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Freshwater mussels (FMs) are useful bioindicators to detect environmental disturbances. However, studies that evaluate FMs suitability for monitoring the hydrodynamic stressors impact are lacking. Since future climatic scenarios predict an increase in frequency and intensity of extreme events, understanding how flood conditions affect freshwater organisms are crucial for their conservation. In this study, we performed experiments in an artificial flume to evaluate the eligibility for FMs behaviour for developing a tailored biological early warning system (BEWS). For this, we used the valvometric technique (Hall magnetic sensors) to measure the FMs valve gaping behaviour when subjected to increasing discharges/sediment transport mimicking the onset of floods. After analysing baseline behaviour in non-stressful conditions, we performed experiments in steady and transient conditions to verify the FMs' response and the threshold that prompted it. Under steady conditions, FMs maintained a constant gaping frequency that characterizes their normal behaviour. The FMs promptly reacted to discharge variations with sediment transport, showing a transition from their normal behaviour to higher valve gaping frequencies. We demonstrated that FM transition behaviour is a useful tool to measure hydrodynamic stressors. A future step will be the application of this BEWS on natural ecosystems to assess possible hydrodynamic changes in real-time. [ABSTRACT FROM AUTHOR]

Stream sediments move at low flow forming migrating ripples. These ripples can cover substantial areas where benthic communities experience erosion-resting cycles of sand grains. Sediment surface and interstitial space is colonized by meiobenthos, an assemblage of microscopic invertebrates. Here we describe how sediment migration influences the structure of the meiobenthic community. We sampled migrating and stationary sediment patches in five streams. Sediments in migrating ripple patches were characterized by coarser grain size and higher oxygen concentration, but less organic matter and chlorophyll than stationary patches. Meiobenthos was more abundant in the superficial layer of stationary sediment compared to the underlying layer, whereas comparable abundances were observed in both layers of migrating patches. This suggests that ripple migration enhances the vertical mixing of interstitial communities. Among the environmental drivers measured, meiobenthos community structure was most related to sediment transport regime: Rotatoria were more abundant in migrating patches, whereas Chironomidae, Ceratopogonidae, Copepoda and Hydrachnidia were more abundant in stationary patches. Body-size structure was affected by sediment migration, with fewer larger organisms in migrating ripples. By modifying the distribution of benthic resources and of meiobenthic consumers, ripple migration likely affects energy flow paths through benthic food webs. [ABSTRACT FROM AUTHOR]

The presented study investigates the evolution of artificial gravel placements for Atlantic salmon and sea trout in Aurlandselva in Western Norway. Various monitoring methods have been applied including (i) quantifying the spatial extent and dynamics of spawning sites over the monitoring period, (ii) grain size distributions as well as (iii) applying numerical hydraulic and sediment transport modelling with the aim to test the predictability of such numerical tools. The spawning sites were not clogged by fine sediments, but were reshaped due to scouring and sediment transport. The scouring resulted in a volume loss of the gravel banks between 32 and 95% in the monitoring period of 5 years. The application of hydrodynamic-numerical modelling, however, showed that the modelling methods were not sufficient to predict erosion of the gravel or the site. The study showed that the areas are sensitive especially to local scale micro-topographical roughness elements. The complex three-dimensional hydraulic processes and the coarse substrate in the non-fluvial river environment makes it impracticable for multi-dimensional modelling to predict dynamics of gravel. A novel sediment criterion was introduced to estimate the near-bottom turbulence by relating the dm of introduced gravel compared to the d90 of the bed surface substrate composition. [ABSTRACT FROM AUTHOR]

Mediterranean rivers are hotspots for biodiversity, and riverine species are adapted to regular physical perturbations that affect channel morphology during flashy rainfall-runoff events. Dams alter flow regimes, changing flood magnitude and frequency; they also interrupt the continuity of sediment transport. Changes in both flood and sediment transport regimes affect downstream channel dynamics and the ecological functioning of fluvial systems. This paper examines the effects of flow regulation on bed disturbance, invertebrate assemblages and their biological traits in a Mediterranean river (the Siurana, NE Iberian Peninsula). Results are put in the broader context of the whole Ebro river catchment. The Siurana Reservoir causes a complete inversion of the seasonal flow regime and reduces flood magnitude notably. Upstream from the reservoir, torrential floods mobilize surface and subsurface bed materials, regularly disturbing the physical habitat; downstream, geomorphological activity in the channel is almost nonexistent. Altogether, damming causes significant differences in taxonomic composition of the benthic invertebrate communities; density and biomass increase notably below the dam although diversity decreases. At the broader scale taxa with active aerial dispersal traits dominate unregulated reaches in areas with marked Mediterranean hydro-climatic regimes, whereas reaches with more stable regimes are characterized by fully aquatic detritivore species. [ABSTRACT FROM AUTHOR]

The effects of compacted algal mats grown attached to sediments on the benthic biogeochemistry and macrofauna were investigated in a tropical estuarine mudflat in northeastern Brazil. During the study, the algal mat was restricted to algal patches and two types of patches were recognized based on the physiological stage (live and decomposing algae). Quantitative analyses of sediment parameters were obtained within and outside each type of algal patch. Sediment biogeochemistry and fauna below the algal patches were significantly affected in comparison with sediment not covered by algae. Physiological stage influenced the sediment concentrations of organic matter, carbohydrates, phaeopigments, total-P, and total-N. Macrofauna declined markedly in both algal patches, with strong effects regardless of the physiological stage. The results showed that the effect of compacted algal mats on environmental parameters depends on the physiological stage of the algae, and this should be considered in analyses of benthic systems. The adverse effects observed on macrofauna highlight the importance of monitoring and managing the development of algal mats in tropical estuaries. [ABSTRACT FROM AUTHOR]