Hydromorphological complexity as a driver of the diversity of benthic invertebrate communities in the Czarny Dunajec River, Polish Carpathians

To verify whether the variability in benthic invertebrate communities along the mountainous Czarny Dunajec River is mainly driven by the variation in hydromorphological or water quality, diversity of the communities was determined for 18 cross-sections with 1-5 low-flow channels and compared with the complexity of physical habitat conditions and with physico-chemical water quality. An increase in the complexity of flow pattern in the river was associated with increasing cross-sectional variability in physical habitat parameters. Distinct hydromorphological characteristics of the cross-sections with a given number of low-flow channels were especially pronounced if the analysis was limited to the parameters measured directly, whereas calculated complex hydraulic and sedimentary variables represented information overload. Taxonomic richness of the invertebrate communities was unrelated to physico-chemical water parameters, which consistently pointed to the high water quality. Instead, the richness positively correlated with a degree of variation in physical habitat parameters and was best predicted by the number of low-flow channels in a river cross-section. This study indicates that physical habitat complexity in a mountain river can be considered a proxy to the diversity of its invertebrate communities and that restoration of such complexity will be necessary for future recovery of invertebrate communities in impacted river sections.