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.
Background: Series of ecological demand are causing significant and irreversible loss to forest resource, thus causing their disappearance at alarming rates due to demand for timber and non-timber products and for agricultural lands. In most communities of Ngor-Akpala in Imo State, where mechanized and sustainable system of agriculture is not practiced, shifting cultivation and subsistence farming are the most obvious causes of forest disturbances. Objective: This study elucidates the phytodiversity and composition of an agrarian impacted site in parts of Amafor forest in Ngor-Akpala, Imo State. Methodology: A total of five quadrate sampling plots of 20×50 m each were systematically sampled and phytosociological data were collected in both the impacted and unimpacted sites. Results: The impacted site had a total representative of 39 species under 17 families recorded in mosaic heterogeneity with herbs (77%) and shrubs (58%) as the most dominant life form of plant species. Phytosociological results showed that among the 39 representative species, Spillanthes filicaulis and Ipomoea involucrata recorded the highest frequency of (100 = 5.81%) occurrence. Andropogon tectorum (giant bluestem) had the highest density value of 11.2 = 18.01%, highest abundance value of 18.7 = 14.70% and highest Importance Value Index (IVI) of 36.20%, respectively. In distribution pattern 20 species (51.28%) had random distribution, 5 (12.82%) species in regular and 14 (35.90%) species in contiguous distribution pattern. The unimpacted site had 19 species under 14 families in climax vegetation structure of six species as herbs, 11 as shrubs and 2 as trees. Phytosociological assessment had four species with the highest frequency of 100 = 7.69% with Manniophyton fulvum having the highest density value of 6 = 10.24% per species and IVI of 25.11%. Funtumia elastica had the highest abundance of 8 = 9.30%. The distribution pattern showed 12 species (63.16%) in contiguous pattern, 4 species (21.05%) in random distribution and 3 species (15. 79%) regularly distributed. Conclusion:The comparative study on the similarity of the impacted and unimpacted sites shows that both sites are dissimilar with an observed index value of 0.79 higher than the 0.21 value of similarity index.
Background: Several biotic and abiotic factors including the influence of hydrocarbon and inorganic activities on population structure and regeneration of vegetation have been noted as agents of species on ecological succession. Similar studies have also been carried out by many workers in different forest ecosystem, but no information has been generated on this aspect for the post remediated Ahia oil-field under local environmental condition in Rivers State, Nigeria. Objective: Therefore, this study was aimed at assessing the post-phytodiversity and regeneration status of post-remediated crude oil impacted site in Ahia oil-field, in Rivers State, Nigeria. Methodology: Despite the heterogeneous mosaic nature of secondary vegetation of the study area, a total representative of 67 species under 15 families are recorded with monotypic heterogeneity of life forms in the study site, with various diversity and abundance. The Poaceae among the prevalent dominant families was the most diverse in species richness. The total representative species were establishing through coppicing, seedling and rhizome with greater percentage (42 = 63%) of the species exhibiting multiplier mode while 25 = 37.31% were solitary in regeneration status. Results: The phytosociological index assessment shows that Oldenlandia herbacea, Axonopus compressus and Heterotis rotundifolia had recorded the highest frequency of 50 = 4.65% occurrence, respectively. Axonopus compressus further had the highest abundance of 100 = 6.19%, Importance Value Index of 11.95%, richness of 0.06 and evenness of 0.03 in species diversity. The spatial distribution of species at the study site recorded a contiguous pattern with Oldenlandia herbacea recording the highest distribution pattern. The increase in the herbaceous life form of the study site is an indication of a primary regenerative succession that tends towards a pioneer vegetation array of shrubby and tree species of climax status. Conclusion: The study, therefore provide a complete view of regeneration trend in the study area, which is rich in regenerating species that could result in establishment of a diverse natural forest if protected with special attention to the scope of biodiversity conservation priority.
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