Abstract
Sediment transport is a fundamental geomorphic process that governs river morphology, ecosystem dynamics, and sediment budgets in mountain environments. Understanding its spatial and temporal variability is essential for predicting how fluvial systems respond to climatic forcing and catchment scale disturbances. From an ecological perspective, analysing sediment dynamics and transport rates is equally crucial, as sediment fluxes influence aquatic habitats, mitigate natural hazards, and support the management of reservoirs by preventing siltation. In recent decades, climate warming has rapidly altered environmental conditions by increasing air temperatures, accelerating glacier melting, and enhancing the frequency of intense storm events responsible for debris flows and landslides, which deliver large amounts of sediment to river networks. For these reasons, monitoring sediment transport dynamics is a key and indispensable component in the study of mountain fluvial systems. Sediment transport can be classified into two main components: bedload and suspended load, three if dissolved ions transport is also considered. Since the 1990s, continuous, indirect, and automated instruments have been increasingly used to monitor sediment transport in rivers. Among the most common are the Swiss geophone plates and Japanese pipe microphones, designed to record bedload transport, and turbidimeters to measure suspended sediment concentration. These indirect methods are typically calibrated and validated using direct sampling techniques such as sediment traps and bottle samplers, which collect both bedload and suspended load samples. The objective of this P.hD. thesis is to analyse and compare bedload and turbidity data recorded at the gauging stations of three mountain catchments: the non-glacial Gader River basin (Gader Valley, 389 km²; monitored since 2019), the glacial Sulden River basin (130 km², tributary of the Etsch River; monitored since 2014), both located in the northeastern Italian Alps, and the volcanic Ashiarai-dani River (6.5 km²; monitored since 2011) in the Central Japanese Alps. The specific aims of the study are: (i) to estimate sediment yield and quantify the proportions of bedload and suspended load over different time scales (hourly, monthly, annual); (ii) to assess the influence of glacial processes on sediment dynamics and determine the additional sediment contribution to a glacial river network due to ice melt, compared with a non-glacial basin; (iii) to examine how climate change affects sediment transport during extreme hydrological events and during glacial ablation under rising temperatures; and (iv) to evaluate sediment availability and source–channel connectivity using hysteresis cycle analysis. The results demonstrate that climate change is influencing Alpine sediment dynamics, by increasing air temperature and reducing snowfall, which prolongs the glacial ablation period due to decreased snow cover. In non-glaciated mountain catchments, precipitation represents the main driver of sediment mobilization. The highest transport rates occur during the summer months (May–October). Intense rainfall and debris flow events can also affect sediment transport patterns in the following years. Moreover, smaller catchments exhibit higher sediment transport rates due to their faster hydrological response compared to larger basins. Across the Italian studied catchments, the suspended load constitutes the dominant transport fraction, typically exceeding 80% in non-glacial basins and 95% in glacial ones. Coarser particles are generally mobilized during high-intensity rainfall events in non glacial systems on the Japanese basin. These findings are significant because they provide a comparative analysis of three mountain catchments with distinct hydroclimatic settings yet exhibiting consistent sediment transport behaviour when monitored using similar instruments.