Limnology is the study of the chemistry, biology, geology, and physics of waters that are found within continents. In contrast, oceanography is the study of open ocean waters. Waters found within continents may be lakes, reservoirs, rivers, or wetlands (land where water covers the surface for at least part of the year) Although most limnologists specialize in freshwaters, the study of saline lakes, like the Great Salt Lake, also falls under the discipline of limnology.
One of the more important goals of limnology is providing guidelines for water management and water pollution control. Limnologists also study ways to protect the wildlife that lives in lakes and rivers as well as the lakes and rivers themselves. Some limnologists are working on construction of artificial wetlands, which could serve as habitats for a variety of animal and plant species and aid in decreasing water pollution.
History of limnology
Limnology is a relatively new academic subject. François-Alphonse Forel (1841–1912), considered the father of limnology, was a Swiss physician who dedicated much of his life to the study of the biology, chemistry, and physics of Lake Geneva. Around 1868, he coined the term limnology to mean the study of lakes. (The root word limn means "lake" and ology means "the study of.") In 1887, American naturalist Stephen Alfred Forbes (1844–1930), a pioneer in the study of lake ecology (the study of the relationships between organisms and their environment), published the paper "Lake as a Microcosm," which is still cited as an important study of lake ecosystems. An ecosystem refers to all of the relationships between the living and nonliving parts of an environment.
George Evelyn Hutchinson (1903–1991) was a British American biologist and a physicist. He made great advancements in limnology beginning in the 1950s and summarized much of the field of limnology in a three-volume text. Hutchinson was extremely influential in bringing modern ecological theories to limnology. Today, limnologists focus much of their attention on integrating ideas from geology, physics, chemistry, and biology into understanding lakes and rivers. They also focus much attention on understanding how humans impact these important ecosystems.
Geological limnology is focused on the formation of lakes and rivers. Many lakes, especially in North America, were formed by the retreat of the glaciers (slow-moving mass of ice) at the end of the Ice Age. As the glaciers melted, they gouged holes in soft parts of the solid rock. When these depressions filled with water, they became lakes. Other lakes form when tectonic plates (mobile pieces of Earth's crust) pull away from each other, leaving rifts called grabens. When these rifts fill with water, very deep lakes can be formed. The deepest lake in the world, Lake Baikal in Siberia, was formed in a graben.
Rivers usually begin as springs in areas of high altitude such as mountains. As they flow downward, rivers gather water from melting snow and other streams, called tributaries, as they flow toward sea level. Geological limnologists are interested in the size and the shape, also called the topography, of the watersheds of lakes and rivers. A watershed is all of the land and water areas that drain into the lake or the river.
Physical limnology deals with the physical properties of the water in lakes and rivers. This includes changes in light levels, water temperatures, and water currents. Water absorbs energy from sunlight, which warms the surface waters. Because the intensity of the sun changes throughout the year, the amount of heat absorbed in the summer is much greater than that absorbed in the winter. During the summer, lakes become stratified or layered, with the warmer, lighter water floating on top of the cooler, deeper water. In the winters, the surface of the lake loses its heat and mixes with the cooler waters below. Understanding the cycle of mixing and stratification is extremely important to understanding the biology of the plants, animals, and microorganisms that live in lakes and the movement of chemicals throughout lakes.
Chemical limnology focuses on the cycling of various chemical substances in lakes and rivers. Several factors affect the chemistry of lakes and rivers including the chemical composition of the soil in the watershed, the atmosphere (mass of air surrounding Earth) and the composition of the riverbed or lake bottom. In modern day, human activities have had a very important influence on the chemistry of lakes and rivers, and chemical limnologists play an important role in understanding these effects. For instance, building construction near lakes and rivers changes the erosion (wearing away of soil) patterns and influences they type of chemicals that reach the water. In some areas, rainwater running into lakes and rivers contains large amounts of fertilizers, oils, and heavy metals.
The concentration of the hydrogen ion (H+) in water is one of the most important chemicals to study. An ion has a positive or negative charge and the hydrogen ion indicates the acidity (charge) of the water, which strongly affects which kinds of organisms can live in the water. Other important substances are the sulfate and nitrate ions, which become concentrated in freshwaters as a result of acid rain. Also, the heavy metal mercury (Hg) is a dangerous pollutant that can circulate in the water and affect the health of animals, along with the humans who eat those animals and use the lake or river.
Lake Baikal, which is located in Siberia in the middle of Asia, is both the oldest (25 million years) and deepest (1 mile or 1,600 meters) lake in the world. It contains one-fifth of all the unfrozen freshwater in the world. Because of its age and its distance from other water bodies, at least 1,200 different animal species and 1,000 different plant species have evolved in it. It is estimated that at least 80% of these species are only found in Lake Baikal.
One of the most interesting animals in the lake is a seal called the nerpa. It is the only mammal that inhabits the lake. Scientists believe that they migrated to the lake about 22 million years ago from the Arctic Ocean. It is estimated that the nerpa population in the lake is about 100,000. They feed on fish that they catch in the lake. During the winter the nerpa swim under the frozen lake, making breathing holes in the ice with their sharp claws. The nerpa can stay underwater for up to 70 minutes at a time.
Crustaceans (aquatic animals with no backbone, jointed limbs, and a hard shell) have flourished in Lake Baikal. The most numerous animal in Lake Baikal is the Baikal epischura crustacean. It is extremely small, about the size of a grain of rice. It feeds on microscopic algae and bacteria by filtering water through appendages around its mouth that look like combs. The total flow of water through the mouths of these tiny animals is equivalent to ten times the flow of all the rivers that enter Lake Baikal each year. The work of these small animals is credited with keeping the lake so clear.
One of the most interesting fish in Lake Baikal is the golomyanka or oil fish. They are relatively small, about 10 inches (24 centimeters) in length, have no scales, and are transparent. About 35% of their body weight is made up of an oil that is a very pure form of vitamin A. Residents who have lived near the lake for many years say that the fish was used to treat many diseases, such as arthritis, and to soothe wounds that would not heal.
Biological limnology is directed at understanding the animals, plants, and microorganisms that live in lakes and rivers. The patterns of distribution of these various organisms depend on the geology, physics, and chemistry of the lake or river. For example, plants require light in order to grow. Because water is very effective at absorbing light, plants must either grow near the shore, where the water is shallow or they must float near the surface of the water. Because the intensity of sunlight changes with season, plants usually have a growth season in the spring when the light levels increase and they die off in the fall when light levels decrease. In the same way, animals require oxygen dissolved in water in order to breath. Warm water holds less dissolved oxygen than cold waters. As a result, trout, which require a lot of dissolved oxygen, are more often found in cold lakes and rivers. Bass, on the other hand, require less dissolved oxygen and can be found in warmer lakes and the surface waters of lakes.
One of the critical challenges facing biological limnologists is the introduction of exotic species into lakes and rivers. Often, humans introduce new species into lakes and rivers. In some cases these species grow faster than the local species and can take over much of the habitat. For example, in 1985 the zebra mussel was released into the Great Lakes of the United States, in the ballast water of a ship coming from the Caspian Sea in Asia. These mussels are able to reproduce extremely fast in the Great Lakes and have become a widespread problem, clogging sewage pipes and overgrowing docks and piers.
Juli M. Berwald, Ph.D.
For More Information
Josephs, David. Lakes, Ponds, and Temporary Pools. New York: Franklin Watts, 2000.
Raven, Peter H., Linda R. Berg, and George B. Johnson. Environment. 2nd. ed. Fort Worth, TX: Saunders College Publishing, 1998.
Rowland-Entwistle, Theodore. Rivers and Lakes. Morristown, NJ: Silver Burdett Press, 1987.
Sayre, April Pulley. Lake and Pond. New York: Twenty-First Century Books, 1996.
Sayre, April Pulley. River and Stream. New York: Twenty-First Century Books, 1996.
"Dedicated to the Memory of G. Evelyn Hutchinson." Soil & Water Conservation Society of Metro Halifax.http://lakes.chebucto.org/PEOPLE/hutchins.html#Hutchinson (accessed on August 24, 2004).
"Lake Baikal Home Page." WWW Irkutsk.http://www.irkutsk.org/baikal/index.html (accessed on August 24, 2004).
"Understanding: Lake Ecology Primer." Water on the Web.http://wow.nrri.umn.edu/wow/under/primer (accessed on August 24, 2004).
Derived from the Greek word limne, meaning marsh or pond, the term limnology was first used in reference to lakes by F. A. Forel (1841–1912) in 1892 in a paper titled "Le Léman: Monographie Limnology," a study of what we now call Lake Geneva in Switzerland. Limnology, also known as aquatic ecology , refers to the study of fresh water communities within continental boundaries. It can be subdivided into the study of lentic (standing water habitats such as lakes, ponds, bogs, swamps, and marshes) and lotic (running water habitats such as rivers, streams, and brooks) environments. Collectively, limnologists study the morphological, physical, chemical, and biological aspects of these habitats.
lim·nol·o·gy / limˈnäləjē/ • n. the study of the biological, chemical, and physical features of lakes and other bodies of fresh water. DERIVATIVES: lim·no·log·i·cal / ˌlimnəˈläjikəl/ adj. lim·nol·o·gist / -jist/ n.