one of the possible causes of a decrease in the species diversity index. 

 Thus, this methodology may only be used in conjunction with other tecni- 

 ques as one of the comparative methods. 



Analysis of the data obtained in this study enabled the development 

 of a new methodology for assessing the level of water pollution. 



In various systems advocating the use of indicator organisms, atten- 

 tion is usually directed to the macrobenthos, ignoring the organisms of 

 meiobenthos. However, meiobenthic organisms may serve as good indica- 

 tors of the degree of water pollution. The investigations of the com- 

 position of meiobenthos performed by S.Ya. Tsckholikhin as a part of this 

 study on various parts of the Moskva River have shown that the representa- 

 tives of two subclasses of nematods (Adenophorea and Secernantea) may be 

 successfully used as indicators of pollution. The subclass Secernantea 

 tend to occur in places containing large quantities of organic matter. 

 Adenophorea, however, prefer unpolluted waters. Ratios of the numbers of 

 the representatives of these subclasses may serve as an index of the pre- 

 sence and degree of pollution. It is apparently sufficient to identify 

 these organisms to the order classification. This, of course, presents 

 no serious difficulties. Further, as a result of their world-wide distri- 

 bution, no geographical restrictions are imposed for using nematods as 

 indicators of pollution. 



In the lists of indicator organisms proposed by different investiga- 

 tors, the number of the chironomid larvae does not exceed 10, and most 

 frequent used are the larval forms identified to genus. Some representa- 

 tives of the family Chironomidae are considered to be most numerous in 

 polluted water, e.g., CbtAonomuA, PfiocladiuA , PAe.cJxotarvtpu.6 . Further 

 definition of the use of species of chironomid larvae as indicators of 

 water pollution is presently impossible because of the lack of taxonomic 

 detail for this group and the need for further understanding of the 

 ecological requirements for separate species of this group. 



It does appear, however, that the use of universally occurring 

 chironomid larvae holds real potential for hydrobiological analysis. 

 Investigations by E.V. Balushkina as a part of this study have shown that 

 a regular change in the ratio of chironomid larvae belonging to the sub- 

 families Chironomidae, Tanypodinae, Orthocladiinae takes place in 

 polluted waters. Clean waters are dominated by Orthocladiinae larvae, 

 and polluted waters by Tanypodinae larvae. A pollution index (K) may be 

 developed based upon the relationship between the representatives of 

 these three subfamilies: 



K = 



a or 



where: 



a^- = index value of Tanypodinae 

 a cn = index value of Chironomidae 

 K or = index value of Orthocladiinae 



147 



