Alan Barraza
University of Texas – El Paso
Los Pinos Mountains
•
Southern part of a mountain system
that extends northward along the Rio
Grande Rift.
•
Uplifted during Laramide Orogeny
(40-70 Ma) and Rio Grande Rift
formation (25 –0 Ma)
•
Pre-Cambrian age rocks (1.8 BA).
Composed of the Sias quartzite
(oldest), Blue Springs muscovite
schist (originally siltstones), White
Ridge
quartzite,
and
Sevilleta
rhyolite, all intruded by the Los Pinos
(pre-Cambrian) granite. (Stark et al,
1946; Luther et al., 2005)
Los Pinos Mountains
Soil Creation Process
Importance of Regolith and Soil
• Regolith and soil can absorb and retain more water than bedrock
• Nutrients can be extracted easily compared to little to no extraction in
bedrock
• Provides the environment needed for the most species of plants to grow.
Importance of Study
• Gain a general understanding of the following:
• landforms present in the eastern side of Los Pinos Mountains.
• processes occurring that are creating regolith and soil in the
area
• abiotic factors affecting plant growth
Hypotheses
•
Soil thickness will be correlated with landform, gradients of slopes, and aspect.
•
Different landforms will entrap and incorporate dust at variable rates, given
differences in landform morphology and age.
•
•
This is because the source of the majority of soil material (i.e., clay,
carbonate, silt) in analogous landforms elsewhere in semiarid slopes of NM
is dust.
Highest plant biomass and diversity will occur in the older Quaternary alluvial fill,
given additional void space for soil water storage and higher soil water retention
associated with clay and silt. Plant growth on the pediment will be influenced by
thinner soil development. South and north facing slopes will be differently
related to plant recruitment and productivity, primarily given soil differences
associated with slope-controlled rates and processes of soil development.
Field Methods
Mark out a 1meter x 1meter plot
Characterization of site:
• GPS coordinates
• Slope and aspect of the area
• Qualitative description of the
surrounding area to include
vegetation, clast size, and any other
items of interest
• Photography of area
Transects
• Create 2 diagonal transects across
the set plot
• Every 10cm along each set
transect, identify and measure
rocks directly on the transect line
and under set mark
Field Methods (cont)
Soil Analyses
• Excavate a small hole (approximately
20cm x 20cm) until bedrock is
reached.
• Collect a grab sample and run the soil
through the soil sieve to remove all
gravel and rocks.
• Analyze a dry soil ped for soil
hardness
• Using 10% HCl, test the soil for any
CaCO3.
• Analyze soil for wet consistency,
plasticity, soil type identification using
the ‘worm test’
• Measure depth of hole and
approximate
vegetation coverage in plot
• Take note of root content
Field Criteria Used in Determining Major Textural Classes
Ability to:
Consistence:
Soil Textural
Class
Feel (moist)
Form Stable Ball
Ribbon Out
"Soils" Hands
Plastic
Prop.
Sticky
Moist
Dry
Sand
Very Gritty
No
No
No
No
No
Loose
Loose
Loamy Sand
Very Gritty
No
Yes (easily
deformed)
Yes (slight)
No
No
Loose
Yes
No
Loose
Very
Friable
Friable
Soft
No
Yes (dull surface;
Sandy loan
Gitty
poorly formed)
Yes (dull surface;
Loamy Sand
Gritty
Yes
poorly formed)
Yes (dull surface;
Silt Loam
Velvety
Yes
poorly formed)
Yes (shiny surface;
Silty Clay Loam
Velvety and Sticky
Yes (very stable)
well formed)
Yes (shiny surface;
Clay Loam
Gritty and Sticky
Yes (very stable)
well formed)
yes (well formed;
Sandy Clay Loam Very Gritty and Sticky Yes (very stable)
shiny surface)
Extremely sticky and Yes (very resistant yes (well formed;
Silty Clay
very smooth
to molding)
very shiny surface)
Extremely sticky with Yes (very resistant yes (well formed;
Clay
slight grittiness
to molding)
very shiny surface)
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes (slight
Yes (slight) to mod.)
Yes (slight Yes (slight
to mod.)
to mod.)
Friable
Friable to
Firm
Soft
Soft
Slightly
Yes (mod.)
Yes
Hard
Slightly
Yes (mod.)
Yes
Firm Hard to Hard
Friable to Slightly
Yes (mod.)
Yes
Firm Hard to Hard
Yes (very Firm to Hard to Very
Yes (strong) sticky)
Extra
Hard
Yes (very Firm to Hard to Very
Yes (strong) sticky)
Extra
Hard
Landform Vs Plant Data (Exerpt)
Landform
mountain backslope
mountain backslope
mountain footslope
mountain footslope
intermediate alluvial terrance
older alluvial fill
older alluvial fill
older alluvial fill
older alluvial fill
youngest alluvial surface
youngest alluvial surface
youngest alluvial surface
youngest alluvial surface
pediment backslope
pediment backslope
pediment backslope
pediment footslope
pediment footslope
pediment shoulder
pediment surface
pediment surface
pediment surface
pediment surface
Plot #
31
49
51
55
15
1
17
39
53
20
37
45
48
7
13
26
11
24
41
3
5
9
22
Veg Cover % Root Content
60
low
30
mod
20
low
20
mod
50
high
55
high
50
mod
75
low
5
very low
0
mod
50
mod
70
mod
5
low
15
low
15
mod
40
low
5
high
5
none
15
low
20
low
25
low
0
very low
5
low
Root Sizes
fine
fine
fine
fine - med
fine - lg
fine - med
fine
fine
small - med
fine - lg
fine
fine - lg
small - lg
fine
fine - med
fine - med
med- xlg
none
fine
fine
fine
fine
fine
Landform Vs Soil Data (exerpt)
Landform
Plot #
mountain backslope
30
mountain backslope
32
mountain backslope
50
mountain footslope
52
mountain footslope
54
mountain summit
28
older alluvial fill
34
older alluvial fill
36
older alluvial fill
40
older alluvial fill
46
younger alluvial surface
6
younger alluvial surface
16
younger alluvial surface
18
younger alluvial surface
56
pediment backslope
8
pediment backslope
14
pediment backslope
23
pediment backslope
42
pediment footslope
12
pediment surface
4
pediment surface
10
pedimet shoulder
25
HCl Test Soil Color
Neg 10YR 4/4
Neg 10YR 4/4
Neg 10YR 3/4
Neg 7.5YR 4/6
Neg 10YR 4/3
Neg 10YR 4/4
Neg 7.5YR 3/4
Pos 7.5YR 5/4
Neg 7.5YR 3/4
Neg 10YR 4/4
Neg 10YR 4/4
Pos 10YR 4/6
Neg 10YR 4/4
Pos 10YR 5/4
Neg 10YR 5/3
Pos 10YR 5/4
Pos 7.5YR 5/4
Neg 10YR 5/4
Neg 10YR 3/6
Neg 10YR 5/4
Neg 10YR 3/3
Neg 10YR 5/3
Soil Type
sandy clay loam
sandy clay loam
silt loam
clay
sandy clay loam
sandy clay loam
clay
silty clay
sandy clay loam
silty clay loam
silty clay loam
silty clay
silty clay
clay loam
silt loam
clay loam
clay
silt loam
loam
silt loam
silt loam
silty clay loam
Discussion
• Very scattered results supports the idea of several processes taking
place creating the various landforms.
• Closely correlated soil thickness and similar clast sizes on all
pediment surfaces suggest that these landform are entrapping and
incorporating dust at similar rates.
• Thicker soil and smaller clasts on alluvial surfaces demonstrate a
different process taking place in the formation of these landforms.
• With a higher sampling size soil thickness versus slope gradient
could possibly be highly correlated.
• Most plant data was very scattered. But, spatial distribution of piñon
trees between older Quaternary alluvial fill and the pediment surface
shows trees prefer the thinner soil. The majority of this soil is eolian
dust thus could be better formed and better suited for plant
recruitment.
Conclusion
• Significant correlation between soil thickness and landform
• Approaching significant correlation between soil thickness and slope
gradient.
• No significant correlation between soil thickness and azimuth
• Highest plant biomass did not occur on the older Quaternary alluvial
fill, but instead on pediment surface. Plant biomass and soil
thickness between pediment surface and slopes were not
significantly different.
• Larger clast size does entrap more dust and this is apparent in the
soil thicknesses of the various landforms except for the alluvial
surfaces, and mountain summit which are undergoing different
processes.
Further Questions…
• What difference in the soil between the older Quaternary alluvial fill
and the pediment surface is causing such a significant difference in
piñon tree biomass?
• Where is the eolian dust forming?
• Why are do some species of plants dominate certain landforms?
• When where the various alluvial fills created?
Questions????