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Ponds
A pond is a body of water smaller than a lake. more...
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In the United Kingdom, where the charity Pond Conservation has made some of the most extensive studies of ponds, the now widely adopted definition of a pond is 'A man-made or natural waterbody which is between 1m2 and 2 hectares in area, which holds water for four months of the year or more' (Biggs et al 2005). In other parts of Europe some biologists prefer to set the upper size limit at 5 ha (Cereghino et al 2008), and in North America even larger waterbodies are often called ponds. The international Ramsar wetland convention sets the upper size limit for ponds as 8 ha. Although the size cutoff between ponds and lakes is partly subjective both are formed by ponding water. Ponds may be man-made or natural in origin and can be made by excavating a hollow in which water may lie, filling an existing depression with ground or surface water or by retaining water from a stream, or by forming a dam to impound the water in a valley. Ponds can be made by a very wide range of natural processes, although in many parts of the world these are now severely constrained by human activity. In some countries backyard ponds or garden ponds are popular and common.
The techniques may be combined to form a reservoir in flat country by enclosing an area with an embankment. Such a pond, unless very small, is usually called a reservoir. In some cultures, the meaning has been extended to include small bodies of water impounded naturally.
The many different definitions traditionally applied by freshwater biologists to ponds (such as a body of water where light penetrates to the bottom of the waterbody, a waterbody shallow enough for rooted water plants to grow throughout its area, a water body which lacks wave action on the shoreline) are very difficult to apply in practice, and may vary according to season, pollution or the presence of trees around the waterbody. For example, when a pond is too heavily shaded by trees for plants to grow throughout, does it cease to be a pond? If the waterbody is polluted, light may be prevented from penetrating to the bottom of even quite shallow ponds by dense blooms of algae - yet the waterbody is still a pond. For this reason more practical definitions based on size, which can be easily measured at all times and change only if the pond is physically modified, are now widely used. In the same way, lakes can simply be defined as waterbodies which are larger than ponds. A review of old definitions of ponds is provided by Biggs et al 2005.
References
Biggs J., Williams P., Whitfield M., Nicolet P. and Weatherby, A. (2005). 15 years of pond assessment in Britain: results and lessons learned from the work of Pond Conservation. Aquatic Conservation: Marine and Freshwater Ecosystems 15: 693-714.
Céréghino, R., J. Biggs, B. Oertli, and S. Declerck. 2008. The ecology of European ponds: Defining the characteristics of a neglected freshwater habitat. Hydrobiologia 597:1-6.
Read more at Wikipedia.org
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