Aquifers
and Springs
I. What is an Aquifer?
A. An underground layer
of permeable rock, sand,
sediment or soil that collects, holds and transmits
water to wells or springs.
B. Mostly commonly known as groundwater and
may create large underground reservoirs of
varying size.
1
II. Springs
A. Develop when groundwater reaches the
surface, which in turn can develops headwaters
giving rise to streams and rivers.
B. Form along fault lines (earthquakes). The
Balcones fault exposed the Edwards Aquifer.
C. More than 3000 springs in Texas.
2
D. Releases water into lakes and rivers when water
tables reach the surface.
E. Wetlands develop when water tables remain
high, but vanish as levels drop below the
surface.
F. The recharge zone is the area where water enters
the aquifer.
G. Water enters the aquifer through faults, fractures,
sinkholes, or percolation through the soil. This
process is called recharge.
H. Limestone is on the surface on the recharge zone.
III. Texas Aquifers
A. Nine Major Aquifers lie below Texas’ land.
1. Contains large amounts of
water spread across large area.
2. Supplies 60% of water used
for agricultural crop irrigation
3. 80% of irrigation water used comes from the
Ogallala Aquifer, the largest in the U.S.
a. Stretches from South Dakota through the
Texas panhandle.
b. Lies under the Texas High Plains region.
c. Averages 95 feet in thickness.
d. Formed about 2 to 6 million years ago
4. New water can move through the aquifers
within a matter of hours flowing through the
limestone and marble rock below.
B. 21 Minor Aquifers contain smaller amounts of
water spread over large areas
or large amounts of water
spread over small areas.
Texas has 9 Major Aquifers
7
IV. Major Types of Aquifers
A. Unconfined aquifer (most common)
1. Directly connected to the surface
2. Ground water flows to the surface when the
water table (upper saturated layer) rises to the
level of the land.
3. Water levels dependent on constant recharge
from rain on the wetlands surface.
4. Playa lakes collect 95 % of recharge water.
a. Naturally occurring wetland formed when
rain fills small depressions in the prairie
b. 20,000 in the Texas High Plains
8
Unconfined Aquifer
Well
Stream
9
10
Playas
11
Recap: Water seeps through porous materials near the surface,
but is trapped by impermeable rock below
B. Confined Aquifers
1. Saturated layers of pervious rock sandwiched between
layers of impervious rock layers.
2. The impervious layers squeeze the groundwater,
pressurizing it, giving rise to artesian wells.
3. Artesian wells feed many Texas springs like the
San Solomon Springs in West Texas.
4. Wells drilled in some confined aquifers may not need a
pump due to the amount of pressure forcing
groundwater to the surface.
FACT: Great Artesian Basin
The world's largest known aquifer
is the Great Artesian Basin, in
Australia, at more than 1.7 million
square kilometers (661,000 square
miles).
13
Water Table Well
Confined Aquifer
Artesian Well
Flowing Well
Aquifer
Bedrock
Potentiometric
Surface
http://www.edwardsaquifer.net/media/san_felipe_springs.mp4
http://www.edwardsaquifer.net/media/comal_springs.mp4
Salado Springs
15
Recap: Impermeable rock above and below. Rock strata must bend
and outcrop at surface for rain to recharge porous material in
between. Water will pressurize if higher than well heads –
artesian system
C. Karst: a special type that occurs in limestone
rocks when a system of caves is connected and
water is flowing through it. –Edwards Aquifer
1. Develops in thick limestone formations, usually
in humid climates. Karst has both surface and
subsurface features.
http://www.watersheds.org/earth/Sinkholes.html
17
2. Water naturally goes
underground through
sinkholes to caves
(solution caverns).
3. Rainwater is slightly
acidic and dissolves
limestone rock to
calcium carbonate &
carries it away
(dissolution).
4. Causes stalactite,
stalagmite, & pillar
formations in caverns
18
5. Caves Associated with the Edwards Aquifer
Inner Space Cavern
Austin, TX
Kickapoo Caverns
State Park
Brackettville, TX
Devil’s Sinkhole
State Natural Area
Rocksprings, TX
Natural Bridge Caverns
Natural Bridge Caverns, TX
19
VII. Ecosystems
A. Most aquifers do not support traditional
aquatic ecosystems.
1. No light, no photosynthesis (for plants)
2. No nutrients
3. No dissolved O2 to support aerobic life.
4. Survivors include: bacteria, protozoans,
and other unicellular organisms.
B. Karst aquifers support a more complex
aquatic ecosystem in underground cave
habitats.
1. Invertebrates, fish and amphibians make
up the majority of the organisms.
2. Nutrients are recycled among the organisms
due to the lack of producers.
3. Have a very low carrying capacity.
4. Adaptations
a. Absence of eyes
b. Many devoid of color
c. Increased sensory development including,
antennae, chemoreceptors and touch
receptors.
d. Consistent water temperature supports a
lower metabolism which means less food
require.
e. Environment stable and predictable.
C. Nutrient Support from the outside
1. Cave-dwellers are depend on the plant and
animal material washed into the caves.
2. Feces dropping from bats and mice provides
nutrients for fungal growth which many
insects eat.
3. Food chain:
Fungi
insects
insect larva
invertebrates
blind salamander
toothless blindcat (catfish). Death of the
catfish would provide nutrients and cycle
continues
22
D. Spring Ecosystems
1. Food provided by aquatic plants and algae
2. Isolated habitats of many springs contain
species found only in that particular location.
3. Consistent water temperatures near the springs
the cave openings prevent organisms from
wandering to the streams and rivers associated
with the spring.
4. Ecosystems are small providing limited
numbers of any one species population to
survive.
23
E. Changes Impact the Habitat
1. Decrease in ground water flow or drought
reduces habitat and stresses many species.
2. Invasive species enter native springs and take
over often eliminating the indigenous species
of the spring.
3. Human impact on springs vary; from building
dams across the springs to building recreations
pools destroying the native species.
24
V. Water Supply Problems for Aquifers and Springs
A. Water Supply Problems
1. Water Quantity
a. Spring runoff is highly dependent on
rainfall
b. Not enough recharge times between
drought
c. Edwards aquifer holds a huge amount of
water but: At less than 95% capacity,
the springs run dry.
d Endemic fauna and flora inhabit springs
and caves and are vulnerable to
extinction if water levels get too low.
2. Water Quality a. Vulnerable because aquifer is relatively
shallow
b. Little reaction time in case of a spill
c. Clean-up of local threats almost impossible
Aquifer has a low self-cleaning ability
(natural remediation)
http://www.watersheds.org/earth/karstmovie.htm
26
3. Sources of Pollution –
a. Solid waste
1. Wild depositions in dolines (sink-holes) are
common in many area
2. Strong precautions for sealing dump-sites
b. Waste water
1. high risk from leaking sewers
2. used water infiltrates aquifer
3. no surface drainage system
c. Agricultural use
d. Industrial contamination
e. Hydrocarbons-explosive
f. Liquid waste injection
VI. Environmental Impact
A. Eight species in the Edwards Aquifer, Comal Springs,
and San Marcos Springs ecosystems are currently
listed by the U.S. Department of Interior, Fish and
Wildlife Service, as either threatened or
endangered species.
Endangered
Comal Springs Dryopid Beetle
Comal Springs Riffle Beetle
Fountain Darter
Peck’s Cave Amphipod
San Marcos Gambusia
Texas Blind Salamander
Texas wild-rice
Threatened
San Marcos Salamander
28