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Diatom indices and indicator system based on benthic diatom communities were used to estimate the water quality and its changes in the Vistula River on the sector between 10 and 337 km of its course. The results showed similar trend in the water quality changes along the river course as those obtained by chemical analyses. Significant correlation was found between the calculated index values and also between indices and selected water chemistry variables related to the organic pollution and trophic state. However, there was no correlation with the concentration of phosphates. Both results, the chemical as well as biological ones based on diatoms, showed differences in water quality along the investigated river sector. Natural, unpolluted water with low nutrient concentration was found only in the upper part of the river (up to 10.9 km of its course). The increased trophic state was observed in changes of all the calculated diatom index values and in the relative abundance of the indicators for eutrophic stage already from 36.6 km, raising up together with organic pollution level along the river course. The heavy pollution occurred mainly on the section from 66.2 km to 185.2 km. At the last part of the investigated sector especially on 336.7km, an improving tendency was observed. The seasonal changes in the diatom community structure and values of diatom indices were connected with fluctuations of current velocity observed in 1997 during big flood at the beginning of July. Distinct differences were found in August and October 1997, when the structure of diatom communities and the values of diatom indices indicated the lowest water quality in the whole investigated sector.
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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