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The characteristics of habitats, individuals and populations of four submerged macrophytes, Lobelia dortmanna L., Isoetes lacustris L., Sphagnum denticulatum Brid. and Fontinalis antipyretica Hedw., were studied in 12 soft water oligohumic lakes which had no inflow of allochtonic DOM and the DOC concentration in the water was <4.0 mg C dm-3 and 13 humic lakes enriched with allochthonous dissolved organic matter (DOM) from drained peat bogs and ranging in DOC water concentration from 4.1 to 44.0 mg C dm-3. The analyses of population disintegration were conducted basing on characteristics of individuals (size, habitat, fertility) and populations (aggregation density index, settlement index of the population area). The settlement index of the population area for Lobelia, Fontinalis, Isoetes, Sphagnum decreased from 8.4 to 6.2 g d.w. m-2, 4.6 to 0.01 g d.w. m-2, 85.4 to <0.001 g d.w. m-2 and 39.3 to 7.2 g d.w. m-2, respectively. Similar trends were observed in aggregation density. The general pattern of the disintegration of populations of these species was always similar. It was independent of the source macrophytes drew resources from or their susceptibility to environmental changes. Individuals began to be eliminated from the deep and central parts of the population area. The remainder of the populations, which persist in the shallowest, best-illuminated part of the area, are themselves endangered by disturbances caused by wavy motion. The only populations of submerged macrophytes which can survive in polyhumic lakes under such conditions are those which are resistant to disturbances common in the shallow littoral (Lobelia dortmanna, Fontinalis antipyretica).
Phytosociological and habitat studies of Sphagnum denticulatum and Warnstorfia exannulata phytocoenoses from Polish Lobelia lakes have been conducted. The present results were compared with data on Isoetes lacustris community. It is demonstrated that both communities of mosses are distinct with respect to their floristic composition. Moreover, they differ significantly from the patches of I. lacustris with regard to many properties of water and substrates. The phytocoenoses of S. denticulatum are associated with softer waters, poorer in Ca2+, Na+, NH4+ and dissolved organic matter, but richer in total Fe than those of I. lacustris. They are also distinguished by lower values of electrolytic conductivity. The substrates they inhabit are more strongly hydrated and richer in organic matter, total N, dissolved SiO2, Ca2+ and Na+, but poorer in PO43-. The W. exannulata phytocoenoses are also confined to softer waters with lower Ca2+, NH4+ and dissolved organic matter contents than those of I. lacustris. Their substrates are more strongly hydrated and have higher contents of organic matter, total N and Na+ but lower amounts of PO43-. In addition the waters of W. exannulata phytocoenoses are characterized by higher pH values and lower concentration of dissolved SiO2. The substrates are less acidic and richer in NO3-, but poorer in total Fe. The differences between the habitats of the S. denticulatum and W. exannulata phytocoenoses are also distinct. The former inhabit more acidic waters, richer in dissolved SiO2 and total Fe, but with lower values of electrolytic conductivity and concentration of Na+. Their substrates are distinguished by higher contents of organic matter and Ca2+, as well as by lower amount of NO3-. In view of the fact that the above phytocoenoses of mosses are distinct with respect to their floristic composition and are associated with specific habitats in which they form dense mats close to the bottom of the lake, they should be classified as distinct associations (Sphagnetum denticulati and Warnstorfietum exannulatae) in the system of aquatic communities (Class: Utricularietea intermedio-minoris).
The aim of the work was to characterize the species composition of the fish assemblages in the littoral zone and to analyze catch statistics from the lobelia-lake Lake Dołgie Wielkie. Catches were conducted with a fry trawl between May and August 2001 in the shallow littoral. Commercial catches from 1952 to 1970 and 1980 to 1999 were also analyzed. Nine fish species were caught and the majority (81.1%) of specimens belonged to the juvenile stages. The greatest contribution (%) to the littoral fish assemblage was made by belica, which was also described by the highest availability coefficient. A small number of species which comprised the lake fish assemblage and the distribution of their frequency of occurrence meant that the Simpson coefficient (D) of species diversity was low at 0.2082. The littoral of Lake Dołgie Wielkie is not very diverse and the ichthyofauna diversity in it is dominated by belica. In comparison with lobelia-lakes in western Pomerania, the structure of the share of various species in commercial catches was different in Lake Dołgie Wielkie, and the fisheries yield was higher. The fish assemblage which inhabits the lake is characteristic of eutrophic lakes.
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