Monday, November 5, 2007
115-3
Soil-Landscape Evolution and Mineralogy Distribution in a Southern Illinois Watershed.
Michael Wilson1, Samuel Indorante1, B.D. Lee2, L.R. Follmer3, D.R. Williams1, B.C. Fitch1, W.M. McCauley1, J.D. Bathgate1, and K. Kleinschmidt4. (1) USDA-NRCS, 5111 W Sumner Circle, Lincoln, NE 68522, (2) Purdue University, Agronomy Department, West Lafayette, IN 47907, (3) Illinois State Geological Survey, 204 Natural Resources Bldg, 615 E. Peabody Drive, Champaign, IL 61820, (4) USDA-Forest Service, 148 E. Pleasant Hill Road, Suite 105, Carbondale, IL 62903
A soil landscape developed from a thick mantle of loess was studied in
southern Illinois to examine forms and distribution of soil minerals as
affected by landscape position and hydrology. Soils in the 10 ha
watershed in Union County, Illinois have developed from 12-25 ka (late
Wisconsinan-aged) Peoria loess overlying the 28-55 ka (middle
Wisconsinan-aged) Roxana silt. A terra-rosa geosol and karsted
Mississippian-aged limestone underlies the Roxana material. Nine pedons
representing two catenas, plus 55 satellite cores, were sampled across
the watershed to represent major soil types. Deep, well drained soils
(Typic Hapludalfs) compose convex ridge top and shoulder slope
positions. Bisequal soils (Oxyaquic Fragiudalfs) with fragipans at
50-100 cm develop in soils on shoulder and backslope positions.
Fragipans are >100 cm or absent in lower backslope/upper footslope
positions and soils classify as Oxyaquic or Aquic Hapludalfs. Silt
(0.002-0.05 mm), the dominant particle size fraction, is mainly composed
of quartz and potassium feldspars (3:1 ratio), with lesser amounts of
plagioclase feldspars, muscovite, and other weatherable minerals. No
mineralogical difference in this fraction was found between the two
loess units. Mineralogy of the clay fraction is similar across the
landscape, composed of kaolinite, illite, and smectite, with vermiculite
that exhibits partial hydroxyl-interlayering. Citrate dithionite (CD)
extractable-Fe ranges from about 1% in lower landscape positions to over
2% on summits. Influence of the fragipan on water movement is evident
from higher ratios of acid oxalate to CD extractable Fe above the pan.
Increases in this ratio indicate a greater noncrystalline component of
the pedogenically-formed Fe oxyhydroxides. Water moves across the
fragipan, accumulating in lower landscape positions. These lower sites
are slightly saline, with 1:2 electrical conductivity ranging from 0.1
to 1.2 dS/m. In lower horizons within these sites, saturated paste
extracts are mainly composed of sodium, bicarbonates, and sulfates.
southern Illinois to examine forms and distribution of soil minerals as
affected by landscape position and hydrology. Soils in the 10 ha
watershed in Union County, Illinois have developed from 12-25 ka (late
Wisconsinan-aged) Peoria loess overlying the 28-55 ka (middle
Wisconsinan-aged) Roxana silt. A terra-rosa geosol and karsted
Mississippian-aged limestone underlies the Roxana material. Nine pedons
representing two catenas, plus 55 satellite cores, were sampled across
the watershed to represent major soil types. Deep, well drained soils
(Typic Hapludalfs) compose convex ridge top and shoulder slope
positions. Bisequal soils (Oxyaquic Fragiudalfs) with fragipans at
50-100 cm develop in soils on shoulder and backslope positions.
Fragipans are >100 cm or absent in lower backslope/upper footslope
positions and soils classify as Oxyaquic or Aquic Hapludalfs. Silt
(0.002-0.05 mm), the dominant particle size fraction, is mainly composed
of quartz and potassium feldspars (3:1 ratio), with lesser amounts of
plagioclase feldspars, muscovite, and other weatherable minerals. No
mineralogical difference in this fraction was found between the two
loess units. Mineralogy of the clay fraction is similar across the
landscape, composed of kaolinite, illite, and smectite, with vermiculite
that exhibits partial hydroxyl-interlayering. Citrate dithionite (CD)
extractable-Fe ranges from about 1% in lower landscape positions to over
2% on summits. Influence of the fragipan on water movement is evident
from higher ratios of acid oxalate to CD extractable Fe above the pan.
Increases in this ratio indicate a greater noncrystalline component of
the pedogenically-formed Fe oxyhydroxides. Water moves across the
fragipan, accumulating in lower landscape positions. These lower sites
are slightly saline, with 1:2 electrical conductivity ranging from 0.1
to 1.2 dS/m. In lower horizons within these sites, saturated paste
extracts are mainly composed of sodium, bicarbonates, and sulfates.