WATER TABLE DYNAMICS ACROSS AN AQUOD-UDULT TRANSITION IN FLORIDA FLATWOODS

Abstract

Spodosol formation in the coastal plain of the southeastern United States is largely restricted to areas where there are fluctuating water table conditions within the zone of podzolization. The purpose of this study was to document specific hydrologic conditions associated with podzolization, and to address the idea that frequency and duration of saturation are critical threshold factors triggering and driving the process regionally. The study was conducted along an abrupt Aquod-to-Udult transition, which showed the commonly observed trend of an upward curving spodic horizon (Bh) that merges with the A horizon of the Udult. Objectives were to (i) compare the Aquod and the Udult with respect to depth and duration of saturation and (ii) determine hydraulic responses of horizons to rainfall events along the Aquod-Udult transition. Water table fluctuations within a rectangular area (15 × 25 m) encompassing the soils were monitored, using piezometers, over a 1-year period. Hydraulic and horizon surfaces were interpolated by Kriging. Results confirmed that the water table sloped sharply downward across the Aquod-to-Udult transition during most of the sampling period but was nearly level for brief periods after heavy rains. The hydraulic response of the Udult argillic horizon to rain events was much slower than that of the Aquod argillic horizon, such that the Udult periodically experienced epiaquic conditions. The hydraulic head of the Aquod argillic horizon was consistently higher than that of the Udult argillic horizon; discharge from the Aquod argillic compensated for evapotranspiration and maintained wetter conditions in the upper sandy horizons. Depth and color development of the Aquod Bh horizon were inversely related to water table depth along the transition. Hence, these factors are not simple functions of central tendencies in water table dynamics but relate to duration of saturated conditions in the near-surface sandy zone.