On June 11, 2025, the public defense of the doctoral thesis by MSc Arianna Varrani entitled Onset of motion of compact-shaped microplastics in open-channel flows was held at the Institute of Geophysics, Polish Academy of Sciences, in Warsaw.
The thesis addressed the issue of microplastic transport in riverine environments, focusing on the incipient motion conditions of compact-shaped particles in open-channel flows with varying bed compositions. Laboratory experiments, conducted at the Hydrodynamic Models Laboratory of the Institute of Geophysics PAS, allowed for determining the bed shear stress thresholds necessary for the mobilization of microplastics on different bed types (homogeneous plastic, gravel, and sand beds). The research involved the use of Doppler velocimetry to characterize near-bed velocity fields and advanced image analysis techniques to track particle motion.
The results provide new insights into the remobilization mechanisms of microplastics in natural channels, contributing to a better understanding of plastic pollution dynamics in aquatic environments.
The thesis was carried out as part of an international collaboration between the University of Bologna, the oldest university in Europe and the Institute of Geophysics PAS. MSc Arianna Varrani pursued her doctoral studies at the University of Bologna, while a part of the experimental research was conducted at the Hydrodynamic Models Laboratory of the Institute of Geophysics PAS in Warsaw, where she is currently employed as an Assistant.
As the candidate emphasised:
“My PhD dealt with a very interdisciplinary topic: microplastics onset of transport in rivers. To complete it, I set up a cotutelle agreement with University of Bologna, Department of Civil Architecture, Environmental and Material Engineering. This allows two titles to be awarded, PhD in Earth Sciences, and in Civil Engineering.”
Supervisors:
- Prof. Paweł Rowiński, DSc (Institute of Geophysics PAS)
- Associate Professor Massimo Guerrero (University of Bologna, Italy)
- Dr Magdalena Mrokowska, DSc, Eng. (Institute of Geophysics PAS, auxiliary supervisor)
Reviewers:
- Prof. Claudia Adduce (Roma Tre University, Italy)
- Dr Alan J. S. Cuthbertson (University of Dundee, Scotland, UK)
- Prof. Rui M.L. Ferreira (Instituto Superior Técnico, University of Lisbon, Portugal)
The public defense attracted numerous attendees. The reviewers participated online, while the second supervisor from the University of Bologna was present on site. The defense included a vivid discussion and a number of questions addressed to the candidate.
Following the defense and discussion, the Scientific Council of the Institute of Geophysics PAS made a positive decision to award MSc Arianna Varrani the degree of Doctor of Earth and Environmental Sciences.
