A Plastic Budget Methodology to Model plastic pathways, degradation and storage in rivers, coastal areas and open seas

A Plastic Budget Methodology to Model plastic pathways, degradation and storage in rivers, coastal areas and open seas

Rivers play a significant role in marine pollution, acting as major conduits for the transport of contaminants, including plastics, from terrestrial environments to the sea. Globally, river systems are responsible for carrying a substantial portion of the plastic waste that eventually accumulates in marine ecosystems, contributing to the growing problem of ocean plastic pollution. Understanding the dynamics of plastic transport via rivers is crucial for addressing this environmental challenge.

In the Italian context, the Arno and Ebro rivers have been identified as critical contributors to marine plastic contamination in the Mediterranean region. Both rivers discharge into areas of ecological and economic significance, making it essential to understand their roles in the transport and fate of plastic waste. Despite the recognition of their importance, significant knowledge gaps remain regarding the mechanisms and pathways of plastic movement from these rivers to the surrounding marine environment.

One major uncertainty lies in quantifying the amount of plastic that moves along the surface of the water versus the portion that sinks to the riverbed or sea floor. Surface plastics can be carried over long distances, potentially impacting regions far from their sources, while submerged or sedimented plastics may settle closer to the river mouth, posing localized risks to benthic ecosystems. The lack of precise data on these processes limits our ability to predict the spatial distribution of plastic pollution and its ecological consequences.

Additionally, the trajectories of plastic particles transported by river currents and oceanographic processes remain poorly understood. Key questions include: How far do plastics travel from the river mouth? What environmental factors influence their pathways, such as wind, tides, and the physical characteristics of the particles? These uncertainties hinder the development of effective management strategies to mitigate plastic pollution and protect marine habitats.

Another critical gap involves the sedimentation of plastics and the distance from the river mouth at which they settle. Determining where and how plastics accumulate on the seafloor is essential for assessing the long-term environmental impact of this pollution. The interaction between riverine plastic inputs and other diffuse sources of pollution along the coast further complicates the picture, as these combined contributions create a more significant and widespread contamination issue.

To address these gaps, interdisciplinary approaches are needed, combining field observations, laboratory experiments, and advanced numerical modeling techniques. By improving our understanding of the transport, trajectories, and fate of plastics originating from rivers like the Arno and Ebro, we can better assess their contributions to marine pollution and inform targeted intervention strategies to reduce their impact on the Mediterranean Sea.

To develop a lagrangian model coupled to the regional oceanic model to model the mediterranean sea area including the two specific areas of the river mouths of river Arno and Ebro, to determine which are the contributions of these rivers in plastic pollution by validating the model through sampling data.

The ROMS (Regional Oceanic Modeling System) model, coupled with the Lagrangian particle-tracking model L-TRANS, is used to simulate the transport and dispersion of particles in the study area. The validation of the model is carried out using field data derived from surface and seafloor sampling, ensuring its reliability for analyzing particle dynamics and understanding the processes influencing their fate and distribution.