Luigi Fraccarollo

Understanding the impact of hydrodynamic variations, induced by climate change or anthropogenic pressures on aquatic habitats is necessary for effective freshwater conservation. In this work, an ecosystem‐impact approach is applied by using freshwater mussels (FMs) as biological indicators of perturbations of aquatic environment. The valvometry technique is used to investigate FMs' response in different substrate compositions and environments. Laboratory flume experiments were performed with Unio elongatulus over two substrates (gravel and sand), and in situ pilot installation with stuck Unio mancus was realized in Paglia river (Umbria, Italy). FMs' response to flow discharge variation was analyzed in terms of average gaping frequency ( Fa ) and gaping amplitude ( Aa ). For the field case, the analysis concerned valvometry data recorded during a moderate flood on 31 March 2022. Both laboratory and field‐based experiments showed that FMs promptly react to flow perturbation increasing values of Fa and decreasing values of Aa as the percentage of flow discharge variation, ΔQ/Q _bp (being ΔQ the flow discharge variation and Q _bp the flow discharge before the perturbation), increased. Based on the data, a threshold condition was derived which can be used as an ecosystem alarm criterion based on mussel behavior. This could help practitioners, academic ecologists and controlling agencies in decision‐making processes. In this view, the paper also presents, to our knowledge for the first time, a [ Fa , ΔQ/Q _bp ] benchmark graph which could be helpful in guiding the selection of the ecosystem alarm criterion in clear water, constituting a base for future development in natural conditions with suspended materials.

Quantifying the effects of external climatic and anthropogenic stressors on aquatic ecosystems is an important task for scientific and management progress in the field of water resources. In this study, we propose an innovative use of biotic communities as real-time indicators, which offers a promising solution for directly quantifying the impact of these external stressors on aquatic ecosystems. Specifically, we investigated the influence of natural river floods on biotic communities using freshwater mussels (FMs) as reliable bioindicators. Using a well-established valvometry technique, we measured the valve-opening behaviour of FMs, considering both amplitude and frequency. The valve gap movement of the FMs was monitored by installing a magnet on one valve and a Hall effect sensor on the other valve and recording the magnetic field between the magnet and the sensor itself using an Arduino board, which changes according to the distance between the two valves. The recorded data was then analysed using the Continuous Wavelet Transform (CWT) analysis to study the time-dependent frequency of the signals. The experiments were carried out in a laboratory flume and in the River Paglia (Italy). The laboratory experiments were carried out with FMs in two configurations: freely moving or immobilised on vertical bars. The immobilised configuration was necessary for the field application to prevent the FRMs from packing against the downstream wall of the protection cage during floods. These experiments allowed us to verify that immobilised mussels show similar responses to abrupt increases in flow conditions as free mussels, but produce more consistent and interpretable signals than free mussels due to the reduced number of features resulting from movement constraints. We then analysed the response of thirteen immobilised mussels in real river conditions during a moderate flood on 31 March 2022. The FMs in the field showed a rapid and significant change in valve gap frequency as the flood escalated, confirming the laboratory results. These results highlight the effectiveness of using FMs as bioindicators for assessing flood impacts on aquatic ecosystems, and emphasise the utility of CWT as a powerful signal processing tool for analysing valvometric time series. The study proposes the integration of FM valvometry and CWT for the development of operational real-time Biological Early Warning Systems (BEWS) aimed to monitor and protect aquatic ecosystems.

Global warming has lead concerns about more frequent high intensity rainfall events and increasing river floods. Changes in the river hydrodynamics affect the biological communities which are controlled by the interplay between physical-chemical and hydraulic processes. Thus, there is increasing interest in identifying the impact of the hydrodynamic stresses, also determined by climate change, on the aquatic environment and, consequently, on the interactions between flow and organisms (Lopez and Vaughn, 2021). To this aim, it is fundamental to use remote sensors to constantly monitor the responses of animals to environmental changes. Among these sensors, bio-indicators have been increasingly used to monitor water quality conditions. Some species, called as “ecosystem engineers”, are especially important in studying the effects of climate changes in rivers (Butler and Sawyer, 2012). The present study considers freshwater mussels which meet the criteria to be considered as typical “ecosystem engineers” and can be considered as sensitive biosensors of environmental disturbance (among others Gerhardt et al. 2006). Monitoring freshwater mussels’ opening and closing valves activities (i.e., valvometric technique) over time has been used to evaluate the behavior of the bivalves in reaction to their environmental exposure. The application of the valvometric technique is not recent and has been mainly applied to analyze the impact of chemical stressors on freshwater mussels. Recent experimental results obtained by the research group of the present work (Modesto et al., 2023; Termini et al., 2023), in sand-bed laboratory flumes with different FMs’ populations, have suggested that the mussels’ behavioural response could be also used as a tool for an early warning system of flow variations in rivers, also in the presence of sediment transport. The present work reports the results both of an experimental investigation conducted in a laboratory flume to analyze the influence of the substrate composition on the freshwater mussels’ response and of an in-situ test conducted in a selected reach of the Paglia river (Italy) to verify the FMs’ response in non-controlled environment. In both cases the FMs’ valvometry data were collected in real-time by using Hall sensors technology. The FMs’ behavioural response was examined in terms of valves’ opening/closure frequency and amplitude. The obtained results have confirmed that FMs’ behavioural response can be used as BEWS for identifying the impacts of hydrodynamic changes in rivers.ReferencesButler DR, Sawyer CF, 2012. Introduction to the special issue: zoogeomorphology and ecosystem engineering. Geomorphology 157–158.Gerhardt A, Ingram MK, Kang IJ, Ulitzur S 2006. In situ on-line toxicity biomonitoring in water: recent developments. Environmental Toxicology and Chemistry 25: 2263–2271.Lopez J. W., Vaughn C.C., 2021. A review and evaluation of the effects of hydrodynamic variables on freshwater mussel communities. Freshwater Biology 66 (9): 1665-1679.Modesto, V. et al. 2023. Mussel behaviour as a tool to measure the impact of hydrodynamic stressors, Hydrobiologia, 850, 807–820.Termini, D. et al. 2023. Identification of hydrodynamic changes in rivers by means of freshwater mussels’ behavioural response: an experimental investigation, Ecohydrology, e2544.

Sediment transport can be observed within the flow of water in rivers, canals, and coastal regions, encompassing both suspended-load transport and bed-load transport. Bed-load transport specifically occurs near the riverbed, playing a crucial role in the formation of the riverbed itself. The current study aimed to explore the process of sediment transport by employing the entropy concept as a theoretical approach. To this end, field data collected using a current meter in the Alaknanda River at Srinagar in India were utilized. A comparison was made between the calculated mean velocity and discharge values and the observed data obtained from the Central Water Commission (CWC), demonstrating a maximum error percentage of 9%. Subsequently, shear velocity was determined for various cross-sections under different flow scenarios. The Shields parameter was then derived from the shear-velocity distribution to evaluate the transport potential of the sediment particles. The model results showed varying bed-load transport rates that increased as the particle size decreased and the discharge rate increased. In conclusion, the study findings highlight the efficacy of utilizing the entropy theory for estimating flow discharge and sediment transport in developing countries.

Directed Energy Deposition (DED) processes necessitate a consistent material flow to the melt pool, typically achieved through pneumatic conveying of metal powder via thin pipes. This study aims to record and analyze the multiphase fluid–solid flow. An experimental setup utilizing a high-speed camera and specialized optics was constructed, and the flow through thin transparent pipes was recorded. The resulting information was analyzed and compared with coupled Computational Fluid Dynamics-Discrete Element Modeling (CFD-DEM) simulations, with special attention to the solids flow fluctuations. The proposed methodology shows a significant improvement in accuracy and reliability over existing approaches, particularly in capturing flow rate fluctuations and particle velocity distributions in small-scale systems. Moreover, it allows for accurately analyzing Particle Size Distribution (PSD) in the same setup. This paper details the experimental design, video analysis using particle tracking, and a novel method for deriving volumetric concentrations and flow rate from flat images. The findings confirm the accuracy of the CFD-DEM simulations and provide insights into the dynamics of pneumatic conveying and individual particle movement, with the potential to improve DED efficiency by reducing variability in material deposition rates.

Quantifying the effects of external climatic and anthropogenic stressors on aquatic ecosystems is an important task for scientific purposes and management progress in the field of water resources. In this study, we propose an innovative use of biotic communities as real-time indicators, which offers a promising solution to directly quantify the impact of these external stressors on the aquatic ecosystem health. Specifically, we investigated the influence of natural river floods on riverine biotic communities using freshwater mussels (FMs) as reliable biosensors. Using the valvometry technique, we monitored the valve gaping of FMs and analysed both the amplitude and frequency. The valve movement of the FMs was tracked by installing a magnet on one valve and a Hall effect sensor on the other valve. The magnetic field between the magnet and the sensor was recorded using an Arduino board, and its changes over time were normalised to give the opening percentage of the FMs (how open the mussels were). The recorded data were then analysed using continuous wavelet transform (CWT) analysis to study the time-dependent frequency of the signals. The experiments were carried out both in a laboratory flume and in the Paglia River (Italy). The laboratory experiments were conducted with FMs in two configurations: freely moving on the bed and immobilised on vertical rods. Testing of the immobilised configuration was necessary because the same configuration was used in the field in order to prevent FMs from packing against the downstream wall of the protection cage during floods or from breaking their connection wires. These experiments allowed us to verify that immobilised mussels show similar responses to abrupt changes in flow conditions as free mussels. Moreover, immobilised mussels produced more neat and interpretable signals than free-moving mussels due to the reduced number of features resulting from movement constraints. We then analysed the response of 13 immobilised mussels under real river conditions during a flood on 31 March 2022. The FMs in the field showed a rapid and significant change in valve gap frequency as the flood escalated, confirming the general behaviour observed in the laboratory in the presence of an abrupt increase in the flow. These results highlight the effectiveness of using FMs as biosensors for the timely detection of environmental stressors related to natural floods and emphasise the utility of CWT as a powerful signal-processing tool for the analysis of valvometry data. The study proposes the integration of FM valvometry and CWT for the development of operational real-time biological early-warning systems (BEWSs) with the aim of monitoring and protecting aquatic ecosystems. Future research should focus on extending the investigation of the responsiveness of FMs to specific stressors (e.g. turbidity, temperature, and chemicals) and on testing the applications of the proposed BEWSs to quantify the impact of both natural stressors (e.g. heat waves and droughts) and anthropogenic stressors (e.g. hydropeaking, reservoir flushing, and chemical contamination).

The aim of this study is to investigate the impact of natural river floods on biotic communities. To this purpose, we used freshwater mussels (FMs), recognized as one of the most reliable bioindicators in aquatic environments. A well-established valvometry technique was applied to measure the FMs valve gaping behaviour, considering both gaping amplitude and frequency. The mussels have been employed in two distinct configurations, either free to move or stuck on vertical bars. We performed experiments in a laboratory flume and in the Paglia River (Italy). The FMs valve gaping movement was first recorded, then the continuous wavelet transform (CWT) analysis was applied to the signals to get the time-dependent frequency of the signals. Laboratory experiments allowed to assess to what extent stuck mussels react differently than free mussels to abrupt increases in flow conditions. Subsequently, we examined the response of thirteen stuck mussels installed in real riverine conditions during a moderate flood occurred on March 31, 2022, with a rapid increase of the water level. The experimental results demonstrate that stuck mussels produce signals that are more consistent and easier to interpret compared to free mussels, primarily due to the reduced number of features resulting from movement constraints. The stuck mussels in the field showed a sharp and timely change of valve gaping frequency as the flood ramped up, thus confirming the findings in the laboratory. The results highlight the effectiveness of using FMs as bioindicators for assessing the impact of floods on the aquatic ecosystem, and the utility of CWT as a suitable signal processing tool for analyzing valvometric time series. These findings provide a pathway towards the integration of FMs valvometry and CWT for the development of operational real-time Biological Early Warning Systems (BEWS) aimed at the monitoring and safeguarding of aquatic ecosystems.