Geoscience Reference
In-Depth Information
A
Figure 2-6.
Marsh complex fed by ground water from
springs and artesian wells in the San Luis Valley, a desert
in south-central Colorado, United States. Russell Lakes
State Wildlife Area; altitude
∼
2300 m, view toward
northeast with Sangre de Cristo Mountains in the far
background. Kite aerial photo by J.S. Aber and S.W. Aber.
B
Figure 2-5.
A. Bimini Islands and Cat Cays, Bahamas
(see Color Plate 2-5A). Shoals of carbonate sediment
show distinctly as pale blue through the shallow, clear
water of Grand Bahama Bank. False-color Landsat
image in which vegetation on islands appears in red.
Field of view
Figure 2-7.
Salt accumulation along the margin of Dry
Lake during a low-water phase, western Kansas, United
States. Note small overturned boat in lower left corner
for scale. Kite aerial photo by J.S. Aber and S.W. Aber.
75 km across; image courtesy of NASA
Goddard Space Flight Center. B. The Tjórsa River
carries highly turbid glacial melt water through a basalt
gorge in south-central Iceland. Photo by J.S. Aber.
∼
peat is compressed and converted into lignite
and coal, which represent former wetlands (Fig.
2-9).
An important indicator is the status of iron
in the soil, which depends on the combination
of acidity (pH) and oxidation potential (Eh). Low
Eh and pH favor reduced iron (Fe
2
+
), whereas
high Eh and pH lead to the oxidized state of
iron (Fe
3
+
) (Davis and DeWiest 1966). This does
not require any chemical instrumentation to
determine; the status of iron is readily portrayed
by its color
-
greenish gray for the reduced
phase and rusty red-orange for the oxidized
reduced iron is present. Such soils are called
hydric soils, and they range from organic-rich
peat and muck to highly saline evaporite depos-
its (Fig. 2-7). The key condition in terms of soil
development is water logging and extended
saturation such that available oxygen is con-
sumed and the chemical environment becomes
reducing. When this condition develops, anaero-
bic bacteria thrive, and organic matter may accu-
mulate to form peat (Fig. 2-8). In ancient rocks,
