Heavy metal contamination and blue carbon sequestration in mangrove ecosystems of Puerto Rico

Abstract

Heavy metal contamination in coastal ecosystems can significantly impact biological activity, metal retranslocation, and biogeochemical cycling. This study assessed the concentrations of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in mangrove sediments and leaves of two ecosystems in Puerto Rico that differed in their proximity to urban areas: La Parguera and Laguna Grande. Metal bioconcentration factors and retranslocation percentages (RT%) were determined. Relationships between metals, between metals and sediment carbon, and metal retranslocation and bioavailability differed between the sites. Metals with high retranslocation percentages by plants, such as zinc and lead at La Parguera, suggest that plant-mediated stabilization processes can reduce immediate bioavailability but may pose latent risks under changing environmental conditions. Conversely, cadmium, with low retranslocation, and nickel, with high retranslocation and high bioavailability at Laguna Grande, indicate greater potential for biological uptake and ecosystem stress. Results suggest that differences in relationships between metals and between metals and carbon may help identify sources and effects of metals. Further research is needed to explore the direct physiological effects of metal exposure on plants and their implications for carbon storage and ecosystem health in mangrove-dominated systems.