Alkaline Lakes
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Alkaline Lakes
INTRODUCTION
Alkaline lakes contain a high concentration of dissolved salts. These lakes are found in arid or
semiarid regions and have no outlet to the sea. Alkaline lakes may also be known as saline
lakes. Alkaline lakes are found on six continents and include the world's largest lake, the
Caspian Sea. The Caspian Sea holds over 70% of Earth's inland salt water. Although there
are few alkaline lakes compared to the number of freshwater lakes, they are important
ecosystems. Alkaline lakes are extreme environments. The organisms living in these hostile
environments have specialized characteristics that allow them to thrive. Scientists study areas
like Mono Lake to search for clues about the kind of life that might have lived on Mars.
Alkaline Lakes
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Courtesy of Larry Malone
View of east shore of Mono Lake.
ABIOTIC DATA
Alkaline, or saline, lakes form in regions where there is little rain. The lakes form in
depressions known as basins. Basins have no outlet to the sea. Water flowing over and
through the ground dissolves minerals (salts) from the rocks and soil. Runoff carrying the salts
collects in the lowest part of the basin, forming a lake. Water in the lake evaporates, but the
salts stay behind. Over time the salts build up, creating an alkaline lake. The kinds of salts that
accumulate vary from lake to lake, but usually they include sodium chloride (table salt),
potassium chloride, magnesium chloride, and carbonate salts.
Alkaline Lakes
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Courtesy of B. Mossel, International Lake
Environment Committee
Lake Eyre is an alkaline lake in Australia.
Salinity is an important abiotic factor in alkaline lakes. Salinity is described by the ratio
between the amount of dissolved salt and the amount of water. The range of salinity in
alkaline lakes is from 3 grams per liter (g/L) to over 300 g/L. Compare this to fresh water,
which has a salinity of less than 3 g/L.
BIOTIC DATA
The organisms that live in alkaline lakes tolerate extreme conditions. Organisms move
between the pelagic (open-water) habitat and the benthic (bottom-dwelling) habitat. The few
species that can thrive in high-salinity water make good use of the available food and energy.
Organisms found in most alkaline lakes include producers, such as planktonic and benthic
algae; consumers, such as brine shrimp, brine flies, and a variety of birds; and decomposers,
such as bacteria. Some scientists use the term extremophiles (lovers of extreme conditions)
for these microorganisms.
Alkaline Lakes
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In the Great Salt Lake of Utah, pelagic, or planktonic, algal blooms occur early in the year
when the water is very cold, 2–3°C (36–37°F). Brine shrimp hatching in April feed extensively
on planktonic algae throughout the summer. As the brine shrimp eat, more light can penetrate
to benthic algae and cyanobacteria. Photosynthetic cyanobacteria are the base of the benthic
food web. Black-fly larvae spend most of their lives grazing on the lake bottom and emerge
from the water as adult flies in summer.
Courtesy of U.S. Geological Survey
Planktonic food web during an algal bloom in the Great Salt Lake.
Alkaline Lakes
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Courtesy of U.S. Geological Survey
Benthic food web in the Great Salt Lake.
Migrating birds may often be seen at these lakes, feeding on brine shrimp and other small
organisms during the spring and summer. The Great Salt Lake supports 2 to 5 million
shorebirds as well as hundreds of thousands of other migrating birds during spring, summer,
and fall.
Both benthic and pelagic habitats use nutrients entering the lake from the surrounding
drainage basin. Algae take up the nutrients during photosynthesis. Brine shrimp and brine-fly
larvae feed on the algae. When organisms die, they drift down to the lake bottom, where
bacteria decompose their remains and recycle the nutrients into the system.
Alkaline Lakes
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Courtesy of U.S. Fish and Wildlife
Service
Migrating birds on Utah's Great Salt
Lake.
ISSUES
Most alkaline lakes support enormous populations of birds. These birds may live in the lake
region all year or may visit only during migration. Maintaining these lakes is important to
support the bird populations. In some areas of the world, water is being taken from the
watersheds that feed the lakes, to support human populations. Water withdrawals increase the
lakes' salinity.
Alkaline Lakes
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Courtesy of San Diego State University
These aerial photographs show how the size of
the Aral Sea has changed since 1973.
For example, water diverted from the Aral Sea in the Middle East has shrunk the sea. The
fishing industries have collapsed. The climate has become drier as the water has
disappeared. Pollution is also an issue; the health of the human population as well as the rest
of the ecosystem has deteriorated.