LOCATION TUKWILA WAEstablished Series
TAXONOMIC CLASS: Diatomaceous, dysic, mesic Limnic Haplosaprists
TYPICAL PEDON: Tukwila muck, pasture. (Colors are for moist unless otherwise noted.)
Oal--0 to 10 inches; black (10YR 2/1) muck, dark gray (10YR 4/1) dry; about 5 percent fiber, less than 1 percent rubbed; moderate coarse granular structure; slightly hard, very friable, slightly sticky, slightly plastic; many roots; extremely acid (pH 4.4); abrupt smooth boundary. (8 to 12 inches thick)
Oa2--10 to 16 inches; black (10YR 2/1) muck, brown (10YR 5/3) dry; dark gray (10YR 4/1) dry coating on prisms; about 5 percent fiber, less than 1 percent rubbed; moderate very coarse prismatic structure; slightly hard, friable, slightly sticky, slightly plastic; many roots; very strongly acid (pH 4.6); clear smooth boundary. (6 to 9 inches thick)
Oa3--16 to 19 inches; dark reddish brown (5YR 3/3) muck, dark brown (10YR 3/3) dry grading to pale brown (10YR 6/3) dry in lower part; black (10YR 2/1) coating on prisms; about 5 percent fiber, less than 1 percent rubbed; moderate very coarse prismatic structure; slightly hard, friable, slightly sticky, slightly plastic; many roots; very strongly acid (pH 4.6); abrupt wavy boundary. (2 to 4 inches thick)
2Ldi--19 to 21 inches; strong brown (7.5YR 5/6) and very pale brown (10YR 7/3) fine sandy loam (diatomaceous earth), light yellowish brown (10YR 6/4) dry; massive; slightly hard, very friable, nonsticky, nonplastic; many roots; very strongly acid (pH 4.6); abrupt smooth boundary. (2 to 10 inches thick)
3O'a--21 to 51 inches; very dark brown (10YR 2/2) muck, very dark brown (10YR 2/2) dry; about 10 percent fiber, less than 5 percent rubbed and 5 to 10 percent woody stems; massive; slightly hard, very friable, slightly sticky, slightly plastic; common roots to 30 inches, few roots below; very strongly acid (pH 4.6).
TYPE LOCATION: King County, Washington; 320 feet west, 1,140 feet south of center section 4, T.21N., R.5E.
RANGE IN CHARACTERISTICS: The organic material in which Tukwila soils formed ranges in thickness from 51 inches to more than 10 feet and is underlain with mineral layers ranging in texture from loamy sand to silty clay. The mean annual soil temperature is 47 to 52 degrees F. The soils are mostly derived from sedges and have 0 to 15 percent decomposing woody fragments. Layers of diatomite, with combined thickness of 2 to 10 inches, occur at depths from 8 to 24 inches. Thin layers of mucky peat, peat, sand, or sandy loam are in the control section of some pedons.
The Oa horizon has hue of 7.5YR, 10YR, 5YR, or 2.5Y, value of 1 to 3 moist, 2 to 5 dry, and chroma of 0 to 6 moist and dry. This layer has moderate to weak granular blocky,platy, or prismatic structure. It is 5 to 25 percent fiber, less than 10 percent rubbed. They are very strongly acid to strongly acid (pH 4.5 to 5.5 in water).
COMPETING SERIES: These are the Dupont, Seattle, and Shalcar series. All of these soils are less acid than strongly acid in some parts. In addition, Seattle soils lack diatomaceous earth strata and have more than 10 inches at hemic material above 36 inches. Shalcar soils have a loamy substratum within 50 inches.
GEOGRAPHIC SETTING: These soils are in depressions on stream terraces and glacial uplands at elevations of 25 to 750 feet. They formed in organic materials with a few mineral layers. Areas are saturated and often ponded in winter and early spring. Tukwila soils occur in a mild climate with cool, dry summers and mild, wet winters. The average annual precipitation is 35 to 80 inches; the average January temperature is 38 degrees F.; the average July temperature is 64 degrees F.; and the mean annual temperature is 50 degrees F. The frost free season ranges from 150 to 200 days.
GEOGRAPHICALLY ASSOCIATED SOILS: These are the Bellingham, Norma, Puget, Seattle, Shalcar, and Snohomish soils. Bellingham, Norma, and Puget soils are poorly drained mineral soils. Snohomish soils have an organic substratum, below a mineral surface, at a depth of 10 to 40 inches.
DRAINAGE AND PERMEABILITY: Very poorly drained; very slow runoff; moderate permeability. A high water table is as high as 1 foot over to 1 foot under the surface at times from October to May and is within 5 feet most of the year unless drained.
USE AND VEGETATION: Some of the Tukwila soils are used for cropland. Pasture hay, oats, green chop, and sweet corn. Some of these soils are used for woodland. Native vegetation is western redcedar, western hemlock, red alder, and Sitka spruce with an understory of rush, sedge, vine maple, trailing blackberry, hardhack, devilsclub, salmonberry, willow, red elderberry, and skunkcabbage.
DISTRIBUTION AND EXTENT: This series is inextensive and occurs in the Puget Sound Basin, Washington.
MLRA SOIL SURVEY REGIONAL OFFICE (MO) RESPONSIBLE: Portland, Oregon
SERIES ESTABLISHED: King County, Washington, 1971.
REMARKS: Diagnostic horizons and features recognized in this pedon are a surface and subsurface tiers from the surface to 36 inches that are sapric material and a layer of diatomaceous earth from 19 to 21 inches..