Water Table Characteristics and Water Chemistry of Seasonally Wet Soils of Southwestern Ohio

The seasonally high water table in Clermont (Typic Glossaqualfs) and Avonburg (Aeric Fragiaqualfs) soils of southwestern Ohio was investigated by monitoring variations in water table depth and in water chemistry of the vadose and upper saturated zones. Piezometers were installed for two pedons at three depths ranging from 70 to 180 cm, and soil-water samples were collected using 0.1-MPa porous ceramic cups installed in triplicate at four depths ranging from 32 to 170 cm. During the period of this study (April 1982–June 1983), the water table occurred within 30 cm of the surface during winter and early spring, fell rapidly to a depth of about 150 to 180 cm during late summer and early fall, and then returned to within 30 cm of the soil surface during late fall and early winter. Soil-water exhibited ranges in pH (5.2–8.6), Eh (153–543 mV), electrical conductivity (7.0–91.5 mS m⁻¹), dissolved O₂ (0.6–6.1 mg L⁻¹), Ca (2.5–64.1 mg L⁻¹), Fe(II) (0–3.87 mg L⁻¹), and Fe(III) (0–11.48 mg L⁻¹). Soil-water chemistry was a function of season and depth below the soil surface. While the dissolved O₂ content decreased with depth, Eh and pH increased. Alternating periods of reduction and oxidation were suggested by significant seasonal variation in the variables monitored. Reducing conditions were indicated by the presence of Fe(II) in solution and an Eh of <400 mV, both of which occurred in the Clermont soil at the uppermost sampling depth during the April through June period. This period was characterized by saturated conditions and a soil temperature higher than 8°C. The highly variable Fe(II) and Fe(III) contents indicated that oxidation-reduction reactions occurred primarily in microenvironments. The soil-water system was not at internal equilibrium as evidenced by (i) the simultaneous occurrence of dissolved O₂ with reduced C (organic matter) and Fe (II), and (ii) a mixed potential for Eh that did not correlate with dissolved O₂ content.