Are geochemical regime shifts identifiable in river waters? Exploring the compositional dynamics of the Tiber River (Italy)

Caterina Gozzi; Vasilis Dakos; Antonella Buccianti; Orlando Vaselli

doi:10.1016/j.scitotenv.2021.147268

Are geochemical regime shifts identifiable in river waters? Exploring the compositional dynamics of the Tiber River (Italy)

Sci Total Environ. 2021 Sep 1:785:147268. doi: 10.1016/j.scitotenv.2021.147268. Epub 2021 Apr 24.

Authors

Caterina Gozzi¹, Vasilis Dakos², Antonella Buccianti³, Orlando Vaselli⁴

Affiliations

¹ University of Florence, Dept. of Earth Sciences, Via G. La Pira 4, 50121 Firenze, Italy. Electronic address: caterina.gozzi@unifi.it.
² ISEM, CNRS, Université de Montpellier, EPHE, IRD, 34095 Montpellier, France.
³ University of Florence, Dept. of Earth Sciences, Via G. La Pira 4, 50121 Firenze, Italy.
⁴ University of Florence, Dept. of Earth Sciences, Via G. La Pira 4, 50121 Firenze, Italy; CNR-IGG Institute of Geosciences and Earth Resources, Via G. La Pira 4, 50121 Firenze, Italy.

PMID: 33940415
DOI: 10.1016/j.scitotenv.2021.147268

Abstract

Rivers are dynamic and sensitive systems that change their chemical composition from source to mouth. This is due to the influence of a set of variables controlled by hydro-litho-eco-atmospheric processes and anthropic pressures which are, in turn, affected by catchment attributes. This work proposes a new way of thinking about river geochemistry focused on environmental interconnections rather than single chemical variables. Abrupt changes in the system state (composition) of a certain environmental media, driven by perturbations, may trigger Geochemical Regime Shifts (GRSs). This eventuality is explored in the Tiber River (central Italy) chemistry by Compositional Data Analysis, robust Principal Component Analysis and score-distance graphs. Data variability and the interlinks between response and forcing variables are investigated for different drained areas. A potential GRS is detected for major elements in the lower reaches resulting from a threshold-like state response caused by lithological forcing. On the contrary, trace elements respond gradually to environmental drivers, showing no abrupt changes. The findings outline mechanisms and factors influencing the river's self-restoring capability at a basin-wide scale, providing a better comprehension of the circumstances controlling the equilibrium dynamics of river water systems.

Keywords: Compositional Data Analysis; Environmental system science; Regime shift; River chemistry; Tiber River.