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The article presents the relations between the saprobic index S as well as the biocenosis structure indices and BOD5, the latter being the main parameter of the wastewater quality. Estimation was carried out for the essential indices: saprobic index S, taxon richness ΔSr(Δ*), Shannon-Wiener index H (H*), evenness index V (V*), MacArthur's index E (E*) and “proportionality” index P (P*), calculated for saprobes present in wastewater with different levels of pollution (characterized by BOD5 values). For the calculation of the above mentioned indices, numbers and abundances of species (indices without asterisk) as well as the numbers and abundances of easily identified morphological-functional groups (indices with asterisk) were used. To determine the dependences between the indices and BOD5, an analysis of correlation was carried out. Results showed that: (i) the value of BOD5 for treated (or self-purified) wastewater can be assessed most accurately by using index E*—a slightly less precise evaluation of this parameter can be obtained on the basis of indices: H*, S, and H; (ii) bioindication based on biocenosis structure indices (E*, H,* and H) gives results comparable to and even more accurate than those obtained with the use of the saprobic index S; (iii) bioindication can be based on counting individuals (without assigning them to a species) in groups easily differentiated by well-observed morphological features.
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