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

## TL;DR

This study examines how heavy metals in mangrove ecosystems of Puerto Rico affect metal retranslocation and carbon storage, revealing site-specific differences in metal behavior and potential risks.

## Contribution

The study identifies site-specific metal-carbon correlations and retranslocation patterns in mangroves, offering insights into metal sources and ecological risks.

## Key findings

- Metal levels in Laguna Grande are higher due to human activity, while La Parguera's levels are influenced by tidal flushing.
- Zinc and lead are retained by plants at La Parguera, reducing immediate risks but posing latent threats.
- Cadmium and nickel at Laguna Grande show high bioavailability, increasing ecological risks.

## 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.

Metal levels vary due to anthropogenic inputs (Laguna Grande) and tidal flushing (La Parguera).This study broadens known metal concentration ranges in mangrove sediments for future research.Metal‐carbon correlations differ by site, serving as indicators of metal sources and conditions.Metal retranslocation and bioavailability depend on type and site conditions, posing potential risks.Site‐specific factors regulate metals, highlighting the need for targeted mangrove management strategies.

Metal levels vary due to anthropogenic inputs (Laguna Grande) and tidal flushing (La Parguera).

This study broadens known metal concentration ranges in mangrove sediments for future research.

Metal‐carbon correlations differ by site, serving as indicators of metal sources and conditions.

Metal retranslocation and bioavailability depend on type and site conditions, posing potential risks.

Site‐specific factors regulate metals, highlighting the need for targeted mangrove management strategies.

Mangrove forests help protect coastlines and store carbon, but they can also trap pollutants like heavy metals. This study examined the levels of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in the sediments and leaves of two Puerto Rican mangrove ecosystems: La Parguera and Laguna Grande. We found that metal levels were generally low, but Laguna Grande had higher levels due to human activity. Metals behaved differently at each site, with some binding to sediment carbon and others being taken up by plants. Some metals, like zinc and lead, were held by plants, reducing immediate risks but potentially causing future problems. Others, like cadmium and nickel, were more available, increasing the chance of harm to plants and animals. These results show that local environmental factors affect how metals move and impact ecosystems, helping scientists and policymakers monitor mangrove health.