Most lakes go through a process called thermal stratification. Its middle layer is the metalimnion , or thermocline. The deepest layer is the hypolimnion. The most important chemicals in a lake are nitrogen and phosphorus. These chemicals allow nutrient -rich plants and algae to grow. Other organisms feed off these plants and algae, creating a complex, healthy ecosystem.
The chemistry of a lake is affected by biological, geological, and human processes. Natural processes such as the eruption of a nearby volcano can alter the chemical aspect of a lake by introducing new gases or mineral s. A lake must have a healthy amount of oxygen to sustain life.
Lakes that do not have enough oxygen to sustain life are abiotic. The pH level is a chemical property of all substances. Substances with a pH of less than 7 are acidic; substances with a pH greater than 7 are basic. Lakes have different pH levels, with life adapting to different chemical environments. It is full of dissolved minerals. Fish such as cichlid s thrive in Lake Tanganyika.
Tilapia, a variety of cichlid, can also thrive in lakes with very low pH. The Life Cycle of Lakes Once formed, lakes do not stay the same. Like people, they go through different life stages—youth, maturity, old age, and death. All lakes, even the largest, slowly disappear as their basins fill with sediment and plant material. The natural aging of a lake happens very slowly, over the course of hundreds and even thousands of years. But with human influence, it can take only decades.
The warm, shallow water of the upper layer of the lake causes plants and algae to decompose , and eventually they sink to the basin. Dust and mineral deposits on the bottom of the lake combine with the plants to form sediment.
Rain washes soil and pebbles into the basin. The lake becomes smaller, starting at the edges and working toward the middle. Eventually, the lake becomes a marsh, bog , or swamp.
Eventually, the lake becomes dry land. Dry lake beds are a perfect place to find and study fossil s. Archaeologist s often excavate ancient lake beds, such as Fossil Butte in the U. The remains of organisms, from single-celled bacteria to dinosaur s, were preserved over time as sediment on the lake bed built up around and on top of them.
In fact, some scientists believe the first living organisms on Earth developed in lakes. Lake Classification There are three basic ways that limnologists classify lakes: how many nutrients lakes have, how their water mixes, and what kinds of fish live in them.
When lakes are classified by the amount of nutrients they have, limnologists are using the trophic system. Generally, the clearer the water in the lake, the fewer nutrients it has. Lakes that are very nutrient-rich are cloudy and hard to see through; this includes lakes that are unhealthy because they have too many nutrients.
Lakes need to have a balance of nutrients. Lakes can also be classified by how the water mixes, or turns over from top epilimnion to bottom hypolimnion. This is called lake turnover. Water in some lakes, mostly shallow ones, mixes all year long. These lakes have very little lake turnover. Deep lakes experience lake turnover on a large scale. The middle layer, the thermocline, mixes and turns over throughout the year. It turns over due to climate , nutrient variations, and geologic activity such as earthquake s.
Most lakes that experience lake turnover are dimictic lake s, meaning their waters mix twice a year, usually in fall and spring. Lake turnover changes with the seasons. During the summer, the epilimnion, or surface layer, is the warmest. It is heated by the sun. The deepest layer, the hypolimnion, is the coldest. During the fall, the warm surface water begins to cool.
As water cools, it becomes more dense , causing it to sink. This cold, dense water sinks to the bottom of the lake. It forces the water of the hypolimnion to rise. During the winter, the epilimnion is coldest because it is exposed to wind, snow, and low air temperatures.
The hypolimnion is the warmest. It is insulate d by the earth. This is why there is ice on lakes during the winter, while fish swim in slightly warmer, liquid water beneath.
During the spring, the lake turns over again. The cold surface water sinks to the bottom, forcing the warmer, less dense water upward. The final way to classify lakes is by the kinds of fish they have. This helps people in the fishing industry identify what kinds of fish they might be able to catch in that lake. For example, calling a lake a cold-water lake tells a fisherman that he can probably expect to find trout, a cold-water fish.
A lake that has thick, muddy sediment is more likely to have catfish. There are other ways of classifying a lake, such as by whether it is closed or fed by a river or stream.
States also divide lakes into ones that are available for public use and ones that are not. Many people refer to lakes by size. They serve as migration stop s and breeding ground s for many birds and as refuges for a wide variety of other animals.
They provide homes for a diversity of organisms, from microscopic plants and animals to fish that may weigh hundreds of kilograms. The largest fish found in lakes is the sturgeon, which can grow to 6 meters 20 feet and weigh more than kilograms 1, pounds.
Plants growing along the lakeshore may include moss es, fern s, reed s, rush es, and cattail s. Small animals such as snails, shrimp, crayfish , worms, frogs, and dragonflies live among the plants and lay their eggs on them both above and below the waterline. Farther from the shore, floating plants such as water lilies and water hyacinth s often thrive. They have air-filled bladders, or sacs, that help keep them afloat. These plants shelter small fish that dart in and out under their leaves.
Waterbugs, beetles, and spiders glide and skitter across the surface or just below it. Small islands, floating plants, or fallen logs provide sunny spots for turtles to warm themselves. Other animals live near the lake, such as bats and semi-aquatic animals, such as mink , salamander s, beavers, and turtles. Semi-aquatic animals need both water and land to survive, so both the lake and the shore are important to them. Many kinds of water birds live on lakes or gather there to breed and raise their young.
Ducks are the most common lake birds. Others include swans, geese, loons, kingfishers, herons, and bald eagles. Many people think of fish when they think of lakes. Some of the most common fish found in lakes are tiny shiners, sunfish, perch, bass, crappie, muskie, walleye, perch, lake trout, pike, eels, catfish, salmon, and sturgeon.
Many of these provide food for people. How People Use Lakes Lakes are an important part of the water cycle; they are where all the water in an area collects. Water filters down through the watershed , which is all the streams and rivers that flow into a specific lake. Lakes are valuable resource s for people in a variety of ways. Through the centuries, lakes have provided routes for travel and trade. The Great Lakes of North America, for example, are major inland route s for ships carrying grain and raw material s such as iron ore and coal.
Farmer s use lake water to irrigate crop s. The effect of very large lakes on climate also helps farmers. Because water does not heat or cool as rapidly as land does, winds blowing from lakes help keep the climate more even. Chicago sits on the shore of Lake Michigan.
When the western part of Illinois is snowing, Chicago often remains slightly warmer. The lake effect can help farmers. In autumn, lakes blow warmer air over the land, helping the season last longer so farmers can continue to grow their crops. In spring, cool lake winds help plants not to grow too soon and avoid the danger of early-spring frost s, which can kill the young crops. Lakes supply many communities with water.
Artificial lakes are used to store water for times of drought. Lakes formed by dams also provide hydroelectric energy. The water is channeled from the lake to drive generator s that produce electricity. Because they are often very beautiful, lakes are popular recreation and vacation spots.
People seek out their sparkling waters to enjoy boating, swimming, water-skiing, fishing, sailing, and, in winter, ice skating, ice boating, and ice fishing. Many public parks are built near lakes, allowing people to picnic, camp, hike, bike, and enjoy the wildlife and scenery the lake provides. For some people, lakes are permanent homes. For example, indigenous people called the Uros have lived on Lake Titicaca in the Andes Mountains for centuries. The lake supplies almost everything the Uros need.
They catch fish from the lake and hunt water birds. The islands are about 2 meters 6. On them, the Uros build reed houses and make reed sleeping mats, baskets, fishing boats, and sails. They also eat the roots and the celery -like stalk s of the reeds. Lake Health: Blue-Green Algae Although lakes naturally age and die, people have sped up the process by polluting the water.
A major problem that threatens many lakes is blue-green algae. It stays on the surface of the water and forms a sort of mat. When the conditions are just right, the algae multiplies quickly. Not only do they supply the human population, animals, and plants with the freshwater they need to survive, but they are great places for people to have fun.
You might be surprised at how little of Earth's water supply is stored as freshwater on the land surface, as shown in the diagram and table below. Freshwater represents only about three percent of all water on Earth and freshwater lakes and swamps account for a mere 0. Twenty percent of all fresh surface water is in one lake, Lake Baikal in Asia. Another twenty percent about 5, cubic miles about 23, cubic kilometers is stored in the Great Lakes.
Rivers hold only about 0. You can see that life on Earth survives on what is essentially only a "drop in the bucket" of Earth's total water supply! People have built systems, such as large reservoirs and small water towers like this one in South Carolina, created to blend in with the peach trees surrounding it to store water for when they need it.
These systems allow people to live in places where nature doesn't always supply enough water or where water is not available at the time of year it is needed. The Earth is a watery place. But just how much water exists on, in, and above our planet? About 71 percent of the Earth's surface is water-covered, and the oceans hold about Water also exists in the air as water vapor, in rivers and lakes, in icecaps and glaciers, in the ground as soil moisture and in aquifers, and even in you and your dog.
This bar chart shows how almost all of Earth's water is saline and is found in the oceans. Of the small amount that is actually freshwater, only a relatively small portion is available to sustain human, plant, and animal life.
In the first bar, notice how only 2. The middle bar shows the breakdown of freshwater. Almost all of it is locked up in ice and in the ground.
Only a little more than 1. The right bar shows the breakdown of surface freshwater. Most of this water is locked up in ice, and another Rivers make up 0.
Although rivers account for only a small amount of freshwater, this is where humans get a large portion of their water from. Source: Gleick, P. In Encyclopedia of Climate and Weather, ed.
Do you really like lakes? Or maybe you'd rather sit by the ocean, or maybe a waterfall is your favorite? Visit our interactive Activity Center and submit your vote for your favorite water body? See how thousands of others all over the world voted. Earth's water is always in movement, and the natural water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above, and below the surface of the Earth. Water is always changing states between liquid, vapor, and ice, with these processes happening in the blink of an eye and over millions of years.
The air is full of water, even if you can't see it. Higher in the sky where it is colder than at the land surface, invisible water vapor condenses into tiny liquid water droplets—clouds. When the cloud droplets combine to form heavier cloud drops which can no longer "float" in the surrounding air, it can start to rain, snow, and hail What is streamflow? How do streams get their water?
To learn about streamflow and its role in the water cycle, continue reading. Note: This section of the Water Science School discusses the Earth's "natural" water cycle without human interference. Perhaps you've never seen snow. Wiley-Blackwell Publishing, Nakano, S. Reciprocal subsidies: Dynamic interdependence between terrestrial and aquatic food webs. Sala, O. Biodiversity - Global biodiversity scenarios for the year Science , Scheffer, M.
Shallow lakes theory revisited: Various alternative regimes driven by climate, nutrients, depth and lake size. Hydrobiologia , Schindler, D. Eutrophication and recovery in experimental lakes - Implications for lake management. Wellborn, G. Mechanisms creating community structure across a freshwater habitat gradient. Annual Review of Ecology and Systematics 27 , Wetzel, R. Limnological Analyses , 3rd ed. Introduction to the Basic Drivers of Climate. Terrestrial Biomes. Coral Reefs. Energy Economics in Ecosystems.
Biodiversity and Ecosystem Stability. Biological Nitrogen Fixation. Ecosystems Ecology Introduction. Factors Affecting Global Climate. Rivers and Streams: Life in Flowing Water.
The Conservation of Mass. The Ecology of Carrion Decomposition. Causes and Consequences of Biodiversity Declines. Earth's Ferrous Wheel. Alternative Stable States. Recharge Variability in Semi-Arid Climates. Secondary Production. Food Web: Concept and Applications. Terrestrial Primary Production: Fuel for Life. Hoverman Dept. Johnson Dept. Citation: Hoverman, J. Nature Education Knowledge 3 6 What is the status of these rich ecosystems?
Aa Aa Aa. Physical and Chemical Structure. Size, formation, and succession. Thermal stratification. The structure and function of ponds and lakes are determined by factors such as turbulence, temperature, water clarity, habitat size, and water depth. Wind turbulence and temperature interact to influence stratification and water circulation within lakes. In the spring, wind turbulence circulates the water throughout a lake supplying oxygen to the entire water column.
However, as the temperature increases during the summer and wind subsides, thermal stratification occurs, producing distinct layers in the water column; the upper warm-water epilimnion is separated from the lower cold-water hypolimnion by the thermocline.
Oxygen concentration in the hypolimnion tends to decline compared to the epilimnion due to the lack of water circulation. Additionally, without mixing to replenish dissolved oxygen, respiration by benthic organisms within the hypolimnion can further reduce oxygen concentrations.
As the temperature begins to cool in the autumn, whole lake circulation is restored and the oxygen concentration is equalized.
In addition to increasing oxygen concentrations, water circulation plays an important role in circulating nutrients. Given that lentic systems are broadly distributed across different elevations and latitudes, there are a number of possible stratification patterns Wetzel Similarly, ponds often show little thermal stratification during the summer due to their shallow depth, which facilitates wind-mediated water circulation.
Light transmission. Another critical factor in lakes and ponds is light transmission, which is required for photosynthesis in primary producers. Generally, the water column is divided into the photic and aphotic zones.
In contrast, light penetration is primary production. However, a deep lake with low water clarity may have a large aphotic zone because light transmission is blocked by suspended particles in the water column.
Nutrient inputs and cycling. As in any ecosystem, nutrient inputs and cycling have important influences on the structure and function of lentic systems. Nutrients are transported into lentic systems via terrestrial run-off, ground water flow, atmospheric deposition e.
The three most important nutrients are nitrogen, carbon, and phosphorus, which are essential elements to all organisms. While phosphorus has historically been considered the most limiting in lentic systems due to low input rates and the high propensity to form complexes with iron, leading to mineralization Schindler , recent work suggests that nitrogen can also be limited in lentic systems Elser et al.
The supply of nutrients into lentic systems determines the amount of primary productivity that can be supported. Oligotrophic systems are characterized by low nutrient supply and low primary productivity where as eutrophic systems are characterized by high nutrient supply and high primary productivity.
While natural systems can be eutrophic, human activity can increase the input of nitrogen and phosphorus into lentic systems leading to anthropogenic eutrophication. Industrial, agricultural, or municipal wastewater can augment nutrient inputs into lentic systems, which can shift the environmental equilibrium and lead to eutrophication.
Anthropogenic eutrophication can dramatically alter the food web structure and reduce water quality. Once eutrophication occurs, it is difficult to reverse owing to internal feedbacks e. In lakes and ponds, much of the species diversity is concentrated in the littoral zone , near the shore, where algae and plants thrive in the abundant light needed for photosynthesis. Living within the plant matter is a cornucopia of animals including snails, amphibians, crustaceans, insects, and fish. Beyond the littoral zone is the limnetic zone.
This is the zone of open water where light is still able to penetrate and support photosynthetic algae i. Consumers in this zone include zooplankton, which feed on the algae, some insects, and fish. Finally, the benthic zone is the bottom sediment e.
Primary producers. Primary producers are broadly divided into three groups, periphyton , phytoplankton , and macrophytes. The consumer species found in lentic habitats include worms, snails, amphibians, crustaceans, insects, reptiles, fish, and birds. Herbivorous groups such as snails, amphibian larvae, and crustaceans play an important role in controlling primary productivity and algal blooms.
Additionally, these groups are a critical resource for predators.
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