Nina Benistati

In contemporary times, it is of utmost significance to identify the impact of climate change on aquatic ecosystems. It is particularly important to evaluate the interactions between the biotic components and water flow. Understanding the influence of vegetation distribution on flow patterns and turbulence structure is cardinal to analysing diffusion and transport processes. Additionally, the alteration of the hydrodynamic conditions impinges on the habitat of living organisms. Literature suggests that freshwater mussels (FMs) are pivotal fauna in rivers, and the suitability of their habitat depends on the type of substrate and the hydrodynamic conditions. However, very little is known about the behavioural response of FMs to flow conditions variations.

The primary aim of my PhD program, partially supported by PRIN2017 “ENTERPRISING” (local unit Palermo University, Resp. Prof. Donatella Termini), in association with the University of Trento, CNR-IRPI, and CNR-IRSA, is to monitor the response of FMs to hydrodynamic stress, particularly during extreme events. The research followed a preliminary analysis of the effects of flexible vegetation on flow characteristics.

The interactions between water flow and vegetation have been investigated using flow velocity data collected in a laboratory channel with submerged and flexible vegetation on the bed. Then, experiments in a laboratory flume with Unio elongatulus freshwater mussels on the bed were conducted over both sand and gravel substrate to monitor the FMs’response to hydrodynamic stress. The valvometry technique was used to record the response of the FMs to the variation of the flow rate, mimicking a flood event. my PhD program also included the analysis of data collected in the Paglia River where another Hall sensors monitoring apparatus has been installed using mussels Unio mancus as part of the ENTERPRISING project.

The results of the study of flow/vegetation interactions confirmed that the presence of vegetation influences the lateral diffusion processes, modifying the sediment transport, and the mixing of transported quantities. Analysis of the FMs’ response to the hydrodynamic stress monitored in the laboratory straight flume showed that the frequency of FMs valve opening/closure increases as the variation in flow rate increases. This behavioural response is more evident in the presence of sediment transport. The analysis of data collected in the Paglia River confirmed the results obtained in the laboratory, demonstrating that FMs may be employed as an ecosystem warning alarm.