Ozama River Case Study: One-Year Multiple-Camera River Monitoring to Establish Baseline Debris Flux from the Dominican Capital into the Caribbean Sea

Key words: Debris flux, Urban Rivers, Plastic Pollution, Long – term monitoring, Caribbean Sea

Plastic pollution is a globally widespread threat to aquatic habitats. Models estimate that rivers carry up to 2.7 million tonnes of plastic waste into the world’s ocean every year, with the highest emission rates associated with seasons of high rainfall and discharge. The Caribbean is markedly impacted by this problem due to poor waste management and high coastline-to-landmass ratio of its multi-insular landscape. Model numbers are stated under multiple orders of magnitude of uncertainty, due to a lack of long-term, continuous empirical monitoring data. Draining the 3.5 million-inhabitant Dominican capital city of Santo Domingo, the Rio Ozama is estimated to emit between 220–22,000 tonnes (midpoint: 2,200) of plastics per year – one of the largest contributors of plastic pollution to the Caribbean Sea. This study seeks to reduce the uncertainty gap through long-term empirical baseline data. For this, we equipped two bridges across the final kilometers of the Rio Ozama with each four water-facing cameras. The sensors collected hourly debris flux data during daylight for one year (2022–2023). The resulting data indicate a median annual anthropogenic debris flux of approximately 630 tonnes year⁻¹, with an uncertainty range between ~294 and ~1,291 tonnes year⁻¹ (25th–75th percentiles), placing the observed emissions within the lower-to-mid range of previously modelled estimates for the Rio Ozama. The upstream Rosario Bridge recorded a median debris load of ~191 tonnes year⁻¹, while the downstream Mella Bridge registered ~439 tonnes year⁻¹. Expressed as Rosario/Mella, the ratio was ~0.43, indicating that debris loads at the Rosario Bridge were approximately 57% lower than those observed at the Mella Bridge over the ~3.3 km monitored river reach. This downstream increase reflects the substantial contribution of urban ravines (cañadas) and localized waste inputs entering the river between both monitoring points. Seasonal variability in debris flux was lower than expected, suggesting that anthropogenic sources and retention–release mechanisms exert a stronger control on debris transport than hydrological mobilization alone. The continuous, high-frequency dataset provides a robust empirical baseline for calibrating riverine plastic emission models and for assessing the effectiveness of waste management policies and cleanup interventions.