| Summary: | Transitional areas between upland and aquatic habitats, commonly known as
wetland, were once viewed as unproductive areas and were drained for farming or
pasture. Wetlands are now accepted as significant ecological resources, and their
protection is a mandate of federal, state, and local land managers. Due to the
diversity of wetland areas, the appropriate assessment of wetland resources cannot
be accomplished without long term monitoring of wetland functions. Knowledge of
the duration of saturation and associated anaerobic conditions of soils in wetlands is
critical to correctly classify and assess wetland areas.
Soil, hydrological, and biogeochemical characteristics of the soils of the
Jackson-Frazier wetland were observed from October 1992 through March 1994.
Weekly observations of water levels and redox potential at depths of 25, 50, and 100
cm were made in order to characterize the degree and duration of saturation and the
anaerobic conditions in the soil over time.
Permanently installed piezometers measured free water in the soil and
indicated the presence of two separated water tables from the onset of the rainy
season in October until February when the entire soil profile became saturated with
free water. Platinum electrodes measured redox potential in the soil and indicated
anaerobic conditions for ten months during the first season of observation and through March of the second season. Anaerobic conditions were considered to be achieved when Fe����� was reduced to Fe����� at a potential of 200 millivolts. The highly reducing conditions correspond to periods of soil saturation indicated by piezometers. Concentrations of iron and manganese observed in soil profiles correspond to conditions of prolonged saturation and reduction confirmed by monitoring.
A soil stratigraphic study done with auger holes revealed a recent alluvial deposit of montmorrillonitic clay overlying lacustrine silts identified as the Irish Bend Member of the Willamette Formation. The clay deposit overlying the surface of the wetland acts as an aquitard and creates extensive surface ponding, which maintains the saturated habitat required for wetland vegetation. The subsurface hydrology is controlled by water flowing through the Irish Bend silts which results in saturation of the soils from below. Biogeochemical transformations of iron and manganese due to suboxic and anaerobic conditions are controlled by this type of soil saturation in the Jackson-Frazier wetland. === Graduation date: 1995
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