Lake and Pond
Lake and Pond
Lakes and ponds are inland bodies of water. Ponds tend to be shallow and small, and most do not have names. Lakes vary greatly in size and most do have names. Lake Superior, for example, which lies between Canada and the United States, has the greatest surface area of any freshwater lake in the world—31,800 square miles (82,362 square kilometers). Lake Baikal in southern Siberia is the deepest at 1 mile (1.6 kilometers). Baikal holds the most water even though its surface area is less than half that of Lake Superior. Ponds and lakes differ in overall water temperature. Ponds have a uniform temperature throughout, but a lake has two distinct layers: an upper layer affected by air temperature, and deeper water that may be either warmer or colder than the upper layer, depending upon the season.
Less than 1 percent of all the water on Earth is held in lakes and ponds. Even so, the amount is considerable. In North America alone, there are at least 1.5 million ponds, totaling as much as 2 million acres (808,000 hectares) of water. Both lakes and ponds tend to be more numerous in the northern hemisphere and in mountain regions. There are relatively few in South America, for instance, but the northern areas of Canada are a large network of lakes and ponds.
All lakes and ponds have a life cycle that begins when they are formed and ends when they are filled in with plant life.
Both lakes and ponds usually form when water collects in undrained depressions, or basins, in the ground and any outlet, such as a stream, does not drain them completely. The source of the water may be precipitation (rain, sleet, and snow), a river, a stream, a spring, or a melting glacier. In any case, there must be enough water to keep the depression
|WORDS TO KNOW|
|Epilimnion : The layer of cold or warm water closest to the surface of a large lake.||Parasite : An organism that depends upon another organism for its food or other needs.|
|Euphotic zone : The zone in a lake where sunlight can reach.||Profundal zone : The zone in a lake where no more than 1 percent of sunlight can penetrate.|
|Eutrophication : Loss of oxygen in a lake or pond because increased plant growth has blocked sunlight.||Sediments : Small, solid particles of rock, minerals, or decaying matter carried by wind or water.|
|Herbivore : An animal that eats only plant matter.||Seiche : A wave that forms during an earthquake or when a persistant wind pushes the water toward the downward end of a lake.|
|Hypolimnion : The layer of cold or warm water closest to the bottom of a large lake.|
|Kettle : A large pit created by a glacier that fills with water and becomes a pond or lake.||Soda lake : A lake that contains more than 0.1 ounce of soda per quart (3 grams per liter) of water.|
filled. In very dry regions, ponds or lakes may form during a rainy season and then disappear when the dry season returns.
Depressions that become ponds and lakes may be created by natural forces, animals, people, and even the wind. Most are made by glacial, volcanic, tectonic (crustal plate movement), or riverine action, and by sinkholes and barriers.
During the Ice Ages, starting 2 million years ago, glaciers (gigantic slow-moving rivers of ice) gouged depressions in the land. Many of these depressions filled with water, creating lakes and ponds. Examples include lakes in Canada, the northern United States, Finland, and parts of Sweden. Glaciers on the tops of mountains, such as in Glacier National Park in Montana, still produce lakes by means of the same process, and most mountain lakes originated in this way. Berg Lake in Canada gets its name from the icebergs that break off a glacier sitting along its shoreline. Glacial basins tend to be shallow and rimmed by rocky shorelines.
When glaciers melt, they sometimes leave pits, called kettles, which fill with the meltwater and become ponds, lakes, or wetlands. Prairie regions in North America have many of these kettles, also called prairie potholes.
The craters of extinct or inactive volcanoes often contain lakes. One example is Crater Lake in Oregon. The walls of laval rock surrounding this lake rise to 1,932 feet (589 meters) above its surface. Lakes in craters often contain islands. Some of these islands are cones of ash and lava created when the volcano went through another active period. The largest crater lake in the world is Lake Toba in Sumatra, although it is undergoing changes due to earthquake activity.
Tectonic action refers to movement of Earth’s crust during earthquakes. Earth’s crust is always in motion causing some pieces to push against one another and others to pull apart. During earthquakes, great cracks may form in the ground. When water fills these cracks, it forms lakes. Examples of lakes created by tectonic action include Lake Tahoe in California and Lake Baikal in Siberia.
During floods, rivers may overflow their banks, creating shallow floodplain lakes. The Amazon River in Brazil, for example, frequently becomes flooded and thousands of lakes form along its great length. Winding rivers often create oxbow lakes during floods. The river jumps its banks and changes course. The abandoned section, which is curved, or bow shaped, becomes a lake.
Sinkholes are formed when the underlying rock is limestone and a source of water, such as an underground river, dissolves the limestone. The ground overhead collapses, leaving a pit. If the pit fills with water, a lake or pond is formed. Sinkhole lakes may be 50 feet (15 meters) or more deep. Several sinkhole pools, called Silver Springs, are located in northern Florida.
Barriers of sand, gravel, mud, rock, lava, and glacial debris can dam up a river or stream, and the area behind the dam fills with water. This type of lake is often short lived because the movement and pressure of the water soon cuts through the debris and the lake is drained.
Lakes and ponds are not permanent, even though some lakes may exist for thousands of years. A volcano or tectonic action, for example, may change the structure of the underlying rock, causing the water to drain away. Streams or other sources that feed the lake may change course or dry up, or the climate may change, yielding little precipitation. Most lakes and
The Killer Lakes
In the Cameroon highlands of West Africa is a series of beautiful but deadly lakes that are responsible for killing nearly 2,000 people during the 1980s. Rolling hills covered in tall grasses and lush vegetation are characteristics of this region, and the soil is so rich that many farming communities of the Bantu and Fulani tribes have located there. Legends of the Bantu and Fulani tell of strange floods that destroyed villages and of spirit women who live in the lakes and pull people to their deaths. There is some truth to these legends.
In 1984 the police in a nearby village were told about people dying on the road near Lake Monoun. When they went to investigate, they saw a smokelike cloud drifting outward from the lake that left seventeen people dead in its wake. Lake Monoun and its sister lakes are pools that formed in the craters of inactive volcanoes. It was determined that a small earthquake had shaken up the lower depths of the lake where carbon dioxide gas was suspended like bubbles in a can of soda. All at once these deep waters were forced upward to where the pressure was less, and the gas was released into the air. In high concentrations, carbon dioxide is deadly, as it was in this case when it suffocated everyone in its path.
Before the mystery was solved and the information was made available, similar clouds had erupted from other lakes in the region, taking many lives.
ponds begin to transform as soon as they are created because they gradually fill with sediments (particles of soil and other matter) and dead plant and animal matter. This ecological process is called succession.
Succession usually follows the same pattern. As sediments fill the bottom of the pond or lake, shore plants, such as reeds and grasses, can gain a foothold and grow. Gradually, they begin to move into ward the center of the lake. The increased waste from dead stems and leaves makes the water thick, shallow, and slow moving. Eventually, shrubs and then trees, such as willows, begin to grow. The open water continues to shrink until the area becomes a wetland. As succession continues, the wetland disappears and is replaced by dry ground.
The speed with which succession takes place varies, depending upon the kinds of sediments and the death rate of plants in the region. A small pond can disappear in fewer than 100 years; a lake takes much longer, perhaps several thousand years.
Lakes and ponds can be classified in many ways. One of the most common ways is by chemical composition. They may contain fresh water, salt water, or soda water.
Water Down Under
Groundwater is what its name implies—water beneath the ground. Over time, water from ponds, lakes, and rain or snow trickles down through the earth and collects between layers of rock. When someone digs a well, the water that fills the well is groundwater.
A spring occurs when groundwater breaks through to the surface. Springs may feed lakes, ponds, and natural wetlands. The world’s largest reported spring is Ras-el-Ain in Syria, with an average yield of 10,200 gallons (38,700 liters) per second. The largest spring in the United States is Silver Springs in Florida, which averages 6,100 gallons (23,000 liters) per second.
Freshwater lakes and ponds
The water in freshwater lakes is relatively pure. It contains many dissolved minerals and salts at very low concentrations. Freshwater lakes tend to be located in temperate or cold regions, and they support much plant and animal life.
Saltwater lakes and ponds
The salt found in salt lakes and ponds may be sodium chloride, which is ordinary table salt, or it may include a combination of other types, including magnesium salt. The Great Salt Lake in Utah contains sodium chloride, whereas the Dead Sea between Israel and Jordan contains a combination of salts.
These salts usually enter the water as it dissolves the surrounding rock, or they are carried in by streams. Salt lakes occur primarily in dry climates where evaporation is sped up and the concentration of salt is able to build.
Salt lakes contain at least 0.1 ounce (3 grams) of salt per quart (liter) of water. The minimum amount produces water less salty than seawater, but the concentration in some lakes makes them much saltier than the ocean. The Dead Sea, which has the highest salt content of any lake on Earth, is nine times saltier than ocean water. When these bodies of water dry up, they leave behind a crust of salt, sometimes referred to as white alkali.
Soda lakes and ponds
Soda (alkali) lakes and ponds contain minerals that are usually produced in hot, volcanic springs. The primary mineral is sodium bicarbonate, which is similar to baking soda. Lake Natron in Tanzania is an example of a soda lake. Like salt lakes, soda lakes usually occur in hot climates. The water in Lake Natron evaporates quickly under midday temperatures as high as 140°F (60°C), but it is fed by geysers (volcanic springs) that help maintain its size.
To be classified as a soda lake, a lake must contain more than 0.1 ounce (3 grams) of soda per quart (liter) of water. The soda in Lake Natron is so concentrated that in places it is thick and hard enough to walk on. Natron’s water kills almost all plant and animal life and can burn human skin seriously enough to require surgery.
The water column refers to the water in a lake or pond, exclusive of its bed or shoreline.
The water in a pond or lake may be fresh, salty, or alkaline; it may be clear or cloudy; it may be polluted or clean. Its characteristics are determined by where it comes from and the nature of its bed or basin. For example, if a river flowing into a lake carries a large quantity of sediment with it, the water in the lake will be muddy.
Different parts of a lake or pond may have different features and support different kinds of plants and animals. These different parts are called zones. Zones may be determined by temperature, vegetation, or light penetration.
Zones determined by temperature
Ponds and small lakes often have a uniform temperature throughout because they are relatively shallow. The water in large lakes may form layers based on water temperature. This difference in
Many books have been written about ponds, but few compare to Walden by Henry David Thoreau (1817–1862). Thoreau, a famous American writer, wrote his book after living two years beside Walden Pond, a small body of water near Boston, Massachusetts.
Born in 1817, Thoreau was an artist whose own life became the material for his book. In a society rapidly growing more urban and industrial, he believed in the wholeness of nature and in a life of principle. In 1845 he sought solitude and simple living beside Walden Pond, where he could think, write, and discover “the great facts of his existence.” He built a small cabin and did some farming. The journals he kept became the basis for his book, which he published in 1854.
The importance of Walden and Thoreau’s other works were not appreciated during his lifetime. These records of what was basically a spiritual journey are now among the world’s finest writings.
temperature prevents the waters from mixing well. In temperate climates (those with warm summers and cold winters) these layers occur seasonally.
In the summer the heat of the sun and the warmth of the air create an upper layer of warm, circulating water called the epilimnion (eh-pihLIHM-nee-uhn). The colder water, which is heavier and noncirculating, sinks to the bottom where it forms a layer called the hypolimnion (HIGH-pohlihm-nee-uhn). The zone in between is called the thermocline.
In the autumn, heat in the epilimnion is lost as cooler weather moves in, and the lake achieves about the same temperature throughout. In winter, the epilimnion is exposed to the cold air temperatures and may freeze, forming a layer of ice, while the hypolimnion remains comparatively warm. The layers do not mix again until the spring when the ice thaws.
Deep within Earth is a core of molten rock that, in places, is close enough to the surface to heat groundwater and turn it into steam. When this steam builds up, it forces its way to the surface in a gush of water and vapor called a geyser (GY-zuhr).
Geysers and hot springs usually occur in regions where volcanoes were or are active, and some, such as Old Faithful in Yellowstone National Park, erupt with clocklike regularity. Pools of hot mineral-rich mud may form in the same region. These naturally hot springs and pools were used by humans as early as 190 BC for their healing properties.
Since 1900, scientists have experimented with tapping the heat within Earth for use as a power source. Called geothermal (jee-oh-THURmuhl) energy, it can be used to drive engines and heat water. In Iceland, many homes and greenhouses are heated using geothermal energy.
Zones determined by vegetation
Along the edges of a pond or lake, areas of vegetation run somewhat parallel (in the same direction) to the shoreline. Here the soil is marshy and wet. The area where shallow water begins to appear around the roots of plants marks the beginning of the littoral zone. This zone is the area near the shore where plants are rooted at the bottom and light penetrates down to the sediment. This zone supports a large variety of animal life. The width of the littoral zone may vary from a few feet to a few miles.
The limnetic zone is the deeper, central region characterized by open water and no vegetation.
Zones determined by light penetration
Deep lakes may be divided into zones based on light penetration. The upper, or euphotic (yooFOH-tik) zone is exposed to sunlight and supports the most life. In clear lakes this zone may reach as deep as 165 feet (50 meters). In muddy lakes, the euphotic zones may only be 20 inches (51 centimeters) deep.
The lower, or profundal (proh-FUN-duhl) zone receives no more than 1 percent of sunlight. No plants grow here, although animals frequent this zone.
Water in a lake is usually in motion, forming both waves and currents.
Waves are rhythmic rising and falling movements in the water. Although waves make the water appear as if it is moving forward, forward movement is actually very small. Most surface waves are caused by wind. Their size is due to the speed of the wind, the length of time the wind has been blowing, and the distance over which it travels. As these influences grow stronger, the waves grow larger.
A seiche (SAYSH) is a wave that forms during an earthquake or when a persistent wind forces the water toward the downwind end of the lake. When the wind ceases, the water flows back and forth from one end of the lake to the other in a rocking motion.
Currents are the steady flow of water in a certain direction. Surface currents are caused by persistent winds, the position of landmasses, and water temperature variations.
Winds tend to follow a regular pattern. They generally occur in the same place and blow in the same direction, and the movement of water follows this pattern. When a current meets a landmass, such as an island, it is deflected and forced to flow in a new direction.
Both horizontal and vertical currents below the surface occur when seasonal temperature changes cause layers of water (the epilimnion and hypolimnion) to form. As the layers take shape or break up, the water turns over (warmer water rises and the cooler water sinks). Most freshwater lakes turn over at least once a year and some twice. In salt and soda lakes, the heating and cooling of the upper layer is not strong enough to cause the water to turn over.
Effect of the water column on climate and atmosphere
The climate surrounding a pond or lake depends upon where the lake or pond is located. If it is located in a desert country, such as Iran, the climate will be hot and dry. If it sits on top of a mountain in the northern hemisphere, the climate will be cold. Ponds in temperate climates are often affected by seasonal changes. A small pond may completely dry up in summer, or
|THE WORLD’S LARGEST LAKES|
|Square Miles||Square Kilometers||Feet||Meters|
|* Saltwater lakes|
|Caspian Sea*||Azerbaijan, Kazakhstan, Turkmenistan, Iran, Russia||144,000||373,000||3,264||995|
|Lake Superior||Canada, United States||31,820||82,732||1,333||406|
|Lake Victoria||Kenya, Tanzania, Uganda||26,828||69,484||270||82|
|Lake Huron||Canada, United States||23,000||59,600||750||229|
|Lake Michigan||United States||22,300||57,757||923||281|
|Aral Sea*||Kazakhstan, Uzbekistan||15,500||40,100||177||54|
|Lake Tanganyika||Burundi, Zambia, Tanzania, Zaire||12,700||32,893||4,708||435|
|Great Bear Lake||Canada||12,096||31,328||1,299||396|
|Lake Nyos||Tanzania, Mozambique, Malawi, Cameroon||11,000||28,749||2,300||701|
freeze to the bottom in winter. Severe spring floods may destroy shoreline plants including the homes and feeding grounds of many animals.
The presence of a large lake can itself create some climatic differences. A large body of water absorbs and retains heat from the sun. In the winter, this stored heat is released into the atmosphere helping to keep winter temperatures around the lake warmer. In summer, when the water temperature is cooler than the air temperature, winds off the lake help cool the nearby region. This is known as the lake-effect. The climate of Chicago, which is located on the shores of Lake Michigan, benefits in this way.
The water in lakes and ponds is partly responsible for the precipitation (rain, sleet, or snow) that falls on land. The water evaporates in the heat of the sun, forms clouds, and falls elsewhere. Large lakes can even influence storms. In winter, for example, as air flows over a lake, it picks up moisture. When the warmer, moister air meets the colder, drier air over land, it produces lake-effect snow. Towns along the eastern shore of Lake Ontario regularly receive 118-157 inches (300-400 centimeters) of snow a year for this reason.
Bodies of water help regulate the levels of different gases in the atmosphere, such as oxygen and carbon dioxide. Too much carbon dioxide in the atmosphere contributes to warmer global temperatures. The presence of ponds and lakes helps moderate such undesirable changes by absorbing some carbon dioxide.
The geography of lakes and ponds involves the process of erosion (wearing away) and deposition (dep-oh-ZIH-shun; setting down), which helps determine the different types of shoreline surfaces and landforms.
Erosion and deposition
As waves slap against a shoreline they compress (squeeze) the air trapped in the cracks in rocks. As the waves retreat, the air pressure within the rocks is suddenly released. This process of pressure and release widens the cracks and weakens the rocks, causing them to eventually break apart. Waves created by storms in a large lake can be high and forceful. In places where wave action is strong, the water stirs up particles of rock and sand from the lake bed throwing them against the shoreline. As a result, particles in the water produce a cutting action, eroding the shoreline even further.
Some of the chunks and particles eroded from a shoreline may sink to the lake bed. Others may be carried by currents farther along the shore and deposited where there is shelter from the wind and the wave action is less severe. Erosion and deposition can change the geography of a shoreline over time.
The general shape of the shoreline is usually determined by the shape of the surrounding landscape. If the lake or pond is on a flat plain, the shoreline will be broad and level. If it is located in the mountains, the shoreline is likely to be steep and rocky. Beaches that develop along rocky shorelines usually consist of pebbles and larger stones, as the waves carry away finer particles.
Movement of Earth’s crust during an earthquake may have given the shoreline a folded appearance. Huge boulders and rocks or piles of gravel and sand may indicate that a glacier once moved across the region. The presence of a river may mean a large quantity of sedimentary deposits on the lake bed or the shoreline near the river mouth. Sandy shores are constantly changing, depending upon the movement of the wind, water, and sand. Some sandy shores may be steep while others have a gentle slope.
Landforms include cliffs and rock formations; beaches and dunes; spits, bars, and shoals; deltas; and islands.
Cliffs and rock formations
Where highlands meet the edge of a lake, cliffs sometimes occur. Waves pounding the cliffs gradually eat into their base, creating a hollowed-out notch. The overhang of the notch may collapse and fall, creating a platform of rubble.
Many shorelines consist of both hard and soft rock. Wave action erodes the soft rock first, sometimes sculpting beautiful shapes, such as arches, along the shore. Caves may be gradually carved into the sides of cliffs, or headlands may be created. A headland is a large arm of land made of hard rock that juts out from shore after softer rock on either side has been eroded away.
Beaches and dunes
Beaches are nearly level stretches of land along the water’s edge. They may be covered by sand or stones. Sand is small particles of rock, less than 0.08 inches (2 millimeters) in diameter. It may be white, golden, brown, or black, depending upon the color of the original rock. Yellow sand usually comes from quartz and black sand from volcanic rock. White sand may have been formed from limestone.
Putting a Nuisance to Work
A water hyacinth is an aquatic plant that lives in ponds, quiet streams, and ditches. Water hyacinths have large violet flowers that float on top of the water, and some species have long, trailing, feathery roots. In the wrong place, these roots can clog otherwise navigable watercourses and irrigation ditches, which makes the plant a nuisance. The water hyacinth may be able to make up for this annoying tendency with another important characteristic: it can absorb large amounts of pollutants. Researchers are experimenting with using the hyacinth in water-treatment systems and sewage-disposal plants.
Sand is carried by water and wind. When enough sand has been heaped up to create a ridge or hill, it is called a dune. Individual dunes often travel, as the wind changes their position and shape. They tend to shift less if grasses and other plants take root in them and help hold them in place.
Spits, bars, and shoals
A spit is a long narrow point or strip of deposited sand, mud, or gravel that extends into the water. A bar is an underwater ridge of sand or gravel formed by currents that extends across a channel. Shoals are areas where enough sediments have accumulated that the water is very shallow. Shoals and bars make navigation dangerous for boats.
Where rivers meet a lake, huge amounts of silt (a type of very small soil particle) can be carried by river currents from far away and deposited in the lake along the shoreline. Large rivers can dump so much silt that islands of mud build up forming a fan-shaped area called a delta. The finer debris that does not settle as quickly may drift around the lake, making the water cloudy.
Islands are landmasses completely surrounded by water. In lake basins dug out by glaciers, islands may be formed from large piles of debris created when the glacier moved across the area. In crater lakes, islands may have formed from secondary cones that developed when the volcano became active again. Other islands may have been created when the water surrounded a high point of land, cutting it off from the shore on all sides.
Basins of ponds or lakes slope gently from the shore down to the center, where the water is deepest. Basins are usually covered with sediments. Some sediments are formed by waste products and dead tissues of plants and animals. Others consist of clay, stone, and other minerals.
Lakes occur at all altitudes. For example, Lake Titicaca, which lies between Bolivia and Peru, is 12,500 feet (3,810 meters) above sea level, while the Sea of Galilee, located between Israel and Jordan, is 695 feet (212 meters) below sea level. (Sea level refers to the average height of the surface of the sea.)
Most lake and pond plants live in the waters around the shoreline. They include microscopic, one-celled organisms; plants commonly referred to as seaweed; and many other types of grasses and flowering plants.
The water offers support to plants. Even a small tree on land requires a tough, woody stem to hold it erect, but underwater plants do not require woody portions because the water helps to hold them upright. Their stems are soft and flexible, allowing them to move with the current without breaking.
Plants in and around a lake or pond may be classified as submergent, floating aquatic (water), or emergent, according to their relationship with the water.
A submergent plant grows beneath the water. Even its leaves are below the surface. Submergents include milfoil, pondweed, and bladderwort, an insect-eating plant.
Floating aquatics float on the water’s surface. Some, such as the water hyacinth, water lettuce, and duckweed have no roots anchored in the bottom soil. Others, such as water lilies and pondweed, have leaves that float on the surface, stems that are underwater, and roots that anchor them to the bottom.
An emergent plant grows partly in and partly out of the water. The roots are usually underwater, but the stems and leaves are at least partially exposed to air. They have narrow, broad leaves, and some even produce flowers. Emergents include reeds, rushes, grasses, cattails, and water plantain.
Plants and plantlike organisms that live in lakes and ponds can be divided into four main groups: algae (AL-jee), fungi (FUN-ji), lichens (LY-kens), and green plants.
Most lake and pond plants are algae. (It is generally recognized that algae do not fit neatly into the plant category.) Algae inhabit even the salt and soda lakes that are unfriendly to other life forms.
Some forms of algae are so tiny they cannot be seen without the help of a microscope. Other species, like many seaweeds, are larger and remain anchored to the bed of the lake or pond.
Algae contain chlorophyll, a green substance used to turn energy from the sun into food. As long as light is available, algae can grow. Growth is often seasonal. In some areas, such as the northern hemisphere, the most growth occurs during the summer when the sun is more directly overhead. In temperate (moderate) zones, growth peaks in the spring but continues throughout the summer. In regions near the equator, no growth peaks occur. Instead, growth is steady throughout the year.
Most algae have the ability to make their own food by means of photosynthesis (foh-toh-SIN-thih-sihs). Photosynthesis is the process by which plants use light energy to change water and carbon dioxide from the air into the sugars and starches they use for food. A byproduct of photosynthesis is oxygen, which combines with water and enables aquatic animals, such as fish, to breathe. These types of algae grow in the euphotic, or sunlit zone where light is available for photosynthesis. Other types absorb nutrients from their surroundings.
Algae require other nutrients that must be found in the water, such as nitrogen, phosphorus, and silicon. In some lakes, when deeper waters rise during different seasons and mix with shallower waters, more of these nutrients are brought to the surface. Algal growth increases when nitrogen and phosphorus are added to a body of water by sewage or by runoffs from farmland.
Reeds have been used for thousands of years as a building material. During the Middle Ages (500–1500) in England, for example, people used reeds to make thatched roofs for their houses. The reeds are bundled tightly together and, when put in place, keep out both rain and cold. If made by a skilled worker with reeds of good quality, a thatched roof will remain waterproof for up to forty years.
Algae reproduce in one of three ways. Some split into two or more parts, each part becoming a new, separate plant. Others form spores (single cells that have the ability to grow into a new organism). A few reproduce sexually, during which cells from two different plants unite and a new plant is created.
Common lake and pond algae
Two types of algae are commonly found in lakes and ponds: phytoplankton and macrophytic algae.
Phytoplankton float on the surface of the water, always within the sunlit zone. Two forms of phytoplankton, diatoms and dinoflagellates (dee-noh-FLAJ-uh-lates), are the most common. Diatoms have simple, geometric shapes and hard, glasslike cell walls. They can live in colder regions and even within arctic ice. Dinoflagellates have two whiplike attachments that make a swirling motion. They often live in tropical regions (regions around the equator).
Macrophytic algae (macro means large) usually grow attached to the bottom of the lake or pond and are submergents.
As with algae, fungi and lichens do not fit neatly into the plant category. Fungi are plantlike organisms that cannot make their own food by means of photosynthesis. Instead, they grow on decaying organic (derived from living organisms) matter or live as parasites on a host. A parasite is an organism that depends upon another organism for its food or other needs. Fungi grow best in a damp environment, which makes the edges of lakes and ponds a favorable home. Common fungi include mushrooms, rusts, and puffballs.
Lichens are combinations of algae and fungi that tend to grow on rocks and other smooth surfaces. The algae produces food for both itself and the fungus by means of photosynthesis. In turn, it is believed the fungus protects the algae from dry conditions.
Hydrophytes are green plants found growing in the water or in very wet places where the soil is saturated (soaked with water). They are similar to plants that grow on dry land and are found along the shoreline of lakes and ponds. Sedges are an example. They have roots adapted to this environment. Large beds of these plants slow the movement of water and help prevent erosion of the shoreline. Some water animals use them for food and hiding places.
Mexico’s Floating Gardens
The Aztecs, the original settlers of Mexico, built rafts that they floated on Lake Xochimilco (sohchee-MEEL-koh), which lies about 12 miles (19 kilometers) southeast of Mexico City. The rafts were used to grow flowers, vegetables, and fruits. But because the lake was shallow, the rafts soon became rooted in the water. Eventually a city formed, and today Xochimilco is famous for these permanent floating gardens.
Mesophytes such as reeds, need moist, but not saturated soil. They occupy the emergent zone between the water-covered area and dry land. The plants that grow on the dry shore are called xerophytes. They are able to survive with little moisture and are more typical of dry, arid lands.
Most green plants need several basic things to grow: light, air, water, warmth, and nutrients. Light and water are in plentiful supply near a lake or pond. Nutrients, primarily nitrogen, phosphorus, and potassium, are usually obtained from the soil. Some soils are lower in these nutrients. They may also be low in oxygen so many lake and pond plants have special tissues with air pockets that help them to breathe.
Common lake and pond green plants
Typical green plants found around lakes and ponds include water lilies, pondweed, and duckweed.
Water lilies are found in both temperate and tropical regions. They have large, nearly circular leaves that float on the water and beautiful white, yellow, pink, red, scarlet, blue, or purple flowers that float or are supported by stems above the water’s surface. Ancient peoples considered the water lily a symbol of immortality because it arose from dried-up pond beds after the return of the rains.
Pondweeds usually have both floating and submerged leaves, although some species are completely submerged. The flowers appear above the water on spikes and bear a nutlike fruit. Pondweeds are important food plants for ducks.
Climate and precipitation affect the length of the growing season. Warmer temperatures and moisture usually signify the beginning of growth. In regions that are cold or receive little rainfall, the growing season is short. Growing conditions are also affected by the amount of moisture in the soil, which ranges from saturated to dry.
Green plants reproduce by several methods. One is pollination, in which the pollen from the male reproductive part of a plant, called the stamen in flowering plants, is carried by wind or insects to the female reproductive part of a plant, called a pistil in flowering plants. Pollen-gathering insects distribute pollen at different times of the day according to when a plant’s flower is open. Water lilies, for example, which are closed in the morning and evening, open during midday when the weather is warmer and insects are more active. Instead of pollination, some shoreline plants grow rhizomes, which are stems that spread out under water or soil and form new plants. Reed mace and common reeds develop underground rhizomes.
Duckweeds are small water plants that may be the size of a grain of rice that float on the surface during spring and summer. During the growing seasons the plants produce an excess of starch that weighs them down, so that by autumn they sink to the bottom. The starch keeps them alive throughout the cold months, and in the spring they float to the surface again.
Changes in the habitat, such as succession, pollution, and new weather patterns, endanger lake and pond plants. Lakes and ponds are endangered by people who collect the pond plants, and who use insecticides (insect poisons) and herbicides (plant poisons) on farms and gardens. These poisons contaminate nearby rivers and streams, which then contaminate the lake or pond. Herbicides in particular are harmful to plant life. Other threats include fertilizer runoff from nearby farms. Saw grass, for example, struggles to survive in water polluted by fertilizer.
Freshwater lakes and ponds support many species of aquatic and land animals. Some aquatic animals swim freely in the water; others live along the bottom. Many land animals, such as opossums, raccoons, and deer, visit lakes and ponds for food and water.
What allows some insects, such as the water strider, to skate along the surface of the water without sinking? A water strider is so small that its body is extremely light. Within a lake or pond, each molecule of water has similar molecules attracting it uniformly in every direction. At the water’s surface, these molecules crowd together to produce what is called surface tension. If a creature or an object is small and light enough, these tightly packed molecules will support its weight. A steel sewing needle, for example, can float on water if it is gently lowered to rest on the surface.
Few species of animals live in the waters of salt and soda lakes. Those that do provide food for birds and other animals. Ducks and wading birds feed on the microscopic brine shrimp that flourish in these lakes. These types of lakes are usually found in desert areas and they may be the only source of food for many miles.
Microorganisms cannot be seen by the human eye without the use of a microscope. Those found in ponds and lakes include transparent daphnia, creatures that catch food with the hairs on their legs; rotifers that sweep algae into their mouths with swirling hair-like fibers; and bacteria. Bacteria make up a large portion of the microscopic organisms found in lakes and ponds. They aid in the decomposition (breaking down) of dead organisms. Bacteria tend to exist in great numbers near the shoreline where larger organisms are found.
Invertebrates are animals without a backbone. They range from simple worms to more complex animals such as insects and crabs.
Many species of insects live in lakes and ponds. Some, like the diving beetle, spend their entire lives in the water. Others, like mosquitoes, live in the water as larvae but are able to breathe air through small tubes attached at the end of their bodies. They leave the water when they become adults. Another type of insects, like backswimmers, have gills, just like fish, which enable them to obtain oxygen from the water.
Crustaceans, such as shrimp, and mollusks, such as mussels, are invertebrates with a hard outer shell that often inhabit lakes and ponds. One species, the brine shrimp, favors salt and soda lakes where it is able to filter out the harmful minerals.
Leeches feed on blood, and as they feed they produce a blood-thinning chemical called hirudin. Hirudin is used for medical purposes, and about 26,000 pounds (57,200 kilograms) of leeches are caught each year commercially. Their numbers have diminished as a result.
Common lake and pond invertebrates
Invertebrates common to lakes and ponds include fisher spiders, leeches, and dragonflies.
Fisher spiders are predators that feed on insects and tadpoles. The fisher’s body is covered with hairs that help distribute its weight and allow it to walk on water. If the spider is submerged, the hairs trap a coating of air so the animal can remain underwater for a long period of time and still breathe.
Leeches are slick, flat parasites that live on the blood of other animals. Some attack fish, and others attack snails, reptiles, and mammals, including humans. Turtles, for example, often have a ring of leeches around their eyes and necks. As it feeds, the body of the leech swells with blood. Many species feed only occasionally because they can store food in their digestive systems.
Dragonfly nymphs, the youthful form of the adult insect, are among a lake or pond’s dominant carnivores (meat eaters). They will eat anything smaller than themselves, including fish, snails, and other insects. Some stalk their prey; others lie in wait and nab it as it passes. The nymph grasps the victim with its lower lip and pulls it into its mouth.
Some insects feed underwater as well as on the surface. They may be either plant eaters, meat eaters, or scavengers that eat decaying matter. The giant water bug is a 3-inch-long (76-millimeter-long) predator that grasps fish, frogs, and other insects in its powerful legs, paralyzes them with injections of poison, and sucks out their body fluids.
The diets of other invertebrates also vary. Some snails are plant feeders that eat algae, whereas crabs are often omnivorous, eating both plants and animals.
Most invertebrates that are insects have a four-part life cycle. The first stage is spent as an egg. The second stage is the larva, which may actually be divided into several stages as the larva increases in size and sheds layers of the outer skin. The third stage is the pupal stage, during which the insect lives in yet another protective casing. The pupal stage is the final stage of development before emerging as an adult.
Amphibians, including frogs, toads, newts, and salamanders, are vertebrates, which means they have a backbone. Amphibians live at least part of their lives in water. They must usually remain close to a
water source because they breathe through their skin, and only moist skin can absorb oxygen. If they are dry for too long, they will die.
Amphibians are cold-blooded animals, which means their body temperatures are about the same temperature as their environment. They need the warmth they get from the sun in order to be active. As temperatures grow cooler, they slow down and seek shelter. In cold or temperate regions, some amphibians hibernate (remain inactive) and dig themselves into the mud. When the weather gets too hot, they go through a similar period of inactivity called estivation.
Common lake and pond amphibians
The most common lake and pond amphibians are salamanders, newts, frogs, and toads. They can be found all over the world, primarily in fresh water.
The bullfrog is the largest North American frog. Its body measures 8 inches (20 centimeters) in length and its legs another 10 inches (25 centimeters). Long legs enable it to leap 15 feet (4.6 meters). A bullfrog spends most of its time floating in the water or diving to the bottom in search of food. It eats insects, crayfish, smaller frogs, small birds, and small mammals.
In their larval form, amphibians are usually herbivorous (plant eating). Adults are usually carnivorous, feeding on insects, slugs, and worms. Those that live part of their lives on land have long, sticky tongues with which they capture food.
Most amphibians lay jellylike eggs in the water. Depending on the species, frogs can lay as many as 50,000 eggs, which float beneath the water’s surface. Frog eggs hatch into tadpoles (larvae) that can swim, and breathe through gills. Spotted newts hatch in the water and live there as larvae, developing gills. Later, they lose their gills and live for a time on dry land. Two or three years later, they return to the water where they live the remainder of their lives.
Reptiles are cold-blooded vertebrates that depend on the temperature of their environment for warmth. They are more active when the weather and water temperature become warmer. Many species of reptiles, including snakes, lizards, turtles, alligators, and crocodiles, live in temperate and tropical lakes.
Many reptiles go through a period of hibernation in cold weather because they are so sensitive to the temperature of the environment. Turtles, for example, bury themselves in the mud. They barely breathe and their energy comes from stored body fat. When the weather becomes very hot and dry, some reptiles go through estivation, another inactive period similar to hibernation.
Common lake and pond reptiles
Two well-known lake and pond reptiles are the grass snake and the painted turtle.
The grass snake is found in Europe, western Asia, and North Africa. Averaging a length of about 28-47 inches (70-120 centimeters), its diet consists primarily of frogs, newts, and fish. Although they do not spend all of their time in water, grass snakes are good swimmers and obtain most of their food from lakes and ponds.
The painted turtle usually lives in shallow, muddy, freshwaters of North America. It grows to between 3.5 and 10 inches (9 and 25 centimeters) and can be identified by the red and yellow markings on their dark colored shell.
All snakes are carnivores. Many that live around lakes and ponds, including the banded water snake, eat frogs, small fish, and crayfish. The pond turtle is an omnivore. When it is young it feeds on insects, crustaceans, mollusks, and tadpoles. Adult turtles eat primarily wetland plants.
The shells of lizard, alligator, and turtle eggs are either hard or rubbery, depending upon the species, and do not dry out easily. Most species bury their eggs in warm ground, which helps them hatch. The eggs of a few lizards and snakes remain inside the female’s body until they hatch, and the females give birth to live young.
The Monster of Loch Ness
Since the Middle Ages (500–1500), people have reported seeing a huge, serpentlike monster swimming in Loch Ness, a deep lake (754 feet; 230 meters) in northern Scotland, and the largest lake in Great Britain. The first recorded sighting was made in 565 when Saint Columba came upon the burial of a man said to have been bitten to death by the monster. According to one account, Saint Columba himself saw the creature.
In 1933, the monster, referred to as Nessie, attracted the attention of the news media when a man and woman driving by the lake noticed a great commotion of water in the middle, and for several minutes they watched “an enormous animal rolling and plunging.” The incident was widely reported.
Since then, many people have tried to find evidence of the creature using such equipment as sonar (sound vibration technology) and even a submarine. In 1972 and 1975, an American expedition sponsored by the Academy of Applied Science obtained startling underwater time-lapse pictures that some researchers believe show a large animal swimming submerged in Loch Ness. A 1987 British expedition failed to confirm the presence of such a creature, and most scientists do not believe Nessie exists.
Crocodiles and alligators keep their eggs warm by laying them in nests, which can be simple holes in the ground or constructions above the ground made from leaves and branches.
Fish are cold-blooded vertebrates. Lakes and ponds support two basic types. The first grouping are parasites and include lampreys, which attach themselves with suckers to other animals and suck their blood for food. The second grouping, the bony fishes, are the most numerous. They use fins for swimming and gills for breathing. Some fish can survive in polluted waters. Others, such as some African and Asian species of catfish, can breathe air and may live for a short time on land.
Many species of fish, such as sticklebacks, swim in schools. A school is a group of fish that swim together in a coordinated manner. The purpose of a school is to discourage predators. Also, the more eyes watching, the more likely it is that a predator will be seen before it can strike.
In the winter, most lakes freeze only on the surface. This surface ice helps insulate the deeper water by trapping the warmth, and allowing fish down below to survive. The ice is comparatively thin, so light can still reach submerged plants and they can photosynthesize, which helps put oxygen into the water, enabling the fish to breathe.
Common lake and pond fish
Typical lake and pond fish include the pike and the carp.
Pike are long, narrow, streamlined fish that live in shallow lakes and large ponds. They may grow as large as 80 pounds (36 kilograms), depending on the size of their habitat. The largest type of pike is the muskellunge, which is found in North American waters. Other species live in Europe and Russia.
Pike are predators and hide among water plants where their striped and spotted bodies blend in with the surroundings. They move swiftly and catch prey in their sharp teeth. When young, they feed on insects and worms, but large adults will attack water birds and small mammals.
Carp prefer warm, weedy water and are found across Europe, North America, South America, and parts of Asia, Africa, Australia, and New Zealand. The world’s largest known carp, the giant Siamese carp, weighed 265 pounds (120 kilograms) and was caught in the lakes of Thailand.
Carp are resistant to pollution and can survive where other fish die. When young, they eat insect larvae and crustaceans. As adults, they eat invertebrates and aquatic plants.
Some fish eat plants while others depend upon insects, worms, and crustaceans (shellfish). Larger fish often eat smaller fish, and a few species feed on carrion (dead bodies). Most fish specialize in what they eat. Bluegills, for example, feed on insect larvae, and pumpkin-seed fish eat snails. Some fish feed on the surface, and others seek food in deep water.
Most fish lay eggs. Many species abandon the eggs once they are laid. Others build nests and care for the new offspring. Still others carry the eggs with them until they hatch, usually in a special body cavity, or in their mouths.
Many different species of birds live on or near lakes and ponds. These include many varieties of wading birds, waterfowl, and shore birds. Most visit lakes or ponds in search of food, and certain species use them as nesting places.
Common lake and pond birds
Birds found around lakes and ponds can be grouped as wading birds, shore birds, waterfowl, or birds of prey.
Wading birds, such as herons, have long legs for wading through shallow water. They have wide feet, long necks, and long bills that are used for nabbing fish, snakes, and other food. Herons are common in
North America, Europe, and Australia, and there are about 100 species worldwide.
Shore birds, such as the plover or the sandpiper, feed and nest along the banks of lakes and ponds. They prefer shallow water. The ruddy turnstone, a stocky shore bird with orange legs, is named for its habit of overturning pebbles and shells in search of food.
Waterfowl are birds that spends most of their time on water, especially swimming birds such as ducks, geese, or swans. Their feet are close to the rear of their bodies, and the skin between their toes is webbed. This is good for swimming but awkward for walking and causes them to waddle. Their bills are designed for grabbing the vegetation, such as sedges and grasses, on which they feed. There are approximately 150 species of these types of birds.
The fish eagles, which are birds of prey, hunt exclusively in freshwater. The bald eagle, the national bird of the United States, occasionally hunts for fish, as do kingfishers and osprey.
Nearly all birds must visit a source of fresh water each day to drink, and many feed on aquatic vegetation or the animals that live in lakes and ponds. An adaptation of birds to aquatic life is their beaks, or bills. Some beaks, like that of the kingfisher, are shaped like daggers for stabbing prey such as frogs and fish. Others have a slender bill, like the least sandpiper, designed to probe through the mud in search of food, such as insect larvae and small mollusks.
All birds reproduce by laying eggs. Male birds are typically brightly colored to attract the attention of females. After mating, female birds lay their eggs in a variety of places and in nests made out of many different materials. Different species of birds lay varying numbers of eggs. The mute swan lays five to seven eggs, which hatch in about thirty-six days. One parent usually sits on the nest to keep the eggs warm.
Mammals are warm-blooded vertebrates covered with at least some hair, they bear live young, and nurse with the mother’s milk. Aquatic mammals, such as muskrats, have waterproof fur and partially webbed toes for better swimming. Other mammals, such as raccoons, often visit lakes and ponds for food or water but spend little time in the water.
Common lake and pond mammals
Although many mammals visit lakes and ponds for food and water, some species spend most of their time in the water. These include muskrats, otters, water shrews, water voles, beavers, and, in summer, even moose.
The water vole is a mouselike rodent that is not a good swimmer but an excellent diver. It lives in burrows dug in the bank of a lake or pond. It eats mainly reeds, sedges, and other shoreline plants, as well as acorns and beechnuts. Nuts are usually stored for use in winter because the vole does not hibernate. The water vole is found in Europe and parts of Russia, Siberia, Asia Minor, and Iran.
At about 4 feet (1.3 meters) long, the beaver can weigh as much as 65 pounds (30 kilograms). The long, reddish-brown fur of the beaver is warm and waterproof, allowing it to swim in icy water. The toes on the hind feet are webbed for swimming, and its tail is shaped like a flat paddle, which helps it maneuver through the water. The front feet resemble small hands, enabling the beaver to carry things. Its large front teeth allow it to cut down trees and other vegetation. Beavers feed mainly on bark from aspen, willow, poplar, birch, and maple trees.
Beavers are social animals who live and work in groups. They live in lodges, a network of tunnels and burrows deep within log structures
called beaver dams. Beavers build these dams by cutting down small trees with their sharp teeth. They then pile logs and sticks across small rivers and streams, damming them up and creating ponds. The lodge usually has an underwater entrance and air holes for ventilation.
The North American beaver once ranged over the continent from Mexico to Arctic regions. It was widely hunted for its fur and for a liquid called castorium, produced in the beaver’s musk glands and used in perfume. As a result, beaver numbers are now greatly reduced, and it is confined largely to northern wooded regions. Beavers were once common throughout northern Europe but are virtually extinct there, except in some parts of Scandinavia, Germany, and Siberia.
The moose is the largest member of the deer family. The largest on record weighed 1,166 pounds (528 kilograms). Moose antlers may span more than 6 feet (2 meters). They feed on twigs, bark, and saplings in winter, and they spend many hours in lakes and ponds in warm weather where they eat aquatic vegetation. They will even submerge completely to get at the roots of water plants.
Moose are found in wooded regions of North America. In other countries they are called elk (a close relative) and may be found in Norway, Sweden, Russia, and northern China.
Certain aquatic mammals, like the otter, are carnivores, eating rabbits, birds, and fish. Muskrats are omnivores, and they eat both animals, such as mussels, and plants, such as cattails. Beavers are herbivorous and eat trees, weeds, and other plants.
Mammals give birth to live young that have developed inside the mother’s body. Some mammals are helpless at birth, while others are able to walk and even run almost immediately. Many are born with fur and with their eyes and ears open. Others, like the muskrat, are born hairless and blind.
As lakes and ponds are filled in or polluted, many species of migratory birds are threatened because they can no longer use them for finding food or as nesting areas. Their numbers decline as a result.
Prehistoric Lake Cabins
During several prehistoric periods, early humans often built homes and villages near the waters of a lake or a marsh. Probably in anticipation of flooding, the homes were built on platforms or artificial mounds. The most famous platform lake dwellings are those of the late Neolithic and early Bronze Ages (approximately 6,000 years ago) found in Switzerland, France, and northern Italy. One village contained about ninety circular huts constructed of close-set vertical timbers. Individual homes called crannogs were built on artificial mounds or islands in certain parts of Ireland and Scotland.
Since prehistoric times, lakes and ponds have played an important role in the lives of the people who lived in the surrounding region.
Impact of lakes and ponds on human life
People use lakes and ponds for water and food, for recreation and building sites, for transportation, and for industrial purposes.
Many lakes, such as Lake Michigan, are sources of drinking water, as well as water for such things as bathing, laundry, and power generation for nearby communities. The world’s use of water has tripled since 1950 and in the United States alone, each person uses an average of 130 gallons of fresh water each day. In developed countries, about half the supply is used by industry. In less wealthy countries, 90 percent is used for crops and irrigation.
The fish and plants in lakes and ponds are often a source of food for humans. Most fish used for food come from the ocean, but commercially important freshwater fish include catfish, lake trout, bass, perch, and whitefish. Some aquatic plant species, such as water chestnuts and watercress, are also popular foods. Farmers often use aquatic plants, such as marsh grass and sedges, for feeding livestock.
Recreation and building sites
Lakes and ponds are popular sites for sport fishing, swimming, boating, and nature appreciation. During warm months, many lakes are crowded with vacationers, and in urban areas their shorelines have become popular sites on which to build homes. Artificial lakes or ponds may be created to add beauty and wildlife to a residential area.
Large lakes, such as the Great Lakes in North America, provide water transportation. The Great Lakes were a way for settlers to travel to the interior of the North American continent. They are still important to commercial vessels and even ocean-going ships, because they are linked to the ocean by the St. Lawrence Seaway. Smaller lakes may be important for local boat traffic.
Hook, Line, and Sinker
Ever since the first humans tried to snatch minnows (tiny fish) from a pond, fishing has not only been a source of food, but also a popular sport. Ancient Egyptian drawings show fishing scenes, and the sport is mentioned in writings from China, Greece, Rome, and the Middle East.
In the United States alone, about 36.5 million freshwater fishing licenses are issued each year. The largest freshwater sport fish is the white sturgeon. Other popular freshwater fish include black bass, various types of trout, sunfish, crappies, salmon, perch, pike, muskies, sturgeon, and shad.
Lake and pond plant materials can be used for building. Reeds are used for huts in Egypt and in stilt houses in Indonesia. Sediments, such as clay and mud, may be used to manufacture bricks.
Lake and pond fish provide more than just food, yielding such products as fish oils, fish meal, fertilizers, and glue.
The water in lakes and ponds may be used to cool power stations and for other industrial purposes. Some industries have used lakes and ponds as dumpsites for industrial chemicals causing serious environmental damage.
Impact of human life on lakes and ponds
The important role of lakes and ponds for plant and animal communities, for human life, and for the environment has not always been appreciated. Many ponds have been drained to eliminate mosquitoes and prevent diseases, to increase land for farming, and to make room for development. The water in others has been carelessly used for irrigation or industrial purposes.
Although all water on Earth is in constant circulation through evaporation and precipitation, some regions may have a limited supply. As populations grow, the supply diminishes even more. In some regions, forests are cut down and replaced by farms. Since trees help conserve underground water, much of this water may be lost. Ponds gradually disappear because they are often supplied by groundwater, springs, and lakes.
Irrigation practices can cause damage, especially in desert regions, because there is not enough precipitation to replace the water used to water crops. The Aral Sea, a large lake in Central Asia has shrunk to half its original surface area because so much water has been removed to irrigate farms in the area.
Use of plants and animals
Many freshwater lakes used for recreation have been overfished, and attempts to stock the lakes with commercially raised fish are not always successful. Overfishing is often more serious in lakes where the local population depends upon fish for their daily food. The fish are rarely restocked and their numbers never recover.
People may wish to live near a lake or pond for its beauty and a sense of being close to nature, but overdevelopment can destroy the very things they are seeking. Overdevelopment results in erosion of the shoreline and loss of the scenic value. Instead of blue water and trees, residents look out on cars and concrete.
Quality of the environment
Pollution by communities, industries, shipping, and poor farming practices has led to poisoning of water and changes in its temperatures. Several environmental problems, including accelerated eutrophication (YOU-troh-fih-kay-shun; becoming over enriched with nutrients) and acid rain, are issues that affect the quality of water in lakes and ponds.
Eutrophication occurs when fertilizers, especially nitrogen and phosphorus, used in farming get into lakes and ponds, spurring a greatly increased growth of algae. These algae form a thick mat on the water’s surface and block the sunlight, causing submerged plants to die. As the dead plants decay, oxygen in the water decreases. Water with little oxygen cannot support most plants and animals. Some of the world’s major lakes, such as Lake Geneva in Switzerland, suffer from eutrophication. Eutrophication results in the lake becoming a wetland (an area where the soil is saturated with water for most of the year).
Acid rain is a type of air pollution dangerous to lakes and ponds. It forms when industrial pollutants, such as sulfur or nitrogen, combine with moisture in the atmosphere to form sulfuric or nitric acids. These acids can be carried long distances by the wind before they fall, either as dry deposits or as rain or snow. Acid rain can damage both plant and animal life. It is especially devastating to amphibians such as salamanders because their skin is so thin and permeable (able to pass through). The pollutants from acid rain pass right through the skin and enter into their bodies.
Lakes of the Poets
The Lake District in northwestern England is a region of mountains, lakes, and waterfalls famous not only for its beauty but also for the many great poets it inspired. William Wordsworth (1770–1850), Samuel Taylor Coleridge (1772–1834), and Robert Southey (1774–1843) all lived in the district.
The Lake District National Park, established in 1951, covers an area of 866 square miles (2,243 square kilometers) and takes in England’s largest lakes and highest mountains, including Scafell Pike. Lakes include Lake Windermere, Ullswater, Bassenthwaite Lake, Derwent Water, and Coniston Water.
The Ramsar Convention
The U.S. Department of the Interior, the U.S. Fish and Wildlife Service, and many environmental groups are working to preserve lakes and ponds and to create new ones. The Convention on Internationally Important Wetlands was signed by representatives of many nations in Ramsar, Iran, in 1971. Commonly known as the Ramsar Convention, it is an intergovernmental treaty that provides the framework for national action and international cooperation for the conservation and wise use of wetlands and their resources.
Humans have always lived near lakes and ponds because they provide a source of food and fresh water. Two groups that continue to depend on lakes for their survival are the Turkana in Kenya and native peoples of the Andes Mountains in South America.
The Turkana people live along the shores of Lake Rudolf in Kenya, renamed Lake Turkana. It covers an area of 2,433 square miles (6,405 square kilometers) and supports many fish species.
The Turkana did not always depend upon the lake for their livelihood. Until the 1960s they were nomads and raised herds of camels, goats, and cattle that they used for milk and blood, their primary foods.
In the 1960s a severe drought (extremely dry period) struck the region and many animals died, causing famine among the Turkana. The people turned to fishing and discovered Lake Turkana to be a rich source of large Nile perch and a smaller fish called tilapia. This discovery changed the Turkana’s lifestyle. They began to catch fish for food, some of which they sold in nearby towns and cities.
The Turkana are having to change their lifestyle again, because Lake Turkana is shrinking, becoming more saline (salty), and has been overfished. The region gets less rainfall than before, and at least one of the rivers that feed the lake has dried up. Many Turkana have gone back to raising animals, although this cannot be a permanent solution because the drier climate has reduced grazing land.
Island People of Lake Titicaca
Lake Titicaca (tee-tee-KAH-kah) is the highest navigable lake on Earth at 12,580 feet (3,834 meters). It is located in the Andes Mountains, on the border between Bolivia and Peru in South America. The Native American people who live there are descendants of the ancient and powerful Inca Empire, and the lake has
been a center of their lives for 2,000 years. The Incas believed the lake was the origin of human life. The lake contains forty-one islands, the largest is Isla del Sol (Sun Island).
A species of reed called totora grows in the lake and forms floating islands on which the people live. They use the reeds to build boats and huts and to make baskets, which they sell. They use submerged plants, called yacco, to feed their cattle that graze along the shore. Around 1930, non-native fish, trout and mackerel, were introduced to the lake, reducing the number of native species of karachi and boga.
The transfer of energy from organism to organism forms a series called a food chain. All the possible feeding relationships that exist in a biome make up its food web. In lakes and ponds, as elsewhere, the food web consists of producers, consumers, and decomposers. These three types of organisms transfer energy within the biome.
Algae and plants are the primary producers in lakes and ponds. They produce organic materials from inorganic chemicals and outside sources of energy, primarily the sun.
Animals are consumers. Those that eat only plants, such as snails, are primary consumers in the lake or pond food web. Secondary consumers, such as certain fish, eat the plant-eaters. Tertiary consumers are the predators, like turtles and snakes. Humans fall into the predator category. Humans are omnivores, which means they eat both plants and animals.
Decomposers feed on dead, organic matter. These organisms convert dead organisms to simpler substances. Decomposers include insect larvae and bacteria.
Harmful to the lake or pond food web is the concentration of pollutants and dangerous organisms. They become trapped in sediments where certain life forms feed on them. These life forms are fed upon by other life forms, and at each step in the chain the pollutant becomes more concentrated. Finally, when humans and other large mammals eat fish, ducks, or other animals contaminated with pollutants, they are in danger of serious illness. The same is true of diseases such as cholera, hepatitis, and typhoid, which can survive and accumulate in certain aquatic animals and then be passed on to people who eat these animals.
Lake Baikal is the largest lake on Earth by volume, 5,521 cubic miles (23,015 cubic kilometers). It contains 20 percent of the world’s fresh water and 80 percent of the fresh water in Russia and Siberia. It is also the world’s deepest lake, reaching 5,712 feet (1,740 meters), with a layer of accumulated sediment on its floor adding another 5 miles (8 kilometers) of depth. Although Baikal has the largest surface area of any lake in Europe or Asia, it is small in comparison to the area covered by the Great Lakes in North America. More than 300 rivers flow into Lake Baikal, but only one, the Angara, flows out.
Area: 12,160 square miles (31,494 square kilometers)
Lake Baikal formed during a shifting of the Earth’s crust 25 million years ago, making it the world’s oldest freshwater lake. Earthquake activity continues in the region, and some scientists think that the Asian continent is splitting apart at this point. If so, Baikal may actually be a “baby” ocean. This theory is supported by the 1990 discovery of hot water springs bubbling up through the floor, a feature usually found in mid-ocean.
Many storms develop over the surface of Baikal because it is so large; often whipping up waves higher than 15 feet (4.6 meters). The lake has a moderating effect on local weather. Its water temperature is cold, never climbing to more than 63°F (17°C) in summer. From January to May the lake is frozen to a depth of 3 feet (1 meters).
Baikal’s water has few minerals. The presence of unique miniature crustaceans (shrimp and crab) that consume the millions of phytoplankton help to keep the lake very clear and blue. It is often called the blue pearl of Siberia.
Of the 1,500 known animal species and 700 plant species found in Baikal, two-thirds are found nowhere else on Earth. Most of these unique species are found in its deepest waters where light never penetrates and water temperature remains at about 32°F (0°C) for the year. Most of the creatures have little eyesight or are blind. One species of fish, the golomyanka, has no scales and contains so much oil in its body that it is translucent. The nerpa seal, one of only two species of freshwater seals, lives in Baikal. These seals feed primarily on fish, which feed on freshwater shrimp, which are being harmed by pollution. Thus, the seals’ food supply is threatened.
At one time, Baikal was one of the cleanest lakes in the world and a popular summer resort. In the 1960s industrial waste began to threaten its purity. By the 1980s, the government had placed severe restrictions on activities that were polluting Baikal. In 1996, the area was deemed a UNESCO World Heritage site, meeting all four criteria: geological significance, biological-evolutionary importance, natural beauty, and outstanding importance for conservation.
The Great Lakes
The Great Lakes are a group of five freshwater lakes— Superior, Michigan, Huron, Erie, and Ontario—that lie along the border between the United States and Canada. Of the five lakes, Lake Superior is the largest and deepest. It covers a surface area of 31,800 square miles (82,362 square kilometers) and is, at its lowest point, 1,333 feet (406 meters) deep. The lakes are linked together by rivers and channels to create a waterway 2,342 miles (3,747 kilometers) long. Taken together, they comprise the largest surface area of fresh water in the world and the second largest in volume, 5,439 cubic miles (22,684 cubic kilometers).
The Great Lakes
Location: North America
Area: 94,950 square miles (245,919 square kilometers)
The Great Lakes began to form about 60,000 years ago when glaciers moved across North America covering the region with ice. The weight of this ice depressed Earth’s crust by as much as 1,500 feet (456 meters), and the movement of the ice carved out large basins in the rock. Glacial meltwater, combined with precipitation, gradually filled the basins, forming the lakes.
The lakes help moderate temperatures in the region, producing milder winters and cooler summers. In winter, the presence of the lakes contributes moisture to the air that helps produce lake-effect blizzards. Buffalo, New York, for example, receives an average 93 inches (236 centimeters) of snow a year. Sudden and severe storms are common. The Great Lakes Storm of 1913, often called the white hurricane, claimed eight large freighters and 235 lives.
In 1700, the Great Lakes supported many species of fish such as lake trout, sturgeon, and whitefish. By the end of the nineteenth century populations were greatly reduced, not only because of heavy fishing, but because of human tampering with the lakes’ many tributaries (rivers and streams that feed lakes). Dams and destruction of surrounding forests destroyed spawning habitat. Ocean fish such as the alewife and the sea lamprey, which normally only lay their eggs in fresh water, have become permanent residents, competing for food with native species. In the 1960s, scientists introduced trout, coho salmon, and other predators that feed on lampreys, to help reduce the undesirable populations.
The sturgeon, which may be 6 feet (1.8 meters) in length, is prized for its meat and caviar. They have been overfished and are rarely found.
Connected by channels or canals, the lakes are navigable from Duluth, Minnesota, in the west to the eastern shore of Lake Ontario. Ocean-going vessels from the Atlantic Ocean can use the lakes by entering through the St. Lawrence Seaway. In 2002, 162 million tons (147 million metric tons) of dry bulk, such as iron ore, stone, coal, and salt, was moved on the lakes.
Fertilizer and farm runoff that has entered the lakes has increased the level of nutrients. This encourages rapid growth of phytoplankton and other plants, which make the lakes age faster. Industrial chemicals, such as dioxin and mercury, and other pollutants have destroyed the purity of the water, leading to destruction of plant and animal life.
The Great Salt Lake lies between the Great Salt Lake Desert and the Wasatch Mountains in northwestern Utah. Most of the region is arid (dry). Approximately 4,200 feet (1,280 meters) above sea level, the lake was formed by glacier action. The Great Salt Lake is a remnant of a prehistoric freshwater lake ten times larger than it is now. Its size fluctuates, as does its depth, depending upon rates of evaporation.
Great Salt Lake
Location: Salt Lake City, Utah
Area: 2,450 square miles (6,345 square kilometers)
The lake is fish free but some species of algae and a few invertebrates, such as brine shrimp and brine (alkali) flies, live in the lake. Many birds, including gulls, pelicans, blue herons, cormorants, and terns, nest on the lake’s islets (tiny islands).
The Great Salt Lake is three to five times more saline (salty) than the ocean. Salts found in the lake include sodium chloride (table salt), and thousands of tons of this salt have been removed over the years for commercial purposes. The lake is used for recreation and has several beaches as well as a yacht harbor. Salt Lake City is built to the southeast and named for the lake.
Mono Lake lies in the shadow of the Sierra Nevada Mountains and was described by American writer Mark Twain (1835–1910) as “solemn, silent, sailless... the lovely tenant of the loneliest spot on Earth.” At least 700,000 years old, Mono was created by glaciers. All the water that enters it eventually evaporates, and for centuries it remained about the same size. Since 1941, many of the streams that normally feed it have been diverted to provide water for the city of Los Angeles. As a result, Mono Lake is shrinking, and the concentration of its minerals is increasing. More than 25 square miles (65 square kilometers) of mineralencrusted lake bottom have been exposed. Winds, picking up alkaline dust, create thick clouds thousands of feet (meters) in the air.
Location: Eastern California
Area: 60 square miles (155 square kilometers)
Mono’s salinity (saltiness) is only three times greater than that of the oceans; however, its alkalinity is 80 times greater. Dissolved carbonates give it a bitter taste and create weird towers of mineral deposits, called tufa towers, that are exposed along the shoreline as the lake recedes.
Blue-green algae, brine shrimp, and brine (alkali) flies are among the few life forms Mono Lake supports. There are no other animals to eat the flies and shrimp, so they multiply unchecked. As many as 4,000 flies have been counted in a single square foot (.09 meter) of shoreline, and 50,000 brine shrimp have been found in a cubic yard (cubic meter) of lake water. The flies and shrimp attract many species of birds, including gulls, grebes, phalaropes, and ducks.
Lake Victoria, also called Victoria Nyanza, is the largest lake in Africa and the second largest freshwater lake in the world. Its coastline is more than 2,000 miles (3,220 kilometers) long, and it lies at an altitude of 3,720 feet (1,134 meters) above sea level. Its greatest depth is 270 feet (82 meters).
Location: Africa, primarily within Uganda and Tanzania and bordering on Kenya
Area: 26,828 square miles (69,484 square kilometers)
Victoria’s basin was created by tectonic (earthquake) activity, and the shoreline is marked by steep cliffs, rocky headlands, swamps, and a river delta. Ukerewe and the Ssese Archipelago are its most important islands, all of which are densely wooded. The islands have become a popular destination for tourists.
The surrounding area has a large population, most of which are Bantu-speaking tribes. Boat building and fishing are important occupations. The introduction of Nile perch and Nile tilapia in the 1930s has caused at least 200 other species of fish to become extinct or near extinction. Lake Victoria yields about 550,000 tons (500,000 metric tons) of fish a year. This predominately includes Nile perch, Nile tilapia, and sardinelike dagaa.
A primary source of the Nile River, Lake Victoria was named for British monarch Queen Victoria (1837–1901) by British explorer John Hanning Speke (1827–1864), who first reached the lake in 1858. Alan Moorhead’s books, The White Nile and The Blue Nile, and a British film titled Mountains of the Moon, tell of Speke’s explorations.
The Caspian Sea is the world’s largest lake in terms of surface area. It is bordered by Russia, Azerbaijan, Kazakhstan, Turkmenistan, and Iran. Lying 94 feet (28 meters) below sea level, its depth reaches 3,360 feet (1,024 meters) in the south. The depth in the northern portion of the sea is only 16 feet (5 meters). Its size fluctuates over time and, until 1977, the lake was shrinking.
Location: On the border between Europe and Asia
Area: 144,000 square miles (373,000 square kilometers)
The Caspian’s basin was formed by both earthquake and glacier activity. Once part of an ocean, much of the surrounding region is covered by greenish clay ocean deposits. Its water is three times less salty than the ocean. The Ural and Volga rivers supply freshwater to the sea, diluting the salt content.
Average winter temperatures in the region are 14°F (-10°C) in the north and 50°F (10°C) in the south. In summer, the average is 79°F (26°C). Precipitation is light with only about 8 inches (20 centimeters) annually. In the shallower northern portion, ice forms during the winter months.
Over 400 species of fish live in the Caspian, including sturgeon, herring, pike, catfish, and carp. The sturgeon, comprising seven species in the sea, are fished for caviar. The Caspian seal, a freshwater seal, also makes its home here.
The lake is important to the economies of the surrounding regions, especially that of Russia and Iran. Many fish are taken from its waters and it is used for transportation. Fluctuations in its size and depth have reduced both the numbers of fish caught and the usefulness of its ports. Large oil fields extend beneath the lake, and there is considerable offshore production.
Located in the Andes Mountains at an altitude of 12,500 feet (3,810 meters), Lake Titicaca is the world’s highest lake that can be used by large ships.
Location: South America, between Bolivia and Peru
Area: 3,200 square miles (8,300 square kilometers)
The presence of the lake moderates the local climate so that crops, such as corn, barley, quinoa (KEEN-wah), and potatoes, which are not usually grown at such high altitudes, can be raised there.
Only two species of fish, killifish, and catfish, inhabit the lake naturally. Trout were introduced in 1939.
The shores of the lake are densely populated by descendents of the Inca Indians. Modern steamboats and traditional Inca reed boats connect villages along the shoreline.
The Dead Sea, a salt lake in the Middle East’s Jordan Trench, has a shoreline located on the lowest point on Earth’s surface—about 1,300 feet (396 meters) below sea level. At its deepest point, the lake descends to 2,300 feet (701 meters). Its basin was created by earthquake action, and at one time it was part of the Mediterranean Sea. Highlands border it to the east and west.
Location: Between Israel and Jordan
Area: 405 square miles (1,049 square kilometers)
The region has a desert climate with warm, dry winters and hot, dry summers. Only about 4 inches (10 centimeters) of rain fall each year. The Dead Sea is fed by rivers but evaporates at the rate of about 55 inches (140 centimeters) each year. About nine times as salty as the ocean, its water is so dense that swimmers cannot sink and nothing grows there.
Minerals, such as potash (used in fertilizer), are mined from the lake, as are its salts. Muds from the shores of the sea are famous for their healing and rejuvenating effects.
The lake is a part of biblical history and figures in the stories of Abraham, Lot, David, Solomon, and the defenders of Masada. The first Dead Sea Scrolls (ancient Jewish manuscripts dating as far back as 350 BC) were found at Qumran on the northeastern shore.
Lake Clark in southern Alaska is located about 125 miles (200 kilometers) southwest of Anchorage. It is part of Lake Clark National Park and Preserve, which is a mountainous region with two active volcanoes— Iliamna (10,016 feet/3,053 meters) and Redoubt (10,197 feet/3,108 meters). Gases are frequently seen venting out of Mount Iliamna, but there have been no recent eruptions. Mount Redoubt last erupted in 1966 and 1989.
Area: 110 square miles (286 square kilometers)
Lake Clark is of glacial origin, and dozens of long valley glaciers, hundreds of waterfalls, and other glacial lakes are present in the park.
Lake Clark is the spawning ground for red salmon, and bald eagles and peregrine falcons live in the park year-round. The lake contains five different mammals: harbor seals, beluga whales, Stellar sea lions, and harbor porpoises. Large animals native to the park include grizzly bears, brown bears, wolves, lynxes, Dall sheep, moose, and caribou. The Dall sheep are the only wild sheep in the world with a white coat.
Crater Lake, the deepest lake in the United States, is located in Crater Lake National Park in the Cascade Mountains of Oregon. The lake occupies the crater of an extinct volcano called Mount Mazama and lies at an altitude of 6,176 feet (1,882 meters). It is surrounded by lava walls as high as 2,000 feet (610 meters), and its depth is 1,943 feet (592 meters). Along the lake’s western shore is Wizard Island, a small volcanic cone. Some geologists believe the volcano is not really extinct but only temporarily inactive.
Location: Southern Oregon
Area: 20 square miles (52 square kilometers)
Originally named Deep Blue Lake, Crater Lake glows intensely blue when the sun shines on it. Precipitation filled the lake and continues to maintain it. An average 44 feet (13.5 meters) of winter snow maintains the lake’s water supply.
The surrounding area is heavily forested with lodgepole, ponderosa, and sugar pines, and white and Douglas firs. At higher elevations, stands of pine and fir are broken by meadows of wildflowers.
Eagles, hawks, owls, beavers, bears, mountain lions, and deer are common animals in the area.
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