Modelling the uptake and exchange of microplastics in marine ecosystems using a novel, integrated system of high-resolution numerical models

Abstract

Microplastic (mP) pollution is indicated as an area of concern in the marine environment. However, there is no consensus on their potential to cause significant ecological harm and a comprehensive risk assessment of mP pollution is unattainable due to gaps in our understanding of their transport, uptake, and exchange processes. To contribute towards addressing these knowledge gaps, an integrated system of numerical models is proposed consisting of a model for the uptake and exchange of mPs at lower trophic levels in marine ecosystems which receives input from a mP transport model and is forced by the NEMO-ERSEM model. The mP uptake and exchange processes that are potentially significant at lower trophic levels are identified in a literature review and translated into mathematical form by drawing analogues with existing models for the uptake and exchange of persistent organic pollutants. The mP transport model is based on the advection-diffusion equation with additional terms for the input and output of mPs and their vertical gravitational transport. Six empirical models to calculate the settling velocity of regularly and irregularly shaped particles are evaluated to identify the most appropriate model for implementation within the mP model framework. The evaluation also provides evidence that the mP transport model can be simplified by assuming that the mP settling velocity is constant over time and depth. A case study is undertaken to consider implementation of the model framework in the Northwest European continental shelf region. Data is extracted to parameterise the riverine input of mPs, which indicates that the North Sea may be exposed to significant levels of mP contamination. Spatial interpolation methods are used to collate the available data and research and make a basic, preliminary estimate of the atmospheric deposition of mPs to the model domain. Based on properties of mPs involved in interactions with lower trophic level organisms in lab and field studies, it is recommended that the mP model framework must simulate fibrous and fragment mPs that are less than 30µm in size and should include positively, negatively, and neutrally buoyant polymers. The available data which is collated for model parameterisation, calibration and validation does not satisfy these requirements and is also impacted by further issues. Therefore, it is not currently feasible to implement the model system in this region. Thirteen recommendations are made to provide information to researchers and policy makers regarding the improvements to sampling activities, additional research and legislative measures required to obtain the necessary data to successfully implement the proposed model framework and produce relevant information for the risk assessment and remediation of mP pollution in the marine environment.

Thesis is embargoed until 31 July 2025.

Date of Award	Jul 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	NERC QUADRAT & Agri-Food and Biosciences Institute
Supervisor	Jennifer McKinley (Supervisor) & Gary Hardiman (Supervisor)