Water Biome: Fresh water

A biome is a large area with similar climate and plants. It is generally agreed that there are seven main biomes.

About three quarters of the earth's surface is covered with water. The water biome is divided into fresh water (water with little or no salt in it, in ponds, rivers, streams) and marine, or salt water (ocean).The animals and plants of the freshwater biome are different in each country.

Fresh water Ponds and Lakes

A pond is a shallow hole where water collects. Plants generally grow around the edges of the pond, and often right across the whole pond. The temperature of the water is similar at the surface and at the bottom of the pond. The bottom is generally covered with mud.

A pond is usually too small to have waves. In places where winters are very cold, the whole pond can freeze solid. Some ponds are seasonal.

A lake is bigger than a pond, sometimes thousands of square metres. Plants only grow along the shoreline because the water is too deep away from the edges. Some lakes are so big that there are waves.

In summer, the temperature of the water in a lake is not the same: the top part of the water gets more of the sun's heat and is warm (about 19-25ºC), the middle layer is cooler because it gets less of the sunlight (about 8-19ºC) , and the bottom layer, which does not get any sunlight, is quite cold (about 4-8ºC).

'Winterkill' and 'Summerkill' in Lakes

More creatures live in the warmer layer of water. Even in the coldest places, most lakes are so big and deep that they don't freeze solid in winter, but a layer of ice can form across the surface. The ice blocks out the sunlight, and oxygen levels in the water drop, killing some plants and animals. This is called 'winterkill'.

In all freshwater areas around the world, algae (say al-gee) can be found. Algae are not plants, animals or fungi. There are different kinds of algae, and most are single-celled but some have more than one cell. As they make their food by photosynthesis, algae release oxygen into the water. Photosynthesis uses sunlight as a source of energy to combine carbon dioxide, water and salts to form chlorophyll (say claw-roe-fill). This means algae are most abundant in summer.When there is too much algae, the decaying algae reduce the oxygen levels in the water, and this can kill plants and animals. This is called 'summerkill'.

Rivers and Streams

Rivers and streams are moving strips of water. The water flows in a channel. The bottom of the channel is called the bed and the sides of the channel are called banks. Rivers are large and flow into the ocean. Rivers and streams make up about 3% of the earth's total fresh water.

Rivers and streams drain the earth of excess water. Water falls from the sky as rain, hail, snow or sleet. Once it reaches the ground, some of the water is absorbed by trees and other plants and the rest filters down into the ground.

Most water runs off the surface and eventually joins a creek or stream. Small streams join together to form rivers. Sometimes small rivers join together to become extremely large rivers. When this happens, the small rivers are called tributaries.

A watershed is an area of land where rain water, streams and small rivers all drain into one large area of water such as a large river, lake or the ocean. Because ground water also drains from a watershed, all kinds of pollution can find its way to the ocean from many kilometres away. The biggest rivers have the biggest watersheds. Therefore, biomes with lots of consistent rain have more rivers and streams. Deserts have little rain and few rivers. Desert rain is short but very intense, so dry rivers and lakes suddenly become full for a short period of time.

The mouth of a river is where it meets the ocean. Rivers carry soil along as they move, and this is dropped at the mouth of the river as it enters the ocean, and gradually builds up, making new land which is called a delta. Rivers tend to branch off in many directions through a delta, creating many islands.

Rivers that are permanently frozen are called glaciers. Glaciers and frozen freshwater, or ice, are found in places such as Antarctica, the frozen continent where the South Pole is located.

Some animals that live in a freshwater biome

The animals that live in a freshwater biome are different in every continent.

Crocodiles or alligators are found in hot areas in some countries, such as Africa, Australia and parts of the USA. Crocodiles generally stay in more salty water near river mouths, while alligators are more common in wetlands and rivers.

Frogs and turtles are generally found in rivers, streams, ponds and wetlands, different species (kinds) in each country. Different fish and the larvae of many insects also live in freshwater.

In Africa, hippopotamus live in freshwater habitats. The common or river hippopotamus lives in water holes and rivers in the grasslands, and the pygmy hippopotamus lives in water in the rainforest.

In parts of eastern Australia, platypus are found in rivers and streams.

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