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Freshwater ecosystems cover 0.8% of the Earth's surface and contain 0.009% of its total water. They generate nearly 3% of its net primary production [1].
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There are three basic types of freshwater ecosystems:
- : slow-moving or standing bodies of water, including , and .
- : rapidly-moving water, for example and . Together with vegetation on the banks this constitutes the
- : areas where the soil is saturated or inundated for at least part of the time. [3] Includes swamps, marshes, , etc.
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During the and , freshwater ecologies were inhabited by a diverse selection of , , sharks, , and early ( and proto-amphibians). and freshwater systems added various further kinds of (basal actinopterygii) fish, , and . and freshwater ecologies included freshwater (e.g. ), , , Leptocleidian plesiosaurs, and . {{Paleogene]] freshwater ecologies were probably similar to current ones, but because more of the world was tropical there were a number of types of amphibious mammals (, , etc), and crocodiles were widely distributed. Ecosystems became increasingly like ones as the progressed, the Earth cooled, and animals and plants took on an increasingly modern appearance. , freshwater ecosystems contain 41% of the world's known fish species. [2]
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In studies of the of online viagra prescriptions , habitats are classified as and . Upland habitats are cold, clear, rocky, fast flowing rivers in mountainous areas; lowland habitats are warm, slow flowing rivers found in relatively flat lowland areas, with water that is frequently coloured by and organic matter.
These classifications overlap with the geological definitions of "upland" and "lowland". In an "upland" is generally considered to be land that is at a higher elevation than the or , which are considered to be "lowlands".
Many freshwater fish and invertebrate communities around the world show a pattern of specialisation into upland or lowland river habitats.
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[1] Alexander, David E. (1999-05-01). Encyclopedia of Environmental Science. Springer. .
[2] Daily, Gretchen C. (1997-02-01). Nature's Services. Island Press. .
[3] Vaccari, David A. (2005-11-08). Environmental Biology for Engineers and Scientists. Wiley-Interscience. .
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Freshwater ecosystems through time MAK061107