Freshwater Described
Freshwater is a word that refers to bodies of water such as ponds, lakes, rivers and streams containing low
concentrations of dissolved salts and other total dissolved solids. In other words, the term excludes seawater
and brackish water.
A pond
is a body of water smaller than a lake, both being examples of terrain features. Although the term pond
is universally used to describe waterbodies that are smaller than lakes, an internationally recognised size cutoff
has not yet been agreed, with values ranging from 2 hectares (20,000 m2) to 8 hectares (80,000 m2) used to
distinguish the smaller from the larger waterbody. Typically, a pond has no surface outflow draining off water and
ponds are often spring-fed. Hence, because of the closed environment of ponds, such small bodies of water normally
develop self contained eco-systems. Ponds in heavily vegetated areas also display the formation of "scum", which is a
common term for dead and decaying vegetation condensing on top of the water. A contributor to this is the presence of
algae, which multiply quickly in a nutrient-Rich eutrophic pond exposed to strong daylight.
Decaying floRa provide significant amounts of such nutrients.
A lake
(from Latin lacus) is a terrain feature (or physical feature), a body of liquid on the surface of a world that is
localized to the bottom of basin (another type of landform or terrain feature; that is, it is not global) and moves
slowly if it moves at all. On Earth, a body of water is considered a lake when it is inland, not part of the ocean,
is larger and deeper than a pond, and is fed by a river. The only world other than Earth known to harbor lakes is
Titan, Saturn's largest moon, which has lakes of ethane, most likely mixed with methane. It is not known if Titan's
lakes are fed by rivers, though Titan's surface is carved by numerous river beds.
Natural lakes on Earth are generally found in mountainous areas, rift zones, and areas with ongoing or recent
glaciation. Other lakes are found in endorheic basins or along the courses of mature rivers. In some parts of the
world, there are many lakes because of chaotic drainage patterns left over from the last Ice Age. All lakes are
temporary over geologic time scales, as they will slowly fill in with sediments or spill out of the basin containing
them.
A river
is a natural stream of water, usually freshwater, flowing toward an ocean, a lake, or another stream. In some cases
a river flows into the ground or dries up completely before reaching another body of water. Usually larger streams
are called rivers while smaller streams are called creeks, brooks, rivulets, rills, and many other terms, but there
is no general rule that defines what can be called a river. Sometimes a river is said to be larger than a creek, but
this is not always the case. A river is a component of the hydrological cycle. The water within a river is generally
collected from precipitation through surface runoff, groundwater recharge (as seen at baseflow conditions / during
periods of lack of precipitation) and release of stored water in natural reservoirs, such as a glacier.
Above is a satellite image of the mouths of the Amazon river in Brazil. |