Potamal

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The Potamal ( old Gr. Ποταμός, river ) is a technical term in limnology and hydrology for the lower reaches of a river (i.e. the river habitat ). The community of the Potamals is the Potamon . Above the Potamal are the Rhithral (brook region) and the Krenal (source region).

The habitat of the Potamal corresponds to a total of three fish regions : barbel region (also called epipotamal ), bream region (also called metapotamal ) and ruff - flounder region (the area where it flows into the sea, also called hypopotamal ).

The annual fluctuation in water temperature in Central Europe is around 20 ° C.

Vegetation and plankton

In the epipotamal the water depth and cloudiness are relatively small, so that a variety of submerged, i.e. mostly submerged, aquatic plants can develop. These are naturally more frequent here than in the Rhithral, ​​because rivers receive relatively more light than brooks due to the higher water table width (brooks rich in macrophytes can therefore usually only develop when the wood on the banks has been cleared).

Typical plant species of the Potamal are the large spawning herbs of the genus Potamogeton , above all Potamogeton nodosus , specular pondweed ( Potamogeton lucens ) and streaked pondweed ( Potamogeton perfoliatus ). Other typical species are yellow pond rose ( Nuphar lutea ), simple hedgehog ( Sparganium emersum f. Fluitans ), arrowhead ( Sagittaria sagittifolia var. Vallisnerifolia ), water crowfoot ( Ranunculus sect. Batrachium , also as a collective species Ranunculus aquatilis agg. ).

These vegetation structures are largely absent in the subsequent metapotamal and hypopotamal. Similar to many stagnant bodies of water, these river sections are characterized by phytoplankton .

fauna

Typical animal species

For the typical fish species in the areas of Epipotamal, Metapotamal and Hypopotamal see fish region .

Typical mammal species of the Potamon are otters and beavers . Typically as breeding birds are sand martins - they nest in steep, eroded by the water's edge breakage - and Sandpiper .

Of the flow-adapted invertebrates ( benthic invertebrates ) fewer species living in potamal than in Rhithral. However, many of the species living in the Potamal are highly specialized and only occur in large rivers. The pollution (historical and current) of most major rivers has made many of these species threatened with extinction. Typical Potamal invertebrates include:

These species are only intended to represent the range of species in the Potamal. Some of them have died out in Germany today or are threatened with extinction. At least one German caddis fly species from the Potamals, Tobias caddis fly ( Hydropsyche tobiasi ), has apparently become extinct as a species (worldwide). It is only known from museum specimens collected on the Middle Rhine. Some others have recovered in the last few decades due to improved water quality, e.g. B. the mermaids.

In addition to specialized Potamal species, a large number of species live in the Potamal with a main distribution in stream underflows (hyporithral), as well as species of stagnant water and freshwater ubiquists .

Neozoa

A particularly large number of animal species that have been introduced by humans ( neozoa ) is also typical of the Potamal . Possible reasons for this are:

  • Due to the heavy water pollution of the past, many rivers were almost uninhabited, so that all newly added species had good starting opportunities
  • By building canals across traditional watersheds (e.g. the Rhine-Main-Danube Canal), many species had new routes of distribution
  • modern transport mechanisms move species over great distances. Aquatic organisms are attached to ships or transported in ballast water . Some species are kept in aquariums or are carried away attached to aquatic plants.

The macrozoobenthos of the Middle Rhine consisted at times of over 90% of the individuals and over 30% of the species of neozoa.

Typical Neozoic species that are widespread in the Potamal today are z. B .:

Mass flights of insects

Some typical Potamal species are noticeable by mass flights. This is the synchronized slip of many millions of individuals in a river section at the same time, which resemble thick fog and can literally darken the sun. Corresponding phenomena are then reported in the daily press. Mass slip phenomena are known from historical reports. Sometimes the dead insects were so numerous that they were fed to the pigs. At the beginning and middle of the 20th century they were only known from Eastern and Southeastern Europe because of the biological desertification of numerous Central European rivers :; for a few years now again from Central Europe (Danube and tributaries, Rhine).

Some species of mayflies ( Ephoron virgo ) and caddis flies ( Hydropsyche contubernalis , Brachycentrus subnubilus ) are known for mass hatching . The mayfly Palingenia longicauda was called “ Tisza blossom” because of its mass flights on the Hungarian Danube tributary Tisza .

Individual evidence

  1. ^ Schaefer, Matthias: Dictionaries of Biology. Ecology. 3rd edition, Gustav Fischer Verlag (Jena), ISBN 3-8252-0430-8 .

literature

  • J. Blab: Basics of biotope protection for animals . Ed .: Federal Research Institute for Nature Conservation. Bonn 1986, p. 1-250 .
  • E. Jedicke, L. Jedicke: Color atlas landscapes and biotopes of Germany . Ulmer, Stuttgart 1992, p. 1-320 .
  • J. Schwoerbel: Introduction to Limnology . Fischer, Stuttgart 1987, p. 1-269 .
  • Dietrich Uhlmann, Wolfgang Horn: Hydrobiology of Inland Waters: A Floor Plan for Engineers and Natural Scientists . UTB, Stuttgart 2001, ISBN 978-3-8252-2206-2 , pp. 1-528 .
  • BA Whitton: River Ecology . Berkeley 1975, ISBN 0-520-03016-8 ( Google Books ).