Alkaline Lakes Page 1 of 7

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 Page 2 of 7

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 Page 3 of 7

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 Page 4 of 7

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 Page 5 of 7

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 Page 6 of 7

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 Page 7 of 7

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.