material stratigraphy and soil development, Cedar County, Iowa

“…The second method of relating soils and stratigraphie units is provided by an analysis of the properties of the soils in soil groups No. 1, 2, and 3 ( Table 14) and his associates and others (Allen, 1971;Vreeken, 1972; Figure ^0. Proposed soil-landçcape-stratigraphic model for the geographic area bound by the primary divide in Cedar and Scott counties, Iowa.…”

“…Ruhe and his associates have continued to use the de oxidized term to imply "relict gleying" (Hall, 1965;Daniels and Jordan, 1966;Fenton, I966;Ruhe et al, 196? ;Ruhe et al, 1968;Ruhe, 1969a;Allen, 1971;Vreeken, 1972;Worcester, 1973).…”