Abstract
Background: Mangroves are among the most productive intertidal ecosystems on earth. They serve as nursery and breeding grounds for several commercially important species of marine fauna. Despite their economic and ecological importance, they are under threat from over-exploitation and organic and inorganic pollution sources. This has led to their use as bio-indicators for pollution monitoring programmes. Therefore, the need to periodically monitor the Cross River Estuary mangroves for heavy metals pollution should not be overemphasized given the high premium placed on this ecosystem. Objectives: The present study was aimed at evaluating mangrove sediments and tissues for heavy metals accumulation in the different tidal levels of Cross River Estuary which will be an indicator for pollution. Method: Ten random samples of composite surface sediments (0-5 cm) were collected from low, mid and high tidal levels using a modified Van Veen (0.1 m 2 ) grab sampler. Also samples of senescent leaves, barks and roots of randomly selected ten individual plants of Nypa fruticans (low tide), Rhizophora racemosa (mid tide) and Avicennia africana (high tide) were also collected for heavy metal analyses during the year 2011. Result: The results showed that there were significant variations (p bark >leaves, the mangrove notwithstanding. It was also observed that cadmium deposition in sediments was comparatively higher than RSV indicating possible cadmium pollution. Generally, accumulation of heavy metals in the mangrove forest of Cross River estuary was within permissible limits. Conclusion: Although the concentrations obtained for the heavy metals studied are generally below documented toxic levels, however, the increasing level of urbanization and industrialization in Calabar municipality and its environs calls for continuous vigilance, surveillance and monitoring of this sensitive and all important ecosystem to protect and ensure that heavy metal pollution is minimal.
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