Transfer of Macroplastic Debris from Low-Tide Tropical Urban Estuaries to the Caribbean Sea: A Case Study from the Ozama-Isabela River

Key words : Caribbean, GPS, Macroplastics, Monitoring, Rivers, Tracking 

Urban tropical rivers serve as critical pathways for macroplastic transport from land to sea, yet their true ocean-emission potential remains poorly understood. This study represents the first application of satellite-enabled GPS tracking in an insular Caribbean river system to quantify the movement of floating macroplastics. A total of 68 GPS drifters were deployed across the Ozama-Isabela river system in Santo Domingo, Dominican Republic, during three distinct seasonal phases in 2022. Devices were released from main river channels and tributary ravines (cañadas), and their trajectories were recorded over periods of up to three months. Results showed that 54% of drifters reached the Caribbean Sea, with river-released devices exhibiting higher transport efficiency (mean speed: 3.47 km/day) compared to those from cañadas (mean speed: 1.38 km/day). Transport dynamics varied significantly by season, with increased connectivity during high-precipitation periods. Instead of a linear predictive model, statistical analysis of the trajectories revealed a bimodal flow regime governed by a high-velocity central "transport hotline." Gaussian Mixture Models distinguished two physical states: rapid advection in the channel thalweg and static retention at the river margins. Furthermore, a significant lateral asymmetry was identified, with the right bank acting as a preferential retention zone (58% of marginal interactions). These findings demonstrate that plastic export is a binary mechanism determined by the debris' capacity to enter and remain within the central hotline. This study offers new empirical insights for regional management, suggesting that mitigation strategies must prioritize interception in tributaries before waste enters the rapid-transit main channel where capture becomes increasingly difficult.