The relationship between the river channel parameters – morphological, hydraulic and substrate – and the composition and distribution of macrozoobenthos communities was studied on the 75 m channel reach of the stream (Teplička brook, Strážovské vrchy Mts., Slovakia) located at the altitude of 256 m; with average width 4 m, depth 0.25m, average current velocity 0.32 m s⁻¹ and discharge in sampling season 0.2 m³s⁻¹. Following the River Morphology Hierarchical Classification (RMHC), the fluvial geomorphological research was realised on the selected channel reach – taxon defined in accordance to RMHC. The plane bed and a riffle-pool channel types have been identified in the investigated channel reach. At the habitat level morphological and hydraulic features represent an alternative approach of habitat assessment in order to gain representative macroinvertebrate sample in stream assessment according to the Water Framework Directive (WFD). The morphological units defined in terms of Froude (Fr) and Reynolds (Re) numbers differed in the extent of the shear stress and turbulence of the water environment. Also Fr and Re values rose in the row of flow types: standing water (SW) – scarcely perceptible flow (SP), smooth flow (S) – rippled (R) – unbroken standing waves (USW) – broken standing waves (BSW) – chute (CH). Different taxa and feeding groups preferred different morphological units and flow types. In terms of morphological units, runs, bars, edgewaters and scours were generally inhabited by the lowest abundance of all invertebrate groups; only Gastropoda reached the higher abundance in these habitats. Glides, pools and backwaters were inhabited by somewhat higher numbers of invertebrates, Oligochaeta and Bivalvia dominated here. Units with organic substrate (moss on boulder clusters and roots) together with rapids and riffles were characterised by high abundance mainly of Gammaridae and Simuliidae. Regarding flow types, standing water separated from others by its low abundances of taxa group but Gastropoda and Bivalvia. SP, S and R types were preferred by Oligochaeta and Chironomidae, while Gammaridae and Simuliidae dominated in standing waves (USW, BSW) and chutes. Also distribution of feeding groups followed the gradient of local environmental conditions. Significant correlations of feeding groups and flow types, current velocity, Fr, Re and depth were observed. Organic substrates played an important role in distribution and abundance of the macrozoobenthos. Overall abundance and also abundance of Ephemeroptera, Trichoptera, Coleoptera and Diptera was significantly higher in the moss or roots compared to other habitats.. Benthos communities of these habitats showed similarities with habitats in the highly turbulent environment (riffles, rapids).
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