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Zooseston of the Vistula River section almost 340 km long was investigated in the years 1997/98. In 99 samples collected 90 species of rotifers, 16 cladocerans, 9 copepods and other animals belonging to: Harpacticoidea, Oligochaeta, Nematoda, Chironomidae, Odonata, Simulidae, Tardigrada and Coelenterata were found. Multiple regression analysis showed that the number of rotifers is significantly correlated with basic chemical indicators of water trophic state - phosphate, nitrate and nitrite as well as with the number of copepods which are usually predators. The numbers of copepods depends on the availability of possible prey, i.e. rotifers and cladocerans. Multiple regression confirmed known dependence of cladocerans from trophic conditions. Clustering of similarity matrices showed complex structure of sestonic assemblages on rhitral-potamal gradient additionally modified by hydrotechnical constructions. These constructions broke old river continuum. Ordination of sites gave complex pattern not only representing a simple gradient rithral - potamal but also all transient stages caused by hydrotechnical construction (large dam reservoir) or by inflows of polluted waters from the tributaries. Ecological meaning of principal component ordination (PC) for river zooseston assemblages is not simple and might be susceptible of various interpretations.
Investigations on the Upper Vistula River course (from 11 to 337 km) in years 1997-1998 comprised: chemistry of water and sediments, indicators of water quality, such as bacteriological indices, metabolic activity of seston, phytoseston indicator taxa, algal growth test, zooseston assemblages, benthic diatom indices and occurrence of oligochaetes fauna. The pollution impact was reflected by distinct changes in chemistry of water and sediments, as well as by bacteriological indicators and alga growth test. No distinct changes have been noted in the structure of benthic diatom communities. Some improving tendency in the water quality was evident between 248-337 km of the river course, where the most tolerant to pollution taxa were partly replaced by less tolerant species. Some changes revealed an increase in numbers of beta-mesosaprobic and meso-eutraphentic Chlorococcales, which dominated over dense populations of cyanobacteria. Benthic animals assemblages indicated a decrease in pollution level between 248-337 km of the river course. In the case of zooseston no evident effect was observed. The sector of the river received on 95 km high load of chlorides from coalmines until last site on 337 km. Load of chlorides was constant, whereas their concentrations diminished. Nitrate concentration arose together with loadings. Phosphate concentrations were constant similarly to loadings, excluding site at 337 km of the rivercourse, where load arose. COD had similar pattern as chlorides. It seems to be better to operate on a greater number of specialised indices or parameters than mixed them into one, which might be confusing index.
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