Environmental changes in river chemistry: A compositional approach for effective monitoring and management

River ecosystems are fundamental to sustaining global water and biogeochemical cycles, as well as supporting biodiversity. However, increasing pressures from human activities and climate change pose significant challenges to the stability of these systems. This study examines the sources of geochemical variability in the river waters of the Tiber River Basin (central Italy) to assess the system's sensitivity to environmental changes, with a special focus on seasonal variations. The proposed methods combine the exploration of multivariate parameters, known as Principal Balances (PBs), within the Compositional Data Analysis framework, with the interpretation of basins of attraction in their density distributions. Results indicate that NO₃^-, largely influenced by human activity, drives higher variability in water chemistry, overshadowing the natural geochemical processes such as water-rock interactions, which manifest at lower variability levels. Additionally, seasonal effects were explored highlighting greater sensitivity during dry periods and relevant changes in the proportions of some solutes (i.e. Cl^-/Na⁺). The PBs approach offers valuable insights into system functioning principles compared to Principal Component Analysis, demonstrating a wider applicability, particularly when combined with the interpretation of the distributions. These findings emphasize the dominant role of anthropogenic factors in shaping river water chemistry, highlighting the importance of identifying key parameters for monitoring environmental changes and informing water resource management and policy decisions. However, much work remains to improve the understanding of the link between basins of attraction and distribution parameters, in order to explore their role in monitoring the system's sensitivity to global environmental changes.