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Fresh water (also spelled "freshwater" as a noun) refers to water with low levels (less than 1% usually) of dissolved salts and total dissolved solids. Most of the world's fresh water is found in icecaps.
There is a wide variety of fresh water habitats, ranging from very small to very large. Fresh water is found in puddles, ponds, swamps/bogs, lakes, rivers, streams, creeks, tarns, underground (aquifers), ice (sheets, caps, etc.), glaciers, water flowing into estuaries, etc.
Fresh water can be flowing, still or groundwater. For a very basic division:
- Rivers and streams are moving water (lotic systems). Moving water can be as small as water running through a field, a river torrent or a gush down a mountainside. Streams and rivers are two types of flowing water; streams are shallow, cool and often have stone, pebble or gravel bottoms. On the other hand, rivers are often deeper, warmer and have sand or silt bottoms.
- Lakes, swamps and ponds are static bodies of water (lentic systems).
- There is also a hyporheic zone, which refers to the area underneath large rivers that cannot be seen and may also connect with underground water beneath.
Fresh water can be temporary (such as a puddle) or of very long duration, measurable only in geological time (such as a lake or ice field). For example, Lake Baikal is approximately 25 millions years old and contains about 20 percent of the world's fresh water. Human-created bodies of fresh water are included, from garden ponds through to large dams.
Formation of fresh water
Fresh water bodies form in varied ways. The majority of fresh water is sourced as a result of precipitation from the atmosphere (rain, mist and snow).
- Ponds and lakes - These bodies of water form when a large enough cavity is filled with water. This can occur as a result of geological action, such as earthquakes, volcanoes, landslides, and glacial movement. It can also result as a result of animal actions, including those of human beings.
Fresh water provides many habitat opportunities for plant and animal species. The flowing or static conditions impact which species thrive in the varied fresh water habitats. Most freshwater bodies are colonised quickly after formation, as a result of activity from microscopic creatures, insect and seeds or spores.
Ramsar sites are wetlands of international importance.
Threats to fresh water
Fresh water threats include pollution, pest invasion, increased sedimentation and changes to the water cycle and drainage.
Fresh water and climate change
With unequivocal evidence that the climate is warming, there are going to be impacts on freshwater habitats. The extent and impact of such changes will vary depending on which local freshwater habitat is being assessed. This is an ongoing learning process. Some freshwater bodies will likely experience shifts in the range of freshwater species and possibly extinctions of some species.
Fresh water as a resource
Fresh water is an important, yet limited resource. It is vital to the maintenance of biodiversity and many species rely on fresh water for survival. Freshwater ecosystems provide many resources to human beings, including recreational, economic, cultural and well-being opportunities.
Sources and citations
- IPCC, Fifth Assessment Report, 2014 at https://www.ipcc.ch/report/ar5/
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