Contrasting elemental and biogeochemical signatures of mangrove and adjacent mudflat soils in the Arabian Gulf

Comparative data on sediment biogeochemistry in vegetated and non-vegetated coastal habitats remain limited in arid regions. This study aims to compare sediment physicochemical properties, carbon and nitrogen content, grain-size fractions, transition metals, and rare earth elements in mangrove and adjacent mudflat sediments along the eastern coast of Saudi Arabia. Significant spatial variability was observed across all sediment properties and elemental groups, with location exerting a stronger influence than habitat type or sediment depth. Mangrove sediments showed site-specific differences in carbon content, carbonate concentration, and C:N ratios, whereas mudflat sediments were comparatively uniform. Transition metals and REEs were consistently enriched at Syhat across both habitats, while Tarut exhibited the lowest concentrations and Darin showed intermediate values. Habitat-related contrasts were element-specific, with some metals showing higher mean concentrations in mangroves and others in mudflats. Multivariate analyses revealed stronger associations between carbon and multiple metals and REEs in mangrove sediments, whereas carbon–element relationships were weaker and more dispersed in mudflats, indicating contrasting geochemical controls. Overall, the results demonstrate that site-specific factors dominate sediment geochemistry in arid mangrove–mudflat systems, highlighting the importance of spatial context when evaluating elemental dynamics and coastal ecosystem functioning.