Aquatic Ecosystems

Fresh Water

Fresh water ecosystems include:

Flowing Water

A stream in Cade’s Cove 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:

Mississippi Sign
Wading across Mississippi River, Lake Itasca, Minn.

Ohio River, Clermont Co., Ohio
Eventually, many streams and small rivers join to form a large river, such as the Ohio River, which forms the border between Ohio and Kentucky...

The following areas may be found within a stream or river,

riffles

These 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

These 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

These substances are carried downstream and deposited in slow-moving areas.

floodplains

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

Meandering Green River in Eastern Utah

Still Water

Lake, Brown Co. State Park, Indiana 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.

Wetland Community on Clermont Campus

Types of wetlands include

marshes

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

swamps

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

bogs

These are areas 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

Ocean, Gulf of Mexico 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

This 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.
• 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

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

intertidal zone

This 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

This 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

This is an estuary with a large number of plants.