2 - Aquatic environments of fresh water
(Robert of the Saint-Seine)

After having seen in the 1st item, the elements which play a part in the balance of the aquatic environment,
I propose to you in detail to see what is the cycle of water and the dangers, which do not miss.
 

As each one knows it, the cycle of water starts with the phase of evaporation. It comes from the share of the sun on the seas and the oceans, but also on the lakes and the rivers without forgetting the negotiable instrument of evaporation on the plants and the ground itself. Because of the importance of the seas and oceans, it is not that they are at the origin of 90% of the water vapor produced on the Earth. The air thus responsible for moisture gives rise to the clouds. The phenomenon of condensation is more or less important and contributes to the appearance of more or less important clouds which under certain conditions will restore water in the form of rain, of snow or hail.

This water thus restored follows several courses. A party will join the ones, whereas another returns at sea after a long course through the brooks, the rivers and the lakes.

This level, the Man weighs on this cycle of water by using this resource of which we know now that it is not inexhaustible. Most worrying is undoubtedly the state of refund of this water used at agricultural or industrial ends, but also for our own consumption. Rejections of poor qualities can only disturb certain balances and thus decrease the quantities and qualities of the phenomenon of evaporation.

But of this routing of water, let us begin again in here essence by looking at more closely the collecting mediums which will completely naturally give again certain balances or which will undergo the aggression of rejections of poor quality.

Stagnant water

In this category, one will as well find the ponds, the ponds and the lakes. This water is of a large variety according to altitude and of the immediate environment.

The ponds are reduced sizes. Very often to be fed only by surface waters, fauna and the flora will be elements determining for a good balance. Generally, one finds there primarily only species which thus support relatively hot water because of the lack of renewal, and thus not very rich in oxygen.

The ponds from their variable sizes and their depths, offer of advantage of wealth. Fauna and the flora to develop to with it in a perfect balance in which the water supplies will play a considerable part.

One as well finds there species benthic (which on the content) that of surface as well as carnivores.

Side of the flora, the distribution of the species is done above all according to the depth. At the edge one will find plants which have only the root in water. It is in this very shallow area that one meets the very often populated reeds (reeds), of whereas a little further, in water 40cm, are present the and the two-handed hammers. In the middle of the pond, one then finds plants known as watery such as Elodea and the .

The lakes have like characteristics to have very often surfaces quite higher than those of the ponds, more important depths and a liquid mass whose thermal aspect is more unstable because of the winds.
 

One meets two types of Lake, the natural lakes and the artificial lakes.

A natural lake has pure water, oxygenated slightly and mineral-bearing. It is known as oligotrophic. Water of these lakes shelters some plant species and animal, with in particular of the plankton. This water .

The lakes whose fauna is varied and abundant and whose bacterial activity is important is known as . This term indicates that its funds are poor.

The eutrophic lakes are lakes in which the oxygen rarefies and whose mechanics of mineralization is reduced. Very often they are filled by accumulation of sediments and see their depths and their surfaces to decrease.

Running water

Source of one brook to the sea or the ocean, water runs. The landscapes change and the change aspects. Sometimes fast, sometimes calm, in a narrow bed or a broad opening, the fishermen find here and there their happiness.

The torrents are born from the cast iron of the glaciers or natural mining areas which recover surface waters (rain, ). The stenothermal species appreciate their cool water (Trout , Chabot), but also the oxygenation of the water supported by turpitudes of water. On the rocks, the vegetable life develops in the form of foams and of lichens, while the funds of small invertebrates such as the .

The rivers receive throughout their courses, water of the torrents, the and the brooks. The width and the depth of a river are relatively modest. The more its bed will be enlarged, the more peaceful its exchange rate will be and its low currents. Throughout its routing, the crossed mediums play their parts with many influences on its high content in fish.

Thus, upstream (higher Exchange rate), when the current is still fast, water is well oxygenated, the stirred funds are covered with stones, gravels and of sand and the vegetation remains still modest. This sector is described as area in Ombres and the piscicultural population accommodates Saumons, , and Nases.

Low in the valley, the current becomes moderate and the more important vegetation. There in this portion called “to Barbeaux”, the fisherman can hope to find , Saumons, , Aspes, Gardons and .

Finally while approaching the estuary (lower Exchange rate), and whereas the river became river, the current is slow. Water is less better oxygenated and the vegetation much more important, as well on the edges as in water. In this area called “to Bremen”, you will find without evil, Anguilles, sturgeons, Tanches, Brèmes and Pikes.

The running water is a fragile medium. That it is by pollution or the climate changes, balance between fauna and the flora () is often threatened by the human activity.