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Stratigraphy and Water Table Relationships of Upland Loess-Derived Soils in South-Central Iowa¹

ABSTRACT

This study was initiated to evaluate the effects of stratigraphy and landscape position on water table levels of loess-derived soils in south-central Iowa. At selected sites on primary divides along two geographically linear traverses, monthly measurements were made of the depth to a zone of groundwater saturation (water table).

The depth to the buried geomorphic surface and (or) loess thickness on the flat and sloping primary divides decreased systematically with distance from the major source area. As the depth to the buried geomorphic surface and loess thickness decreased and distance from the source area increased, the internal natural drainage of the more extensive soils became poorer, and the depth to the water table decreased. The character of the water table seems to be cyclic. The highest water tables were observed during the spring months and, the lowest, during the fall months on the flat and sloping divides. However, the water table showed less of a cyclic nature as the depth to the buried geomorphic surface decreased. The shallower depths to water tables on the southeastern end of the traverses were attributed to the stratigraphic and geomorphic characteristics of the divides.

The relationship between the depth to the buried geomorphic surface and the average depth to the water table on the divides was expressed mathematically by the regression equations Y = -83.32 + 0.85X and Y = 20.03 + 61X for the flat and sloping divides, respectively. The relationship between month (X1), depth to the Yarmouth-Sangamon surface (X2), temperature (X3), and depth to the water table (Y) was expressed mathematically by the multiple-regression equations Y = 109.04 - 60.06X1 + 3.21X1² + 0.84X2 - 5.60X3 + 0.67X1X3 and Y = 201.69 - 58.81X1 + 3.20X1² + 0.62X2 - 4.91X3 + 0.60X1X3 for the flat and sloping divides, respectively.

Key Words: loess thickness • paleosols • weathering profiles • geomorphic surfaces

¹ Contribution from the Dep. of Agron., Iowa State University. Journal Paper no. J-10153 of the Iowa Agric. and Home Econ. Exp. Stn., Ames, IA 50011. Project no. 2,100.

² Research Associate and Professor of Agron., respectively, Dep. of Agron., Iowa State Univ., Ames, IA 50011.

Received for publication February 23, 1981. Accepted for publication September 11, 1981.