A 21-Year Analysis of Turbidity Variability in Cartagena Bay: Seasonal Patterns and the Influence of ENSO

Cartagena Bay, a coastal estuary in northern Colombia, receives significant sediment inputs from the Canal del Dique, an artificial channel with average discharge rates of 55 m3/s during the dry season and 250 m3/s during the rainy season. This study presents the variability of turbidity in Cartagena Bay for 21 years (2002–2022) using MODIS satellite imagery. Turbidity series were determined by using a remote sensing empirical algorithm developed for Cartagena Bay in 2024. In the present study, this algorithm was validated using MODIS data, demonstrating an adequate performance (R2 = 0.88, RMSE = 3.1, MAPE = 29.5%). Spatial and temporal turbidity patterns were analyzed for three representative months: February (dry season), July (low precipitation), and November (high rainfall). The role of the El Niño–Southern Oscillation (ENSO) on the dynamics of the Canal del Dique discharge and turbidity levels was studied through anomaly analysis and Fourier Transform Analysis (FTA). Results highlight a marked spatial variability in turbidity, with the highest turbidity levels observed near the canal mouth from April to September. FTA revealed a dominant annual cycle in turbidity and discharge, with additional semi-annual and multi-year periodicities linked to the rainfall periods and ENSO. Turbidity variability appears primarily driven by seasonal and local hydrodynamic processes, with a long-term increasing trend in turbidity. This approach can be applied to other tropical estuaries under strong fluvial influence.