Using High-Resolution Hydrodynamic Models to Assess the Environmental Status of Highly Modified Transitional Waters in Salt Marshes

Effective management of transitional waters requires collaboration between administrative and scientific institutions, in line with the sustainable water management principles established by the Water Framework Directive (WFD, 2000/60/EC). The Cadiz and San Fernando salt marshes, classified as wetlands of international importance, currently exhibit an ecological and chemical status that is “worse than good.” However, there is still a lack of high-resolution, spatially explicit tools to identify where contaminants are most likely to accumulate in highly modified transitional waters, which limits effective monitoring and management strategies. This study aims to fill this gap by combining a high-resolution hydrodynamic model with a Lagrangian-particle-tracking approach to determine areas most vulnerable to contaminant accumulation from wastewater discharges. Simulations across multiple tidal cycles revealed that contamination is concentrated near discharge points and in low-flow channels, with tidal dynamics strongly influencing transport patterns. Key findings indicate that certain marsh sectors consistently experience higher contaminant exposure, highlighting priority areas for monitoring and management. The study provides novel insights by integrating modeling tools to produce a vulnerability classification of high-, medium-, and low-risk zones. These results contribute to the broader scientific understanding of contaminant dynamics in transitional waters and offer a transferable framework for improving wetland management in other heavily modified coastal systems.