SEASONALLY SATURATED SOILS IN THE PUGET LOWLAND .1. SATURATION, REDUCTION, AND COLOR PATTERNS

The depth and duration of seasonal saturation are important factors affecting land use and management decisions. Soil chromas less-than-or-equal-to 2 have been used to indicate the depth of seasonal saturation, but in many soils this relationship is not valid. This study was conducted to determine the relationships among seasonal saturation, soil color patterns, and soil redox in soils derived from glacial till, alluvium, and volcanic mudflow material in the Puget Sound Lowland of western Washington. Soil profiles were described at key positions on landscapes typical of each parent material. Water tables, soil redox potentials, ground water dissolved oxygen (DO), and soil moisture tensions were measured in selected soil horizons and the results compared with soil color patterns. Seasonal high water tables could be predicted using chroma 2 colors on the glacial till and volcanic mudflow landscapes. Soil colors did not appear to indicate current redox conditions in the alluvial sites, although they could be used to predict seasonal high water tables on the overwash plain landscape. The duration of DO levels <5 mg/L could be related to soil redox status. Soil horizons with DO <5 mg/L for more than 80% of the time they were saturated had low soil redox potentials and were clearly reduced for at least part of the year. Soil horizons with DO <5 mg/L for 60-80% of the time were reduced only in microsites. Other soil horizons remained oxidized throughout the year.