LOCATION SWILLNA AK
Established Series
Rev. MHC/JPM
02/2022
SWILLNA SERIES
The Swillna series consists of poorly and very poorly drained soils formed in a discontinuous organic mat overlying strongly cryoturbated silty lacustrine deposits. Permafrost occurs at a depth of 8 to 38 inches. Swillna soils are on broad lacustrine terraces. Slopes range from 0 to 8 percent. Mean annual temperature is about 26 degrees F. and the average annual precipitation is about 16 inches.
TAXONOMIC CLASS:
TYPICAL PEDON: Swillna peat - on a 1 percent slope under black and white spruce forest with cottongrass tussucks at 2050 feet (625 meters) elevation. (All colors are for moist soil). This profile is separated into two parts the first part is in an intermound area between a frost boil; the second part is from within the mound or boil. Mound-intermound topography consists of about 60 percent intermounds and 40 percent mounds. One complete cycle of mound-intermound occurs about every 4 meters.
Part I -- Sixty percent intermounds
Oi1--0 to 6 inches (0-15 cm); dark yellowish brown (10YR 3/6) peat; slightly decomposed eriophorum stems and root fibers; abrupt irregular boundary. (5 to 8 inches thick)
Oi2--6 to 9 inches (15-23 cm); dark yellowish brown (10YR 3/4) peat; slightly decomposed eriophorum stems and root fibers; abrupt wavy boundary. (2 to 5 inches thick)
Bg--9 to 18 inches (23-46 cm); dark gray (5Y 4/1) and 40 percent olive brown (2.5Y 4/4) silty clay loam; moderate medium subangular blocky structure; friable, very sticky and very plastic; few very fine and fine roots; slightly acid (pH 6.1); abrupt wavy boundary. (4 to 12 inches thick)
Oib--18 to 21 inches (46-53 cm); very dark brown (10YR 2/2) and 20% dark yellowish brown (10YR 3/6) slightly decomposed fibrous eriophorum stems and roots; slightly acid (pH 6.1); abrupt wavy boundary. (0 to 4 inches thick)
Cf--21 to 40 inches (53-102 cm); dark grayish brown (2.5Y 4/2) silty clay loam; slightly acid (pH 6.2); frozen on August 12, 1994.
Part II -- Fourty percent mounds
Oi--0 to 1 inch (0-3 cm); dark yellowish brown (10YR 3/4) peat; slightly decomposed eriophorum and ericaceous shrub stems and root fibers; abrupt wavy boundary. (0 to 1 inch thick)
AC--1 to 7 inches (3-18 cm); dark grayish brown (2.5Y 4/2) silty clay loam; strong coarse granular structure; friable, very sticky and very plastic; many very fine and fine roots; slightly acid (pH 6.4); abrupt wavy boundary. (2 to 8 inches thick)
C1--7 to 17 inches (18-41 cm); dark grayish brown (2.5Y 4/2) silty clay loam; strong fine subangular blocky structure; friable, very sticky and very plastic; common very fine and fine roots; slightly acid (pH 6.4); abrupt irregular boundary. (6 to 22 inches thick)
C2--17 to 40 inches 94 (41- 102 cm); dark grayish brown (2.5Y 4/2) silty clay loam; massive; friable, very sticky and very plastic; slightly acid (pH 6.4); abrupt irregular boundary. (8 to 26 inches thick)
Oab--40 to 41 inches (102-104 cm); dark grayish brown (2.5Y 4/2) muck; slightly acid (pH 6.2); abrupt irregular boundary. (0 to 3 inches thick)
Cf--41 to 51 inches (104-130); dark grayish brown (2.5Y 4/2) silty clay loam; slightly acid (pH 6.2); frozen on August 12, 1994.
TYPE LOCATION: Gulkana River Area, Alaska; about 32 miles west of Sourdough; the NW1/4 of the SE1/4 of section 8, T.10N., R.6W., Copper River Meridian.
RANGE IN CHARACTERISTICS: The mean annual soil temperature is less than 32 degrees F. The mat of organic material is 0 to 4 inches thick in mounds and 8 to 14 inches thick in intermounds. Depth to permafrost ranges from 23 to 40 inches below the surface of the mineral soil in mounds and 18 to 33 inches in intermounds two months after the summer solstice. There is from 18 to 35 percent clay and less than 15 percent fine sand or coarser by weighted average in the particle size control section. Textures include silt clay loam, silty clay, and silt loam. Coarse fragment content ranges from 0 to 5 percent. The reaction ranges from slightly acid to slightly alkaline.
The A or AC horizon (when present) have moist hue of 10YR or 2.5Y; moist value of 3 or 4; and moist chroma of 1, 2, or 3.
The Bg horizon (when present) has moist hue of 2.5Y, 5Y, 5G, or 5GY; moist value of 4 or 5; moist chroma of 0, 1, or 2; redoximorphic features include redox concentrations with moist hue of 7.5YR, 10YR, or 2.5Y; moist chroma of 4 through 6.
The C horizons have moist hue of 2.5Y or 5Y; moist value of 4 or 5, and moist chroma of 1 or 2. Coarse fragment content ranges from 0 to 5 percent with 0 to 5 percent cobble and 0 to 5 percent gravel. A lag concentration of coarse fragments is common along the upper boundary of the horizon.
Oab, Oeb and Oib horizons are common in most pedons.
Ice content in the Cf horizon is variable and includes disseminated or segregated ice crystals, seams a few millimeters to several centimeters thick and massive ice features.
COMPETING SERIES: These are the
Mosquito series in the same family. Mosquito soils have less than 18 percent clay in the particle-size control section.
GEOGRAPHIC SETTING: Swillna soils formed in a organic mat of varying thickness overlying strongly cryoturbated silty lacustrine sediments on lacustrine terraces. Slopes range from 0 to 8 percent.
The climate is subarctic continental with long, cold winters and short, warm summers. Mean annual precipitation ranges from 14 to 18 inches. The mean annual temperature ranges from 23 to 27 degrees F.
GEOGRAPHICALLY ASSOCIATED SOILS:
DRAINAGE AND PERMEABILITY: Swillna soils are poorly or very poorly drained; runoff is very slow to medium; permeability is moderate above the impermeable permafrost. The profile typically is saturated with water at lower depths in mounds than intermounds.
USE AND VEGETATION: Most areas of Swillna soils are in native vegetation of white spruce and black spruce forest with understories of eriophorum and ericaceous shrub in intermounds and exposed soil and ericaceous shrubs on mounds. This soil is used primarily for wildlife habitat. Soils are underlain by massive ice features and disturbance by fire or other activities may result in differential subsidence and mass wasting.
DISTRIBUTION AND EXTENT: Copper River Basin, Alaska. The series is of moderate extent.
SOIL SURVEY REGIONAL OFFICE (SSRO) RESPONSIBLE: WASILLA, ALASKA
SERIES ESTABLISHED: Gulkana River Area, Alaska. 1999
REMARKS: Diagnostic horizons and features recognized in these pedons are: a histic epipedon from 9 inches to 0 and permafrost at 12 inches in the intermound part; permafrost at 40 inches in the mound part; fine-silty particle size class from 0 to 14 inches; pH >5.5 (1:1,H2O) in control section. Formerly classified as Pergelic Ruptic-Histic Cryaquepts.
National Cooperative Soil Survey
U.S.A.