Aquatic Ecosystems

Fresh Water

• Flowing Water:
  Typically, rills join to form gullies, which join to form streams, which join to form a river. Rivers can also begin as springs or seepage or outlets of ponds/lakes, for example: Eventually. . .
  Within a stream or river,

  riffles

  are also known as rapids or white water. Riffles are the sites of primary production. Typically, organisms attach to the substrate to avoid being swept away by the current. Riffle areas have a high O₂ content because of the churning.

  pools

  are the sites of decomposition. They serve as catch basins for organic materials and produce the CO₂ used by the producers in the next riffle.

  silt and debris

  are carried downstream and deposited in slow-moving areas.

  floodplains

  are those parts of the stream or river channel used at high tide or after spring rains, etc.

  
  
• Still water:
  Still water includes ponds and lakes. Often, these have an autumnal temperature change or “turnover” as the upper water cools, becomes more dense, and sinks. Simultaneously, the lower water (now warmer) rises. In midsummer, a lake has the typical epi-, meta-, and hypolimnion layers and other zones, as previously discussed, and the temperature in the epi- and hypolimnion are fairly constant. The temperature in the metalimnion changes with depth (there is a thermocline).

• Wetlands:
  Wetlands are areas that range alone a gradient from permanently flooded to periodically saturated soil that supports “hydrophytic” plants. Types of wetlands include
  

  marshes

  where there is much emergent vegetation (cattails, etc.). A marsh is a “wet prairie.”
  
  

  swamps

  which are wooded wetland (such as cypress or mangrove swamps).
  

  bogs

  which can range from a filled-in lake to a mat of accumulated organic material with much water. Bogs depend heavily on precipitation to supply nutrients, so they usually are low in mineral salts and are acidic.

Salt Water

Salt concentration is a limiting factor for organisms which live in salt water. While open sea contains about 35 ppt of salt, estuary areas contain much less, and the concentration is more variable. Oceans have a temperature gradient or thermocline like lakes, and overall water temperature is also based on latitude (arctic vs equatorial). Water pressure increases with depth.

• Regions or zones of the ocean include

  pelagic zone

  which includes all the water and may be further subdivided as with the lake, but different names are used for the same things.

  • The photic zone is the epilimnion, and photosynthesis occurs here. Seaweeds such as kelp, sea turtles, porpoise, numerous fish, sharks, crustaceans, and corals all live here.
    Here are some of Jeff Gordon’s videos of various SCUBA dives:
    

    Shark movie

    Stingray movie

    Porpoise movie

  • The mesopelagic zone is the metalimnion, which has a thermocline, and not much seasonal variation in temperature.
  • The bathypelagic zone is the hypolimnion where there is total darkness, low temperature, and high pressure.

  benthic zone

  which is divided into the continental shelf or neritic zone and deeper water or the oceanic zone.

  intertidal zone

  which is the shoreline area between high and low tide. Organisms living in these areas must be able to tolerate changes/fluctuations in the amount of water.

  estuary

  which is the area where fresh and salt water mix (at the end of a river). Organisms in an estuary must adjust to variable salt concentrations.

  tidal marsh

  which is an estuary with a large number of plants