Tracing the dispersion of the Coatzacoalcos river plume in the Gulf of Mexico: a numerical experiment

River runoff plays a crucial role in the transport of sediments, nutrients, and pollutants into the oceans. Among the rivers in the Gulf of Mexico (GoM) carrying the largest volumes of anthropogenic pollutants include the Mississippi, Grijalva-Usumacinta, and Coatzacoalcos. This study focuses on the Coatzacoalcos river, we study the dispersion and coverage of passive tracers into the GoM. Implementing a high-resolution regional ocean model (MITgcm), we investigate the temporal and spatial variability of this tracer and its transport along the coast. The Coatzacoalcos river-flow-forcing was obtained from a climatology corresponding to the flow upstream of the river mouth. The tracer transport into the GoM has a strong seasonal dependence. Westward transport is dominant from January to August and eastward transport from September-December. The last one associated with the northerly winds that dominate during this period. Our results show that after one year of simulation, the area covered by concentrations larger than 0.1\% of the tracer extends over 656,000 km${}^2$ (45\% of the GoM’s area), while concentrations larger than 10\% extend over 16,000 km${}^2$ in just 8 months. In situ environmental impact studies for this region are limited; our findings suggest that coastal areas with higher pollutants concentrations, represented here by the passive tracer, present ecological risks such as eutrophication or hypoxia, and pose as well potential regional economic loss.