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Soil Science Society of America Journal 67:612-619 (2003)
© 2003 Soil Science Society of America

DIVISION S-5—PEDOLOGY

Genesis of Bisequal Soils on Acidic Drift in the Upper Great Lakes Region, USA

J. G. Bockheim*

Dep. of Soil Sci., 1525 Observatory Dr., Univ. of Wisconsin, Madison, WI 53706-1299

* Corresponding author (bockheim{at}facstaff.wisc.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 Study Area
 METHODS AND MATERIALS
 NOTES
 RESULTS
 DISCUSSION
 REFERENCES
 
Seventeen bisequal pedons were characterized on drift primarily from the Greatlakean advance [ca. 12 000 yr before present (BP)] in northern Wisconsin and the upper Michigan. The pedons, Alfic Haplorthods and Alfic Oxyaquic Fragiorthods, contain an Orthod sequum over an Udalf sequum and are derived primarily from coarse-loamy or coarse-silty materials overlying stratified sand and gravel or coarse-loamy materials. The upper sequum contains abundant roots and is very strongly acidic (pH 4.8), low in clay (<4.8%) and base cations (<20% base saturation), and high in exchangeable acidity (13 cmolc kg-1) and exchangeable Al (60% saturation). The lower sequum contains few roots, is strongly acidic (pH 5.4), is more enriched in clay (8.0%) and base cations (45% base saturation), and has lower exchangeable acidity and Al than the upper sequum. The occurrence and position of argillic and fragic horizons in the profile are favored by a lithologic discontinuity. The two horizons may form exclusive of one another. On the basis of soil solution chemistry data and mass-balance studies, the argillic horizon has formed from neoformation of clays with some clay migration. The fragic materials are of pedogenic origin and are forming in the upper part of a degrading argillic horizon. The soils have undergone environmental changes during the past 12 000 yr, but they appear to have originated from processes that are occurring today that result from extensive leaching during melting of the spring snowpack and solute movement in two-storied parent materials. The soils are strongly developed in view of the short snow-free season.

Abbreviations: BP, before present • CEC, cation exchange capacity


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
Study Area
 METHODS AND MATERIALS
 NOTES
 RESULTS
 DISCUSSION
 REFERENCES
 
BISEQUAL SOILS, that is, soils with two distinct sequa, are common in the upper Great Lakes region (Cann and Whiteside, 1955; Yassaglou and Whiteside, 1960; Beaver, 1966; Hole, 1975; Habecker et al., 1990; Miller et al., 1993; Schaetzl, 1996). In our study area, these soils (i) occur on glaciated terrain with a complex history, (ii) often contain a lithologic discontinuity that includes coarse-loamy or coarse-silty materials over stratified sand and gravel, (iii) have an Orthod sequum over a Udalf sequum, and (iv) often contain a fragipan that transgresses the lithologic discontinuity. Alfic Haplorthods and Alfic Oxyaquic Fragiorthods cover {approx}970 000 and 210 000 ha, respectively, in Michigan and Wisconsin. These soils generally support eastern hemlock [Tsuga canadensis (L.) Carriere] and northern hardwood forest, dominated by sugar maple (Acer saccharum Marshall), basswood (Tilia americana L.), and yellow birch (Betula alleghaniensis Britton). The objective of this study was to interpret the genesis of bisequal soils from an examination of 17 pedons from northern Wisconsin and western upper Michigan.


   Study Area
TOP
 ABSTRACT
 INTRODUCTION
 Study Area
METHODS AND MATERIALS
 NOTES
 RESULTS
 DISCUSSION
 REFERENCES
 
The study was conducted in three subsections of the Lake Superior Upland Section of the eastern United States (Keys et al., 1995), including the Winegar Moraines subsection (212Jc; 11 sites), the Brule and Paint Rivers Drumlinized Ground Moraine Subsection (212Jl; 5 sites), and the Northern Highlands Pitted Outwash subsection (212Jm; 1 site) (Fig. 1) . The study included managed stands primarily in the Ottawa, Nicolet, and Chequamegon National Forests and old-growth stands in the Sylvania Recreation Area that were never logged.



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  		Fig. 1. Location of pedons within the Southern Superior Uplands, including the Winegar Moraines Subsection (212Jc), the Brule and Paint Rivers Drumlinized Ground Moraine Subsection (212Jl), and the Northern Highland Pitted Outwash Subsection (212Jm).

 
The northern hardwoods and hemlock stands have a basal area of 30 to 36 and 43 m2 ha-1, respectively (Table 1). Whereas the dominant trees in old-growth stands are {approx}200 to 240 yr in age (Frelich et al., 1993), overstory trees in managed stands range from 75 to 90 yr in age. The northern hardwood stands are of the sugar maple-basswood, sugar maple, and sugar maple-yellow birch associations; the hemlock stands are of the hemlock-yellow birch association. The habitat type for all stands was Acer-Tsuga-Dryopteris (Kotar et al., 1988).


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  		Table 1. Site characteristics and classification of bisequal soils.

 
The climate of the region is continental, but Lake Superior exerts a moderating influence. Mean annual precipitation ranges from 800 to 870 mm, of which about half falls during the growing season (National Oceanic and Atmospheric Administration, 1980). The mean annual air temperature ranges from 3.7 to 5.6°C; and the growing season ranges from 70 to 130 d. The soil temperature and moisture regimes are frigid and udic, respectively. On the basis of data from the Natural Resources Conservation Service's, Soil Climate Analysis Network (Natural Resources Conservation Service, 2002), the soils of the study area rarely freeze because of early and deep snow cover.

The dominant landform of the area is the Winegar Moraine (212Jc; Fig. 1), which was deposited by the south-flowing Ontonagon Lobe during the late Wisconsin glaciation, {approx}12 000 yr BP (Peterson, 1982; Attig, 1985). The hummocky moraine contains till and debris flow sediments. The western end of the study area contains drumlinized ground moraine often with a thin (<0.2 m) silt cap. Elevation of the sites ranges from 370 to 550 m.

Four soil subgroups are common to the area; Alfic Oxyaquic Fragiorthods and Alfic Haplorthods occur on moraines and drumlins, and Entic and Typic Haplorthods dominate outwash plains.


   METHODS AND MATERIALS
TOP
 ABSTRACT
 INTRODUCTION
 Study Area
 METHODS AND MATERIALS
NOTES
 RESULTS
 DISCUSSION
 REFERENCES
 
Field
Soils were excavated to the C horizon or to a minimum depth of 1.4 m. Seventeen pedons were described and sampled by pedogenic horizon (Soil Survey Division Staff, 1993). Key characteristics of the sampling sites are given in Table 1. Parent materials were distinguished using field criteria of Attig (1985). Lithologic discontinuities were identified from field observations of texture, coarse fragment content, and degree of compaction and corroborated by laboratory investigations of particle-size distribution and bulk density.

Eight sites were selected for collecting natural waters, including four with Alfic Oxyaquic Fragiorthods (Sylvania 2A, Sylvania 2B, Tamarack Lake 1, and Sucker Lake 2) and four with Typic Haplorthods (Sylvania 14, Sylvania 15, Taylor Lake 1, and Coral Lake 2 (Bockheim and Crowley, 2002). Three throughfall collectors consisting of 20-cm diam. polyethylene funnels mounted on stakes 1.4 m above the ground surface were randomly located at each site. Along a 2- to 3-m radius from each throughfall collector, porous-cup soil-water samplers (model 1900, Soilmoisture Equipment Corp., Santa Barbara, CA)1 were installed at each of three depths, including the bottom of the E horizon at a depth of 5 to 18 cm, within the Bs at 48 cm, and either within the fragipan (70 cm) for Alfic Fragiorthods or within the BC or C horizon (70–120 cm) for Typic Haplorthods.

Replicate bulk precipitation collectors, following the design of the throughfall collectors, were installed in open areas. Three bulk precipitation collectors were installed at Sylvania 2A/2B, three at Sylvania 14/15, three at Tamarack Lake 1, two at Taylor Lake 1, and three each at Coral Lake 2 and Sucker Lake 2 (Bockheim and Crowley, 2002). Bulk precipitation and throughfall collectors were rinsed and scrubbed using deionized water between collection intervals. The soil water samplers were evacuated between collection periods using a hand vacuum pump to a negative pressure of 70 kPa.

Solutions from all collectors were sampled every 1 to 3 wk depending on the amount and intensity of rainfall. Samples were collected during two growing seasons, 27 June to 12 Oct. 1996 and 16 May to 28 Sept. 1997. A total of 1210 solution samples were collected during 15 sampling intervals. Solutions were kept in a cooler on ice until they were returned to the laboratory where they were stored in a refrigerator at a temperature of 0 to 5°C until analyzed. Mass balances were prepared using the general procedures outlined in Cann and Whiteside (1955).

Laboratory
Soil samples were air-dried at 22°C and passed through a 2-mm screen. The samples were sent to the Missouri Soil Characterization Laboratory, where all analyses were performed on the <2-mm fraction using methods established by the Soil Survey Staff (1996), including particle-size distribution with sand fractionation (Method 3A), pH in distilled water (8C1a), organic C (6A1c), NH4OAc-extractable bases (5B1), BaCl2–triethanolamine-extractable acidity (6H1), cation exchange capacity (CEC) by NH4OAc at pH 8.2 (5A2), KCl-extractable Al (5B3), and base saturation from NH4OAc.

Solutions were passed through a 0.45-µm membrane Millipore filter (Millipore Corp., Bedford, MA). The concentrations of Fe, Al, and Si were analyzed by mass spectrophotometry at the University of Wisconsin Soil and Plant Analysis Laboratory with a detection limit of 0.01, 0.35, and 0.07 mg L-1, respectively.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 Study Area
 METHODS AND MATERIALS
 NOTES
 RESULTS
DISCUSSION
 REFERENCES
 
Parent Materials
All but two of the pedons have lithologic discontinuities, including fine sandy loam (interpreted as till or debris flow materials using the criteria of Attig [1985]) or silt loam (interpreted as loess) materials over stratified sand and gravel deposits (interpreted as outwash) (Table 1). The two pedons that lack a lithologic discontinuity (Sylvania 2B and Sucker Lake 2) are interpreted to have originated from a thicker deposit of acidic till, with a sandy loam texture throughout. There is evidence for eolian deposition in the area as silt-enriched materials ranging from 50 to 94 cm in thickness occur at the Sylvania 4, Butternut Lake North and South, and Gagen sites (Table 1).

Evidence for Podzolization
All of the soils have spodic materials in the upper sequum. In all but one pedon (Sylvania 2A), the spodic materials underlay albic materials. In all but four pedons, the spodic materials could be identified from color alone, that is, a 5YR or redder hue, a value <=5, and a chroma <=4 (Table 2). In the other four pedons, spodic materials were inferred from adjacent pedons meeting the color requirements of Spodosols.


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  		Table 2. Key morphological properties of pedons from bisequal soils.

 
The formation of spodic horizons in the region is favored by the acidic, sandy, free-draining parent materials (Franzmeier et al., 1963; Hole, 1975), the sustained imprint of hemlock vegetation (Hole, 1975; Frelich et al., 1993), and a thick snowpack that inhibits soil frost and allows for large fluxes of snowmelt water to percolate through the profiles (Schaetzl and Isard, 1996).

Evidence for Argilluviation
All of the soils selected for the study have an argillic horizon in the lower sequum. Argillic horizons were identified on the basis of field properties such as the presence of clay coatings, pore infillings of clay, and bridging of sand grains by clay particles (Table 2), laboratory measurements such as an increase in percentage clay from an overlying epipedon (Table 3), and mass balances.


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  		Table 3. Analytical properties of selected Alfic Oxyaquic Fragiorthods and Alfic Haplorthods in the upper Great Lakes region.

 
The upper surface of the argillic horizon occurred at depths of 51 to 128 cm and averaged 82 cm; and the thickness of the argillic horizon ranged from 11 to 64 cm, averaging 42 cm (Table 2). Evidence for clay movement into in the 2Btx horizon ranged from a few, thin pore infillings to abundant, moderately thick clay coatings on ped faces and within pores. The increase in clay from the Ex to the 2Btx or Bt ranged from 0.8 to 15.8% and averaged 6.4% (Table 3).

In the upper Great Lakes region, argillic horizons often occur in soils with lithologic discontinuities (Khakural et al., 1993; Miller et al., 1993; Schaetzl, 1996). Their formation in these soils appears to be favored by (i) highly porous parent materials low in calcium carbonate that are conducive to clay movement (Yassaglou and Whiteside, 1960), (ii) a textural discontinuity that enables the water bearing solutes to hang up (Khakural et al., 1993), (iii) ample moisture from the melting snow pack that enables translocation of clay (Schaetzl, 1996; Schaetzl and Isard, 1996), and (iv) conditions that enable synthesis of clay minerals from the soil solution (Karathanasis, 1989; Miller et al., 1993).

Five pedons examined in this study had evidence of silt movement, including Sylvania 2A, Sylvania 9, Tamarack Lake 1, Taylor Lake 2, and Butternut Lake North (Table 3). The increase in silt from the lower horizon of the upper sequum (Bs2 or Bs3) to the E/Btx, Btx, or Bt/E horizon in the lower sequum ranged from 6.6 to 30.4%, averaging 16.1%. Silt may move in soils due to translocation in suspension (Locke, 1986) or from vertical frost sorting (Van Vliet-Lanoe, 1985).

Evidence for Fragipan Formation
Eleven of the 17 pedons examined contain fragic soil properties (Table 2). The fragipans were identified from field properties, including a very firm rupture-resistance class, a prismatic structure, and slaking in water (Soil Survey Staff, 1999). Fragic soil properties were also identified from bleached prism faces, a vesicular porosity, a low concentration of roots, and observations of water moving over the surface of the fragipan during the spring (Yassaglou and Whiteside, 1960; Habecker et al., 1990; Lindbo and Veneman, 1993; Miller et al., 1993; Soil Survey Staff, 1999). Nine of the 11 Fragiorthods contain lithologic discontinuities (Table 1). The surface of the fragipans ranged from 35 to 111 cm, averaging 63 cm; and the fragipan thickness ranged from 35 to >79 cm, averaging {approx}58 cm (Table 2).

In Michigan and Wisconsin, fragipans rarely form in the absence of an argillic horizon and are most common in soils with lithologic discontinuities (Yassaglou and Whiteside, 1960; Franzmeier et al., 1989; Habecker et al., 1990; Schaetzl, 1996). According to the NASIS database (National Soil Information System, 2002), 10 Fragiorthods have been correlated in northern Wisconsin and Michigan and they invariably contain coarse-loamy materials over acidic sandy loam till in a udic, frigid soil climate.

Soil Chemical Properties
The upper sequum of the soils is extremely acidic (pH 4.8), low in exchangeable bases (<20% base saturation), and high in exchangeable acidity (12 cmolc kg-1) and exchangeable Al (60% saturation) (Table 3). In contrast, the lower sequum is very strongly acidic (pH 5.4), higher in exchangeable bases (45% base saturation), and lower in extractable acidity (3 cmolc kg-1 and exchangeable Al (30% saturation) than the upper sequum.

The acidity in the upper sequum likely originates from removal of base cations by the northern hardwood vegetation, which has a high demand for base cations, withdraws large amounts of bases from the soil, and accumulates them in the biomass (Franzmeier et al., 1989; Bockheim, 1997). These soils are acidic because they are leached at rates that are faster than the trees can take up the bases. In addition, the CEC is so low that bases cannot be retained as fast as they are released by weathering of the parent material.

The Al on exchange sites in the upper sequum originates from hydrolysis of the abundant aluminosilicate minerals in the parent materials (Brown and Jackson, 1958; Whittig and Jackson, 1956). The Fe and Al complexes with organic matter and, therefore, is important in podzolization.

Solution Chemistry
Bulk precipitation contributed low amounts of Fe, Al, and Si to the ecosystems (Fig. 2) . Throughfall concentrations were about two-fold greater than those in bulk precipitation. Ions in soil solution collected at three depths could be ranked: Si > Al > Fe. There were no major differences in solution chemistry between fragic and nonfragic soils. Iron and Al were readily immobilized in the spodic horizon of both soils. In contrast, Si was highly mobile and was likely released by weathering, particularly in the fragic horizon of Alfic Fragiorthods. Karathanasis (1989) proposed that dissolved Si plays a major role in binding soil particles in fragipans.



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  		Fig. 2. Distribution of Fe, Al, and Si in bulk precipitation, throughfall, and the soil solution at three depths, the bottom of E the horizon (ca. 18 cm), within the Bs horizon (ca. 48 cm), and within the fragipan or BC horizon (70-120 cm) of Alfic Oxyaquic Fragiorthods and Typic Haplorthods.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 Study Area
 METHODS AND MATERIALS
 NOTES
 RESULTS
 DISCUSSION
REFERENCES
 
Genesis of Bisequal Soils
Bisequal soils in the upper Great Lakes region generally have a sandy loam or finer textured upper sequum. Whereas an argillic horizon may form in the lower sequum of soils derived from loamy sand or sandy materials, fragipans most commonly form in materials with a sandy loam or finer texture. Argillic horizons and fragipans may form exclusive of one another but occur together most commonly in soils with lithologic discontinuities.

On the basis of depth-distribution of Si in soil solutions (Fig. 2) and mass-balance estimates, clay in the argillic horizon forms from neoformation of secondary minerals from solutions percolating through the profile and translocation from eluvial horizons. Fragipans are common on drumlins in the Brule and Paint River Drumlinized Ground Moraine Subsection of the Lake Superior Upland Section. In soils of the upper Great Lakes region, fragipans likely are of pedogenic origin in that they form within the upper part of the argillic horizon and at a lithologic discontinuity, particularly where loess overlays sandy loam till or debris flow sediments. The fragipans occur in the Ex horizon, which has totally lost all of the argillic characteristics, or in the upper part of argillic horizons that appear to be degrading.

There is some uncertainty as to the role that permafrost may have played in the development of fragipans in the upper Great Lakes region. Habecker et al. (1990) cited the occurrence of prismatic and platy structure, vesicular porosity, silt accumulation, and vertical sorting in fragic soil materials as evidence for former permafrost. However, all of these features may be explained on the basis of contemporary soil-forming processes. For example, the prismatic structure could originate from wetting and drying of the lower sequum. The vesicular porosity may form as a result of saturation of the upper sequum during spring snowmelt. As the water penetrates into the underlying argillic horizon, air must be displaced. As the Ex horizon above the argillic horizon dries, it may entrap some of the rising air, forming preserved vesicular pores (Miller et al., 1993). Silt may be translocated into the lower sequum by the same mechanism as clay, rather than by vertical frost sorting. I am unaware of fragipans in permafrost-affected soils.

The soils examined in this study differ from those studied by Beaver (1966) and Schaetzl (1996) in that they do not occur within a climate-vegetation ecotone and they are derived from acidic till or outwash in the lower sequum rather than base-rich till. Although the theory cannot be discounted, there is no evidence that the Spodosols within the upper sequum are derived from a thick E horizon in Udalfs developed during the warmer Hypsithermal interval (Hole, 1975; Wang et al., 1995). Podzolization may have intensified since the more widespread establishment of hemlock in the region during the past 3000 yr (Frelich et al., 1993). However, our data suggest that an Orthod upper sequum and an Udalf lower sequum can form simultaneously in two-storied parent materials where large volumes of water percolate through the profile.

A preliminary model for the evolution of upland soils in the upper Great Lakes region is given in Fig. 3 . The model illustrates the pathway of soil development on two kinds of parent materials. On sandy loam materials (upper panel), a Typic Haplorthod requires at least 4000 yr to form (Franzmeier et al., 1963; Barrett and Schaetzl, 1992). In areas receiving extensive infiltration from snowmelt, an argillic horizon may form at the depth of water percolation; this type of soil is represented by the Keweenaw series (Alfic Haplorthod). Fragic properties may originate from degradation of the argillic horizon, as evidenced by bleached prism faces (Lindbo and Veneman, 1993). The fragipan may further inhibit internal drainage and lead to subsurface lateral flow and formation of an Ex horizon.



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  		Fig. 3. Evolution of soils on sandy loam and sandy loam materials that are underlain by sand and gravel in the upper Great Lakes region.

 
Soil development may be even more rapid on two-storied materials such as coarse-loamy materials over sand and gravel outwash (Fig. 3). The somewhat excessively drained Pence series (Typic Haplorthod) represents an early stage in development of these soils. Under well-drained conditions, an argillic horizon may form at the contact between the two parent materials, leading to the development of an Alfic Haplorthod (represented by the Padus series). In moderately well-drained areas, a fragipan may develop in the upper part of the argillic horizon and at the contact between the two parent materials. The fragipan may further restrict internal drainage, causing oxyaquic conditions. The Gogebic soils, classified as Alfic Oxyaquic Fragiorthods, are very common in the study area and represent this condition.

The soils examined in this study show considerable pedogenesis given the limited snow-free season (about mid-May to mid-October). The profiles range from deep to very deep and show evidence of podzolization, argilluviation, and formation of fragic soil properties. The upper sequum is strongly leached of bases, clay, and silt and has a superactive cation exchange activity class; Al dominates the exchange sites. The lower sequum contains greater amounts of bases and clay than the upper sequum.

The conditions contributing to this strong degree of development include (i) lack of freezing of the soils during the winter, (ii) buildup of a 1- to 2-m snowpack that melts rapidly in the spring, and (iii) permeable parent materials, and (iv) lithologic discontinuities that cause water to hang up, thereby short circuiting the depth for leaching. These conditions enable rapid translocation of weathering products to form the various horizons, properties, and materials found in these soils.


   ACKNOWLEDGMENTS
 
The Wisconsin Department of Natural Resources and the USDA Cooperative State Research Service (Hatch) provided funding for this project through the Univ. of Wisconsin Agricultural Experiment Station. J. Rich and R. Fujinuma assisted in the field. S. Crowley provided the solution chemistry data.


   NOTES
TOP
 ABSTRACT
 INTRODUCTION
 Study Area
 METHODS AND MATERIALS
 NOTES
RESULTS
 DISCUSSION
 REFERENCES
 
1 Mention of a company and/or product does not constitute endorsement by the Univ. of Wisconsin-Madison. Back

Received for publication March 22, 2002.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 Study Area
 METHODS AND MATERIALS
 NOTES
 RESULTS
 DISCUSSION
 REFERENCES
 




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