Freshwater is defined as water that has a low salt concentration, as opposed to marine waters. Humans depend on water for survival, as it makes up one-half of the body. A person can survive for only a few days without water, but can live without food for more than a month. Freshwater is found in many different forms.
Ponds can be seasonal, with a limited species diversity, since they are generally isolated from one another.
Lakes are fed by rivers, streams, springs or local precipitation and depend upon continuing runoff from these sources. Lakes, including the Great Lakes, suffer from deteriorating water quality because of industrial and municipal uses, fluctuating water levels, flooding and shoreline erosion.
Scientists have identified over 360 chemical compounds existing in the Great Lakes, resulting in potentially harmful levels to both humans and the entire aquatic ecosystem. Seven of the ten most highly valued fish species have almost totally disappeared from Lake Ontario. In order to deal with these problems, Canada and the United States have signed The Great Lakes Water Quality Agreement, calling for cleanup of all the Great Lakes.
Streams and Rivers are universally found and are defined as bodies of flowing water moving in one direction. They can start as springs, snowmelt or lakes and travel to either another water channel or the ocean.
Wetlands have been greatly abused by humans, who considered them to be a nuisance and an obstacle only to be filled in and used for other purposes. In the Great Lakes basin alone we have lost two-thirds of the original wetlands and they continue to disappear. But we now know wetlands are essential to the health of the nearby lakes and streams. A wide variety of fish depend upon them for food, cover, spawning and resting areas; waterfowl use wetlands as both nesting and migration rest stops. It is estimated that 68 bird species, 20 species of mammals, 28 species of amphibians and 27 species of reptiles. Of all ecosystems, wetlands contain the highest species diversity.
In 1971, in Ramsar, Iran, 158 countries signed The Ramsar Convention on Wetlands, identifying 1,782 wetland sites totaling 161 million hectares to be protected worldwide.
Groundwater is an important aspect that is often overlooked. It exists almost everywhere underground in the spaces between particles of rock and soil and is usually within 100 metres of the surface. Groundwater flows very slowly and can be found even in the desert, but many countries are now tapping into this dwindling resource as industries and cities continue to grow.
Freshwater Ecosystem References: