Do mangroves act as a secondary source of plastic during extreme events?

Marine plastic pollution is one of the most visible environmental problems in and around the coastal regions of South East Asia. To fully address the marine plastic pollution problem, there must be a source-to-sink approach, reducing litter at each stage of its pathway to the open ocean. Mangroves are an important and widespread ecosystem in South East Asia on the interface between terrestrial and marine environments, and a key habitat and nursery for a number of species. Mangroves have also been reported to trap plastic litter, potentially acting as secondary sources to coastal marine environments. The Philippines are particularly vulnerable to compound hydrological events due to the seasonal monsoon and typhoons which regularly cross the region. South East Asia is a complex region oceanographically and hydrologically with high loads of plastic litter being exported into the regional seas. To correctly estimate local plastic pollution budgets and understand the transboundary movement of plastic from land to sea, modelling studies must account for the different environmental drivers and strong seasonality of the region. 

Here, we present preliminary results of a modelling study investigating the impact of Typhoon Rai on the retention and contribution of plastic litter by mangrove ecosystems of Cebu Island, the Philippines. The results of a three-dimensional, hydrodynamic model (ROMS) with wind, tidal and wave forcing will be presented. Future plans to apply a Lagrangian particle tracking model informed by in-situ measurements to investigate the behaviour of plastic litter within this typhoon weather system will also be outlined. 

This will help to understand how plastic litter is retained or exported during extreme events around Cebu Island and assess the likelihood of mangroves to act like a temporary sink or secondary source during extreme and mean events. Understanding the role of mangroves under different environmental conditions could clarify another step in the source-pathway-sink model of plastic litter in the region.