Environmental Engineering Reference
In-Depth Information
Source: National Oceanic and Atmospheric Administration
Freshwater
Only 2.5 percent of Earth's water is freshwater, most of which is locked in polar ice caps and glaciers. There-
fore, only about 21 percent of the 2.5 percent is available in the form of groundwater, lakes and rivers, and wa-
ter vapor in the atmosphere. Freshwater is critical for life on Earth because most life forms need water on a
daily basis in order to survive, and freshwater ecosystems support an abundance of life.
Oceans/Saltwater
Most saltwater is found in Earth's oceans, with a small amount in terminal lakes such as the Great Salt Lake in
Utah. On average the salt content in the oceans is 3.5 percent. Ocean water is a mixture of salts, with sodium
chloride (NaCl), magnesium chloride (MgCl), and calcium chloride (CaCl) being the three primary salts. The
salts are transported mainly in runoff and wind as sediment from continental land. There are many unique and
diverse ecosystems that depend on the saltwater environment.
