Due to mismanagement, large quantities of macroplastics are transported through rivers toward the oceans. In this research, floating debris transport through the final 20 kilometers of the urban section of the Ozama-Isabela River water network (Santo Domingo, Dominican Republic) and into the Caribbean Sea was investigated. This study intended to mimic macroplastic transport in the watershed by deploying and analyzing the travel routes of 68 floating GPS drifters (cylinder, 10 x 8 cm, 500 g, 0.7 g cm^-1). The drifters were deployed in three seasonal batches in 2022 (March – dry, August – wet-hurricane, December – wet-dry) and covered five tributary ravines (cañadas) and ten locations on the main rivers. One-third of all deployed drifters moved through the river network and out to sea. Of the drifters deployed in the main rivers alone (n = 53), 40%–90% transferred to sea, depending on the season. The mean main river transition time before emission to the sea was only six days. Four out of 15 drifters deployed in tributary ravines were flushed to sea – they took 20 to 50 days to reach the Caribbean. Mobility and river-ocean transition probability is associated with rainfall intensity during drifter lifetime. Ocean emission probability was roughly halved within 10 km deployment distance from the river mouth during the experimental period (R² = 0.5; p < 0.005). Seaborne drifters moved westwards in the Caribbean current, stranding along the coast of Hispaniola Island. Although the investigated river length is relatively short, the results are surprising, considering the presence of structural impediments and riverbank vegetation. The presented data contrasts study findings from more tidal estuaries where the river mouth is regarded as a potential debris sink. With this study, we aim to strengthen macroplastic transport modeling in river watersheds to enhance macroplastic emission estimates.

Primary Presenter: Rafael Garcia, Instituto Tecnologico de Santo Domingo (rafael.garcia@intec.edu.do)

Authors:

Rafael Garcia, Instituto Tecnologico de Santo Domingo (INTEC)  (rafael.garcia@intec.edu.do)

Winston Gonzalez, Instituto Tecnologico de Santo Domingo (INTEC)  (winston.gonzalez@intec.edu.do)

Carlos Sanlley, Instituto Tecnologico de Santo Domingo   (carlos.sanlley@intec.edu.do)

Thomas Mani, The Ocean Cleanup  (t.mani@theoceancleanup.com)