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MONTEZUMA WELL: THE LIVING DESERT OASIS
Prepared for the National Park Service
©1987.
Vincent T. Wagner and Dean W. Blinn
Department of Biological Sciences
Northern Arizona University
Flagstaff, Arizona 86011
Montezuma Well contains several forms of plants and animals not
found in any other waters in the world. In part, this may be due
to the constant input of large quantities of warm water that
enter the Well through underground springs which keeps the
environment within the Well very stable. Also, there are NO
FISH in the Well, due to concentrations of dissolved carbon
dioxide that are nearly 600 times higher than other natural
aquatic environments. These unusual conditions have allowed the
aquatic organisms in the Well to look and act differently than
they do in other ponds and lakes. Therefore, Montezuma Well
provides an opportunity for scientists to carefully study the
interactions between these unique plants and animals.
THE BIRTH OF THE WELL
The story of Montezuma Well starts about
12 million years ago when the Verder Valley was covered by a
large shallow lake 27 miles long and 15 miles wide. Lake Verde
was full of tiny floating plants which, while they produced
food, caused dissolved limestone to form minute crystals. These
crystals slowly sank to the bottom of the lake and over several
million years accumulated into thick layers of limestone rock.
About 2 million years ago Lake Verde eroded away the volcanic
dam at its southern end and the gigantic lake dried up.
Scientists think that an underground
stream dissolved away some of the softer limestone deep under
the ground and formed caverns below the surface of the Verde
Valley. Over the years, churning water carved these underground
caves larger and larger. Along various points of the
underground stream, water would come to the surface and form a
spring. Over several million years these springs deposited large
quantities of salts, called travertine, around their openings.
As the salts accumulated, large circular mounds were formed like
the one surrounding the Well (see photograph above). As
recently as 11,000 years ago, the roof of one of the underground
caverns supporting a heavy travertine spring mound may have
gradually crumbled into a sunken pool and hence MONTEZUMA WELL
was formed!
Presently, Montezuma Well is located at
an elevation of 3,681 ft. (1,122 m) in the Upper Sonoran desert
of Arizona. The terrestrial vegetation on the outside rim of
the Well is adapted to the dry climate of the Verde Valley and
includes juniper and acacia trees as well as assorted grasses,
hedgehog and prickly pear cactus plants, and the exotic
joint-fire, Ephedra, from which the nerve stimulant
ephedrine is extracted.
Montezuma Well is 368 ft. (112 m) across
and the water is 55 ft. (17 m) deep. The Well is still an
active spring with a constant flow of 1,100 gallons of water
entering at the bottom every minute (4,164 l per min). The water
exits through a side cave and empties into an irrigation ditch
outside the Well; the water level in the Well rarely changes!
Because the water of Montezuma Well comes from an underground
stream, it has a constant temperature of 76 °F (25 °C).
High concentrations of odorless gas, carbon dioxide, are
dissolved into the water as it passes through the miles of
underground limestone deposits before entering the Well. As the
water enters the Well, the limestone falls out of solution and
the carbon dioxide is released as a dissolved gas into the
water. The rich supply of dissolved carbon dioxide has
apparently prevented many aquatic animals, especially fish, from
living in these waters.
THE LIFE IN THE WELL
Montezuma Well contains several plants
and animals that are only found in its unique environment.
Scientists think that birds and possibly flying insects brought
some of these small creatures, or at least their ancestors, to
the Well. As the waterfowl traveled across the desert, they
would stop at various water spots to drink and eat. At each
stop the birds would deposit creatures and/or trap more new
organisms in their feathers and webbed feet to be transported to
their new destinations. Eventually, when the ducks visited
Montezuma Well, some of the small creatures would be deposited
in their new home. If they were tolerant of their new
environment they would survive, if not, they would remain
dormant or die! This dispersion process of aquatic organisms is
still going on today in Montezuma Well with the annual visits of
American widgeons, coots, mallards, rudy ducks, cinnamon teal,
gadwalls, and the occasional Canadian goode. These waterfowl
make Montezuma Well their winter home between November and April
of each year and then migrate to their summer home in the
north.
Today in Montezuma Well we find several
aquatic animals that have adapted to the unusual conditions in
the Well. The proposed food chain in Montezuma Well is
illustrated below.
Some of the small aquatic plants (called
algae), many of which could fit on the tip of a pin, float in
the water and use light energy and the rich supply of dissolved
carbon dioxide to manufacture food. These algae in turn serve
as food for the numerous shrimp-like animals called amphipods
that are less than one-eighth of an inch long. The unique
amphipods have developed small food collecting hairs to trap the
microscopic plants floating in the water.
Blood sucking leeches are also abundant
in the aquatic vegetation. They probably feed on the turtles and
muskrats in the Well. The most abundant species of leech in the
Well does not suck blood, but has tiny sensory hairs all over
their 2-inch long body which enable them to find, and in one big
gulp, eat the amphipods in the total darkness of night.
Occasionally, the always-hungry water scorpion will also creep
out into the night to capture the shrimp-like creatures. There
are no fish found in the Well because of the high concentration
of carbon dioxide released from bottom springs, however, turtles
seem to thrive in the environment.
A DAY IN THE WELL
During the day, the algae are found
floating at all depths, but tend to concentrate as a glistening
film at the water surface during calm periods, especially during
the summer when light is plentiful. The two photographs below
illustrate the variety of sizes and shapes of these tiny
plants.
Without concern for predators, the
amphipods swim freely throughout the water except in the top 3-5
ft (1-1.5 m). Oddly enough, scientists have discovered these
amphipods prefer to swim 8-12 ft (2.5-3.5 m) below the surface
during the day. As many as 100 animals per quart (0.95 l) of
Well water may be found at this layer, while substantially few
amphipods are found deeper. Perhaps they are escaping from the
bright sunlight as well as the hungry waterfowl and turtles from
above and yet maintaining a safe distance above the ravenous
leeches located near the bottom of the Well.
SCUBA divers have witnessed the entire
bottom waving with slimy leeches protruding from soft mud
tunnels during the day. Biologists think the leeches remain
near the dimly lit bottom to avoid being seen and eaten by the
turtles that are often basking in the sun on logs and dense
aquatic plants. Some also think that the leeches may feed on the
tiny worms that slither through the soft bottom mud.
Within the dense aquatic
vegetation around the Well, the highly camouflaged stick-like
water scorpion (pictured below) awaits quietly on stems and
foliage and occasionally grabs an unsuspecting insect of
amphipod that ventures too close to its claw-like legs. Female
water scorpions also use the stems of aquatic plants to deposit
their eggs. These cylindrical eggs with two air-breathing
appendages can be seen in the stem in the picture below.
The leeches wait for the amphipods for
their dinner, and the amphipods in turn, remain at subsurface
depths in expectation of the tasty algae, while the always
ravenous water scorpion awaits quietly in the vegetation for its
evening meal, but all remain stationary until the protection of
darkness.
Along the pathways around the Well,
especially during the summer and fall, visitors will frequently
encounter the beetles searching for food and, when harassed,
these insects will take a protective stance with their posterior
ends pointed upward ready to release a pungent spray to ward off
potential enemies. Numerous damselfly and dragonfly adults will
also be seen flying along the shoreline of the Well in search of
unsuspecting smaller aquatic insect prey.
A NIGHT IN THE WELL
Once the protection of darkness sets in,
the disadvantages of being seen by a hungry predator are
reduced, at least so it seems! As the sun sets, an exciting
sequence of biological events begins. Around the margins of the
Well, hungry daddy long leg spiders and assorted tarantulas
scamper over the damp soil in search of food. Numerous bats and
swallows leave the crevices and caves in the surrounding cliffs
to feast on a variety of insects. Event the resident Great
Horned Owl takes advantage of the many small mammals that use
the protection of darkness to feed and hopefully reduce their
chances of being seen by a hungry predator.
A number of similar events also occur in
the water. First, the resident muskrats leave their mud burrows
along the shore of the Well and swim into the aquatic plants to
feed. Also, many of the amphipods swim to the surface of the
open water and gorge themselves on algae by trapping these tiny
plants in specialized feeding hairs near their mouth (see
illustration below). The amphipods can no longer be fed upon by
the ducks and turtles because they can't be seen, but they must
escape from a new predator. . . .the leech.
Soon after sunset, the leeches leave
their soft mud tunnels and slowly swim to the surface and feed
on the abundant amphipods near the water surface. Fortunately,
the leeches do not need to see the tasty amphipods, but instead
hunt their food by using tiny sensory hairs (pictured below) to
detect the water vibrations produced by the swimming amphipods.
The amphipod's only defense is to curl up and expose the spines
found on their backs (see above picture of amphipod).
Man first came to the Well around 11,000
years ago, just after its formation according to some
scientists. Large groups of wandering hunters would stop at the
Well to drink and rest while tracing down wild game such as
elephants, horses, and camels. For the next 9,000 years the
Well was used as a resting spot, but no permanent settlements
were built. Before the time of Christ, groups of wandering
Indians first decided to live in the area around the Well,
hunting small game (deer, ducks, and turtles) and gathering wild
plants.
Around the year 600 A.D., another group
of Indians called the Hohokam, (and Indian word meaning "those
who have gone") moved in from southern Arizona. Archeologists
think that they may have moved north due to the lack of water
and overpopulation. These people lived in primitive pithouses
around the Well and started to grown their own food. They
diverted water from the constantly flowing Well and used it for
irrigating their crops of corn, beans, and squash.
Around the year 1125 A.D., another group
of Native Americans came from the northern part of Arizona
(Walnut Canyon and Wupatki settlements). Scientists think these
Sinagua Indians (Spanish for "no water") may have moved down to
the Verde Valley because of the cold winters, disease, and
overpopulation experienced at higher northern elevations. Their
impact on the village is reflected by slow replacement of the
pithouses with cliff dwellings, differences in pottery, and
changes in burials. They did however continue to irrigate
cr
Soon the community grew and the cliff
dwellings expended to consist of as many as 50-60 rooms.
Sometime in the early 1400's the village was abandoned. It has
been theorized that fear of war, crop failures, intra-village
rivalry, and/or disease made them leave. In 1853, the first
white men saw Montezuma Well. These early Spanish explorers
found only the abandoned pueblos and some local Indians living
in primitive huts. These Native Americans were not the
irrigation farmers or the cliff dwellers of the past, but were
gatherers, hunters, and stream-bank farmers. The people of this
once large village were now gone, never to return. Montezuma
Well became a National Monument on April 1, 1947. Its lands are
now protected so our children will be able to enjoy its very
special natural beauty.
Electronic edition in memory of
long-time NPS volunteer, Jack Beckman.
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