Heavy Metal Contamination in Urban Coastal Wetlands, The Mallorquín Case, Colombia

Coastal wetlands are highly productive ecosystems that are increasingly threatened by heavy metal contamination from urban and industrial activities. The Mallorquín coastal wetland, located near Barranquilla (Colombia), is subject to multiple anthropogenic pressures that may affect metal mobility and ecological risk. This study evaluates the concentration, spatial distribution, and ecological risk of heavy metals in water and surface sediments by integrating field sampling, mineralogical characterization (XRD), geochemical modeling (PHREEQC), and hydrodynamic simulations (Delft3D). Elevated Pb concentrations were observed in water during the wet season, reaching up to 0.97 mg/L and significantly exceeding regulatory limits, while Pb remained below detection limits during the dry season. Zn concentrations ranged between 0.08 and 0.12 mg/L. In sediments, Zn concentrations reached up to 169 mg/kg, with localized enrichment near anthropogenic discharge zones. Pollution indices (HEI, PLI, Igeo) indicate moderate contamination, with hotspots associated with low-energy hydrodynamic zones identified through Delft3D simulations. Geochemical modeling suggests that under alkaline and high-salinity conditions (pH 7.6–8.1; conductivity >30,000 µS/cm), Pb and Zn are predominantly present as carbonate and hydroxide complexes, influencing their speciation and mobility in the aquatic environment. The combined influence of hydrodynamic conditions and geochemical processes controls the spatial distribution of heavy metals in the wetland, promoting accumulation in low-circulation zones. This study highlights the importance of integrating field observations and modeling tools to support environmental monitoring and management of coastal wetlands under anthropogenic pressure.