Application of various modifications of the method of saprobic indica- 

 tor organisms (including the methods of Knepp, Pantle and Buck, Zelinka 

 and Marvan, Rotshain, Sladecek) was made to collections of phytoplankton, 

 planktonic ciliates, rotifers and crustaceans. The results lead to very 

 similar evaluations of the quality of the waters. 



Detailed algological investigations on the 5 rivers showed that 50 

 percent of the species observed and nearly 80 percent of the dominating 

 species are cited in the lists of saprobic indicators by Sladecek. This 

 enabled a comparison of the methods of treating the data by Knepp, 

 Zelinka and Marvan, Rotshine and Sladecek. The greatest possibility of 

 differentiation of the stations with varying degrees of pollution are pro- 

 vided by the estimation of the mean saprobic valency according to Zelinka 

 and Marvan. This method, while useful, can not compensate for the ad- 

 vantages of simplier methods which generally lead to similar results. 

 This is especially true of the method of Sladecek, or to be more correct, 

 his modification of the method of Pantle and Buck. 



All the 5 investigated rivers must be classified as 6 mesosaprobic 

 waters in spite of evident differences in their degree of pollution 

 according to the saprobic index. Within this class, however, the rivers 

 are arranged in a sequence by ranking the mean saprobic index correspond- 

 ing to relative pollution. 



Of 120 species of planktonic crustaceans and rotifers, 97 are included 

 in the list of Sladecek. Estimation of the saprobic index lead to the 

 same general conclusions as were drawn by data available on the phycology. 

 The methods based on the application of the lists of saprobic indicators 

 of phytoplankton, planktonic crustaceans and rotifers generally reflected 

 the correct varying degrees of pollution of the investigated rivers, but 

 they displayed only poorly the differences between stations on the same 

 stream, especially when the influence pollution levels were low. This 

 fact naturally established boundaries for the application of these 

 methods. 



The results of the zoobenthic assays lead to other conclusions rela- 

 tive to the application of the system of saprobic indicator organisms. 

 The proposed systems of indicator organisms appeared to be not applicable 

 in many cases for conditions in the USSR. One of the reasons is the 

 difference between the fauna of the Middle European countries, and the 

 rivers of the USSR. For example, 132 species of macrobenthic forms are 

 presented in the table of indicator organisms. Of 170 species of benthic 

 animals from our collections, only 17 can be found in the table of indica- 

 tor organisms. The average number indicator species in a sample usually 

 did not exceed 28 percent. At some stations on the Moskva and Vuoksa 

 Rivers, the indicator organisms in the zoobenthos were absent entirely. 

 The difference between the fauna and the number of the indicator species 

 will be even greater for the areas of the Far East, Kamchatka, Sakhalin, 

 Middle Asia, the Caucases and the like. 



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