Estuarine Hydrodynamics and Its Influence on the Survival of the Coral Reef, Cartagena de Indias Bay

Coral reefs persisting beneath buoyant, sediment-rich estuarine plumes remain poorly represented in coupled hydrodynamic–optical studies, particularly in tropical semi-enclosed bays. This study investigates the estuarine processes that may sustain the El Varadero reef in Cartagena de Indias Bay (Colombian Caribbean) despite high surface turbidity. A 60 m-resolution three-dimensional model, incorporating turbulence closure, conservative transport of fine suspended sediments, and light attenuation, was applied to the Canal del Dique plume and the bay’s stratified circulation. The model configuration was evaluated against sea-level records, drifter-derived discharge, particle-size measurements, and water-column turbidity, Secchi depth, and irradiance observations. The bay developed a strongly stratified surface plume controlled mainly by freshwater discharge and seasonally modulated wind forcing. Clay (mean diameter 0.2 µm) and fine silt (8.8 µm) dominated the suspended load and remained concentrated in the upper layer because of very low settling and inhibited vertical mixing. The measured irradiance profiles showed decreasing attenuation below the turbid surface layer. The resulting physical mechanism—a turbid buoyant plume that is exported seaward while the pycnocline restricts downward sediment transport—explains how adequate subsurface light conditions can persist over the reef. The study provides a transferable framework for assessing coral habitats beneath stratified estuarine plumes and identifies the need to evaluate ecological consequences before altering freshwater and sediment inflows.