Biomes

Tropical Rain Forest

The tropical rain forest is a forest of tall trees in a region of year-round warmth. An average of 50 to 260 inches (125 to 660 cm.) of rain falls yearly. Rain forests belong to the tropical wet climate group. The temperature in a rain forest rarely gets higher than 93 °F (34 °C) or drops below 68 °F (20 °C); average humidity is between 77 and 88%; rainfall is often more than 100 inches a year. There is usually a brief season of less rain. In monsoonal areas, there is a real dry season. Almost all rain forests lie near the equator. Rainforests now cover less than 6% of Earth's land surface. Scientists estimate that more than half of all the world's plant and animal species live in tropical rain forests. Tropical rainforests produce 40% of Earth's oxygen. A tropical rain forest has more kinds of trees than any other area in the world. Scientists have counted about 100 to 300 species in one 2 1/2-acre (1-hectare) area in South America. Seventy percent of the plants in the rainforest are trees. About 1/4 of all the medicines we use come from rainforest plants. Curare comes from a tropical vine, and is used as an anesthetic and to relax muscles during surgery. Quinine, from the cinchona tree, is used to treat malaria. A person with lymphocytic leukemia has a 99% chance that the disease will go into remission because of the rosy periwinkle. More than 1,400 varieties of tropical plants are thought to be potential cures for cancer. All tropical rain forests resemble one another in some ways. Many of the trees have straight trunks that don't branch out for 100 feet or more. There is no sense in growing branches below the canopy where there is little light. The majority of the trees have smooth, thin bark because there is no need to protect the them from water loss and freezing temperatures. It also makes it difficult for epiphytes and plant parasites to get a hold on the trunks. The bark of different species is so similar that it is difficult to identify a tree by its bark. Many trees can only be identified by their flowers. Despite these differences, each of the three largest rainforests--the American, the African, and the Asian--has a different group of animal and plant species. Each rain forest has many species of monkeys, all of which differ from the species of the other two rain forests. In addition, different areas of the same rain forest may have different species. Many kinds of trees that grow in the mountains of the Amazon rain forest do not grow in the lowlands of that same forest. Layers of the Rainforest There are four very distinct layers of trees in a tropical rain forest. These layers have been identified as the emergent, upper canopy, understory, and forest floor. Emergent trees are spaced wide apart, and are 100 to 240 feet tall with umbrella-shaped canopies that grow above the forest. Because emergent trees are exposed to drying winds, they tend to have small, pointed leaves. Some species lose their leaves during the brief dry season in monsoon rainforests. These giant trees have straight, smooth trunks with few branches. Their root system is very shallow, and to support their size they grow buttresses that can spread out to a distance of 30 feet. The upper canopy of 60 to 130 foot trees allows light to be easily available at the top of this layer, but greatly reduced any light below it. Most of the rainforest's animals live in the upper canopy. There is so much food available at this level that some animals never go down to the forest floor. The leaves have "drip spouts" that allows rain to run off. This keeps them dry and prevents mold and mildew from forming in the humid environment. The understory, or lower canopy, consists of 60 foot trees. This layer is made up of the trunks of canopy trees, shrubs, plants and small trees. There is little air movement. As a result the humidity is constantly high. This level is in constant shade. The forest floor is usually completely shaded, except where a canopy tree has fallen and created an opening. Most areas of the forest floor receive so little light that few bushes or herbs can grow there. As a result, a person can easily walk through most parts of a tropical rain forest. Less than 1 % of the light that strikes the top of the forest penetrates to the forest floor. The top soil is very thin and of poor quality. A lot of litter falls to the ground where it is quickly broken down by decomposers like termites, earthworms and fungi. The heat and humidity further help to break down the litter. This organic matter is then just as quickly absorbed by the trees' shallow roots. Plant Life Besides these four layers, a shrub/sapling layer receives about 3 % of the light that filters in through the canopies. These stunted trees are capable of a sudden growth surge when a gap in the canopy opens above them. The air beneath the lower canopy is almost always humid. The trees themselves give off water through the pores (stomata) of their leaves. This process, called transpiration, can account for as much as half of the precipitation in the rain forest. Rainforest plants have made many adaptations to their environment. With over 80 inches of rain per year, plants have made adaptations that helps them shed water off their leaves quickly so the branches don't get weighed down and break. Many plants have drip tips and grooved leaves, and some leaves have oily coatings to shed water. To absorb as much sunlight as possible on the dark understory, leaves are very large. Some trees have leaf stalks that turn with the movement of the sun so they always absorb the maximum amount of light. Leaves in the upper canopy are dark green, small and leathery to reduce water loss in the strong sunlight. Some trees will grow large leaves at the lower canopy level and small leaves in the upper canopy. Other plants grow in the upper canopy on larger trees to get sunlight. These are the epiphytes such as orchids and bromeliads. Many trees have buttress and stilt roots for extra support in the shallow, wet soil of the rainforests. Over 2,500 species of vines grow in the rainforest. Lianas start off as small shrubs that grow on the forest floor. To reach the sunlight in the upper canopy it sends out tendrils to grab sapling trees. The liana and the tree grow towards the canopy together. The vines grow from one tree to another and make up 40% of the canopy leaves. The rattan vine has spikes on the underside of its leaves that point backwards to grab onto sapling trees. Other "strangler" vines will use trees as support and grow thicker and thicker as they reach the canopy, strangling its host tree. They look like trees whose centers have been hollowed out. Dominant species do not exist in tropical rainforests. Lowland dipterocarp forest can consist of many different species of Dipterocarpaceae, but not all of the same species. Trees of the same species are very seldom found growing close together. This bio diversity and separation of the species prevents mass contamination and die-off from disease or insect infestation. Bio diversity also insures that there will be enough pollinators to take care of each species' needs. Animals depend on the staggered blooming and fruiting of rainforest plants to supply them with a year-round source of food. Animal Life Many species of animal life can be found in the rain forest. Common characteristics found among mammals and birds (and reptiles and amphibians, too) include adaptations to a life in the trees, such as the prehensile tails of New World monkeys. Other characteristics are bright colors and sharp patterns, loud vocalizations, and diets heavy on fruits. Insects make up the largest single group of animals that live in tropical forests. They include brightly colored butterflies, mosquitoes, camouflaged stick insects, and huge colonies of ants. The Amazon river basin rainforest contains a wider variety of plant and animal life than any other biome in the world. The second largest population of plant and animal life can be found in scattered locations and islands of Southeast Asia. The lowest variety can be found in Africa. There may be 40 to 100 different species in 2.5 acres ( 1 hectare) of a tropical rain forest. When early explorers first discovered the rainforests of Africa, Southeast Asia and South America, they They were amazed by the dense growth, trees with giant buttresses, vines and epiphytes . The tropical vegetation grew so dense that it was difficult to cut one's way through it. It was thought at the time that the soil of a rainforest must be very fertile, filled with nutrients, enabling it to support the immense trees and other vegetation they found. Today we know that the soil of the tropical rainforests is shallow, very poor in nutrients and almost without soluble minerals. Thousands of years of heavy rains have washed away the nutrients in the soil obtained from weathered rocks. The rainforest has a very short nutrient cycle. Nutrients generally stay in an ecosystem by being recycled and in a rainforest are mainly found in the living plants and the layers of decomposing leaf litter. Various species of decomposers like insects, bacteria, and fungi make quick work of turning dead plant and animal matter into nutrients. Plants take up these nutrients the moment they are released. A study in the Amazon rainforest found that 99% of nutrients are held in root mats. When a rainforest is burned or cut down the nutrients are removed from the ecosystem. The soil can only be used for a very short time before it becomes completely depleted of all nutrients. Where the Rainforests Are Found The tropical rain forest can be found in three major geographical areas around the world. Central America in the the Amazon river basin. Africa - Zaire basin, with a small area in West Africa; also eastern Madagascar. Indo-Malaysia - west coast of India, Assam, Southeast Asia, New Guinea and Queensland, Australia.

Aquatic Biomes

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Coral Reef

Coral Reefs Coral Reefs have been called the rainforests of the ocean because of their rich biodiversity. Unfortunately they are also in becoming increasingly threatened. Not only is global warming going to affect the survival of coral reefs, but other human activities threaten the entire ecosystem. What are Coral Reefs? Let us start our definition of this biome by defining what a what corals are. Corals are small animals that belong to the phylum Cnidaria together with anemones, jellyfish and hydroids. All Cnidarians have stinging organs called cnidocysts. If you've ever been stung by a jellyfish you know the effects of these stinging organs. Corals are generally divided up into hard (scleratinian) corals and soft corals. It's the hard corals that build the framework of the coral reefs. In the Indo-Pacific waters, approximately 500 species of hard corals are known. Soft corals, also called octocorralina, lack the hard calcium carbonate structure that hard corals build. Most have a fleshy structure with small silica spicules, like internal spines, that give them extra support. The majority of the corals are colonial with several thousand small individuals. Where are Coral Reefs found? Coral Reefs are almost exclusively found in tropical and sub-tropical waters across the globe. Scientists have recently found coral reefs in temperate waters such as off the Atlantic coast of Norway, but in general when we talk about coral reefs we refer to the diverse tropical reefs that may hold several hundreds of species of hard reef building corals alone. These reefs form the framework for an incredible diversity of other organisms. The longest coral reef system on Earth is the Great Barrier Reef off the east coast of Australia. This massive reef system stretches more than 2,000 km and can be seen from space! For most reef building corals to survive they need to have a few special requirements met. For example, at any time the average water temperature can not be less than about 18-20 degrees Celsius. For this reason, tropical coral reefs are generally found between 30 deg. North and 30 deg. South of the Equator. Since there is no shortage of sunlight nutrients soon become the limiting factor for primary producers. So the waters around tropical coral reefs are in fact relatively nutrient poor. Yet still, they support this incredible diversity of life. The answer to the energy equation is working together. Most corals have developed a symbiotic relationship with a small microalgae called a zooxanthellae. This small dinoflagellate is incorporated in the coral tissue and actually is what gives corals their beautiful colors. As other algae, the zooxanthellae use sunlight to photosynthesis and it produces so much energy that it can also provide the coral with almost all of its energy needs (scientists have found that about 98% of the energy may be from the zooxanthellae). In return the algae can take up nutrient-rich waste products from the coral. Because of this symbiotic relationship corals can only grow relatively close to the surface where the water is clear enough for the zooxanthellae to perform photosynthesis. The hard coral reef structure is made of calcium carbonate that the coral secretes as it grows and expands the colony.Animals on a Coral Reef: It would be impossible to list all the animals that live on a coral reef here. There are simply too many. Some of the groups of animals frequently seen on the reefs though include: Sea Fans (type of soft coral), Sharks, Butterfly fish, Nudibranchs, Sea stars, Cuttlefish, and Clownfish. But also even some reptiles such as turtles and sea snakes. All in all there are thousands of animals that make the coral reefs there home. Threats to Coral Reefs Coral reefs are being threatened around the world because of many different factors. Their special requirements to survive also make them relatively sensitive to change. We know that most ecosystems are able to adjust to changes fairly well, given enough time to adjust. The problem today is that changes are happening so fast that most animals don't have time to keep up. And coral reefs especially. Many of the coral reefs are relatively close to land. This makes them easy to access and also easily affected by everything that goes on on land. Road construction, coastal clearing, agriculture etc. results in a lot of sediment and pollutants that get washed out to sea with the monsoon rains that fall in tropical areas. Simple sedimentation in the water may be enough to kill the reefs both by directly covering the corals but also by decreasing light penetration of the water so much that the symbiotic zooxanthellae algae are unable to photosynthesis. Another factor is over fishing. when too many fish are taken out of a system the balance is disturbed. Many of these fish eat algae and control the abundance of algae on the reef. When the fish is removed, the fast-growing algae can take over. Destructive fishing methods such as cyanide and dynamite used in some parts of the world also directly affect the structure of the coral reefs. A coral reef that has been blown away by dynamite need many many years to recover. Global warming is also causing the sea temperatures to rise. Even though corals need relatively warm water so survive, there is a limit. When the water gets too warm, it affects the corals and the zooxanthellae algae negatively. The algae disappears from the coral and the corals become "bleached". Thsi basically mean that the coral structure is left naked but still alive without the symbiotic algae. Most corals can only survive a short period without the symbiotic algae. If water conditions don't change back to normal during this time also the coral will die. One more thing, by directly breaking of a branch of a coral could mean removing more than 10 years of construction. Don't encourage breaking the corals for souvenirs. Leave them in the water to look at don't encourage people who sell the corals to continue. In other word, don't break or buy corals, please.

Marine

Marine regions cover about three-fourths of the Earth's surface and include oceans, coral reefs, and estuaries. Marine algae supply much of the world's oxygen supply and take in a huge amount of atmospheric carbon dioxide. The evaporation of the seawater provides rainwater for the land.

Tundra

Tundra is the coldest of all the biomes. Tundra comes from the Finnish word tunturi, meaning treeless plain. It is noted for its frost-molded landscapes, extremely low temperatures, little precipitation, poor nutrients, and short growing seasons. Dead organic material functions as a nutrient pool. The two major nutrients are nitrogen and phosphorus. Nitrogen is created by biological fixation, and phosphorus is created by precipitation. It is also the driest biome next to the desert. Characteristics of tundra include: Extremely cold climate Low biotic diversity Simple vegetation structure Limitation of drainage Short season of growth and reproduction Energy and nutrients in the form of dead organic material Large population oscillations

Desert

A Hot and Dry Desert is, as you can tell from the name, hot and dry. Most Hot and Dry Deserts don't have very many plants. They do have some low down plants though. The only animals they have that can survive have the ability to burrow under ground. This is because they would not be able to live in the hot sun and heat. They only come out in the night when it is a little cooler. A cold desert is a desert that has snow in the winter instead of just dropping a few degrees in temperature like they would in a Hot and Dry Desert. It never gets warm enough for plants to grow. Just maybe a few grasses and mosses. The animals in Cold Deserts also have to burrow but in this case to keep warm, not cool. That is why you might find some of the same animals here as you would in the Hot and Dry Deserts. Deserts cover about one fifth of the Earth's land surface. Most Hot and Dry Deserts are near the Tropic of Cancer or the Tropic of Capricorn. Cold Deserts are near the Arctic part of the world. Hot and Dry Deserts temperature ranges from 20 to 25° C. The extreme maximum temperature for Hot Desert ranges from 43.5 to 49° C. Cold Deserts temperature in winter ranges from -2 to 4° C and in the summer 21 to 26° C a year The precipitation in Hot and Dry Deserts and the precipitation in Cold Deserts is different. Hot and Dry Deserts usually have very little rainfall and/or concentrated rainfall in short periods between long rainless periods. This averages out to under 15 cm a year. Cold Deserts usually have lots of snow. They also have rain around spring. This averages out to 15 - 26 cm a year. Hot and Dry Deserts are warm throughout the fall and spring seasons and very hot during the summer. the winters usually have very little if any rainfall. Cold Deserts have quite a bit of snow during winter. The summer and the beginning of the spring are barely warm enough for a few lichens, grasses and mosses to grow. Hot and Dry Deserts vegetation is very rare. Plants are almost all ground-hugging shrubs and short woody trees. All of the leaves are replete (packed with nutrients). Some examples of these kinds of plant are Turpentine Bush, Prickly Pears, and Brittle Bush. For all of these plants to survive they have to have adaptations. Some of the adaptations in this case are the ability to store water for long periods of time and the ability to stand the hot weather. Cold Desert's plants are scattered. In areas with little shade,about 10 percent of the ground is covered with plants. In some areas of sagebrush it reaches 85 percent. The height of scrub varies from 15 cm to 122 cm. All plants are either deciduous and more or less contain spiny leaves. Hot and Dry Deserts animals include small nocturnal (only active at night) carnivores. There are also insects, arachnids, reptiles, and birds. Some examples of these animals are Borrowers, Mourning Wheatears, and Horned Vipers. Cold Deserts have animals like Antelope, Ground Squirrels, Jack Rabbits, and Kangaroo Rats.

Deciduous Forest (also known as temperate forest)

Deciduous forests can be found in the eastern half of North America, and the middle of Europe. There are many deciduous forests in Asia. Some of the major areas that they are in are southwest Russia, Japan, and eastern China. South America has two big areas of deciduous forests in southern Chile and Middle East coast of Paraguay. There are deciduous forests located in New Zealand, and southeastern Australia also. The average annual temperature in a deciduous forest is 50° F. The average rainfall is 30 to 60 inches a year. Animals American Bald Eagle American Black Bear Coyote Duckbill Platypus Eastern Chipmunk European Red Squirrel Fat Dormouse Least Weasel White-tailed Deer

Estuaries

Estuaries are bodies of water formed where freshwater from rivers or streams connect with salt ocean water. The mixed water is called brackish, and the salinity may fluctuate dramatically for example depending on freshwater input from rains and waves and tides influences from the ocean. Estuary areas include river mouths, bays, lagoons and salt marshes.

Freshwater

Freshwater is defined as having a low salt concentration—usually less than 1%. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration (i.e, ocean). There are different types of freshwater regions: ponds and lakes, streams and rivers, and wetlands. The following sections describe the characteristics of these three freshwater zones.

Grassland

Grasslands are characterized as lands dominated by grasses rather than large shrubs or trees. In the Miocene and Pliocene Epochs, which spanned a period of about 25 million years, mountains rose in western North America and created a continental climate favorable to grasslands. Ancient forests declined and grasslands became widespread. Following the Pleistocene Ice Ages, grasslands expanded in range as hotter and drier climates prevailed worldwide. There are two main divisions of grasslands: Tropical grasslands or savannas Temperate grasslands

Coniferous Forest (also known as Taiga)

The Coniferous Forest is a forest of Conifers (too much to handle, isn't it?). A Conifer is a tree that produces its seeds in cones. The Pine tree is the most common example. Conifer leaves conserve water with the thick, waxy layer that covers their leaves, also known as needles. The vegitation in the Coniferous forest is small in size, but large enough to feed the vast herbivore population. Most of these animals survive the brutal winters by migrating or hibernating. Average Annual Rainfall- 14-29.5 in. Average Temperatures in the Summer- 57.2°F Average Temperatures in the Winter- 14°F PLANTS Many softwood trees such as fir, pine, spruce, and hemlock. ANIMALS Most animals are herbivores, however some carnivores and omnivores are thrown in. Animals in Coniferous Forests include the red fox, moose, snowshoe hare, great horned owl, and the crossbill. FUN FACTS The largest Carniferous forest exists in a ring in Alaska, Canada, northern Europe, and northern Asia, in a ring in the Northern Hemisphere. This forest is called the "Taiga". Most of the world's commercial softwood timber, used for paper, comes from the Taiga. Coniferous Forests are the largest land Biome of the World.

Chaparral

The chaparral biome is found in a little bit of most of the continents - the west coast of the United States, the west coast of South America, the Cape Town area of South Africa, the western tip of Australia and the coastal areas of the Mediterranean. Lay of the land: The chaparral biome has many different types of terrain. Some examples are flat plains, rocky hills and mountain slopes. It is sometimes used in movies for the "Wild West". Chaparral is characterized as being very hot and dry. As for the temperature, the winter is very mild and is usually about 10 °C. Then there is the summer. It is so hot and dry at 40 °C that fires and droughts are very common. Fortunately, the plants and animals are adapted to these conditions. Most of the plants have small, hard leaves which hold moisture. Some of these plants are poison oak, scrub oak, Yucca Wiple and other shrubs, trees and cacti. The animals are all mainly grassland and desert types adapted to hot, dry weather. A few examples: coyotes, jack rabbits, mule deer, alligator lizards, horned toads, praying mantis, honey bee and ladybugs. So, if you ever go somewhere that is like chaparral, make sure to bring some sunscreen and lots of water!

Coastal Zone

The coastal oceans of the world, while amazingly diverse, are also fairly similar. Because these zones are close to land, there are certain related plants and animals that have adapted to these conditions, and are likely to be found around the globe. This zone is also one of the most important for humans. While they cover only a very small percentage of total ocean body, they harbor most of the seafood caught for human consumption. Coastal Oceans include many other habitat types not covered in this "temperate" ocean video. These include waters around coral reefs, and mangrove habitats - both found only in tropical waters. Kelp forests are another major habitat type found in coastal oceans. In this video we highlighted three species found in swedish temperate coastal oceans. However, it is important to realize there are many different types of animals in coastal oceans around the world. To expand on this point here are the current estimates for but a few of the species found in the coastal oceans.

Aphotic Zone

The deepest layer of the world's oceans gets no sunlight at all. This dark ocean layer is called the midnight zone or the aphotic zone (aphotic means "no light" in Greek). The depth of this zone depends on the clarity or murkiness of the water. In clear water, the aphotic zone begins at depths of about xx feet; in murky water, it starts around xx feet. It is usually somewhere between these two extremes. On average, the depth of the ocean is about 13,000 feet (4,000 m). Temperature is nearly freezing and decreases with depth. Pressure is extremely high and increases with depth. bioluminescence trenches The aphotic zone is divided into two parts- the bathyal zone and the abyssal zone. The bathyal zone extends from 200 meters to 2000 meters. The abyssal zone extends from 2000 meters to the bottom. Creatures in this area must be able to live in complete darkness and in close to freezing water. In the aphotic zone, there no light, so no photosynthesis can take place, and thereare no plants or other photosynthetic organisms. The only food/energy sources in this zone is from ccc. Animals: colored red and black as camouflage. Examples of aphotic zone animals include algae, anemones, anglerfish, arrow worm, cookie-cutter shark, copepods, crabs and other crustaceans, ctenophores, dinoflagellates, fangtooth, lanternfish (Myctophids), mussels, nudibranchs, some squid (like the vampire squid), segmented worms, siphonophores, swallower fish, tripod fish, tubeworms, pelican eel, umbrellamouth gulper and viperfish.

Intertidal Zone

The intertidal zone is defined as the area between the high tide and low tide mark. Organisms that live in this zone have to deal with difficult environmental conditions. They have to deal with being both submerged in sea water and exposed to the air. They have to bear the great physical impact of waves, desiccation, and sunlight. Occasionally there are rains which saturate them in fresh water. There are lots of moving rocks and sediment in the water which can damage small critters. Plus, there is a risk of predation, not only from ocean based animals, but terrestrial animals as well.

Flowing

These are bodies of flowing water moving in one direction. Streams and rivers can be found everywhere—they get their starts at headwaters, which may be springs, snowmelt or even lakes, and then travel all the way to their mouths, usually another water channel or the ocean. The characteristics of a river or stream change during the journey from the source to the mouth. The temperature is cooler at the source than it is at the mouth. The water is also clearer, has higher oxygen levels, and freshwater fish such as trout and heterotrophs can be found there. Towards the middle part of the stream/river, the width increases, as does species diversity—numerous aquatic green plants and algae can be found. Toward the mouth of the river/stream, the water becomes murky from all the sediments that it has picked up upstream, decreasing the amount of light that can penetrate through the water. Since there is less light, there is less diversity of flora, and because of the lower oxygen levels, fish that require less oxygen, such as catfish and carp, can be found.

Land Biomes

These are the 8 different land biomes in order from coldest to warmest

Standing

These regions range in size from just a few square meters to thousands of square kilometers. Scattered throughout the earth, several are remnants from the Pleistocene glaciation. Many ponds are seasonal, lasting just a couple of months (such as sessile pools) while lakes may exist for hundreds of years or more. Ponds and lakes may have limited species diversity since they are often isolated from one another and from other water sources like rivers and oceans. Lakes and ponds are divided into three different "zones" which are usually determined by depth and distance from the shoreline. The topmost zone near the shore of a lake or pond is the littoral zone. This zone is the warmest since it is shallow and can absorb more of the Sun's heat. It sustains a fairly diverse community, which can include several species of algae (like diatoms), rooted and floating aquatic plants, grazing snails, clams, insects, crustaceans, fishes, and amphibians. In the case of the insects, such as dragonflies and midges, only the egg and larvae stages are found in this zone. The vegetation and animals living in the littoral zone are food for other creatures such as turtles, snakes, and ducks. The near-surface open water surrounded by the littoral zone is the limnetic zone. The limnetic zone is well-lighted (like the littoral zone) and is dominated by plankton, both phytoplankton and zooplankton. Plankton are small organisms that play a crucial role in the food chain. Without aquatic plankton, there would be few living organisms in the world, and certainly no humans. A variety of freshwater fish also occupy this zone. Plankton have short life spans—when they die, they fall into the deep-water part of the lake/pond, the profundal zone. This zone is much colder and denser than the other two. Little light penetrates all the way through the limnetic zone into the profundal zone. The fauna are heterotrophs, meaning that they eat dead organisms and use oxygen for cellular respiration. Temperature varies in ponds and lakes seasonally. During the summer, the temperature can range from 4° C near the bottom to 22° C at the top. During the winter, the temperature at the bottom can be 4° C while the top is 0° C (ice). In between the two layers, there is a narrow zone called the thermocline where the temperature of the water changes rapidly. During the spring and fall seasons, there is a mixing of the top and bottom layers, usually due to winds, which results in a uniform water temperature of around 4° C. This mixing also circulates oxygen throughout the lake. Of course there are many lakes and ponds that do not freeze during the winter, thus the top layer would be a little warmer.