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. Frangois-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.
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.
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.