A pond ( estang , Latin stagnum ) is stagnant water an extent, not very deep, of relatively small surface (until a few tens of hectares), resulting from the impermeability of the ground.
DefinitionThere exist many definitions of the pond . It is about a water level, continental, of origin natural or anthropic, of which dimensions and the uses (draining, assec) always do not make it possible to establish the zonation nor the staging of the various processes stagnustres in a durable way. The pond is smaller than a lake, but larger than a pond, which is defined like a stretch of water to generally limited renewal, of variable size (5 000 m ² to the maximum). Certain definitions consider that the water of a pond must be stagnant. Others that only banks, and the zones having a depth lower than 2 meters 50 are to be regarded as wetland. One also speaks - in France in particular - ponds about fishing, and/or hunting.
Formation and evolution of the ponds
The majority of the ponds are the result of human installations, either by the establishment of a dam on a River, or by clearing out of a place naturally wet and supplied with water of Pluie, of source, streaming or by digging until in lower part of the Ground water (case of the gravel pits). In Europe of many ponds are contained by artificial dams which often date from hydraulic work of the medieval abbeys. These ponds (or fish ponds) often constituted water reserves and of fish after the great drainages made disappear number of the peat bogs and natural wetlands from the landscape.
The formation of a pond requires a water supply and a rather impermeable ground or a communication with the ground water. The food can consist of a channel taking water on a natural river. It is frequent that the course of a Ruisseau was used to create a flowing chain of ponds one in another. The dam of a pond is consisted a ground cluster, stones and of Argile or very seldom by a wall Barrage out of concrete or masonry.
When the ponds are surrounded by trees, located downstream from a zone subjected to erosion, a regular maintenance (clearing out) is necessary to push back the silting, and if water is eutrophized to limit the proliferation of the watery vegetation (clearing of weeds of the Roseau X, and cuts Arbre S on banks). In the areas where it is present, the Muskrat can impose the filling of the holes which it digs in the dams. The draining of certain ponds retained by a dam can be done by pumping, siphoning, or by a valve (plug or monk , kind of well of which an east coast made up of boards that one can pile up to regulate the level of filling closing a tube placed in the lower part of the dam). A too full (in threshold or notch) possibly barred by a grid often is dug or built in the upper part of the dam to evacuate a possible surplus of water in period of Crue.
HistoryIn the beginning the ponds were arranged mainly for the Pisciculture, the resources of the Agriculture or the breeding not being sufficient in the areas where the ground was at the same time poor and marshy. The exploitation of the hydraulic power has constrained the miller to channel the river to exploit and often to create a water reserve to control the variations of flow upstream. With the development of the steam engine, the pond lost its role of reserve of energy or water for industry, besides some Moulin S and Scierie S which still uses a paddle wheel incidentally. The pond became a place of leisure: fish, drives out with Water sports, waterfowl… Certains ponds are always exploited for the production of Poisson S of fresh water, others are maintained for simple approval or to constitute a soft water reserve for consumption, the Irrigation or watering.
Contrary to what is commonly allowed, of the studies of limnologic geography showed the presence of temporary thermal stratification in the ponds, as of two meters of depth.
The pond is a ecosystem particular very sensitive to the Pollution S (in particular the Eutrophisation related to the Nitrate S). The fauna and the Flore which it shelters contain of the specific species, from which some are protected. The pond became in many places a place of conservation of the Flore and fauna often emphasized for the sensitizing of the public at nature.
EnvironmentThe establishment of a pond is not neutral for its environment. Its impact can be positive or harmful. If it diverts water of a river, or flows in a brook, the warming of the water of the pond in summer can have important consequences on the evolution of the fauna and the flora of the river. Many ponds were poisoned with undesirable in the natural environment, and sometimes planted species exotic species decorative but become invasive out of their medium of origin (ex: jussy of the marshes).
The pond is a water reserve on relatively constant level, which can sometimes control the flow of a river and gum partially the risings and the periods of low water level but which does not allow the normal expression of the species pionnières or the écotone S; it makes it possible to maintain a certain hygroscopy and its losses often feeds the Water table. N the other hand, are evaporation is often compensated by taking away in the rivers, in the tablecloth (pumping) to even maintain its level in period of dryness, thus worsening the effects of the low water level.
During its brutal draining, the pond injects into the receiving river of the mineral and organic matters modifying the composition of running water but by its vegetation (floating and enracinées plants, Phytoplancton…), it contributes to the purification of water.
Lastly, certain ponds collect the water polluted by urban, industrial or agricultural wastes (manures pesticides), and the ponds of hunting and/or fishing often contain significant quantities of lead of fishings and/or (toxic shot) which have settled there for several decades, before their recent prohibition in the wetlands can pose problems of Pollution Sédiment S and of Saturnisme to the birds which nourish themselves there
Fresh water ponds
The natural (impermeable) of the ground combined with weak slopes often characterize the areas of ponds, among which one notes France-:
- the the Sologne, which counts more 2800 ponds
- the Dombes
- the Haute-Saône and its Plateau of the Thousand Ponds
- the Brenne, Pays of the thousand ponds registered with the Convention of Ramsar
- the the Limousin
There exist also salted ponds, which are in fact of the Lagune S which communicate more the share of time with the sea by graus. One can quote the pond of Thau, the Étang of Berre, the Étang of Gold.
Ponds of productionThe ponds, particularly if they easily drainable or are arranged for that, for a long time allow an important production of fish. The Pisciculture in pond developed in Europe as of the Moyen-âge, in particular because of monastic communities , and in China as of before our era.
Certain forms of Aquaculture intensified are also based on ponds or equivalent structures, like the breeding of shrimps, with the detriment of the Mangrove S in general.
Another useA mode of purification of waste water called the Lagunage is composed of a series of lagoons or ponds. An organic load of pollution, if it is not excessive can be degraded under good conditions indeed there.
External bondsPole relays wetlands intérieures
The House of the Ponds of Saint-Viâtre (the Sologne)
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