It is difficult to agree with those values for the saprobic valencies 

 and indicator weights which Zelinka and Marvan give for Tubifi&x Tubi&zx, 

 Lunnodfulu-i ko^mzA stcii , and PotamothfUx moldavien&is . The first two 

 species are indicated as characteric of a and p saprobic zones, and the 

 latter only for a saprobic zones. At the same time, it is well known 

 that all of them are typical also of P saprobic zone, and T. tubl^zx is 

 one of the primary species of oligochaets in oligotrophic lakes. 



Other varieties of the system of Kolkwitz and Marson (Knepp, Pantle 

 and Buck) contain arbitrary evaluations of the number of organisms. These 

 do not seem to be sufficiently correct to be applied to benthic animals. 

 The use of the terms "many" "few" in these systems for quantifying 

 organism abundance will have a variable meaning and cannot be applied 

 with certainty. 



Of current wide use for the evaluation of the degree of pollution is 

 a system based on the application of large numbers of benthic taxa. It 

 has been evident for some time that groups of aquatic insect larvae occur 

 in clean waters. Oligochaets, on the other hand, easily resist pollutions 

 and attain great abundance in the sediments enriched with organic matter. 

 Therefore, it is not surprising that indices which account for abundance 

 or biomass of oligochaets, or their separate species (Parele, 1975; Carr 

 and Hiltunen, 1965; Goodnight and Whitley, 1961; Zahner, 1964, and 1965), 

 or compare the ratio of the biomass of insects to that of oligochaets 

 (King and Ball, 1964) are the most widely occurring. 



Evaluation of the degree of river pollution with these indices has 

 shown that some of them are probably correct only for those water-bodies 

 for which they were proposed (American Great Lakes, Boden Lake, the 

 Daugava and the Lielupe Rivers). The index of King and Ball does not 

 account for the seasonal dynamics associated with numbers of insect 

 larvae. Thus, one time collections may lead to incorrect values. The 

 index which deserves attention is the one suggested by Zahner which 

 considers the number of oligochaets, T. tubi^&x and species of the genus 

 LimnodfuZu6. In this system, seasonal dynamics of oligochaets are con- 

 sidered in quite an unusual way. 



The method with the greatest perspective for biological analysis of 

 polluted waters using the composition of the bottom animals seems to be 

 the one proposed by Woodiwiss (1964) for the Trent River. The undis- 

 puted advantage of this method is that it unites the principles of indi- 

 cator values of separate taxa (distinctly fewer than the indicator 

 species list), and the principle of decreases in diversity of the fauna 

 under the conditions of pollution. It is important that Woodiwiss' 

 system of "grouping" is understood to be rather broad. For some animals 

 this implies separate species (larvae Plecoptera, Ephemeroptera), for 

 others it suggests large taxa (e.g., the famely Tubificides) . At the 

 same time, this system reflects a simplification of trophic relationships 

 with respect to pollution, e.g., the decrease in the numbers or disappear- 

 ance of predatory animals. 



143 



