This file was created by scanning the printed publication.
Errors identified by the software have been corrected;
however, some errors may remain.
Physical Characteristics and Pedogenesis of Soils
in Riparian Habitats Along the Upper Gila River Basin1
John H.
;:>
Brock~
Abstract.--Knowledge of soils in southwest riparian
habitats is minimal. Soil profiles in the riparian zone on
the Gila and San Francisco Rivers were studied. The soils
that support trees can be cl assif i ed as Torri fl uvents or on
the more stable sites as Haplustolls. Coarse textures and
low water holding capacity are dominant characteristics.
INTRODUCTION
RELATED LITERATURE
Riparian communities of the southwest are
dominated by tall broadleaf woody pI ants whi ch
affect the mi crocI imates of adj acent aquatic
habitats while providing cover, nesting sites
and food i terns for many desert animals. Since
the early 1800's riparian habitats along river
systems of the arid southwest have undergone
significant biological, physical and hydrologic
changes, primarily from increased human activity
( C ar 0 the r s 1 9 7 7 ).
Al tho ugh rip a ria n are as
represent 1 ess than four percent of the 1 ands in
the western United States, they are of great
importance in arid land ecosystem functions,
particularly as wildlife habitats.
The
importance of ri pari an communi ties as wildlife
habitat has been well described in the
1 i terat ur e (Todd 1972, and Carothers 1977).
Riparian communities fit in the wetland
classification under riverine systems (Cowardin
1982). One attribute of this wetland system,
according to a Fish and Wildlife Service
definition, is "the substrate is nonsoil and is
saturated with water or covered by shallow water
at some time during the growing season"
(Cowardin 1982). The "nonsoil" of such riverine
systems would be placed into the order Entisols
since soil horizonation does not exist in
streambed materials and because pedogenetic
processes are slower than transport activities
(Soil .survey Staff 1975).
Soils of arid and semi-arid regions
typically exhibit limited pedogenesis,
especially along drainages. \oJestern (1972)
a d v 0 cat e d t hat so i 1 t ext 1..1 r e, de gr e e 0 f
depositional stratification and effective soil
depth be given major consideration for
descri bing such soils. Using the deposi tional
approach, defining vertical variability of
texture as closely as possible would be
accentuated since stratification may alter water
movement and root penetration and emerge as a
dominant soil characteristic. Under the soil
classification system used by Western (1972)
these type of soils would be placed into the
sedosols category.
Study of ri pari an zones has pr evi ousl y
focused on the organisms that occupy the nar'row
habitats. As research intensified, it became
evident that little was known about the soil
supporting the vegetation that characterizes the
riparian zone.
Very limited literature exists
on riparian soils except that reported by Martin
and Fletcher (1943) and recently completed work
by Medina (1985).
This paper will present
information concerning soils in the riparian
habitat of the upper Gila River Basin.
Classification of the soil, its physical
characteristics and its pedogenesis will be
di scussed.
Very limited literature exists for the
southwest riparian zone soils.
Martin and
Fletcher (1943) described soil great groups that
included drainages on Mount Graham in
southeastern Arizona but not soils specifically
within the drainages.
The most detailed work
available on riparian soils in the southwest was
recently completed from research ini tiated in
1981 (Medina 1985). The riparian soils were on
upland watersheds near Fort Bayard in western
New Mexico.
The taxonomic subgroup units
identified for those drainages included: Mollic
Ustifluvents, Aquic Ustifluvents, Aquic
1
Paper presented at the symposium on
Riparian Ecosystems and their Management:
Reconciling Conflict Uses. [Tucson, Arizona,
Apri1 16-18, 1985J
2
John H. Broc k i s Ass 0 cia t e Prof es s or of
Agriculture, Arizona State University, Tempe,
Ari zona.
49
Haplustolls and Cumulic Haplustolls
1985).
Coarse materials were sorted to three size
classes (rock> 7.5 cm, cobbles from 7.5 cm to 2
cm and gravel from 2.0 cm to 2 mm) (fig. 1).
The 1 arger two cl asses wer e vi s uall y es ti rna ted
from a known total volume. Gravel content was
determined by sieving and weighing.
The
material that passed the 2 mm sieve was
separated into sand, silt· and clay sized
parti cl es in the 1 aboratory us ing the hydrometer
method.
(Medina
Soils along the drainages of the upper Gila
River Basin (Eastern Arizona and Western New
Mexico) that support mature woody riparian
species were surveyed as a complex of Ellicott
and Paymas ters seri es (USDA S oi 1 Sur vey 1983).
These soils at the subgroup level are Ustic
Torrifluvents (Ellicott) and Cumulic Haplustolls
(Paymaster).
Both soils are subject to su.mmer
flooding with the flood event being rarer for
the Hapl ustolls. The soil material in the most
active part of the streambed was designated in
the soil survey report as riverwash.
HETHODS
The study area included six research sites.
Two were on the San Francisco River in Eastern
Arizona and four were on the Gila River in
Western New Mexico. The San Francisco River
sites were 8 and 24 km, respectively, upstream
(northeas t) fran Cl if ton , Ari zona. The four New
Mexi co si tes were located from south to north
along the Gila river as follows:
(a) 0.8 km
north of the bridge near Red Rock, (b) 12 km
south of U.S. Highway 180 near the U.S. Forest
Service Bird Management area, (c) 11 km north of
the towns of Cliff and Gila near Mogollon Creek
and (d) 19 km upstream from Cliff and Gila in
the vi cini ty of Tur key Creek. Thi s study ar ea
also included a well defined mesquite bosque.
F i gur e 1. - - C 0 a r s e f r a gm e n t s are com m0 n i n
riparian soils. Sample is of riverwash
material near Red Rock, New Mexico.
Since coarse soils rapidly transport water,
a water movement laboratory study for soils of
the riparian habitat was conducted. Large
graduated cylinders (1000 ml) were filled with
35 em of soil mat.erial leaving approximately 5
cm of space for the addi ti on of wat er. Thr ee
cylinders were filled with fine sands (less than
0.42 mm in size), three with coarse sands (1 to
2 mm in size) and three with coarse unsieved
ri verwash materi a1. Two hundred mill il iter s of
water was added to each cyl inder and the rate of
water movement over thirty minutes was measured
by following the wetted front.
The flood plains are mixed alluvium derived
from granite, rhyolite and conglcmerate (USDA
Soil Survey, 1983).
Average annual
preCipitation is approximately 35 cm and the
growing season is 150 to 180 days. Mean annual
soil temperature and air temperature are
approximatel y the same at 14 0 c (USDA Soil Sur vey
1983).
Slopes range fran zero to three percent
and elevation ranges from 1200 to 1900 m.
Water movement rates and water storage
capaci ty in coarse soils is an important factor
to relate availability of water to riparian
plants. Water retention capaci ty was determined
for the mature forest and riverwash soil
materi al s. The saturati on poi nt was found by
wetting samples to super saturation wi th the
superfluous water drained by gravity. Soilwater retention was also determined at moisture
tension levels of -0.03 (field capacity), -0.1,
-0.25, -0.75 and -1.5 (wilting point) MPa of
tension using a pressure plate apparatus.
Percent soil-water retention capacity was
determined gravimetri cally.
At each of the six sites a soil profile in
a stand of mature trees, including the mesquite
bosque, was examined. The exposed profiles were
approximately one meter in width to a depth of
two meters. The profiles were separated into
soil layers based on color differences or
appreciable changes in texture or structure.
The thickness of the soil layers was measured
and duplicate samples from each layer were
returned to the laboratory for further anal ys i s
as needed to classify soils.
Normally, to estimate soil texture, soils
are sieved to 2 mm to determine sand, silt and
clay content. However, riparian soils may
co nt ai n alar ge vol ume of coarse fragments and
the standard procedure would not give an
accurat.e representation of texture. Alexander
(1981) described a technique to estimate the
coarse soil fraction that employs a combination
of visual estimates of volumes and weighing.
RESULTS AND DISCUSSION
Three soils were identified in the riparian
zone. Two soils were located in the proximi ty
of perennial woody vegetation and the othe~ was
the raw material of the flood plain. Of the
50
Table 1.--Profile description for a typical Ustic Torrifluvent on the
upper Gila River Basin.
seven soil profiles examined in the vicinity of
mature woody perennials, four were classified to
the greatgroup Torrifluvents and three were
placed in the Haplustolls great group.
The
third soil was ri verwash.
Horizon Designation
C 1
0-66 em, 10 YR 5/2 grayish brown (dry), fine
sand, 10 YR 3/3 dark grayish brown (wet);
single grain, loose; numerous roots, abrupt
boundry, bedding planes.
C 2
66-142 em, 10 YR 5/2 grayish brown (dry),
cobbly sand, 10 YR 3/2 dark grayish brown
(wet); single grain, loose.
C 3
142-167 em, 10 YR 5/2 grayish brown (dry),
coarse sand, 10 YR 3/2 dark grayish brown
(wet). Abrupt boundry to rounded cobbles.
Soil Profile Descriptions
The Torrifluvent soil was further
classified to the Ustic subgroup. A profile
description of the Ustic Torrifluvents fran the
site located 11 km upstream fran Cliff and Gila,
New Mexico is contained in table 1. The deep,
well-drained Torrifluvents have a sandy surface
that averaged 42.5 cm in depth. The number of
soil strata present was directly related to
Descri ption
Table 2.--Profile description for a typical Fluventic Haplustoll on the
upper Gila River Basin.
deposi tional patterns as may be expected from
hlestern's (1972) paper and ranged from three to
seven. The separation of the layers was based
primarily on textural differences resulting from
the energy of water that had transported the
alluvial material. Thin lenses of fine textured
material such as loams or silt loams were
present in some of the pedons.
The mean soil
depth of the Torrifluvents was 174 cm.
Descri ption
Hori zon Designation
The placement of the soils into the Ustic
Torrifluvents subgroup agrees well wi th the soil
survey of western Grant County, New Mexico (USDA
Soil Survey 1983). The soils are in the great
group Torrifluvents because they have a mean
annual soil temperature of approximately 14 0 c
but may also lack water within the top 50 cm for
more than 90 consecutive days during the year.
They are in the subgroup Usti c because they do
have moisture available for plant growth during
favorable growth periods, primarily in the
spring and early summer. The Haplustolls were
classified to the subgroup Fluventic. A typical
pedon of a Fluventic Haplustoll is given in
t a bl e 2 from the sit e a p pro xi mat ely 1 9
kilometers above the towns of Cliff and Gila.
The profile description is for the deep, well
drained soils that form in more stable alluvium.
The Haplustolls surface had a mean depth of 30
em.
A 1
0-53 em, 10 YR 4/2 dark grayish brown (dry),
ver y fine sand, 10 YR 2/2 very dark brown
(wet); weak crumbly, very friable; worm cas ts
in upper 5 em, common macropores, few fine
roots; weakl y efferves cent; gradual boundry.
C 1
53-107 em, 10YR 5/2 grayish brown (dry), fine
sandy loam, 10 YR 2/2 very dark brown (wet);
weak subangular blocky, very friable; few
laminar planes; coarse roots, neutral; gradual
boundry.
C 2
107-213 em, 10
sand, 10 YR
grain, loose;
abrupt contact
YR 5/3 brown (dry), very fine
3/3 dark brown (wet); single
coarse roots, few cobbles;
wi th large rounded cobbles.
woody ri pari an speci es. These ri pari an seedbeds
are at present commonly referred to as nurse§y
bars by Brady et al. (1985) and Brock .
Riverwash would be in the suborder Fluvents. No
profile description will be attempted in this
paper since there was no stratification;
however, the physical characteristics of the
ri verwash materi al will be presented.
Physical Characteristics of Riparian Soils
The coarse textural nature of soils in
riparian areas provides unique qualities
compared to finer soils. The riparian soils of
the southwest are characterized by large
fragments. The Haplustolls contained 10% coarse
fragments (> 2mm) by weight, the Torrifluvents
had 23% coarse material and the riverwash
contained approximately 63%. Of the 63% coarse
fragments in the riverwash, the portions of
rocks, cobbles and gravel was 14, 16 and 33%
respectively of the total volume. The remaining
37% of "fine" material in proportion to the
Unlike the soil survey information that
placed the Haplustolls along the water courses
i nth e C um u 1 i c sub g r 0 up, the Hap 1 us t oIl s
examined in this study did not have a thick
enough epi pe don (more than 50 cm) to be pl ace d
in that category.
Alluvial deposition was
evident in the surface soil material.
As a
res u 1 t, the sub g r 0 u pel as s i f i cat ion for the
Haplustolls along these reaches of riparian
habitats was the Fluventic extragrade.
The third soil material identified was
confined to the most active part of the flood
plain. Unlike the Ustic Torrifluvents and the
Fluventic Haplustolls it lacked any signs of
pedogenesis. The material is unconsolidated,
very coarse and contains raw parent materials
best referred to as riverwash. While riverwash
may be consi dered by some to be only soil parent
material, it is the seedbed for many of the
3 Brock, J. H. 1984. Some autecological
studies on regeneration and maintenance of
selected riparian plant species. Unpublished
report.
Arizona State University, Division of
Agriculture, Tempe, Arizona. 166 p.
51
Pedogenesi s
whole soil was 33% fine sand, 2% silt and 2%
clay.
Riverwash material, excluding the coarse
fragments, was 84% sand, 9% silt and 7% clay.
Soil longevity in active water courses,
especially in the southwest, strongly influences
the degr ee of pedogenesi s. In the ari d or semiarid southwest, soils along water courses are
more a result of geomorphology resulting from
stream flows. Thi s concept is supported by the
paper of Western (1972) that dealt wi th soils of
arid streams. Brady et al. (1985) described the
development of ri pari an ve ge t at i on stan ds from
initial establishment to maturity. Soils
continue to deepen by aggradation and, wi th good
vegetative protection, stabilize against the
geomorphic forces.
The coarse fragment content of the more
developed soils ranged from 0 to 55 percent.
The mean amount of coarse fragments was 16.5%
for the Torrifluvents and Haplustolls. Textural
analyses of the Torrifluvents and Haplustolls
for the fine portion of the soi Is are pr es en ted
in table 3. As might be expected, both soils
have a dominance of sand in the surface. The
evidence of pedogenesis in the Haplustoll is
seen best by examining the texture of the
subsurface soil. While sand was the dominant
textural fraction, the increase in silt and clay
in the Hapl us tolls Has evi dent.
The degree of pedogenesis in riparian soils
is directly tied to stability of the substrate
and magnitude of streamflow events.
The
dynamics of the soil forming-stability process
in the Gila River Basin was demonstrated in
October 1983. On the San Francisco River of the
upper Gila basin, major areas of Ustic
Torrifluvents were changed to ri verwash by
flooding (fig. 2).
At this site, (24 km
upstream from Clifton, Arizona) a depth of
approximately 1.5 to 2.0 m of stable soil was
moved fran an area approximately 50 m in width.
Flooding is the major factor influencing the
nature of riparian soils in the southwest Uni ted
States from a pedogenic viewpoint and is the
force that largely determines their physical
properties.
Water readily moves through coarse soils.
The rapidity of water movement through the
riparian soil material was greater than
expected. Laboratory tests resulted in water
movement rates of 0.9, 1.4 and 2.4 cm/minute for
fine sand, coarse sands and cobbly sand
materials, respectively. While riparian soils
may rapidly absorb water they release water
freely as well. Water retention percentages
were determined for the Torrifluvents,
Haplustolls and riverwash materials.
Water
holding capacity, at saturation, averaged 45.6%
across all soils and was highest for Haplustolls
and lowest in the ri verwash (table 4). Water
retention capacity decreased rapidly with even
small increases in pressure that forces water
from the soil matrix. Haplustolls maintained
higher water holding capacity which corresponded
to the finer textures. At higher tensions,
water retention capacities were slightly lower
in the ri verwash materi al. At wilting poi nt (1.5 MPa), all soils had less than 7% water
content.
CONCLUSION
Pedogenesis of soils in riparian habitats
of the southwest, gi ven adequate soil anchor age
and aggradation of fine sediments is from the
Entisols to the Mollisols order. The major
factor determining the characteristics of, the
soils is the energy of streamflow. In general,
ri pari an soils are geomorphically very young and
coarsely textured. As a resul t, they readil y
transmit water and have a low water retention
capacity. The primary management criteria of
riparian soils as a growth media for woody
riparian species would be a dependable soilwater supply.
Table 3.--Textural analyses for percent sand, silt and clay fractions
Ustic Torrifluvents and Fluventic Haplustolls in surface and
subsurface soils in the riparian zone of the upper Gila River
Basin.
Hapl us toll s
Torri fl uvents
Textur al Fract ion (%)
Sand
Silt
Clay
Surface
71.4
20.4
8.2
Subsurface
Surf ace
Su bsurf ace
83.9
9.6
6.6
64.5
13.2
56.4
26.3
13.2
17.3
ACKN OVJL EDGEMENT S
Table 4.--Water retention capacity for three riparian zone soils found
in the Upper Gila River Basin.
This research was conducted under an
Interpersonal Agreement (IPA) with the author
and the Rocky Mountain Forest and Range
Experiment Station, USDA Forest Service.
Funding was through the Bureau of Reclamation,
USDI, Boulder City, Nevada. Chris Brock was
instrumental in aiding initial soil profile
sampling. Charmaine Tso and Julie Sturgeon
deserve recognition for their assistance in
collecting and summarizing water retention
capacity data.
Water Retention Capaci ty ( %) at Water Tensions (-MPa)
Soil
Torri fl uvents
Hapl ustolls
Ri verwash
Saturated
48.3
52.6
36.1
-0.03
15.7
18.1
12.0
-0.10
-0.25
-0.75
-1.5
7.4
8.8
4.8
6.8
8.6
4.9
6.5
6.9
3.3
9.5 1
22.0
6.8
'Mean in -0.10 (MPa) column is significantly different at p
=
0.05.
52
F i gur e 2. - - So i 1 s tab i 1 i t yin a rip a ria n h a bit a t as
influenced by high storm flow. Twenty-four kilometers
upstream from Clifton, Arizona. Left photograph date
is August 1983.
Right photograph is of the same site
in November 1983 following flooding.
Medina, A. L. 1985. Riparian plant communities
and soils of the Fort Baryard Watershed in
Southwestern New Mexico (In Press).
Southwest Association of Naturalists.
LITERATURE CITED
Alexander, E. B. 1981.
Volume estimates of
coarse fragments in soils:
A combination
of vi sual and wei ghing procedur es . Jour nal
of Soil and Water Conservation. 36:360-361.
Soil Survey Staff. 1975. Soil Taxonomy. U.S.
Department of Agriculture.
Soil
Conservation Service. Agriculture Handbook
No. 436. 754 p.
Brady, W. W., D. R. Patton, and J. Paxson. 1985.
The development of southwestern riparian
gallery forests. In Symposium of Riparian
Ecosystems and their Management:
Reconciling Conflicting Uses.
[Tucson,
Arizona, April 16-18, 1985J.
Todd, R. L. 1972. Biol ogi cal report on a mars h
near Tuzigoot National Monument. Ari zona
Game and Fish Department Special Report w53-23. 4p.
Carothers, S. W. 1977. Importance, preservation
an d management of ri par ian ha bi tats: An
Overview. In:
Importance, Preservation
and Man a gemen t 0 f R i pa ria n Ha bit at:
A
Symposium. USDA Forest Service. General
Technical Report. RM-43. p. 2-4.
U.S. Department of Agriculture 1983.
Soil
survey of Grant County, New Mexico, Central
and Southern parts. U.S. Department of
Agriculture, Soil Conservation Service and
New Mexico Agricultural Experiment Station.
216 p.
Cowardin, L. M. 1982. Wetlands and deepwater
habitats:
A new classification. Journal
of Soil and Water Conservation. 37: 83-85.
Western, S. 1972. The classification of arid
zone soils. I.
An approach to the
classification of arid zone soils using
depositional features.
Journal of Soil
Science. 23: 266-277.
Martin, W. P., and J. E. Fletcher. 1943. Great
soil groups on Mount Graham. Uni versi ty of
Arizona Agricultural Exper'irnent Station.
Technical Bulletin. 99: 87-153.
53