Big Bang Theory Essay

1572 words - 7 pages

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Freshwater ecosystem
From Wikipedia, the free encyclopedia

Freshwater angelfish
Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes and ponds, rivers, streams, springs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be classified by different factors, including temperature, light penetration, and vegetation.
Freshwater ecosystems can be divided into lentic ecosystems (still water) andlotic ecosystems (flowing water).
Limnology (and its branch freshwater biology) is a study about freshwater ecosystems. It is a part of hydrobiology.
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Common chemical stresses on freshwater ecosystem health include acidification, eutrophication and copper and pesticide contamination.
Contents
  [hide] 
* 1 Extinction of freshwater fauna
* 2 See also
* 3 References
* 4 Bibliography
* 5 External links
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Extinction of freshwater fauna[edit]
Over 123 freshwater fauna species have gone extinct in North America since 1900. Of North American freshwater species, an estimated 48.5% of mussels, 22.8% of gastropods, 32.7% of crayfishes, 25.9% of amphibians, and 21.3% of fishes are either endangered or threatened. Extinction rates of many species may increase severely into the next century because of invasive species, loss of keystone species, and species which are already functionally extinct. Projected extinction rates for freshwater animals are around five times greater than for land animals, and are comparable to the rates for rainforest communities. Recent extinction trends can be attributed largely to sedimentation, stream fragmentation, chemical and organic pollutants, dams, and invasive species.
Freshwater Ecosystems
Only 3% of the world's water is fresh. And 99% of this is either frozen in glaciers and pack ice or is buried in aquifers. The remainder is found in lakes, ponds, rivers, and streams.
Lakes and Ponds
Deep lakes contain three distinct zones, each with its characteristic community of organisms.
Littoral zone
The zone close to shore. Here light reaches all the way to the bottom. The producers are plants rooted to the bottom and algae attached to the plants and to any other solid substrate. The consumers include
* tiny crustaceans
* flatworms
* insect larvae
* snails
* frogs, fish, and turtles.
Limnetic zone
This is the layer of open water where photosynthesis can occur.
As one descends deeper in the limnetic zone, the amount of light decreases until a depth is reached where the rate of photosynthesis becomes equal to the rate of respiration. At this level, net primary production no longer occurs.
The limnetic zone is shallower in turbid water than in clear and is a more prominent feature of lakes than of ponds.
Life in the limnetic zone is dominated by
* floating microorganisms - called plankton
* actively swimming animals - called nekton.
* The producers in this ecosystem are planktonic algae.
* The primary consumers include such animals as microscopic crustaceans and rotifers - the so-called zooplankton.
* The secondary (and higher) consumers are swimming insects and fish. These nekton usually move freely between the littoral and limnetic zones.
Profundal zone
Many lakes (but few ponds) are so deep that not enough light reaches here to support net primary productivity. Therefore, this zone depends for its calories on the drifting down of organic matter from the littoral and limnetic zones.
The profundal zone is chiefly inhabited by primary consumers that are...

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