Freshwater

From Palaeos

[edit] Freshwater ecosystems

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].

[edit] Types of Freshwater Ecosystems

There are three basic types of freshwater ecosystems:

• Lentic: slow-moving or standing bodies of water, including ponds, and lakes.
• Lotic: rapidly-moving water, for example streams and rivers. Together with vegetation on the banks this constitutes the Riparian zone
• Wetlands: areas where the soil is saturated or inundated for at least part of the time. [3] Includes swamps, marshes, mangroves, etc.

[edit] Freshwater ecosystems through time

During the Devonian and Carboniferous, freshwater ecologies were inhabited by a diverse selection of bivalves, arthropods, Xenacanthid sharks, sarcopterygian fish, and early tetrapods (amphibians and proto-amphibians). Permian and Triassic freshwater systems added various further kinds of palaeonisciform (basal actinopterygii) fish, temnospondyls, and diapsid reptiles. Jurassic and Cretaceous freshwater ecologies included freshwater teleosts (e.g. Leptolepis), lissamphibians, turtles, Leptocleidian plesiosaurs, and Mesoeucrocodylian crocodiles. {{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 (Coryphodon, Moeritherium, etc), and Eusuchian crocodiles were widely distributed. Ecosystems became increasingly like extant ones as the Cenozoic progressed, the Earth cooled, and animals and plants took on an increasingly modern appearance. Today, freshwater ecosystems contain 41% of the world's known fish species. [2]

[edit] Upland and Lowland

In studies of the ecology of freshwater rivers, habitats are classified as upland and lowland. 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 sediment and organic matter.

These classifications overlap with the geological definitions of "upland" and "lowland". In geology an "upland" is generally considered to be land that is at a higher elevation than the alluvial plain or stream terrace, 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.

[edit] References

[1] Alexander, David E. (1999-05-01). Encyclopedia of Environmental Science. Springer. ISBN 0412740508.

[2] Daily, Gretchen C. (1997-02-01). Nature's Services. Island Press. ISBN 1559634766.

[3] Vaccari, David A. (2005-11-08). Environmental Biology for Engineers and Scientists. Wiley-Interscience. ISBN 0471741787.

[edit] Credits

http://en.wikipedia.org/wiki/Upland_and_lowland_%28freshwater_ecology%29 Freshwater ecosystems through time MAK061107