The Southern Piedmont region extends from northern Virginia to eastern
Alabama and includes large parts of North Carolina, South Carolina, and
Georgia, as well as a small part of Tennessee with a total land area of
16,698,600 ha. Most of this area is in small farms, but a sizable acreage
is controlled by woodland companies. Land adjacent to major cities is used
for residences and associated urban development. Although most of the land
was once cultivated, much has reverted to mixed stands of pine and hardwoods.
Most of the open land is pasture, but some crops, such as soybeans, small
grain, corn, cotton, wheat, and, to a lesser extent, tobacco, are grown.
Dairy cattle and poultry are important locally (USDA, 1981).
Average annual precipitation varies from 1,150 to 1,400 mm. Precipitation
is evenly distributed throughout the year, but the lowest is in autumn;
snowfall is light. Average annual temperature varies from 14 to 18°C.
The average freeze-free period varies from 205 to 235 days (USDA, 1981).
The majority of the Piedmont major land resource area (MLRA 136) is
underlain by metamorphic and igneous rocks ranging in age from Precambrian
to late Paleozoic (Hack, 1989). Over most of the region, these rocks have
been weathered to saprolite. Both grade of metamorphism and rock composition
vary considerably across the region. The area is dominantly felsic (light-colored,
acid, high in silica) igneous and metamorphic rocks (granite, granite gneiss,
mica gneiss, mica schist), but large areas of intermediate and mafic (dark-colored,
basic, magnesium- and iron-rich, low in silica) rocks occur. In addition,
mafic dykes often occur in regions of more acid rocks which alter parent
material composition and complicate soil patterns.
There are two minor areas within the Piedmont with considerably different
geology and thus, soils than the rest of the region. The first is a series
of down-faulted basins containing sedimentary sandstones, siltstones, mudstones,
and shales of Triassic and Jurassic age (Hack, 1989). The second is generally
referred to as the Carolina Slate Belt which is an area of low relief containing
Cambrian and Precambrian low-grade metamorphic rocks of volcanic origin
(slate, acid and basic tuff, breccia, and flows) (Hack, 1989). Because
these rock types are different than most of the Piedmont, different soils
occur in these regions.
The Piedmont is generally well dissected with commonly accordant summits
constituting a broad plateau-like surface. Maximum relief in the region
is generally less than 350 m though higher isolated peaks occur (Murray,
1961). The region slopes to the east and south with general surface slope
being about 4 m km-1. The lack of topographic expression on
the interfluves has been used as evidence that the Piedmont is a peneplain
(Thornbury, 1965; Holmes, 1964). An alternate hypothesis is that this surface
is the result of long-term weathering and uplift in the region. Mineralogy
and water chemistry in the region suggest that 1 m of saprolite will form
in about 250,000 years (Pavich, 1986). This rate of saprolite formation
is within a factor of two of the estimated rates of erosion and uplift
for the region (Pavich, 1985). Thus, as saprolite and soil form from the
underlying rock and mass is lost to solution, stream divides are lowered
and flattened. As this process continues, the surface rebounds in response
to lowered overburden pressure, and the result is the broad plateau-like
surface observed in the Piedmont.
The high stream gradient in the region results in relatively narrow
floodplains and deeply incised streams. Flooding in the region, though
common, is generally of short duration (3 to 7 days), and the strong gradient
from the floodplain to the incised stream results in a large portion of
the soils in floodplains being well or moderately-well drained. These level,
well-drained floodplains were the sites of choice for settlement when European
man came to the region in the mid to late 1700s. Only after the floodplains
were completely settled did these settlers venture into the more rolling
(and erodible) uplands (Trimble, 1974).
Because the region is characterized by rolling summits and relatively
steep backslopes, most soils are well drained and at least moderately permeable
(> 0.036 cm h-1 , Table 1 and
Fig. 1). Thus, differences among soils are more often related to nature
of the saprolite parent material and landscape position than to major differences
in permeability and internal drainage. Historically, the soils have been
considered to have developed in residual parent materials, but recent evidence
suggests that many of the soils on lower slope positions have, at least
in part, developed in colluvial parent materials (Stolt et al., 1993).
However, other than limited mixing of acid and mafic rocks, the composition
of the colluvium is similar to that of the residuum, and it is difficult
to separate colluvial materials from residual saprolite unless a stone
line or other readily observable marker is available (Daniels et al., 1984).
Thus, few soil distinctions have been made based on this difference in
For purposes of the remainder of this discussion, soils in the Piedmont
will be divided into four broad groups based on parent material composition:
1) soils developed from felsic igneous and metamorphic parent materials,
2) soils developed from intermediate to mafic igneous and metamorphic parent
materials, 3) soils developed from fine-grained sedimentary and metamorphic
parent materials, and 4) soils developed from alluvium from mixed crystalline
Soils Developed from Felsic Igneous and Metamorphic Parent Materials
The majority of the Piedmont is underlain by felsic igneous and metamorphic
rocks such as granite, granite gneiss, mica gneiss, and mica schist. Soils
associated with these bedrock types comprise about 51% of the soils that
have been mapped in the Piedmont and include Appling, Cecil, Helena, Louisa,
Louisburg, Madison, Pacolet, Tallapoosa, Vance, and Wedowee (Table
1). These soils generally have sandy loam surface horizons overlying
clayey argillic horizons. The soils are acid, have low base saturation,
and kaolinite is the dominant clay mineral. The abundance of low activity
clays in these soils results in low cation exchange capacity (CEC), low
shrink-swell potential, and moderate rates of water movement through the
soil. Because of their low pH, low base saturation, and kaolinitic mineralogy,
these soils have often been considered to be old and highly weathered.
Granted, many of the soils and landscapes in the Piedmont are quite old,
but similar chemical and mineralogical characteristics are found in relatively
young soils developed in these acid crystalline rocks. Free movement of
water through the coarse-textured saprolite results in rapid transformation
of K-feldspars and biotite to kaolinite and rapid leaching of the limited
amounts of basic cations contained in the parent rock. Thus, the characteristics
of these soils are related to the nature of the parent rock as much as,
if not more than, age and degree of soil development.
Most of the differentiating criteria among soils associated with acid
crystalline rocks in the Piedmont are based on solum thickness and color
of the Bt horizon. Cecil, Appling, Helena, and Vance soils have sola thicker
than 1 m. Appling soils have Bt horizons with hues of 5YR to 5Y while Cecil
soils have Bt horizons with a hue of 2.5YR or redder. These soils occur
on a variety of landscape positions but are more commonly found on more
gently sloping landscapes. Vance and Helena soils are developed from a
mixture of felsic and mafic rock or from a slightly more mafic residuum
than Appling and Cecil. The presence of iron (Fe) and magnesium (Mg) bearing
minerals in the parent materials for the Vance and Helena soils results
in their having mixed mineralogy (more than 10% 2:1 expandable clay minerals)
and slower permeability than Appling and Cecil. Vance soils occur on the
same landscapes as Appling and Cecil, and separation of Vance and Appling
can be difficult. Helena soils commonly occupy concave areas along intermittent
streams and heads of drains and have a seasonal water table within the
upper Bt horizon.
Louisburg, Madison, Pacolet, and Wedowee soils have sola from 0.5 to
1 m thick. Pacolet and Wedowee soils are analogous to Cecil and Appling
with Pacolet soils having red Bt horizons and Wedowee soils having yellowish
brown Bt horizons. Pacolet and Wedowee commonly are found on steeper slopes
than Cecil and Appling. Madison soils have red Bt horizons and common or
many mica flakes in the upper part of the Bt horizon. These soils commonly
occur on more broken topography than Cecil. Louisburg soils have discontinuous,
coarse-loamy Bt horizons and are commonly formed in saprolite from granite
or granitic gneiss. Louisa and Tallapoosa soils have soft rock (Cr horizons)
within 0.5 m, loamy Bt horizons, and abundant mica within the solum.
Appling and Wedowee commonly occupy broad summits or lower backslope
positions, and the yellowish brown color of their Bt horizons may be related
to very short periods of saturation and reduction in these horizons (Macedo
and Bryant, 1987). Hematite has been shown to be more easily reduced than
Al-substituted geothite (Macedo and Bryant, 1989). Thus, short periods
of saturation may be causing reduction and loss of hematite from these
horizons. The residual geothite would give the horizons the yellowish brown
Soils Developed from Intermediate to Mafic Igneous and Metamorphic
Soils associated with intermediate to mafic crystalline rocks comprise
about 10% of soils that have been mapped in the Piedmont and major soils
include Davidson, Enon, Gwinett, Hiwassee, Mecklenburg, and Wilkes. The
relationships among these soils and between soils and bedrock are complex.
Felsic crystalline and more mafic rock are intimately associated which
results in a very complex soil pattern. Alfisols and dark red Ultisols
from residuum or locally derived alluvium or colluvium from mafic rock
occur on the landscape with red and yellow Ultisols derived from felsic
rock. In addition, all gradations of rock composition from ultra-mafic
to acid granite occur.
Davidson, Gwinett, and Hiwassee are commonly considered to be associated
with rocks or local alluvium with intermediate content of Fe and Mg bearing
minerals (Daniels et al., 1984). These soils are well drained Ultisols,
have sandy loam surface horizons overlying clayey Bt horizons, and the
clay minerals are dominantly kaolinite. Thus, CEC and shrink-swell is low,
and rate of water movement through the soil is considered to be moderate.
Because of higher contents of Fe bearing minerals in the parent rock, these
soils generally have higher contents of Fe and manganese (Mn) oxides than
soils from felsic rocks. The increase Fe and Mn oxide content gives Bt
horizons in these soils a dark or “dusky” red color (hue of 2.5YR or redder
and value of 3 or less; Rhodic subgroup) and well-expressed fine structure
(Daniels et al., 1984).
Differentia among the three soils are related to presence of this color
and solum thickness. Davidson soils have thick sola, and Bt horizons are
dark red throughout their thickness. Gwinett soils have similar colors,
but solum thickness is 0.5 to 1 m. Hiwassee soils are also deep but lack
the dark red color in the lower part of the Bt horizon and are often associated
with old alluvium or colluvium.
Enon, Mecklenburg, and Wilkes soils are associated with mafic crystalline
rock, and the higher content of basic cations in these rocks has resulted
in these soils being classified as Alfisols. In addition, these soils have
more than 10% 2:1 expandable clay minerals in Bt horizons and thus, mixed
mineralogy. The two soils with thick sola, Enon and Mecklenburg, have tight,
clayey Bt horizons, moderate shrink-swell, and slow rates of water movement
through the soil. Even though the Bt horizon of the Wilkes soil has loamy
texture, the presence of appreciable 2:1 clays in these horizons result
in the soil having a moderately-slow permeability.
Soils Developed from Fine-Grained Sedimentary and Metamorphic
Soils associated with fine-grained rocks of the Carolina Slate Belt,
the Triassic basin, and other isolated areas of fine-grained metamorphic
rocks comprise about 12% of soils that have been mapped in the Piedmont.
Major soils include Badin, Georgeville, Herndon, Mayodan, Nason, and Tatum.
Within the Carolina Slate Belt, interfluves are irregular, and sharp topographic
breaks are common. Deep soils generally occupy more gently sloping parts
of the region, and shallow soils occur on convex parts of the landscape.
Valley sides are short (Daniels et al., 1984).
The Triassic Basin is topographically lower than the bulk of the Piedmont
landscapes that surround it, and local relief is generally less than most
of the Piedmont. The Triassic rocks include shales, dark and light colored
sandstones, mud-stones, siltstones, and conglomerates. These rock types
are apparently easier to erode than the surrounding crystalline rocks which
accounts for the topographic low nature of the basin (Daniels et al., 1984).
The fine grain size of the rocks associated with the Carolina Slate
Belt results in soils with higher silt and very fine sand contents than
the rest of the Piedmont. Surface textures are generally silt loam and
Bt horizon textures range from silty clay loam to clay. As in other Piedmont
soils, the dominant clay mineral in most of these soils is kaolinite. There
are, however, more 2:1 clay minerals in these soils than is normally present
in soils associated with felsic crystalline rocks. Thus, CEC is greater
than the maximum allowed for placement as Kanhapludults or Kandiudults
(16 cmol kg-1 clay), and many of the soils have mixed rather than kaolinitic
mineralogy in upper Bt horizons (Table 1).
Another similarity with soils developed from felsic crystalline rocks
is differentiation among the major soils based on soil depth and Bt horizon
color. Georgeville soils are deep and have Bt horizons with hues of 5YR
or redder. Herndon soils are also deep, but Bt horizons have yellower hues
than Georgeville. Tatum soils have Bt horizons with red hues, and Nason
soils have Bt horizons with yellower hues. These soils, however, have soft
rock (Cr horizons) between 1.0 and 1.5 m below the soil surface. Badin
soils have strong brown to red Bt horizons, but the Cr horizon occurs within
a 1 m depth. In general, the deep soils associated with these fine-grained
rocks occupy the more gently sloping parts of the landscape, and the soils
with rock within 1.5 m are found on convex landscape components and in
more dissected areas. As in soils associated with felsic rocks, the difference
in Bt horizon color (brown or red) may be related to preferential reduction
and solubilization of Fe in hematite under short periods of saturation
or may be related to differences in the parent rock.
Mayodan soils have moderate permeability, are well drained, and occupy
narrow interfluves and other better drained areas. Creedmore soils occur
on smooth landscapes that are lower lying that Mayodan landscapes. This
soil is moderately-well drained, has a slowly permeable Bt horizon, and
has redox depletions within 60 cm of the upper boundary of the Bt horizon.
White Store soils are somewhat-poorly drained Alfisols with mixed mineralogy.
The Bt horizon of these soils has redox depletions and is slowly permeable.
Soils Developed from Alluvium from Mixed Crystalline Rocks
Soils developed in alluvium in the Piedmont comprise about 5% of soils
that have been mapped in the Piedmont. Major soils include Chewacla, Toccoa,
and Wehadkee. These soils occur on floodplains and terraces of streams
in the region which represent the major area of nearly level land within
the Piedmont. Broad floodplains and terraces only occur on major rivers.
Because of high stream gradients, smaller streams have narrow floodplains
and small discontinuous terrace remnants (Daniels et al., 1984). In most
years, these soils will flood, but because of deep incision of the stream
channels and high stream gradient, the floods are normally for only a few
Texture and composition of the alluvial soils greatly depend on the
texture and composition of the soils and saprolite from which the parent
sediments were derived and stream energy at the time the materials were
deposited. Surface horizon textures range from sandy loam to silt loam.
Subsoil horizons generally have a similar textural range. C horizons are
texturally variable ranging from extremely gravelly sand to clay. Variation
in drainage class among the floodplain soils is related to topographic
position within the floodplain and addition of water from upland sources.
Because of deep incision of the stream channel, the gradient for water
movement is from the floodplain to the channel. Seeps are common along
escarpments into the upland, and most water creating seasonal water tables
in these soils is saturated return flow from upland sources.
Chewacla soils have a weakly-developed Bw horizon that is often thin
but can be up to 1.5 m thick. Clay content in the Bw horizon ranges from
18 to 35%, and the soil has moderate permeability. Redox depletions and
concentrations occur with 60 cm of the soil surface. Toccoa soils are moderately-well
and well drained and have moderately-rapid permeability. The profile consists
of a thin A horizon overlying a C horizon with less than 18% clay. Wehadkee
soils are poorly or very-poorly drained and have moderate permeability.
These soils are wet and redox depletions occur immediately below a thin
A horizon. Clay content in the Bg horizons ranges from 18 to 35%.
In the southern Piedmont region, the ground water system is an unconfined
two-layer system composed of a zone of saprolite underlain by fractured
bedrock (Le Grand, 1988). The saprolite layer consists of highly weathered
crystalline rock and averages 20 m in thickness. Saprolite thickness up
to 100 m has been reported, however (Hack, 1989). Recent studies have shown
that the saprolite layer is an integral part of the ground water system
and acts as an important water storage zone for the deeper fractures (Brackett
et al., 1991; Cressler et al., 1983; Radtke et al., 1986; Rose, 1992).
Recharge occurs throughout the uplands in this shallow groundwater system.
Bracket et al. ( 1991) concluded “since almost all ground water in the
Piedmont/Blue Ridge can be considered as being part of the surface or water
table aquifer, it is quite prone to pollution from man-made sources.” Many
rural older homes in the Piedmont region obtain their drinking water from
dug or bored wells that draw water from the saprolite storage layer and
do not penetrate the bedrock. Newer homes, commercial operations, and farms
that require high yielding wells are likely to have deeper, more expensive
drilled wells that are cased through the saprolite zone and penetrate bedrock
to draw water from fractures. The depth to the water table may be as shallow
as 2 to 6 m in upland areas during the winter and the water table elevation
generally follows the surface topography (LeGrand, 1988).
Pavich et al. (1989) examined saprolite cores in three types of parent
rock in the Piedmont of Virginia: felsic (quartzofeldspathic), mafic (diabase),
and ultra-mafic (serpentine) rocks. Saprolite was thickest in the sites
with felsic parent material (average of 15 to 30 m). This was attributed
to a high content of quartz and muscovite that resists weathering. These
minerals provide a stable, porous matrix through which water can move,
dissolving away the less resistant minerals (such as plagioclase). The
chemical dissolution front occurs near the base of the saprolite layer
so that saprolite can be subdivided into a relatively inert upper half
and a relatively reactive lower half. The mafic and ultra-mafic material
have less resistant minerals so they form thinner saprolite layers (a few
to 10 m in mafic rock and none in ultramafic rock).
Water and Solute Transport
Saturated Water Flow
Saturated hydraulic conductivity (Ks ) varies sharply among horizons
in soils of the Southern Piedmont. Most studies have found that Ks is highest
in the Ap and BA horizons and reaches a minimum near the bottom of the
Bt and top of the BC or CB horizons where the transition between soil and
saprolite occurs. Bruce et al. (1983) examined nine pedons of the Cecil
soil and found that Ks in the Ap horizon was usually 10 cm h-1
or more, whereas Ks in the lower Bt and BC horizons were often 10-2
or 10-3 cm h-1 . Workers in North Carolina also found
that the minimum Ks occurred in the lower B and BC or CB horizons (Schoeneberger
and Amoozegar, 1990; Vepraskas et al., 1991; Williams et al., 1994) (Fig.
2). Radcliffe et al. (1990) measured steady state ponded infiltration rates
in a series of adjacent Cecil and Pacolet soils and found that the infiltration
rate was higher in the Cecil. This was attributed to the thicker Ap and
BA horizons in the Cecil. Chiang et al. (1987) studied three soils (Cecil,
Davidson, and Iredell) from the Southern Piedmont and showed that clay
dispersion could significantly reduce topsoil Ks . Increasing the soil
sodium adsorption ratio and pH and decreasing the soil solution electrolyte
concentration reduced Ks . The soils derived from mafic rock (Davidson
and Iredell) were less dispersive than the soil derived from felsic rock
Unsaturated Water Flow
Bruce and coworkers measured water characteristic (q[h])
and unsaturated hydraulic conductivity (K[h]) functions in the A and B
horizons of a Cecil and used numerical simulations and measurements of
infiltration rates to estimate the effect of these horizons on unsaturated
water flow. Bruce and Whisler (1973) and Bruce et al. (1976) compared predictions
of a numerical model to measured infiltration rates in the Cecil. The model
predicted that infiltration rates would decrease sharply as the wetting
front moved through the upper B horizons and reach a relatively constant
minimum rate as the wetting front reached and passed beyond the lower B
horizons. The model also predicted positive pressure potentials would develop
in the lower B horizons as the wetting front arrived. The model accurately
predicted measured infiltration rates in sod plots but overestimated infiltration
rates in tilled plots. This was attributed to surface sealing in the tilled
plots which was not accounted for in the model.
Extensive information on water characteristic and unsaturated hydraulic
conductivity functions for the Cecil soil are also contained in the report
by Bruce et al. (1983). A total of 15 pedons in Alabama, Georgia, South
Carolina, and Virginia are described. Cores were taken from each horizon
and a water characteristic curve was developed. Saturated hydraulic conductivities
for these cores were also reported so this data can be used to develop
unsaturated hydraulic functions using indirect methods (van Genuchten and
Leij, 1992; McVay and Radcliffe, 1998). They also used the instantaneous
profile method (Cassel, 1972) to measure in situ K(h). Tensiometer data
showed that during drainage pressure potentials increased in the lower
B horizons where flow was restricted. The authors found that the water
contents in the field associated with a given K(h) in the lower B horizons
were less than the water content estimated from the laboratory water characteristic
function, due perhaps to entrapped air. This was not the case for the A
and upper B horizons.
Another source of information on water characteristic and unsaturated
hydraulic conductivity functions is the Unsaturated Soil Hydraulic Database
(UNSODA) of Leij et al. (1994). The database contains descriptions of soils
from all over the world and includes 21 soils (all Cecil series) from the
Few studies have been reported on water movement in the unsaturated
zone below a couple of meters (vadose zone) in the Piedmont, despite the
fact that this zone can be quite thick. One such report is that of Ligon
and Wilson (1972). They installed neutron access tubes to a depth of 9.7
m near Clemson SC and monitored water contents for two years. The water
table occurred at a depth of about 18 m. An extremely dry summer at the
beginning of the study caused a depletion of water down to the deepest
depth of measurement (9.7 m) as water drained to the water table under
unsaturated conditions. The resumption of normal rainfall, supplemented
by 20 cm of irrigation, produced a wetting front that moved to the deepest
depth of measurement in 5.5 months. Wells showed that the wetting front
arrived at the water table three weeks later, indicating faster movement
at deeper depths. This may have been due to the higher water content near
the water table and consequently, a higher K(q).
In bare soils, crusts or surface seals can sharply reduce infiltration
rates. Peele et al. (1945) were the first to document crusting in Southern
Piedmont soils noting that in two sandy loams and two sandy clay loams
from South Carolina “compact, relatively impermeable surface layers formed
on all soils types and these layers... were the determining factor in runoff
and erosion.” Crusts form when soils are exposed to raindrop impact which
disperses clay and allows a thin, dense layer to form at the surface. The
clay in many of these soils will not disperse “spontaneously,” but it readily
disperses with raindrop impact (Miller and Radcliffe, 1992). Water-dispersible
clay was highly correlated with both runoff and soil loss in 15 agricultural
topsoils of the region (Miller and Baharuddin, 1986). Surface applications
of gypsum have been shown to reduce dispersion and crusting by raising
the soil solution ion concentration (Miller and Scifres, 1988). Chiang
et al (1993) measured crust Ks in six freshly tilled soils as they developed
and found that Ks dropped sharply in the first 10 min of simulated rain
(Fig. 3). After 45 minutes, Ks was less than 10 % of the initial value.
Part of the effect of crusts in reducing infiltration rates is that the
suction that develops beneath the crust keeps the soil in an unsaturated
Macropores are large, continuous voids in soil and include structural
and tillage fractures, old root channels, and earthworm and insect burrows.
Suggested lower limits for macropore diameters and widths are in the 0.03
to 3.00 mm range (Beven and Germann, 1982; Luxmoore, 1981; White, 1985).
Macropores are important because they can increase infiltration and may
result in bypass flow of water and solutes (Bouma, 1991). Schoeneberger
and Amoozegar (1990) studied macropores in a Cecil-Pacolet series and identified
five types: (1) inter-ped planar voids mostly in the B horizon, (2) old
root channels in the B, B/C, and C that were either filled or partially
filled with clay, (3) foliation or bed planes in the B/C and C, (4) fractured
planar quartz veins in the B, B/C and C, and (5) oxide coated fracture
faces. They found that the minimum Ks occurred in the bottom of the B and
the B/C horizons despite the presence of macropores (Fig. 2). They concluded
that foliation planes and quartz veins had little effect on water flow.
This was attributed to plugging by iron and manganese oxides and clay (Vepraskas
et al., 1991; Williams et al., 1994).
Gupte et al. (1996) examined macropores using computed tomography and
dyes in 38 columns taken from the top 50 cm or so of a Cecil soil. They
found that the number of macropores decreased in the B horizon compared
to the Ap and BA. Like Schoeneberger and Amoozegar (1990), they observed
old root channels or burrows filled with light-colored material, but it
was not possible to determine if the material was topsoil, faunal secretions,
or decayed organic matter. The presence of in-filled macropores has important
hydrologic implications. Since these features were dye-stained, they apparently
had a higher conductivity than the surrounding soil matrix. In contrast
to open macropores, entry to filled macropores would not require a positive
pressure potential. Thus macropore flow might occur under unsaturated conditions.
Phillips et al. (1989) showed that water could continue to flow in open
macropores under slightly negative pressure potentials, provided that a
continuous water film had been established on the wall over the entire
length of the macropore.
Bathke and Cassel (1991) measured macroporosity in horizons of a Cecil
landscape as porosity minus the water content at a pressure potential of
-6.9 kPa (equivalent diameter of 0.04 mm). They found that macroporosity
was the factor that showed the highest correlation with Ks at all sites.
One of the unique features of soils of this region is that, to a limited
extent, anions such as nitrate are adsorbed and movement consequently is
retarded. Thomas (1960) demonstrated Cl adsorption in three soils from
the Southern Piedmont (Cecil, Davidson, and Lloyd), but not in a Yolo soil
from California. Bellini et al. (1996) used packed columns to show that
anion retardation was pH and concentration dependent. In an unlimed Cecil
subsoil with pH 4.26, the retardation coefficient (R) for Cl was 2.39;
liming the soil to a pH of 6.56 reduced R to 1.12 (Fig. 4). The anion exchange
capacity (AEC) of the unlimed soil was 1.43 cmolc kg-1
compared to 0.70 cmolc kg-1 in the limed soil. Retardation
rose more slowly as the anion concentration increased above the level required
to saturate the soil AEC. Anion adsorption is due to the variable charge
of kaolinitic and oxide surfaces in these soils.
Chemical movement can be affected by the timing of rainfall or irrigation
events. Golabi et al. (1995) demonstrated that Cl leaching was reduced
in intact columns of Cecil soil when a small rain was applied immediately
after application. In this treatment Cl had an opportunity to diffuse into
stagnant regions of the matrix and, as a result, was excluded from flow
in macropores in subsequent large rainfall events. The same effect was
demonstrated earlier by Shipitalo et al. (1990) using soils from Ohio.
Often there is a need to predict soil profile leaching losses of chemicals
such as nitrate at the field or regional scale, but parameters used in
transport models are usually measured at the pedon or local scale (Dagan,
1986). Radcliffe et al. (1996) measured Cl transport parameters in a Cecil
soil under steady flow conditions at different scales in two irrigated
12.5 by 30.5 m plots. Tile drains were used to determine field-scale transport
parameters. Most of the dispersion in the tile drain breakthrough curves
(BTC) was caused by two-dimensional flow to the drains. Once this effect
was removed, the field-scale dispersivities ()were
relatively low (5.3 and 3.4 cm for the two plots) compared to other measurements
of field-scale in the literature
(3-97 cm in Biggar and Nielsen , 6-29 cm in Butters and Jury ,
and 5 to 20 cm in Jury et al. ).
Local-scale pore water velocity (V) and Ks measured on 38 columns (average
length of 49 cm) from one of the irrigated plots were highly variable (CV’s
of 77 and 74 %, respectively) and log-normally distributed (Gupte et al.,
1996). The mean local-scale
was 6.6 cm. In spite of the large variation in V among columns, a deterministic
approach based on the mean local-scale
adequately predicted the field-scale tile drain BTC. This may have been
because flow was predominately unsaturated in the irrigation experiment
and saturated in the column experiment. In a second study (Radcliffe et
al., 1997), transport parameters were measured using time domain reflectometry
(TDR) waveguides installed vertically at 80 locations on one of the irrigated
plots studied earlier. Field-scale
were 5.3 and 11.4 cm in the 0-30 and 0-60 cm depth intervals. The increase
in with depth was attributed
to saturated conditions (the water table was at 30 cm) which caused more
macropore flow in the Bt horizon. Although the variability among local-scale
V was large (CV of 35% and 46% in the 0 to 30 and 0 to 60 cm depth intervals,
respectively), the variability in velocities within the local-scale caused
by hydrodynamic dispersion (and quantified by )
was greater. As a result, a deterministic approach based on the mean local-scale
parameters more accurately predicted the estimated field-scale breakthrough
curve than a stochastic approach.
In a recent study, we measured Br transport (a conservative tracer for
nitrate) in intact columns from the Ap/BA and Bt1 horizons of a Pacolet
pedon that had been in Bermuda grass sod for over 10 years. The pedon is
shown in Fig. 5 and a morphological description is given in Table
2. One set of five columns (15-cm diameter) were extracted from the
surface. Since the columns were 30 cm in length, these columns encompassed
the Ap and BA horizons. The top of the Bt1 horizon was then exposed in
a pit and a second set of columns were extracted. These columns were also
30 cm in length and encompassed the Bt1 horizon and approximately 5 cm
of the Bt2 horizon. The columns were taken to the lab and Ks was
measured. A Br BTC was conducted and transport parameters were determined
using CXTFIT (Parker and van Genuchten, 1984). Finally the columns were
leached with methylene blue dye and sectioned at two depths to determine
the percent dyed area. Saturated hydraulic conductivities were quite high
and similar in the two horizons (Table 3).
Retardation coefficients for Br (which should be similar to that for NO3
) were lower in the Bt1 due to an increase in pH at this site. Dispersivities
were low for both horizons because the fractional mobile water (qm/q)
was low in this soil. There was less mobile water in the Bt1 horizon than
in the Ap/BA. The dye measurements indicated that a significant portion
of the soil matrix was bypassed and that more stagnant regions existed
in the Bt1 than in the Ap/BA horizon.
Landscape position can have a significant effect on chemical movement
in these soils. Bruce et al. (1985) applied KBr to the surface of a Cecil/Pacolet
landscape at six different sites and followed the movement of Br in response
to natural rainfall. Highest concentrations of Br were found in the upper
Bt horizon and there appeared to be some lateral downslope movement of
Br. Bathke and Cassel (1991) established sites on interfluve, shoulder,
linear slope, and foot slope positions in a Cecil landscape. They measured
Ks on cores sampled vertically and horizontally by horizon at each site.
Horizontal Ks were greater than vertical Ks in most horizons
in all but the foot slope position. In the footslope position, more horizons
had vertical Ks greater than horizontal Ks . This implied that lateral
movement of water and solute was likely in all positions except the footslope
Afyuni et al. (1994) surface applied Br in transects of Georgeville
soil to study vertical and lateral movement under natural rainfall. Each
transect included a footslope, linear slope, and interfluve landscape position.
Lateral movement of Br occurred to some extent in all positions. Both vertical
and lateral movement of Br were greatest in the footslope position. This
was attributed to the lower clay content of the footslope position and
the fact that this position received water for a longer period of time
from the higher elevation positions.
Spatial variability of sorptivity was evaluated by van Es et al. (1991)
in a cultivated 2.2-ha field of Georgeville soil in the Carolina Slate
Belt in North Carolina. The topography of the field was complex and contained
a summit, broad gently sloping interfluve with side slopes facing from
north to southeast with gradients raging from 10 to 25%, and footslopes.
Sorptivity (the ratio of cumulative infiltration to the square root of
time during the early stage of infiltration) was measured at 290 sites
in the field on three separate dates. Global semivariograms for each date
had a large nugget value and a range of 12 m or less indicating a very
short-range spatial dependence. Definite regions of higher and lower sorptivity
were found. However, the overall variation within each region was large.
Maps showing sorptivity on 5 June and 8 September 1986 as a function of
the topography are shown in Fig. 6.
Management and Landuse
Management can have a very significant effect on soil physical, chemical,
and biological properties that affect water and chemical movement. Many
studies on soils from other regions have shown that conservation tillage
systems affect infiltration, evaporation, nutrient cycling, and chemical
leaching (Bond and Willis, 1969; Edwards et al., 1988; Isensee et al.,
1990; Kanwar, 1991; Triplett, et al., 1968). Conservation tillage systems
have been promoted in the Piedmont region because they reduce erosion and
increase water retention (Langdale et al., 1979a; Reicosky et al., 1977).
Within the region, studies on Cecil and Pacolet soils have shown that infiltration
rates are higher under conservation tillage because crop residues and more
stable aggregates reduce crusting compared to conventional tillage (Radcliffe
et al., 1988) and because there are more macropores in conservation tillage
(Golabi et al., 1995). Freese et al. (1993) measured infiltration with
a rainfall simulator in a Wedowee sandy clay loam in a long-term experiment
with moldboard plow, disk, and no-tillage treatments. Measurements were
made before tillage, immediately after tillage, two weeks after tillage,
and after harvest. Infiltration was highest in the no-tillage and chisel
plow treatments on all dates except immediately after tillage when the
moldboard plow treatment had the highest infiltration rate.
The number of macropores is greater in conservation tillage systems
than conventional systems because macropores in the tillage zone are not
disrupted by annual tillage and faunal activity is greater due to the more
favorable moisture and temperature regime. This has led to concern that
macropores may cause accelerated leaching of groundwater contaminants such
as pesticides and nitrates under conservation tillage. Some studies from
other regions have found more rapid leaching of solutes in no-tillage compared
to conventional tillage (Andreini and Steenhuis, 1990; Dalal, 1989; Germann
et al., 1984; Isenesee et al., 1990; Zachman et al., 1987) but other studies
found the reverse or no difference (Kanwar, 1991; Shipitalo and Edwards,
1993). Studies from other regions have also shown that nonlegumenous winter
cover crops can reduce nitrate leaching due to their effect on nitrogen
and water uptake (Meisinger et al., 1990). On a Cecil-Pacolet series, McCracken
et al. (1995) found that nitrate leaching losses were not affected by tillage
over a three-year period, except one summer when heavy rainfall occurred
shortly after fertilization. In this case, leaching losses tended to be
greater under no-tillage compared to conventional tillage. They also found
that a winter cover of rye significantly reduced nitrate leaching losses.
Several studies have found that groundwater quality is affected by animal
agriculture. Gould (1995) sampled 236 wells in the Little River/Rooty Creek
watershed in North Georgia where there is a high concentration of dairy
farms. Thirteen percent of the wells had NO3 -N concentrations
above the EPA drinking standard of 10 mg L-1 . Thirty nine percent
had NO3 -N concentrations above background (3 mg L-1
). Drommerhausen et al. (1995) used ground electromagnetic conductivity
measurements on nine dairies in this area to determine the source of the
nitrate in the wells. They concluded that dairy loafing areas (the corrals
and areas of fields where the herd stays when it is not being milked or
on pasture) were the most likely source of contamination. These loafing
areas were usually located close to the milking barns where the well was
also located. Monitoring wells installed in the loafing areas at three
of these dairies had NO3 -N concentrations between 60 and 138
mg L-1. There was evidence that NO3 -N was seeping
from three of the six lagoons surveyed, but this was considered an unlikely
source of the NO3 -N in the wells because the lagoons were a
substantial distance down-gradient of the wells. A 15- county survey of
domestic well water in Georgia in 1993 found that nitrate concentrations
were higher near swine, dairy, and poultry operations (5.36, 4.12, and
3.69 mg NO3 -N L-1 ) compared to irrigated
agriculture and nonagricultural wells (2.21 and 1.44 mg NO3-N
L-1 ) (Bush et al., 1997). The study included five counties
in the Coastal Plain region.
Industrial landuse has also had an effect on contaminants in Piedmont
soils and shallow groundwater. Christian et al. (1992) reported that as
of 1989 there were eight CERCLA (Comprehensive Environmental Response,
Compensation, and Liability Act or “superfund”) sites, 49 RECRA (Resource
Conservation Recovery Act) sites, and 841 contaminated sites in the Piedmont
region of North Carolina. Two-thirds of these were underground storage
tank (UST) leaks of petroleum products. Seventy percent of the sites were
in urban settings, but on a per capita basis, rural residents were as likely
as urban residents to be affected. Approximately three-quarters of the
contaminated wells were residential supply wells. Various methods for remediating
contaminated soil and shallow groundwater at sites in the Piedmont have
been reported including in situ vapor extraction (Wisniewski, 1992; McClinton
and Workentine, 1992), pump and treat (Furt, 1992; Kasper, 1992), and bioremediation
Contamination of surface waters has received a large emphasis in recent
years and several studies in the Piedmont have related contaminant levels
to land use. In North Carolina, Simmons and Heath (1992) compared water
quality of streams that had less than 10% of the watershed area in agriculture
with that of streams with greater than 10% in agriculture. Phosphorus (P)
levels were 2 to 13 times greater in storm runoff from the high agriculture
watersheds. Total nitrogen (N) and P in storm runoff increased as the percent
of the basin in agriculture increased. Kuykendall et al. (1996) measured
soluble reactive phosphorus (SRP) in runoff from pastures in Georgia that
received 10 Mg broiler litter per ha in split spring and fall applications.
Concentrations of SRP reached values as high as 8 mg L-1 . This
is significant considering that the EPA has established guidelines of 0.1
mg L-1 total P for streams and 0.05 mg L-1 total
P for lakes. Jordan et al. (1997) compared N concentrations in 10 Piedmont
and 17 Coastal Plain streams in the Chesapeake Bay area. They found that
flow-weighted nitrate concentrations were consistently higher in Piedmont
streams and speculated that the difference might be due to less effective
filtering of nitrate in Piedmont forested riparian zones due to deep groundwater
Limited research has been done on the effect of riparian buffers on
stream water quality in the Piedmont. Daniels and Gilliam (1996) examined
surface runoff from cultivated areas into riparian zones consisting of
a grass buffer or a grass and forest buffer in North Carolina. Riparian
buffers reduced total P by 50% but soluble P was reduced by only 20%. Forested
ephemeral gullies transported nutrients through the riparian zone with
little reduction in nutrient concentrations. Parsons et al. (1994) also
examined surface runoff in grass and forested riparian zones in North Carolina.
Nitrate and total N showed substantial reductions, but not soluble P. Verchot
et al. (1997a and 1997b) used level spreaders that forced runoff out of
ephemeral gullies in forested riparian zones, but N loads in runoff were
not substantially reduced in the riparian zones. Nitrate concentrations
in the subsoil dropped from 6-10 mg L-1at the edge of fields
to less than 1 mg L-1 in the riparian zones. Sweeney (1993)
examined a forested Piedmont watershed in Pennsylvania. The author reported
limited data on N that showed springs and deep (>25 m) groundwater had
relatively high NO3 -N concentrations (averaging > 7 mg L-1
) compared to shallow (<3 m) groundwater (<0.1 mg L-1
) and streamwater (3 mg L-1 ).
Water quality in urban streams of the Piedmont has received attention
lately. Hippe and Garrett (1997) compared streamwater samples from groups
of small watersheds representing the predominant land uses in the Appalachicola,
Chattahoochee, and Flint river basin. Pesticides were detected most frequently
and at highest concentrations in urban watersheds, followed by suburban,
row crop agriculture, poultry and livestock production, and forested watersheds.
Insecticides were detected at concentrations exceeding the maximum recommended
level for aquatic life in urban and suburban watersheds. Pesticides with
large runoff-potential ratings were the most commonly detected and had
the highest concentrations. Pesticides having medium runoff potential were
detected primarily in urban and suburban watersheds. This may have been
due to over application or more impervious surfaces in these areas.
The Southern Piedmont is one of the larger MLRAs in the southeastern
United States and we have considerable information on the major soils of
this region. Parent material (felsic vs. mafic rock) is important in determining
the properties of the soil and the thickness of the saprolite layer, which
is an important storage zone for groundwater. Soil horizons differ sharply
in texture and structure and this affects water and solute movement. Variable-charge
mineralogy is common and this makes these soils dispersive at high pH and
capable of adsorbing anions at low pH. Lateral movement of water and solute
may occur in these soils depending on landscape position. Ground water
and surface water contamination has been documented in association with
livestock, industrial, and urban landuse. More information is needed on
poorly drained soils that have not been important for agriculture production,
but are important in urban/suburban landuse and on the transport properties
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