Dispersão de microplásticos induzida por eventos extremos na Baía de Pemba

Abstract

The Pemba Bay region is an area of enormous ecological importance for the marine environment, recognized for its rich biodiversity in marine and coastal resources, including the shelter of one of the largest coral reefs in Mozambique. However, Pemba Bay and its associated resources have been threatened by extreme weather events, such as intense tropical cyclones. Tropical cyclones are known to cause enormous destruction of infrastructure and ecosystems in the regions through which they move. In addition to the destruction, cyclones can also alter the dynamics of the sea, and therefore impact on the transport and distribution of several pollutants, including microplastics, which are tiny particles derived from plastics. The present research aimed to study the dispersion of microplastics in Pemba Bay, under normal hydrodynamic conditions and during the occurrence of extreme weather events such as tropical cyclones. For its implementation, the study used the Delft3D model to simulate hydrodynamics and its influence on the transport of microplastics in the Pemba region. Simulations were carried out for the year 2019, the period of occurrence of tropical cyclone Kenneth, one of the most intense cyclones to occur in the Mozambique Channel region in the last 100 years. The model revealed that the hydrodynamics of the region is characterized by semi-diurnal tidal oscillations with the tide height reaching approximately 2.2 m. And with currents associated with the tides, they were between the maximum magnitudes of 0.3 and 0.4 m s-1 during the spring tide and 0.12 m s-1, at neap tide. The in-situ occurrence of microplastics was also analyzed to later identify the locations of their highest concentration, considering the normal local hydrodynamics and under the effects of cyclonic winds. In situ analyses indicate the identification of approximately 130 particles from a total of 9 water samples and 7 coastal sediment samples. The particle dispersion model revealed that during both the flood and ebb tides, the particles were mostly transported to the northeast of the bay, driven by tidal currents and surface winds. Concentration peaks were identified during the neap tide and the spring tide. For the scenario of the occurrence of Cyclone Kenneth, with winds of magnitudes of approximately 25 m s⁻¹ and currents of 0.55 m s⁻¹, there was an intensification in the transport and accumulation of particles along the northeast coast of the region.