A risk assessment of marine plastics in coastal waters of a small island: Lessons from Ambon Island, eastern Indonesia

This study provides the first implementation of environmental risk assessment (ERA) regarding marine plastic accumulation (environmental threat) in the water body of small islands in the Indonesian Coral Triangle region (a case study in Ambon Bay of Ambon Island). Ambon Bay is a tropical fjord system with outer Ambon Bay (OAB) separated from inner Ambon Bay (IAB) by a shallow sill. The emphasis of ERA was to combine coastal demography determining the probability of occurrence of the threat and flushing capacity of Ambon Bay determining the vulnerability of the system to the threat to evaluate risk during the peak rainfall season (easterly monsoon, June-August). Supplementarily, ERA considered the coral ecosystem in the bay contributing to the vulnerability parameter. This study only calculated flushing time (& tau;) of OAB due to available information on IAB flushing, and used three simple flushing models: 1D numerical advection-diffusion, salt-exchange and land-ocean interaction in coastal zone (LOICZ) models. The flushing time of the entire OAB was found to be 1-1.5 weeks. Inshore OAB was found to be flushed within 1.5-2 weeks while & tau; of mid OAB was 1-1.5 weeks. The flushing time of offshore OAB was & LE;1 week. Regarding the ERA implementation, the probability of occurrence of marine plastics was very high in IAB and inshore OAB (linked to dense-populated areas) compared to in mid and offshore OAB (i.e. moderate-to-low, where sparsely population areas are located). It was also true for the vulnerability of Ambon Bay to marine plastic accumulation that was found to be high in IAB and inshore OAB, linked to slower flushing in these locations than in mid and offshore OAB, located close to the open ocean. Combining this, IAB and inshore OAB showed a high risk of marine plastic contamination than mid and offshore OAB. The knowledge of ERA regarding marine plastic accumulation presented here is informative for other embayments in Indonesia's Coral Triangle region due to their similarity to Ambon Bay in shape and demographic aspects. & COPY; 2023 Elsevier B.V. All rights reserved.