Are microplastics changing biogeochemical cycles as we know them?

As the main repository for plastic waste, the ocean is negatively affected by persistent synthetic contaminants. Marine plastic pollution has been observed to negatively affect ecosystems through entanglement, smothering, and exposure to pathogens or toxic chemicals upon ingestion. Unintentional ingestion of microplastics can lead to health issues in organisms across all trophic levels and more recently have been found to impact biogeochemical cycles. Microplastics can cause a decline in carbon sequestration by reducing the ability of microalgae to take part in carbon fixation and impacting the sinking rates of faecal pellets egested by zooplankton. In addition to microplastics physically altering the carbon cycle, photo-oxidised microplastics can release methane, hydrocarbons, dissolved organic carbon (DOC), and other chemical additives into the marine environment. This can potentially lead to changes in nutrient cycling due to microbial interactions with an alternative source of carbon. 

This project will investigate microbial interactions with plastic in fjordic systems and the impact of the altered activity on biogeochemical cycles. The study area is Loch Etive, which is located on the west coast of Scotland and is ecologically complex with a range of biodiversity due to the various habitats across the salinity gradient. In addition to ecological importance, Loch Etive is home to fish farms which serve as a major industry in the Scottish economy. Understanding potential issues that come from microplastic pollution in Loch Etive is vital to protecting the ecosystem services and the aquaculture industry this sea loch provides. 

Supervisors

Professor Bhavani Narayanaswamy (DoS; SAMS-UHI) 

Dr Arlene Ditchfield (SAMS)

Professor William Austin (University of St Andrews)

Start date: 2nd March 2026

Funder: SUPER DTP

Sampling site: Loch Etive, Scotland