Krenal

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The krenal ( old Gr . Κρήνη krḗnē , "source") is the source region as a limnological river type . Its habitat community is the krenon . A distinction is occasionally made between the actual source region, the eukrenal, and the source stream, the hypocrenal. Towards the mouth, the Rhithral (stream region) joins, followed by the Potamal (river region).

Mark

It is characterized by:

  • a water temperature that fluctuates only slightly during the day and the year. Sources fed by the deeper groundwater have a constant temperature, which corresponds to the annual average temperature of this place. In large parts of Central Europe, temperatures are around 10 ° C or just above.
  • low nutrient content . Today, this mostly only applies to springs with a wooded catchment area. Most springs with a lot of arable land in the catchment area have increased nitrate levels.
  • a changing flow velocity in the smallest of spaces
  • a low oxygen saturation , since spring water is exposed groundwater . In the course of the stream, however, the oxygen content can increase significantly due to strong turbulence and rapid runoff . As a rule, source streams are already saturated with oxygen.

Since the erosion in the krenal is stronger than the sedimentation , the water usually runs within a narrow notch valley . Also springs on steep slopes are mostly sunk into the slope; possibly through comb formation. The influence of the body of water on its surroundings is minimal, a floodplain has not yet formed. On the banks of the Krenal there are individual alders or ash trees , otherwise the water in Central Europe flows through the zonal beech forest.

flora

Due to the low summer temperatures, the flora of the spring water is mostly poor in species than that of other water types, but includes a number of highly specialized species that grow almost exclusively here. Many springs in the forest are heavily shaded and have almost no vegetation. They completely lack real aquatic plants. Typical types of forest springs and spring streams are, for example, opposed-leaved milkweed , alternate-leaved milkweed and brook springweed . Sunlit seepage springs in the grassland have a species-rich flora with numerous remarkable plant species, if they are not due to intensive use, e.g. B. excessive fertilization, have been devalued. The source corridors form the “Montio-Cardaminetea” class in the plant-sociological system. Typical and characteristic types are e.g. B. bitter foam cabbage and brook chickweed . Lime springs with tufa formation are particularly rich in moss, especially Palustriella commutata and Cratoneuron filicinum . Other typical spring mosses belong to the genera Philonotis (e.g. Philonotis fontana ) and Pellia .

fauna

The fauna of the Krenal is also poorer in species than that of the Rhithral , but it is also characterized by characteristic species. Some of the species found here are particularly adapted to the low summer temperatures. Some of these are species with their main distribution area in the far north or in the Alps, so-called boreoalpine species. In part, their Central European occurrence is interpreted as a relic occurrence since the Ice Age. The caddis fly family is particularly rich in spring species. Typical types of krenal are e.g. B.

The krenal usually has no fish. The only typical vertebrate species is the fire salamander .

literature

  • Josef Blab: Basics of biotope protection for animals (= series of publications for landscape maintenance and nature protection. Issue 24). Published by the Federal Research Institute for Nature Conservation and Landscape Ecology. 2nd edition, extended revision. Kilda-Verlag, Greven 1986, ISBN 3-88949-115-4 , pp. 1-250.
  • Leonie Jedicke, Eckhard Jedicke: color atlas landscapes and biotopes of Germany . Ulmer, Stuttgart 1992, ISBN 3-8001-3320-2 , p. 1-320 .
  • Jürgen Schwoerbel : Introduction to Limnology (=  Uni-Taschenbücher . Volume 31 ). 6th, revised edition. Fischer, Stuttgart 1987, ISBN 3-437-20395-9 , pp. 1-269 .
  • Dietrich Uhlmann, Wolfgang Horn: Hydrobiology of inland waters. A floor plan for engineers and natural scientists (=  UTB for science. Biology, geology, geography . Volume 2206 ). Ulmer, Stuttgart 2001, ISBN 3-8252-2206-3 , p. 1-528 .