Bio-Monitoring of Mangal Sediments and Tissues for Heavy Metal Accumulation in the Mangrove Forest of Cross River Estuary

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<0.05) in heavy metals deposition across the tidal levels. In the mangrove sediments, iron (Fe) content (415.8 mg gG 1 dry weight) was highest in the high tidal level where A. africana was predominantly sampled while N. fruticans (low tide) had the lowest deposition of the metal (304.4 mg gG 1 dry weight). The accumulation of heavy metals in the mangrove tissues took the general trend of root >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.

Assessment of metal enrichment and their bioavailability in sediment and bioaccumulation by mangrove plant pneumatophores in a tropical (Zuari) estuary, west coast of India

“…than A. officinalis is likely due to physiological differences and variations that exist in accumulation strategies of different plant species (Defew et al 2005). The variations in metal accumulation with respect to the two species and location in the estuary might be due to the metal need of the specific tissues, variation in salinity, the amount/quantity of metals deposition in the sediment of the mangrove and sea water intrusion during high tide as observed by Edu et al (2015). Also, the plant species, types of plant components, physiological age of tissue and seasons likewise, have significant influence on metal accumulation ability of the plants (Jones, 1998).…”

Estimating Economic and Livelihood Values of the World’s Largest Mangrove Forest (Sundarbans): A Meta-Analysis

“…Dasgupta et al [64] reported that Heritiera fomes show a higher photosynthesis rate than other mangrove species. In addition to this, Edu et al [65] reported that mangrove ecosystems serve as sinks for the deposition of waste from anthropogenic sources such as domestic, industrial, and agricultural discharges, and the same study also examined that Nypa fruticans absorbs significant amounts of heavy metals (i.e., Zn, Mn, Cr, and Fe) along with other mangrove species. The density of stands, including the two abovementioned species, tends to be higher in the Bangladesh Sundarbans [55,56]; this could be the reason for the higher economic values of waste assimilation and gas regulating of ES reported for the Bangladesh Sundarbans compared to the Indian part.…”