Testing the coherence of several macroinvertebrate indices and environmental factors in a large lowland river system (Volga River,Russia)

In contrast to most large rivers in Europe, the biggest European river Volga including its tributaries has still remained uncontaminated in its headwaters. Therefore the upper Volga River system represents an appropriate system for investigation of relations of bioassessment indices with natural environmental factors. Moreover, it allows the definition of reference conditions for medium-size and large lowland rivers in Europe. The aim of this study was to analyse relations between Saprobic Index (SI), SPEAR indices, and other macroinvertebrate community indices and basic environmental factors in the upper Volga River system. Besides, preliminary ecological status classification (according to the EU Water Framework Directive) was proposed for SI and SPEAR_pesticides indices for the system investigated. The analysed data set contained information on macroinvertebrates, basic habitat characteristics and water physico-chemical parameters from 53 sample sites. The results showed that SI and SPEAR indices were independent of channel width and related river longitudinal factors. Furthermore, the results indicated the index SPEAR_pesticides to be potentially applicable across different types of watercourses as well as across different biogeographical regions in Europe showing similar boundaries of ecological status classes (at least between High, Good, and Moderate). A Multi-Habitat-Sampling method was recommended for SPEAR_pesticides. Saprobic reference conditions of the lowland rivers were found to be beta-mesosaprobic. The relatively high boundary between High and Good classes resulted from naturally high organic matter concentrations. Due to indicating common pollution sources (i.e. organic, agricultural and industrial), the herein suggested methodologies have a potential to be applied in other large river systems in Europe. The reference condition characteristics described for the headwaters of the Volga River system can be used as a reference for medium-sized and large rivers in the regions where establishment of reference sites of these types is impossible (e.g., many regions in Europe).