TEMPORAL AND SPATIAL PATTERNS OF EPISATURATION IN A FRAGIXERALF LANDSCAPE

Relatively low saturated hydraulic conductivities associated with fragipans result in seasonal perched zones of saturation (episaturation). This study was conducted to monitor seasonal episaturation in a Fragixeralf landscape of northern Idaho. Perched zones of saturation above a fragipan in a 1.4-ha field were monitored during a 2-yr period using 64 piezometers arranged on a 15-m grid spacing. During the winter of 1991-1992, relatively mild temperatures and high rainfall resulted in development of perched zones of saturation lasting from early December into May. Average quantities of perched water present within the landscape during the winter and early spring months ranged from 8.4 to 15.4 cm, representing between 34 and 43% of the seasonal precipitation that had been received at the study site. During the 1992-1993 winter, colder temperatures and relatively large quantities of snow delayed development of episaturation. When the snow pack began to melt in early March, an average of >20 cm of water was present in the saturated zone above the fragipan. This water represented 58% of the seasonal precipitation that had been received. Soil morphological characteristics and elevation were correlated with quantities of perched water present on sampling dates when potential evapotranspiration was low. For all sites, quantity of perched water was most strongly correlated with the thickness of the zone above the fragipan exhibiting redoximorphic features; depth to the fragipan was less strongly correlated. Elevation was generally a poor indicator of episaturation. Results of this study indicate that significant periods of episaturation occur in fragipan-dominated landscapes under xeric moisture regimes.