How physicochemical factors shape coastal vegetation patterns: Redox zonation drives coupled metal-nutrient dynamics in Nanhui Wetland, Shanghai

Coastal wetlands, which are vital for global carbon storage, face unprecedented stress due to changing water levels and salinity. Their resilience depends on complex biogeochemical interactions, particularly the cycling of redox-sensitive metals (Fe, Mn, Cu, and Zn), which control nutrient availability and vegetation patterns. This study decouples how these physicochemical factors drive the ecosystem structure in the Nanhui Wetland, Shanghai.

Here, we report physicochemical parameters across a salinity gradient, measuring nutrients, trace metals, pH, and dissolved oxygen. The results demonstrate that hydrological oscillations create distinct redox zones. This fluctuating oxygen availability drives competitive reductive dissolution and re-precipitation reactions of Fe and Mn oxides. Concurrently, these redox shifts modify the ligand environments and sulfide availability, thereby regulating the complexation, solubility, and potential toxicity of Cu and Zn. These dual pathways involve nutrient processing via Fe/Mn cycling and metal toxicity modulation. Geochemical shifts govern nitrogen processing and carbon stabilization at the sediment-water interface. This creates an observable geochemical template that directly filters salt-tolerant plant zonation based on species-specific tolerances to nutrient and metal stress. By quantifying these core interactions, our study establishes a mechanistic foundation required to constrain next-generation biogeochemical models, enabling targeted strategies for managing blue carbon ecosystems to enhance their resilience and sequestration.