Everything about Freshwater totally explained
A term that refers to bodies of water such as
ponds, lakes, rivers and streams containing low concentrations of dissolved
salts and other
total dissolved solids. Freshwater is an important
renewable resource, necessary for the survival of most terrestrial
organisms, and is required by humans for
drinking and
agriculture, among many other uses. The
UN estimates that about 1.2 billion people (18 percent of the world's population) lack access to safe drinking water.
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Numerical definition
Freshwater is defined as water with less than 0.5 parts per thousand dissolved
salts. Freshwater bodies include
lakes and
ponds,
rivers, some bodies of
underground water and many kinds of man-made freshwater bodies, such as canals, ditches and reservoirs. The ultimate source of freshwater is the precipitation of
atmosphere in the form of
rain and
snow.
Water distribution
Access to unpolluted freshwater is a critical issue for the survival of many species, including humans, who must drink freshwater in order to survive. Only three percent of the water on
Earth is freshwater in nature, and about two-thirds of this is frozen in
glaciers and
polar ice caps. Most of the rest is underground and only 0.3 percent is surface water. Freshwater lakes, most notably
Lake Baikal in Russia and the
Great Lakes in North America, contain seven-eighths of this fresh surface water. Swamps have most of the balance with only a small amount in rivers, most notably the
Amazon River. The atmosphere contains 0.04% water. In areas with no freshwater on the ground surface, freshwater derived from precipitation may, because of its lower density, overlie saline ground water in lenses or layers.
Aquatic organisms
Freshwater creates a
hypotonic environment for aquatic organisms. This is problematic for some organisms, whose cell membranes will burst if excess water isn't excreted. Some
protists accomplish this using
Contractile vacuoles, while
freshwater fish excrete excess water via the
kidney. Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity,
diadromous fish have the ability to
migrate between freshwater and
saline water bodies. During these migrations they undergo changes to adapt to the surroundings of the changed salinities; these processes are hormonally controlled. The eel (
Anguilla anguilla) uses the hormone
prolactin, while in salmon (
Salmo salar) the hormone
cortisol plays a key role during this process.
Further Information
Get more info on 'Freshwater'.
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