Sustainable Marine Structures

Small island environments are highly vulnerable to plastic and microplastic pollution due to constant exposure to ocean debris and limited waste management. Con Co Island in the Gulf of Tonkin is a prime example. Despite its rich marine ecosystem, the island faces severe environmental stress from household activities, commercial fishing, shipping, and tourism. To monitor the distribution of plastic waste across ecological zones, this study employed a comprehensive, multi-method approach. The methodology combined drone (UAV) imagery analyzed with the ResUNet50 deep-learning model, SCUBA diver seabed surveys, domestic water testing, and Delft3D-Part numerical simulations. The findings revealed that plastics account for over 90% of coastal solid waste, with an estimated total accumulation of 8,379 t (an average density of 1.4 kg/m). Underwater surveys showed that plastic litter covers between 1.0% and 31.25% of the seabed, primarily concentrated near residential areas and the local harbor. Furthermore, microplastics were detected in every single domestic water sample tested, with concentrations ranging from 0.34 to 2.75 ng/L. Simulation data also indicated distinct seasonal variations in microplastic dispersion, heavily driven by local currents, monsoons, and eddy formations. Unlike previous studies that relied on single-method assessments, this integrated approach merges surface, benthic, water, and hydrodynamic data to offer a unified perspective. These insights provide a robust scientific foundation for developing better pollution mitigation strategies and managing marine protected areas in small island settings.