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The succession of periphyton developing on artificial substrate immersed in a polysaprobic wastewater reservoir was studied during a two-year period. Three stages in the periphyton development: initial, inter­mediate and mature, were observed. The initial stage was characterized by domination of euglenophytes; Carchesium polypinum was dominant during the intermediate stage, while diatoms and chrysophyceans dominated the mature stage. However, the most characteristic component of periphyton consisted of de­tritus that contributed more than 50% (by volume). The periphyton development dynamics in the second year of the experiment, when that formation was already firmly established on the polyethylene sheets, was quantitatively similar to the process of periphyton development in the first year of substrate exposure.
The study was carried out in the main branches of the Lower Oder River, differentiated in terms of sediments composition. The aim was performing a comparative studies on the differences in Ostracoda fauna inhabiting various types of sediments. Following bottom sediments were distinguished: hard, sapropel/hard, sapropel and Chironomidae mat. The packet of CANOCO v.4.5 programs was used to investigate the interdependence between the species composition and environmental parameters. Eighteen taxa were found of which 16 were identified to the species level. It was a comparatively high number considering the fact that the samples were collected exclusively from the benthic zone and solely from the main river bed, without floodplain. Physocypria kraepelini was an eudominant and Darwinula stevensoni and Cypria ophtalmica were dominants. The samples collected from the sapropel were characterised by the highest density. The case of hard sediments the status of domination was retained as above, but there appeared a new dominant, i.e. Potamocypris unicaudata . The most unique structure of domination was observed in the case of Chironomidae mat, with Limnocythere inopinata as an eudominant and Cypridopsis vidua and P. unicaudata as dominants. As for the species diversity, the hard sediments were characterised by the highest value of Shannon-Wiener Diversity Index, the sapropel/hard sediment was the lowest. The type of river bottom to a great extent affects the density and taxonomic composition of the Ostracoda in rivers. The waters of the Oder River, rich in oxygen, provide favourable conditions for the development of ostracods even on the surface of sapropel sediment.
The malacofauna of the middle and lower Odra (Oder River), a large river degraded by human ac- tivities, is still rich and diversified. Fifty five mollusc species were recorded from 31 studied localities: 32 Gastropoda and 23 Bivalvia. The highest number of species (47) inhabited the areas between groynes, whereas the fewest species (20) were found in the river current outside groynes. As many as 14.5% of the re- corded species were alien to the Polish fauna: Lithoglyphus naticoides, Potamopyrgus antipodarum, Physella acuta, Ferrissia fragilis, Menetus dilatatus, Corbicula fluminalis, C. fluminea, and Dreissena polymorpha. The presence of so many alien species shows that the Odra, together with the system of canals (which through the Spree and the Havel connect it to the drainage basin of the Elbe), is a major route along which alien molluscs migrate to Poland.
Azolla filiculoides Lam. is the second most widely distributed alien aquatic plant in Europe. A native of America, it has become — on account of human mediation — a cosmopolitan species. In Poland, it has been known so far from a few stands in ponds and old river beds. In 2016, it was recorded at six new sites in-between the groynes at the main Oder river bed between Maszewko near Krosno Odrzańskie (52°3′10.69″N, 14°57′13.56″E) and Owczary (52°28′53.59″N, 14°37′30.43″E). The assemblages containing the fern were identified as representing the association Ceratophyllo-Azolletum filiculoidis Nedelcu 1967. Azolla has also entered the phytocoenoses of other floating plant communities. Mean values of several chemical parameters of the water like conductivity, salinity, total dissolved solids and nitrate content at the fern stations were significantly higher than the mean values found in the Azolla-devoid sites while the values for hardness (Ca), pH and visibility (Secchi Disc depth) were lower at Azolla sites. In 2017, this alien fern was found to had successfully overwintered in the main bed of Oder river, and its further spread down the river was observed. The appearance of Azolla filiculoides in the Oder may be associated with an exceptionally warm winter; its emergence may also accelerate the species' invasion in Poland.
W trakcie obserwacji terenowych prowadzonych w latach 2000–2009 stwierdzono 12 nowych stanowisk pijawki lekarskiej Hirudo medicinalis Linnaeus, 1758, zlokalizowanych w zachodniej Polsce. Bezkręgowce te zasiedlały niemal wyłącznie niewielkie (do 1 ha), śródleśne zbiorniki wodne. Gatunek ten preferuje płytkie, szybko nagrzewające się akweny o mulistym dnie i obfitej roślinności przybrzeżnej. Większość wykrytych stanowisk była izolowana, czyli rozmieszczona w znacznej odległości od siebie. Głównym zagrożeniem dla tego taksonu wydaje się zanik siedlisk, a zwłaszcza torfianek, glinianek i starorzeczy
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