Geomorphology 122 (2010) 117–128
Contents lists available at ScienceDirect
Geomorphology
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / g e o m o r p h
Ecoregions and stream morphology in eastern Oklahoma
Dale K. Splinter a,⁎, Daniel C. Dauwalter b,1, Richard A. Marston c, William L. Fisher d,2
a
Department of Geography and Geology, University of Wisconsin-Whitewater, Whitewater, WI 53190-1790, USA
Oklahoma Cooperative Fish and Wildlife Research Unit and Department of Zoology, Oklahoma State University, Stillwater, OK 74078, USA
c
Department of Geography, Kansas State University, Manhattan, KS 66506-2904, USA
d
United States Geological Survey, Oklahoma Cooperative Fish and Wildlife Research Unit and Department of Natural Resource Ecology and Management, Stillwater, OK 74078-3051, USA
b
a r t i c l e
i n f o
Article history:
Received 31 January 2008
Received in revised form 25 May 2010
Accepted 2 June 2010
Available online 9 June 2010
Keywords:
Fluvial geomorphology
Streams
Ecoregions
Oklahoma
a b s t r a c t
Broad-scale variables (i.e., geology, topography, climate, land use, vegetation, and soils) influence channel
morphology. How and to what extent the longitudinal pattern of channel morphology is influenced by broad-scale
variables is important to fluvial geomorphologists and stream ecologists. In the last couple of decades, there has
been an increase in the amount of interdisciplinary research between fluvial geomorphologists and stream
ecologists. In a historical context, fluvial geomorphologists are more apt to use physiographic regions to distinguish
broad-scale variables, while stream ecologists are more apt to use the concept of an ecosystem to address the broadscale variables that influence stream habitat. For this reason, we designed a study using ecoregions, which uses
physical and biological variables to understand how landscapes influence channel processes. Ecoregions are
delineated by similarities in geology, climate, soils, land use, and potential natural vegetation. In the fluvial system,
stream form and function are dictated by processes observed throughout the fluvial hierarchy. Recognizing that
stream form and function should differ by ecoregion, a study was designed to evaluate how the characteristics of
stream channels differed longitudinally among three ecoregions in eastern Oklahoma, USA: Boston Mountains,
Ozark Highlands, and Ouachita Mountains. Channel morphology of 149 stream reaches was surveyed in 1stthrough 4th-order streams, and effects of drainage area and ecoregion on channel morphology was evaluated using
multiple regressions. Differences existed (α≤ 0.05) among ecoregions for particle size, bankfull width, and width/
depth ratio. No differences existed among ecoregions for gradient or sinuosity. Particle size was smallest in the
Ozark Highlands and largest in the Ouachita Mountains. Bankfull width was larger in the Ozark Highlands than in
the Boston Mountains and Ouachita Mountains in larger streams. Width/depth ratios of the Boston Mountains and
Ozark Highlands were not statistically different. Significant differences existed, however, between the Boston
Mountains and Ozark Highlands when compared individually to the Ouachita Mountains. We found that
ecoregions afforded a good spatial structure that can help in understanding longitudinal trends in stream reach
morphology surveyed at the reach scale. The hierarchy of the fluvial system begins within a broad, relatively
homogenous setting that imparts control on processes that affect stream function. Ecoregions provide an adequate
regional division to begin a large-scale geomorphic study of processes in stream channels.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
1.1. A regionalized landscape
The late-19th and early-20th centuries produced a series of works
(e.g., Powell, 1895; Fenneman, 1931, 1938; Loomis, 1937; Atwood,
1940) in North America that constructed the landscape into distinct
physiographic regions. For the most part, these regional delineations
⁎ Corresponding author. Tel.: + 1 262 472 5156.
E-mail address: splinted@uww.edu (D.K. Splinter).
1
Current address: Trout Unlimited, 910 Main Street, Suite 342, Boise, Idaho 83702.
2
Current address: United States Geological Survey, New York Cooperative Fish and
Wildlife Research Unit, and Department of Natural Resources, Cornell University, Ithaca,
NY 14853.
0169-555X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.geomorph.2010.06.004
were determined by differences in geologic structure, altitude, relief,
and topography (Thornbury, 1965). By the mid-20th century,
however, the casual relationships of natural phenomena (i.e.,
physiography) had been elaborated on using a more detailed and
systematic geomorphic analysis of landform origin. For example, the
morphometric analyses of watersheds and stream networks (Horton,
1945; Strahler, 1950a,b, 1952, 1956; Schumm 1956; Hack, 1957;
Melton, 1957; Morisawa 1962) set forth methods by which the
quantitative understanding of landforms was possible (Strahler,
1968). In turn, fluvial geomorphologists, hydrologists, stream ecologists, and watershed managers now use statistical analyses that link
similar landscapes to morphometric analyses, regional channel
geometry, water quality, and aquatic assemblages (Larsen et al.,
1986; Rohm et al., 1987; Lyons, 1989; Griffith et al., 1999; Marchant
et al., 2000; Rabeni and Doisy, 2000; Cinotto, 2003; Dauwalter et al.,
2007, 2008; Johnson and Fecko, 2008; Splinter et al., in press).
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D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
Montgomery (1999) argued that understanding how geomorphic
processes relate to ecosystem function is necessary for ecosystem
management with diverse physiographic regions. In addition to
physiographic regions, regional boundaries have been set by
ecological regions. Landscapes that constitute similarities in climate,
geology, vegetation, soils, and land use comprise ecological regions.
These regions encompass an area where a holistic approach to
ecosystem management is focused (Bailey, 2002). The United States
Bureau of Land Management, Fish and Wildlife Service, Forest Service,
and National Parks Service have worked to implement ecological
regions into their ecosystem management strategies (Bailey, 2002).
The two most common delineations of ecological boundaries in the
United States have been constructed by Bailey (1995) and Omernik
(1987). Ecoregion delineations of Bailey were developed primarily for
application by the United States Forest Service and are based chiefly
on climate and vegetation. Ecoregions delineated by Omernik were
originally developed by the U.S. Environmental Protection Agency for
water quality management. The purpose of any ecoregion delineation
is to differentiate regions with contrasting ecosystem function
(Omernik and Bailey, 1997). Considering the recent attempts to link
ecology and geomorphology (Urban and Daniels, 2006; Renschler
et al., 2007), the implementation of ecoregions in the fluvial hierarchy
can be a useful way to help satisfy this linkage. For this reason, we
completed a study that explained how the longitudinal patterns of
channel morphology varied among Omernik's ecoregions in eastern
Oklahoma, USA.
The ultimate objective of this study was to establish whether
trends in channel morphology (i.e., particle size, bankfull width,
width/depth ratio, gradient, and sinuosity) differed among the Ozark
Highlands, Boston Mountains, and Ouachita Mountains ecoregions. If
differences exist among channel morphology by ecoregion, then the
processes that dictate channel form are also different, which has
implications for stream management and stream restoration.
1.2. Hierarchy in fluvial geomorphology and stream ecology
Studies in fluvial geomorphology are organized by a spatial
framework. A hierarchical framework has been established that
exhibits smaller scale components nested into larger scale components; the smaller scale component is influenced by the variables that
constitute that next larger scale (Frissell et al., 1986; Kondolf et al.,
2003). For example, a region with similar lithology, climate,
geomorphology, and land use history would support similar channel
characteristics (Kondolf et al., 2003). This hierarchical approach is
widely accepted as a measure to assess the factors that influence
stream morphology and the ecological characterization of rivers
(Vannote et al., 1980; Lotspeich, 1980; Brussock et al., 1985; Biggs et
al., 1990; Montgomery, 1999; Brierley and Fryirs, 2000; Thompson et
al., 2004; Schmitt et al., 2007). A landscape that has been regionalized
by both physical and biological components (i.e., ecoregions) provides
a broad-scale hierarchy by which investigations into fluvial studies
begin.
Interdisciplinary approaches to river science attempt to comprehend the relationship between biological and physical components
(Parsons and Thoms, 2007). Fluvial geomorphologists are asked to
decipher how the causal relationships of the holistic environment
underpin processes associated with channel morphology and biotic
function (Brierley and Fryirs, 2005; Parsons and Thoms, 2007).
Phillips (2007) recently stated “landscapes are indeed shaped and
controlled by deterministic, global laws, but the operation of these
laws in specific geographical and historical contexts means that
landforms and landscapes are often circumstantial, contingent outcomes, not derivable from global laws alone.” Whereas predicting
channel morphology at a given point in space is difficult, the
longitudinal trends in channel morphology might differ significantly
among regions where biotic and abiotic components are interrelated.
The importance of interdisciplinary research between stream
ecology and fluvial geomorphology has become increasingly apparent
over the last quarter-century. Geomorphology plays a role in the
functioning of ecosystems, while ecosystems influence geomorphic
forms, processes, and associated stream management (Brierley and
Fryirs, 2005; Urban and Daniels, 2006; Renschler et al., 2007). The
importance of developing a stronger interdisciplinary approach
between ecology and geomorphology was realized at 36th International Binghamton Symposium in 2005. The symposium “Geomorphology and Ecosystems,” brought researchers together to discuss the
current and future status for bridging geomorphology and ecology
(Renschler et al., 2007).
1.3. Omernik's ecoregions
Ecoregions of the conterminous United States were established to
help environmental managers comprehend landscape characteristics
that influenced regional patterns of aquatic and terrestrial resources
(Omernik, 1987). In addition, ecoregions provide a framework for
comparative analysis of environmental problems (Loveland and
Merchant, 2004a,b). Omernik's ecoregions were delineated by similar
associations of climate, soils, land use, topography, and potential
natural vegetation. A short review of how Omernik's maps were
constructed follows; however, we suggest reading the original
document (Omernik, 1987) for specifics.
A series of component maps were used to delineate ecoregions.
These include: Major Land Uses (Anderson, 1970), Classes of LandSurface Form (Hammond, 1970), Potential Natural Vegetation (Kuchler,
1970), and soil maps from multiple sources. Additional maps were
used to verify the accuracy of the component maps. These include:
Surficial Geology (Hunt, 1979), Physical Divisions (Fenneman, 1946),
Land Resource Regions and Major Land Resource Areas of the United
States (U.S. Department of Agriculture, 1981, Climates of the United
States, (Baldwin, 1973) and Census of Agriculture (U.S. Bureau of the
Census, 1969, 1974, 1978).
Omernik's ecoregions are commonly 130,000 km2, but range
between 15,000 km2 and 330,000 km2. These ecoregions encompass
watersheds of 500 km2. Ecoregion boundaries were delineated after a
rough draft of the region was sketched. Component maps were used
via a map overlay process to delineate each ecoregion. Boundaries
reflect the main condition that defined each ecoregion. The ecoregion
boundaries of the Ozark Highlands, Boston Mountains, and Ouachita
Mountains resemble physiographic boundaries describe by Fenneman
(1938), Atwood (1940), and Hunt (1967). Fenneman (1938),
however, included the Boston Mountains in his regionalized Ozark
Plateaus. He did recognize the Boston Mountains as a “general
denudation of the Ozark dome.”
Ecoregion boundaries are potentially better than geomorphic
provinces for delineating the hierarchical structure of the fluvial
system because of the greater number of variables used in the
delineation and the lesser influence placed solely on geologic
structure. In addition, most geomorphic boundaries do not incorporate land use variables for delineation. One hundred twenty Level III
ecoregions exist in the United States according to Omernik (1987),
which is twice the number of geomorphic provinces in Hunt (1974).
We selected Omernik (1987) ecoregions as an alternative to Bailey
(1995) ecoregions to decipher whether the characteristics of stream
channels differed among ecoregions. We did this because Omernik's
ecoregions were originally intended for surface water quality and
management (Loveland and Merchant, 2004a,b) and are constantly
being revised.
2. Longitudinal trends in channel morphology
Characteristics that define stream channel morphology (e.g.,
particle size, width, depth, gradient, and sinuosity) vary along the
D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
longitudinal profile of the stream (Vannote et al., 1980; Rosgen,
1996). Variation in channel morphology occurs for different reasons.
These include, but are not limited to, changes in discharge, sediment
regime, climate, and local geology. Human modification of the
landscape (i.e., logging, grazing, dam building, and urbanization)
impacts the spatial and temporal changes of river systems and
morphology. For this reason, it is difficult to develop a model that
accurately predicts longitudinal changes in channel morphology
among different regions; however, regional trends have been
established (Brussock et al., 1985; Johnson and Fecko, 2008). Grant
and Swanson (1995) reported that high gradient mountain streams
greatly differ from lower gradient streams. High gradient mountain
stream morphology is often influenced by external factors (e.g.,
landslides, alluvial fans, and bedrock outcrops), whereas lower
gradient alluvial streams are more often impacted by flooding,
riparian disturbance, and hard stabilization.
Particle size generally decreases along the longitudinal profile of
the stream (Knighton, 1998). This downstream fining of particles is
associated with the abrasion, hydraulic sorting, and weathering of the
particles (Sambrook Smith and Ferguson, 1995; Knighton, 1998). In
addition, a decrease in gradient lowers the transport capacity and
competence of a stream to move bedload sediment, which reduces the
frequency of larger particles in the downstream direction (Sambrook
Smith and Ferguson, 1995). In gravel-bed streams the downstream
fining of bed material does not always occur orderly because of the
influence of tributaries, large woody debris, and colluvial deposits
(Dawson, 1988; Rice and Church, 1996; Powell, 1998). Land use
disturbance in the Missouri Ozark Highlands is responsible for
increased sediment in select basins, which has led to increased
sediment routing through the system (Jacobson and Gran, 1999).
As discharge increases in the downstream direction, channels
adjust to the increase of water volume and sediment supply in the
stream system. In doing so, channels generally widen and deepen
(Leopold and Maddock, 1953). Variation in cross-section geometry
occurs, however, because of boundary composition, bank vegetation,
and valley slope (Knighton, 1998). Sand bed channels with noncohesive banks tend to be wider than channels with cohesive banks
(Osterkamp and Hedman, 1982). This occurs because cohesive banks
are harder to erode than non-cohesive banks, resulting in more
confined channels. For example, some downstream reaches in the
Driftless Area of southwestern Wisconsin are narrower than their
upstream counterparts because a decrease in particle size occurs in
bank material, which increased bank stability and narrowed the
channel (Knox, 1987).
Trimble (2004), also working in the Driftless Area, reported that
streams flowing through non-grazed grasslands had smaller width/
depth ratios than streams flowing through forests. This occurred
because instream large woody debris in the forested stream reaches
increased water velocity through constriction, which facilitated
erosion and the widening of the channel. Other studies report that
channels lined with grass, however, are up to 30% wider than
streams flowing through forests (Charlton et al., 1978). The
protective role of riparian vegetation is difficult to quantify, but it
is important for understanding channel morphology longitudinally
(Knighton, 1998).
Bankfull channel width is used in the calculation of width/depth
ratios. Bankfull width must be precisely defined in the field to
accurately calculate the width/depth ratio of a stream. Establishing
bankfull width in the field is a somewhat challenging task (Johnson
and Heil, 1996). This is especially true where the channel bottom is
narrow (i.e., entrenched) and the floodplain has not developed a
series of stepped morphological surfaces (Knighton, 1998). Another
problem in defining bankfull width is directly related to the many
ways that are used to define bankfull (Leopold et al., 1964; Carlston,
1965; Williams, 1978; Gordon et al., 1992; Nash, 1994). Defining
bankfull width accurately is important because bankfull estimates
119
serve to help planners and geomorphologists in stream restoration
designs (Johnson and Heil, 1996).
Bankfull channel width is linked to the discharge stage at which
channel maintenance is most effective (Dunne and Leopold, 1978).
This maintenance is affected by the cross-section geometry of the
channel, transportability of bedload, forming and removal of channel
bars, and altering meander bends in stream reaches. Events
controlling channel maintenance may have a recurrence interval of
∼ 1.5 years (Dunne and Leopold, 1978), although other studies have
reported larger recurrence intervals (up to 25 years) for bankfull
discharge (Williams, 1978; Nash, 1994; Petit and Pauquet, 1997).
Regardless, consistency in field verification of bankfull indicators is
important when establishing bankfull width.
Along the longitudinal profile, gradient generally portrays a
concave upward profile. Some of the controls on the degree of
concavity include particle size, the influence of sediment from
hillslopes, tectonic uplift, a decrease in base-level, and log-steps
(Knighton, 1998; Montgomery and Buffington, 1998). Dams can also
impact the concavity of channel gradient, especially if water release is
sediment free and downstream scour occurs at the dam outlet.
Headward reaches (i.e., 1st- and 2nd-order streams) may have steep
gradients because they flow through bedrock lithologies with large
particles that are resistant to erosion. Large particles cannot be
abraded or sorted because stream discharge is below transport
competency (Knighton, 1998). For most alluvial streams, gradient is
generally a function of rock lithology, particle size, and discharge
(Hack, 1957).
Sinuosity generally increases along the longitudinal profile in
alluvial single thread streams. Upstream reaches with high gradients
are often confined by valley walls or large bed material that decreases
the ability of the stream to meander and transport sediment. As
particle size decreases down-gradient, the bedload/total load ratio
decreases, which allows streams to meander (Schumm, 1981, 1985).
Changes in sinuosity throughout bedrock outcrops, riprap reaches,
and dam construction, however, can alter the ability of channels to
meander and may not accurately depict upstream-to-downstream
changes along the channel. For example, sinuosity downstream of
Jackson Lake Dam in Wyoming has fluctuated significantly in response
to changes in maximum discharges and sediment delivery from
tributaries over an 80-year period (Marston et al., 2005).
3. Study area
Ecoregions in eastern Oklahoma consist of the Central Irregular
Plains, Ozark Highlands, Boston Mountains, Arkansas Valley, South
Central Plains, and Ouachita Mountains (Omernik, 1987). The Ozark
Highlands, Boston Mountains, and Ouachita Mountains (Fig. 1) were
selected because they have high fisheries value and the Oklahoma
Department of Wildlife Conservation (ODWC) has an active stream
habitat management program, which uses procedures that incorporate the morphology, habitat, and classification of streams in these
regions (Fisher et al., 2002, 2004; Dauwalter and Fisher, 2008). The
ODWC recognizes that management of these streams is important to
the overall well-being of the fisheries-related economy in eastern
Oklahoma (Fisher et al., 2002; Dauwalter et al., 2007; Dauwalter and
Fisher, 2008).
The Ozark Highlands exist in parts of Kansas, Missouri, Arkansas,
and Oklahoma. In Oklahoma, the ecoregion encompasses 2795 km2.
The eastern edge of the Ozark Highlands exists in eastern Oklahoma
and incorporates part of the Springfield Plateau. Woods et al. (2005)
described the region as being dominated by watersheds that are high
to moderately dissected. Lithology consists of Mississippian-aged
limestone with interbedded chert. Mean annual precipitation is 100–
125 cm. Land use consists of grazing, logging, poultry and livestock
farming, and quarrying. The potential natural vegetation consists of
mainly oak–hickory forest and grassland. Soils on uplands consist of
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D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
Ultisols, Alfisols, and Mollisols. Mean watershed relief ranges from
59 m in 1st-order streams to 153 m in 4th-order streams (Splinter et
al., in press). Much of the native forest and prairie was removed
during the logging boom at the turn of the 20th century.
The Boston Mountains lie to the south of the Ozark Highlands in
Oklahoma. In Oklahoma, the Boston Mountains ecoregion encompasses 1891 km2. This region is a deeply dissected Plateau (Woods et
al., 2005). Lithology consists of Pennsylvanian-age sandstone, with
minor amounts of Pennsylvanian- and Mississippian-age limestone
and shale. Mean annual precipitation is 110–130 cm. Land use
consists of forest and woodland, with flatter areas used for ranching
and farming. The potential natural vegetation consists mostly of oak–
hickory forest (Woods et al., 2005). Soils on uplands consist of Ultisols,
Inceptisols, and Entisols. Mean watershed relief ranges from 119 m in
1st-order streams to 380 m in 4th-order streams (Splinter et al., in
press).
The Ouachita Mountains are separated from the Boston Mountains
to the north by the Arkansas Valley ecoregion. In Oklahoma, the
Ouachita Mountains ecoregion encompasses 10,100 km2. Woods et al.
(2005) describes the region as being a mosaic of low mountains and
high hills of folded Paleozoic rocks. Lithology varies throughout the
ecoregion with rock types of sandstone, shale, and novaculite. Mean
annual precipitation (110–145 cm) is greatest on south-facing ridges.
Land use consists of forestry, logging, ranching, woodland grazing,
and recreation. The potential natural vegetation is oak–hickory–pine
forest. Soils are Ultisols, Alfisols, and Inceptisols. Mean watershed
relief ranges from 157 m in 1st-order streams to 380 m in 4th-order
streams (Splinter et al., in press).
4. Methodology
4.1. Site selection
A random point generator model in ArcView 3.3© and ArcGIS 9.1©
was applied to a stream network constructed for eastern Oklahoma
using 30-m DEMs (Fig. 1). The stream network was stratified into
stream orders (1–4) for each ecoregion. Points (i.e., reaches) were
proportionally allocated to each ecoregion based on ecoregion area
and distributed among stream orders within ecoregions. One hundred
and forty-nine reaches were surveyed for particle size, bankfull width,
width/depth ratio, channel gradient, and sinuosity. Thirty-five reaches
were surveyed in the Boston Mountains, 34 in the Ozark Highlands,
and 80 in the Ouachita Mountains. When access was denied by
landowners or the reach was primarily disturbed (i.e., gravel mined,
channelized, or no stream existed), the reach point was reselected.
Point coordinates were downloaded into a Trimble GEOXT© Global
Positioning System (GPS) receiver for exact navigation to the starting
location of the reach.
4.2. Reach variables
Reaches were surveyed upstream of the randomly selected point
unless restricted by access or affected by human disturbance. Reach
length was calculated using 20 times bankfull width. At each reach,
three to four stream channel cross-sections were surveyed with a
stadia rod and transit. Two cross-sections were surveyed in pools and
two in riffles when available. Cross-sections were placed perpendicular to the stream channel and across alternating pool and riffle
sequences where bankfull indicators were well-established. When the
stream was dry, the reach was divided into four equal sections, and
four cross-sections were placed accordingly. Each cross-sectional
transect was surveyed for particle size, bankfull width, and width/
depth ratio. In addition, the reach (i.e., from upstream-to-downstream) was surveyed for gradient and sinuosity. Reach data were
compiled for particle size, bankfull width, and width/depth ratio by
averaging data collected at each cross-section. We believe that
averaging bankfull width and the width/depth ratio of riffles and
pools provided the best measure of the overall geometry of the reach
because: (1) lumping takes the subjectivity out of identifying different
types of pools (e.g., scour, mid-channel, bedrock, and log jams); and
(2) the high amount of dry channels in small watersheds makes it
difficult to accurately define riffles, especially in streams with finegrained sediments and high distributions of large woody debris.
Fig. 1. Randomly selected stream reaches (with ID) by stream order in three ecoregions in eastern Oklahoma, USA.
D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
121
Fig. 1 (continued).
Particle size analysis was conducted at each channel cross-section
(Wolman, 1954). Particles were collected along transects and picking
clast under the toe of the measurer. Particles were collected and
measured from right-side bankfull (looking downstream) width to
left-side bankfull width. In some instances, measuring particles out of
the wetted portion of the pool or riffle occurred. When bankfull width
surpassed the wetted width, bar deposits were measured. This
technique led to sampling in a non-homogeneous population
(Kondolf, 1997). For this reason, we did not try to separate pool
from riffle transect particle sizes. Rather, our goal was to examine the
sediment sizes flowing within the channel, not compare differences in
particle size between riffles and pools. We understand that this
method probably increased our residual scatter within each ecoregion; however, regardless of sampling scheme, particle size can have
lateral variability (Bunte and Abt, 2001). The particle size results,
however, provide a good quantitative representation of changes
occurring along the longitudinal profile of streams by ecoregion,
which is better than a simpler qualitative assessment of particle size.
Particles b2 mm were classified as fines, and boulders were clasts
N256 mm. Bedrock size was not measured, but counted as a
percentage of the reach. In all, 100 units of measure (i.e., sand
through bedrock) were collected at each cross-section. The distribution of particles was entered into the software program RIVERMorph
3.0©, which is used to create a particle size frequency distribution.
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D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
Table 1
Dummy variables assigned to each of the reaches within the three regions.
Region
Reachesa
CBM
COH
COM
BM
OH
OM
0–38
40–79
80–940
1
0
0
0
1
0
0
0
1
a
Numbering of OM reaches is not continuous from 80 through 940. A total of 80
reaches were surveyed in the region. Continuous numbering did occur in the BM and
OH regions; however, not all of the sites were surveyed.
During data entry, fines were classified into the 2.0–1.0 mm fraction;
and boulders, which were not measured in the field, were classified
into the 256–362 mm fraction.
Bankfull width was determined as the horizontal distance from
right bank floodplain to left bank floodplain. At each transect, bankfull
was identified by: (i) differentiating the modern floodplain from low
terraces; (ii) defining breaks in coarse and fine sediment deposition;
and (iii) utilizing the differences in vegetation along the channel.
Where no obvious floodplain existed, erodable boundaries, root
zones, and soil development served as bankfull indicators. Width/
depth ratio was calculated by dividing bankfull width by the mean
channel depth. Mean channel depth was calculated by dividing
bankfull area by bankfull width. Gradient was calculated by dividing
the elevation of water surface change from upstream-to-downstream
by reach length. Water surface elevation was surveyed using a level
and stadia rod from the top to the bottom of the reach. Reach length
was obtained in the field using a tape measure or upstream and
downstream GPS boundaries. Sinuosity was calculated by dividing
stream length by valley length. Valley length was attained using
upstream and downstream GPS boundaries.
4.3. Statistical analysis
Regression analysis was used to evaluate whether longitudinal
trends in geomorphic variables differed among ecoregions. Ecoregions were modeled as dummy variables. Dummy variables are
categorical variables (i.e., ecoregions) that take the value of zero or
one in the regression. The Ouachita Mountains (OM) were used as the
baseline region because it had the most sites and was expected to
differ most from the Ozark Highlands (OH) and Boston Mountains
(BM). The independent variable was drainage area (km2) above the
reach. The dependent variables, compared in separate regression
equations, were particle size, bankfull width, width/depth ratio,
gradient, and sinuosity. Drainage area (A; km2) and the dependent
variables were transformed using natural logs prior to analysis. The
fitted model is portrayed in Eq. (1):
log ð ŷÞ = β0 + β1 CBM + β2 COH + β3 log A
ð1Þ
+ β4 CBM log A + β5 COH log A
where ŷ is the predicted value for the dependent variable; CBM and
COH is the categorical variable (0,1) of the BM and OH, respectively,),
and β0 to β5 are constants.
Parameter estimates were used to interpret differences in channel
morphology among ecoregions and differences in the rate at which
channel morphology changed with drainage area. The interactions
were evaluated to determine if channel morphology in an ecoregion
β4CBMlogA or β5COHlogA changed at a different rate with drainage area
than it did in the baseline ecoregion (β3COMlogA, where COM is the
categorical variable of the OM). Intercepts were interpreted as
consistent differences between ecoregions (β1CBM or β2COH) and the
baseline ecoregion
(β0) regardless of drainage area. The analytical software program
STATA 8.0© was used to perform statistical analysis. Type I error rate
was set at α ≤ 0.05.
The predicted regression value for the Ouachita Mountains (i.e.,
baseline region) was obtained when the Boston Mountains and Ozark
Highlands were given 0 values in the regression equation and the
Ouachita Mountains received a value of 1 (Table 1). Predicted
regression values for the reaches in the Boston Mountains were
obtained when the Ouachita Mountains and Ozark Highlands received
a value of 0 and the Boston Mountains received a value of 1 (Table 1).
The predicted regression equation for the Ozark Highlands was
obtained when the Boston Mountains and Ouachita Mountains
Table 2
Summary statistics of dependent variables used in the regression analysesa.
Region
Order
OH
1
N
7
BM
1
7
OM
1
19
OH
2
8
BM
2
10
OM
2
22
OH
3
9
BM
3
9
OM
3
20
OH
4
10
BM
4
9
OM
4
19
A
Dd
D16
D50
D84
BFW
WDR
G
S
3.48
(1.95)
2.10
(0.68)
3.12
(2.40)
11.65
(9.71)
8.20
(5.00)
10.18
(4.90)
56.71
(34.58)
73.67
(50.94)
49.22
(31.76)
329.26
(263.58)
291.28
(170.19)
183.80
(99.55)
0.39
(0.24)
0.32
(0.25)
0.50
(0.26)
0.69
(0.16)
0.51
(0.08)
0.64
(0.13)
0.68
(0.08)
0.63
(0.04)
0.71
(0.10)
0.69
(0.04)
0.66
(0.03)
0.72
(0.05)
8.64
(7.20)
9.24
(10.75)
17.84
(11.21)
11.30
(9.45)
5.31
(4.01)
21.02
(26.36)
10.79
(5.13)
11.88
(3.01)
25.10
(26.50)
10.83
(4.01)
17.92
(4.58)
24.75
(20.00)
33.52
(35.70)
27.00
(19.06)
60.00
(40.61)
29.40
(13.84)
26.51
(9.66)
74.46
(75.44)
27.42
(5.78)
47.02
(20.10)
88.70
(63.69)
27.60
(2.94)
55.34
(21.48)
92.27
(68.75)
80.20
(83.23)
83.38
(40.05)
138.46
(76.19)
58.35
(15.97)
81.88
(29.97)
157.86
(101.82)
53.76
(5.92)
131.08
(77.47)
195.69
(100.93)
54.12
(10.63)
129.83
(58.81)
184.48
(87.72)
5.54
(1.98)
6.82
(2.41)
6.59
(1.60)
8.68
(3.18)
11.19
(3.82)
9.20
(2.31)
13.80
(6.73)
21.20
(7.69)
17.02
(5.89)
37.33
(15.15)
37.62
(9.18)
27.73
(7.00)
16.86
(9.07)
13.15
(5.96)
14.09
(3.80)
16.27
(5.45)
17.97
(7.37)
15.07
(4.65)
18.68
(7.28)
24.49
(8.87)
17.02
(6.04)
43.36
(21.18)
28.06
(5.46)
19.34
(6.66)
0.015
(0.011)
0.016
(0.006)
0.016
(0.011)
0.010
(0.004)
0.013
(0.006)
0.009
(0.006)
0.005
(0.003)
0.004
(0.003)
0.004
(0.003)
0.002
(0.001)
0.002
(0.001)
(0.003)
(0.003)
1.16
(0.28)
1.11
(0.08)
1.17
(0.45)
1.13
(0.18)
1.14
(0.11)
1.21
(0.21)
1.23
(0.26)
1.12
(0.13)
1.12
(0.12)
1.15
(0.14)
1.18
(0.16)
1.14
(0.12)
a
For the purpose of simplicity, summary statistic means are portrayed by stream order and ecoregion. Parenthesis below means ± 1 standard deviation. Note, however, that the
regression analyses use drainage area (A) as the independent variable by which conclusions were drawn. Drainage density (Dd) was included because some of the conclusions about
channel morphology involve differences in Dd among ecoregions. D16, D50, D84 = 16th, 50th, 84th percentile particle size; BFW = bankfull width; WDR = width/depth ratio; G =
channel gradient; S = channel sinuosity.
D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
123
received a value of 0 and the Ozark Highlands received a value of 1
(Table 1). For example, the predicted regression value for D16 particle
size (mm) for reach 1 (1.20 km2) in the Boston Mountains is
calculated as:
log ð ŷÞ = 2:316 + −1ð1Þ + −0:62ð0Þ + 0:079ð0:18Þ
ð2Þ
+ 0:173ð0:18Þ + 0:048ð0Þð0:18Þ
Each dependent variable (i.e., D16, D50, D84, bankfull width, width/
depth ratio, gradient, and sinuosity) had a predicted regression value
calculated for each reach. These predicted regression values were
plotted for each dependent variable by ecoregion. Y-intercepts and
slope coefficients for each regression were compared among
ecoregions to test for statistical differences. Summary statistics, by
stream order and ecoregion, are given in Table 2.
5. Results and discussion
5.1. Particle size
The D16, D50, and D84 particle sizes were selected for analysis
because they span the lower, middle, and upper frequency distribution of particle size. Although not always statistically different in
terms of the y-intercept, the largest particles occur in the Ouachita
Mountains (Table 2) and the smallest particles in the Ozark Highlands
(Figs. 2 and 3). The y-intercept coefficients for D16 regression models
differed between the Boston Mountains and the Ouachita Mountains
(α ≤ 0.015) (Table 3). D50 did not differ among ecoregions (Table 4);
however, D84 y-intercept coefficients differed between the Ozark
Highlands and the Ouachita Mountains (α ≤ 0.016) (Table 5). The D84
comparison provided statistical validation that small streams of the
Ozark Highlands (gravel bed) are quite different from small Ouachita
Mountain streams (cobble bed). Slopes of the particle size regression
did not differ among ecoregions. The rate of change in particle size
from upstream-to-downstream was constant in all ecoregions.
In general, streams in the Ozark Highlands had the smallest
particle sizes of the three ecoregions (Fig. 2). Lithology of the Ozark
Highlands is predominantly cherty limestone and sandstone. The
cherty limestone of the Ozark Highlands impacts the particle size
distributions found in these streams. Limestone is easily weathered
and dissolvable in streams, which exposes the more resistant chert
nodules. The resultant chert is difficult to weather through physical
and chemical processes as it moves from upstream-to-downstream.
Chert exposed through the dissolution of limestone retains a fairly
consistent particle size along the longitudinal profile.
Landowners in the Ozark Highlands of eastern Oklahoma report
that streams are undergoing aggradation. Within the Baron Fork Creek
watershed, local landowners gave us personal accounts of pool depth
decreasing. In addition, increases in large woody debris are occurring
in the streams. Studies of similar stream changes have been
documented in the Missouri Ozark Highlands (Jacobson, 1995;
Jacobson and Primm, 1997; Jacobson and Gran, 1999). Increased
amounts of sediment from land use change, predominantly grazing, in
the Missouri Ozark Highlands have caused streams to aggrade
(Jacobson, 1995). Streams in the eastern Oklahoma Ozark Highlands
are also undergoing this transformation.
Summary statistics (Table 2) report that the Boston Mountain
streams have the second largest particle sizes, while the Ouachita
Mountain streams have the largest particle sizes. Particle sizes in
Boston Mountain streams are larger than those in the Ozark Highland
because the Boston Mountains have a higher watershed relief, which
has the potential to supply larger particles to the fluvial system
(Splinter et al., in press). The sandstone lithology of the Boston
Mountains is more resistant to weathering and abrasion, which makes
erosion of the sandstone difficult in this fluvial system. Boulder size
Fig. 2. Longitudinal trends in D16, D50, and D84 particle size by ecoregion.
particles are common in Ouachita Mountain streams (Smithson and
Johnston, 1999; Marion and Weirich, 2003). This region has the
highest watershed relief of all the ecoregions in this study (Splinter
et al., in press). Steep V sideslopes and bedrock outcrops are common,
which result in large particles in the streams of this region (Fig. 2).
Particle size increased in the downstream direction (D84) because of
the local geologic setting of steep sideslopes and bedrock outcrops.
Resistant sandstone and novaculate prohibit the weathering and
abrasion of sediment. Large sediment is seldom moved in these
locations because of a lack of stream power and streams remain
relatively stable.
5.2. Bankfull channel width
It is well understood that bankfull channel width increases
downstream with the addition of tributaries associated with
increased drainage area (Leopold et al., 1964). In turn, bankfull
124
D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
Fig. 3. Photographs portraying substrates for different size streams in the Ozark Highlands, Boston Mountains, and Ouachita Mountains. Although statistical differences do not occur
in all regressions, field observations suggest a definite difference in channel substrate by ecoregion. Note that the second-order stream of the Ozark Highlands is typical of small
streams in this region. These tend to be dry, highly vegetated, and maintain narrow bankfull widths.
channel width has been correlated with increased drainage area in
ecoregions of the conterminous United States (Faustini et al., 2009).
Bankfull width of the Ozark Highlands increased approximately 49 m
along its longitudinal profile, whereas the Boston Mountains
and Ouachita Mountains widened 43 m and 33 m, respectively
(Fig. 4). Y-intercept (α ≤ 0.001) and slope coefficients (α ≤ 0.010)
between the Ozark Highlands and the Ouachita Mountains and yintercept coefficients between the Boston Mountains and Ozark
Highlands differed (α ≤ 0.000), providing evidence for contrasting
stream sizes among regions (Table 6). The widest predicted bankfull
widths are in the Boston Mountains (Fig. 4). Although no y-intercept
or slope difference existed between the Boston Mountains and
Ouachita Mountains, a difference existed between the Ozark Highlands and the other two ecoregions (Table 6).
Bankfull channel widths in 1st- and 2nd-order streams of the
Ozark Highlands were narrower than the Boston Mountains and the
Ouachita Mountains (Fig. 4). This is probably a function of the lower
watershed relief of the region and the jointed and fractured limestone
D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
Table 3
Comparison of the D16 particle size among ecoregions using slope and y-intercept
coefficients.
Comparisona
Intercept
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
Slope
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
Coefficients
2.316
−1.000
−0.620
SE
0.229
0.407
0.432
P N |t|
t
10.13
−2.46
−1.43
Prob N F
0.000
0.015
0.154
0.446
0.079
0.173
0.048
0.068
0.114
0.118
1.16
1.52
0.41
0.248
0.130
0.686
0.344
a
OM = Ouachita Mountains; BM = Boston Mountains; OH = Ozark Highlands;
Degree of freedom is 5 for the model and 143 for the residual; significance level is
α = 0.05.
bedrock (i.e. karst topography) that allows rainfall runoff to be
reduced because of higher infiltration rates (Splinter et al., in press).
Low-order streams surveyed in the Ozark Highlands were dry and
flowing only after rainfall events. Ten of 15 1st- and 2nd-order
streams were completely dry and two were intermittent, which
probably leads to narrower bankfull channel widths in low-order
reaches (Fig. 3). In addition, a rapid increase in drainage density exists
in medium and larger watersheds in the Ozark Highlands which
functions to increase bankfull channel width downstream (via
tributaries) then in other ecoregions (Splinter et al., in press). The
slope of the regression line in Fig. 4 depicts how bankfull channel
width increases faster with stream size in the Ozark Highlands than in
the other ecoregions.
The wider bankfull channel width in smaller watersheds of the
Boston Mountains and Ouachita Mountains is probably a function of
the higher watershed relief in these regions. Overland flow in these
higher relief watersheds collects in streams and is more readily
available for sediment transport and erosion of stream banks, which
widen the bankfull channel width of the streams.
125
Table 5
Comparison of the D84 particle size among ecoregions using slope and y-intercept
coefficients.
Comparisona
Intercept
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
Slope
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
a
Coefficients
SE
t
P N |t|
4.535
−0.204
−0.797
0.173
0.308
0.327
26.23
−0.66
−2.44
0.000
0.509
0.016
Prob N F
0.117
0.117
−0.050
−0.054
0.051
0.086
0.089
2.28
−0.58
−0.61
0.024
0.564
0.544
0.966
See Table 3.
events. A lack of streamflow produces channels that are narrow and
shallow. As the drainage area increased in the Ozark Highlands, a
considerable increase occurred in width/depth ratio. The relatively
high drainage density and transport capacity of gravel helps establish
high width/depth ratios in the Ozark Highlands. Splinter et al. (in
press) showed that drainage density increased dramatically from 1st
to 2nd-order streams in the Ozark Highlands.
Stream studies in the adjacent Missouri Ozarks show that land use
change led to the headward extension of the stream network into
unchanneled upland valleys (Jacobson, 1995). In turn, gravel was
added to the system and is currently being routed during higher flow
events (Jacobson and Primm, 1997; Jacobson and Gran, 1999).
Remshardt and Fisher (2008) reported that high flow events
(between 1999 and 2000) along a section of Baron Creek (Oklahoma
Ozark Highlands) altered the cross-sectional profile between 62% and
93%. We believe that during high flow events, gravel is being
5.3. Width/depth ratio
The width/depth ratio of streams increased in the downstream
direction in all three ecoregions. The Boston Mountains and Ozark
Highlands have slope coefficients different (α ≤ 0.05) from the
Ouachita Mountains (Table 7), which signifies a greater rate of change
downstream in the Ozark Highlands and Boston Mountains. The
lowest width/depth ratios (although y-intercept coefficients are not
different from the other ecoregions) occurred in low-order streams of
the Ozark Highlands and transitioned into the highest values
downstream (Table 7; Fig. 4).
The low width/depth ratios of streams in small Ozark Highland
watersheds are the result of little streamflow except during rainfall
Table 4
Comparison of the D50 particle size among ecoregions using slope and y-intercept
coefficients.
Comparisona
Intercept
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
Slope
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
a
See Table 3.
Coefficients
SE
t
P N |t|
3.619
−0.659
−0.726
0.204
0.363
0.385
17.74
−1.81
−1.88
0.000
0.072
0.062
Prob N F
0.881
0.116
0.051
−0.018
0.061
0.102
0.105
1.92
0.50
−0.17
0.057
0.615
0.867
0.562
Fig. 4. Longitudinal trends in bankfull width and width/depth ratio. Width/depth ratio
changes only slightly longitudinally in the Ouachita Mountains when compared to the
Ozark Highlands and Boston Mountains. This reflects the regions large substrate and
structural controls.
126
D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
Table 6
Comparison of bankfull width among ecoregions using slope and y-intercept
coefficients.
Comparisona
Intercept
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
Slope
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
a
Coefficients
SE
t
P N |t|
1.561
0.880
−0.397
0.060
0.107
0.114
25.95
0.82
−3.49
0.000
0.413
0.001
Prob N F
0.000
0.330
0.018
0.080
0.018
0.030
0.031
18.46
0.59
2.59
0.000
0.555
0.010
0.075
Table 8
Comparison of gradient among ecoregions using slope and y-intercept coefficients.
Comparisona
Intercept
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
Slope
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
a
Coefficients
SE
−4.131
0.427
0.138
0.053
0.312
0.332
P N |t|
t
−8.57
1.37
0.42
Prob N F
0.000
0.174
0.678
0.450
−0.453
−0.010
0.059
0.176
0.088
0.091
−23.47
−0.11
0.65
0.000
0.910
0.514
0.497
See Table 3.
See Table 3.
transported from streams in the upper watersheds and deposited
downstream. Higher-order streams in the Ozark Highlands are
aggrading, which causes high magnitude flood events to accelerate
erosion on the stream banks. Aggradation of the streambed decreases
mean depth. This coupled with increasing channel width supports
streams with high width/depth ratios (Schumm, 1960). Evidence for
aggradation comes from communication with landowners in the
region who recall past periods when the pools were much deeper.
Five of the six highest width/depth ratios conducted in this study
occurred in the Ozark Highlands.
Streams in the Ouachita Mountains have the most consistent
width/depth ratios from upstream-to-downstream of all the ecoregions (Fig. 4). The width/depth ratios of these streams are controlled
by large substrate and bedrock outcrops. Streams cannot downcut
through the large substrate and are forced to laterally migrate or
remain confined by local geology even in large streams. The large
particle size and bedrock outcrops serve to retard increases in the
width/depth ratio from those observed in streams of the Boston
Mountains and Ozark Highlands. The width/depth ratios of streams in
the Boston Mountains are more similar with those in the Ozark
Highlands than those in the Ouachita Mountains. Streams in the
Boston Mountains generally have substrate particles larger than the
Ozark Highlands and smaller than the Ouachita Mountains. The larger
substrate, along with bedrock, influences the width/depth ratio of
streams in the Boston Mountains, but not to the extent it does in the
streams in the Ouachita Mountains.
is defined by hills and mountains with high relief in its interior and
low gradient flats at the base of hills, in floodplains of large rivers, and
in the lowlands at the region's western edge (Woods et al., 2005). In
addition, some larger stream reaches in the Ouachita Mountains
consisted of a single large pool with a very low slope. Other large
streams in the Ouachita Mountains had a series of riffle-run-pool
sequences that increased reach slope. This contrast in channel unit
frequency and type led to a large range in gradient of high-order
streams.
5.5. Sinuosity
Sinuosity was not significantly different among ecoregions
(Table 9). No longitudinal pattern in sinuosity was evident among
ecoregions (Fig. 5). When compared along the longitudinal profile of a
stream, sinuosity remained the same. In part, sinuosity increases
5.4. Gradient
Stream gradient was not statistically different among ecoregions
(Table 8). The gradient variability was greatest in the Ouachita
Mountains and least variable in the Boston Mountains (Fig. 5). The
high variability in the Ouachita Mountains resulted from having more
regional variability than the Ozark Highlands or Boston Mountains
(Splinter, 2006). The Ouachita Mountains encompass a landscape that
Table 7
Comparison of width/depth ratio among ecoregions using slope and y-intercept
coefficients.
Comparisona
Intercept
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
Slope
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
a
See Table 3.
Coefficients
SE
t
P N |t|
2.561
−0.095
−0.253
0.807
0.144
0.153
31.72
−0.66
−1.66
0.000
0.508
0.100
Prob N F
0.372
0.059
0.100
0.159
0.024
0.040
0.041
2.47
2.48
3.82
0.015
0.014
0.000
0.210
Fig. 5. Longitudinal trends in gradient and sinuosity. No significant trends existed
among ecoregions.
D.K. Splinter et al. / Geomorphology 122 (2010) 117–128
Table 9
Comparison of sinuosity among ecoregions using slope and y-intercept coefficients.
Comparisona
Intercept
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
Slope
OM, baseline
BM vs. OM
OH vs. OM
BM vs. OH
a
Coefficients
SE
t
P N |t|
0.141
−0.047
−0.026
0.033
0.060
0.063
4.24
−0.80
−0.41
0.000
0.427
0.684
Prob N F
0.767
−0.002
0.013
0.010
0.010
0.017
0.017
−0.20
0.76
0.56
0.843
0.451
0.578
0.877
See Table 3.
where localized bank erosion occurred and a redistribution of energy
in the water column developed (Knighton, 1998; Ritter et al., 2002).
Schumm (1981) classified streams with the highest sinuosity as those
primarily having small sediment size. In the Ozark Highlands, Boston
Mountains, and Ouachita Mountains, particle size is most often gravel
or cobble. Sediment movement is primarily bedload. The majority of
stream reaches surveyed had a sinuosity b1.5, which indicates
generally straight reaches.
6. Conclusion
This study investigated how longitudinal patterns in channel
morphology differed among ecoregions. The results showed that
longitudinal patterns differed for three (particle size (D16 and D84),
bankfull width, and width/depth ratio) of the five variables tested.
Variables not found to be statistically significant were gradient and
sinuosity. Our findings are similar to other studies that have shown
using broad-scale variables (geology, topography, climate, land use,
vegetation, and soils) provide a spatial organization by which the
characteristics of stream channels can be classified and studied
(Brussock et al., 1985; Cohen et al., 1998; Montgomery, 1999; Snelder
et al., 2004). We recommend using ecoregions to study the
longitudinal characteristics of stream morphology for the following
reasons: (1) regional curves can be characterized for the region; (2)
disturbance reaches can be quickly identified once the regional curve
is developed, and (3) ecoregions provide fluvial geomorphologists
and stream ecologists a regional picture that portrays broad-scale
variables that influence the physical and biological aspects of streams.
Acknowledgements
We thank Raymond Ary, Valerie Horncastle, Alycia Krystyniak,
Bryce Marston, James Morel, Mark Murray, and Kyle Winters for field
assistance. Comments and suggestions made by Jack Vitek, Robert
Pavlowsky, Takashi Oguchi, and two anonymous reviewers greatly
improved this paper. This study was funded by a grant (F-55-R) from
the Oklahoma Department of Wildlife Conservation. The Oklahoma
Cooperative Fish and Wildlife Research Unit is jointly sponsored by
the U.S. Geological Survey, Oklahoma State University, the Oklahoma
Department of Wildlife Conservation, the Wildlife Management
Institute, and the U.S. Fish and Wildlife Service.
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