Lake Mikolajskie is seriously affected by Mikolajki town and tourism. The amount of sewage entering the littoral zone is increasing as also is the area of the artificially transformed shore. During the past 20 years the area occupied by macrophytes has decreased markedly. The decline of Phragmites australis, changes in species composition, and reductions in biomass and in the depth-ranye colonized by submerged plants have been observed. Simultaneously the biomass of algae has incrersed mrrkedly. Animals chwacteristic of polluted sites have become more abundant. Changes in animal numbers result to a great extent from changes in the availability of n a t u r d substrates.Zonation of the occurrence of organisms has been observed for years on sites directly affected by sewage-quantitatively and qualitatively poor communities are found a t sewage discharge points and the richer ones a t a greatt?r distvnce in the zone fertilized by diluted sewage.
A 294 cm long sediment core is divided into 1 cm disks at intervals of 7 cm. The disks are pollen‐stratigraphically dated. At the same time, the pigment content is determined by two‐dimensional thin‐layer chromatography. The pigments were determined spectrophotometrically between 200 and 800 nm, six pigments having been identified, whereas in the chromatograms 13… 36 spots are found. Chlorophyll conversion products as well as epiphasic and hypophasic carotenoids were determined by liquid adsorption. The greatest variety was found with the pigments in the Atlantic period, the minimum of diversity lies in the Subboreal period. The concentration of the chlorophyll derivatives decreases with the age of sediments, whereas the carotenoids have maxima in the Atlantic and Subatlantic periods. On the basis of the ratio of chlorophyll derivatives to carotenoids and of the ratio of epiphasic carotenoids to hypophasic ones, the trophic state of the lake between oligotrophic and eutrophic as well as the relative share of autochthonous and allochthonous feed of matter to the sediment can be represented well.
Laboratory experiments showed that both cladocerans and copepods are able to overcome a filamentous algae barrier, and are able to move within algal mats . This suggests that the crustaceans noted in large numbers in accumulations of algae actively colonize these mats and live inside of them.
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