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We present the results of a comprehensive study of five saline rivers in the arid region of Lake Elton, including hydrobiological surveys of plankton and benthic communities. The DIABLO method was used for a statistical analysis of the associative links between the species structures of the macrozoobenthos, meiobenthos, and zooplankton communities. This method combines multidimensional ordinations based on n blocks of observations and uses special algorithms of canonical correlation. It is shown that a significant portion of the cumulative variation in the data can be explained by a consensus configuration based on information common for all the three groups of observations. The diagrams, constructed and analyzed with the use of the cluster and Generalized Procrustes analysis, enable us to isolate stable associations of taxa typical for particular biotopes with homogeneous environmental conditions. We have constructed graphs of correlation pleiades and calculated indicator significance for particular species of macrozoobenthos, meiobenthos, and zooplankton. It is shown that highly mineralized systems of arid regions are not always characterized by a pronounced specification of life forms of plankton and benthic communities. The interpenetration between benthic and plankton animals results in a high portion of mixed ecological groups. Plankton and benthic communities correlate well enough with each other, which testifies to a close relationship between them due to both biotic interactions and a mutually agreed response to changes in aquatic environment factors. These data enable us to consider the plankton and benthic communities of highly mineralized rivers a nonequilibrium dynamically changing consortia of species.

The data on seasonal and interannual changes in the taxonomic, structural, and quantitative characteristics of macrozoobenthos communities in rivers with a high salinity gradient are given. A total of 91 benthic invertebrate taxa have been revealed, which were dominated by Cricotopus salinophilus, Chironomus salinarius, C. aprilinus, Tanytarsus kharaensis, Microchironomus deribae, Glyptotendipes salinus (Diptera: Chironomidae), Culicoides (M.) riethi, Palpomyia schmidti (Diptera: Ceratopogonidae), Paranais simplex (Oligochaeta), and Ephydra sp. (Ephydridae) in different years. The fauna of benthic communities is mainly represented by eurybiontic halotolerant species with different ranges of resistance to salinity. The taxonomic composition and diversity of macrozoobenthos communities are closely correlated with water salinity in the range from 4 to 41 g/L; the complex of hydrological and hydrophysical factors (depth, overgrowing, water temperature, pH, etc.) control the distribution and abundance of species.

Indicator valences, taking into account the regional features of the middle and lower Volga River basin of water quality classes for the benthofauna of lowland rivers, are calculated. The lists of 450 species that can be used to indicate pollution are given. An advanced method of estimating bioindication factors of bottom organisms is used. The results of calculations can be used for the quality intercalibration of the surface water of lotic systems.