TEMPORAL AND SPATIAL PATTERNS OF EPISATURATION IN A FRAGIXERALF LANDSCAPE

Relatively low saturated hydraulic conductivities associated with frag ipans result in seasonal perched zones of saturation (episaturation). This study was conducted to monitor seasonal episaturation in a Fragix eralf 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 1 991-1992, relatively mild temperatures and high rainfall resulted in d evelopment of perched zones of saturation lasting from early December into May. Average quantities of perched water present within the lands cape during the winter and early spring months ranged from 8.4 to 15.4 cm, representing between 34 and 43% of the seasonal precipitation tha t had been received at the study site. During the 1992-1993 winter, co lder temperatures and relatively large quantities of snow delayed deve lopment of episaturation. When the snow pack began to melt in early Ma rch, an average of >20 cm of water was present in the saturated zone a bove the fragipan. This water represented 58% of the seasonal precipit ation that had been received. Soil morphological characteristics and e levation were correlated with quantities of perched water present on s ampling dates when potential evapotranspiration was low. For all sites , quantity of perched water was most strongly correlated with the thic kness of the zone above the fragipan exhibiting redoximorphic features ; depth to the fragipan was less strongly correlated. Elevation was ge nerally a poor indicator of episaturation. Results of this study indic ate that significant periods of episaturation occur in fragipan-domina ted landscapes under xeric moisture regimes.