oa Differential Metal Retention Depending on Land Use: The Role of Organic Matter and Sulfur in Two Semi Arid Mangroves (Brazil)

Mangrove are often considered natural metal sinks, yet their retention capacity varies significantly depending on sediment composition and anthropogenic pressures. This study investigates metal-sediment interactions in two semi-arid mangroves, Jaguaribe and Pacoti (northeastern Brazil), focusing on the role of organic matter (OM) and sulfur in metal retention and bioavailability. Sediment cores were analyzed for granulometry, OM composition, total sulfur, and metal concentrations (Zn, Hg, Co, Cr). Copper complexation was assessed using fluorescence quenching, and metal excess inventories were calculated using Al as a granulometric reference.

Findings reveal that in Jaguaribe, Hg and Zn strongly associate with nitrogen-rich OM, influenced by shrimp farming and urban inputs, while in Pacoti, Hg interacts with sulfur compounds, such as pyrite. Cr concentrations exceed Brazilian regulatory limits in both sites, yet show no correlation with sediment parameters, indicating potential external pollution sources. Weak OM-metal interactions challenge the assumption of mangroves as effective metal sinks, with implications for metal mobility and bioavailability in these environments.

This study highlights metal-organic interactions in tropical sediments. These findings contribute to global discussions on metal fate in organic-rich systems and the resilience of mangroves facing anthropogenic pressures.