Ortstein and Placic Horizons - Soil Geography of the USA: A Diagnostic-Horizon Approach - page 197

et al. 2004 ). Ortstein often occurs adjacent to and down slope from peat deposits,
not only in the Maritime Provinces of Canada (Wang et al. 1978 ) but also in the
Great Lakes region, western OR and WA, and FL. Lapen and Wang (Lapen and
Wang 1999 ) noted that ortstein tends to form in soils on gentle slopes. In the present
review, slope was one of the few site factors that differed significantly among the
three broad soil groups considered in the analysis. Soils with ortstein were most
common on slopes averaging 10-12 % (Table 18.6 ).
There is considerable disparity in the literature regarding the drainage conditions
related to ortstein development. Whereas many investigators report ortstein hori-
zons in soils with free internal drainage (Kaczorek et al. 2004 ; Karavayeva 1968 ;
Moore 1976 ), some cite the occurrence of ortstein in depressions with restricted
drainage (Lapen and Wang 1999 ; Wang et al. 1978 ) or in areas with a fluctuating
water table (Dubois et al. 1990 ). In this analysis, ortstein was common not only in
poorly drained soils of FL and soils with a seasonally high water table in all of the
regions but also in well-drained to excessively drained soils derived from relatively
uniform outwash sand in northern MI.
Parent materials such as till, glaciolacustrine deposits, and beach sediments
composed primarily of medium and coarse sands are particularly prone to ortstein
formation (Wang et al. 1978 ; Moore 1976 ). In the present study, 84 % of the soil
series containing ortstein were derived from sandy materials of all sand-size
classes. Materials enriched in ferromagnesian minerals, such as hornblende and
olivine, are a key source of Fe, Al, and Si and are important not only in the
podzolization process but also in cementing ortstein (Moore 1976 ). A few studies
stress the importance of fines, largely clay-size particles, in bridging sand grains to
form ortstein (Kaczorek et al. 2004 ; McKeague and Wang 1980 ). However, many
of the soils included in the present study have 2 % clay content.

Lapen and Wang (Lapen and Wang 1999 ) suggested that coarse fragments

<

( 2 mm), which are abundant in soils containing ortstein in southeastern New-

foundland, may serve as “nuclei” for precipitation of cements that eventually bind
these fragments into ortstein. However, there were no significant differences in
coarse fragment contents among the three soil groups. Furthermore, soils with
ortstein contained on average less than 10 % coarse fragments (Table 18.6 ).
Ortstein requires a minimum of 2,000-6,000 yr to form (Barrett 1997 ; Moore
1976 ). Most of the soils examined in the present study are of late Wisconsinan
age, ca. 10-14 ky BP or older (Bockheim et al. 1991 , 1996 ).
Therefore, the key factors accounting for the occurrence of soils with ortstein
within the Spodosol regions of the USA appear to be (i) low elevations in coastal
areas or areas with large lakes, (ii) the bottoms or edges of depressions in areas with
complex relief, (iii) gentle slopes, (iv) a sparse vegetation cover with minimal
bioturbation, and (v) a soil age in excess of ca. 2,000 yr.
Statistical comparisons of site factors were made among the three soil groups:

>

50 % ortstein, and no ortstein in the spodic horizon. The percent
slope was significantly less ( p

50 % ortstein,

<

0.001) on soils with ortstein than in those lacking
ortstein (Table 18.6 ). In addition, soils with ortstein tend to occur at lower eleva-
tions than those without ortstein ( p

¼

¼ 0.015). The drainage (coded class) was