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Distribution and Deposition Characteristics of Trace Metals and Carbon and Nitrogen in the Sediments of Karnafuli River Estuary, a Semi-inclosed Bay Area of Northern Bay of Bengal.

Abstract: Surface sediments were collected in August 2015 from 6 sites along the Karnafuli estuary and analyzed for grain size, total organic carbon (TC), total nitrogen (TN) contents, and Major Trace metals. The overall distribution characteristics of the TOC and TN content exhibited a gradual reduction from north to south in the estuary, and the high values were distributed in near the bay area. Contamination of heavy metals in the aquatic environment has attracted global attention owing to its abundance, persistence and environmental toxicity. Eight heavy metals such as chromium (Cr), copper (Cu), Cobalt (Co), lead (Pb), Arsenic (As), nickel (Ni), zinc (Zn) and Aluminum (Al) in surface and core sediments were investigated from the Karnaphuli River estuary in Chittagong. The distribution of trace metals in the sediments has been determined by using X-ray Fluorescence method and studied, the enrichment factors, the index of geo-accumulation and degree of contamination. The results showed that the levels of selected potential hazardous trace element were not varied from different sampling sites significantly. The contamination rank of Cu were light, but As and Pb was a moderate degree and Cr was considerable degree. The geo accumulation index of the study areas were moderately polluted by Cr but rest of the metals was unpolluted status. The enrichment factors of all studied metal’s result were minor enrichment to moderately enrichment. The contamination factor Cexisted in the order of Cr ˃As> Pb ˃ Ni ˃ Zn>Cu>Co in the surface sediment of  the Karnafuli river mouth for all metals were low pollution degree. But the contamination factor of Cr was considerable pollution degree and Pb, Ni and Zn was moderate. The major composition of surface sediment in KR estuary was silt and sand, and the surface sediment was contaminated by Cr and Pb. The core sediment between 20 cm and 8 cm below surface mainly originated from terrestrial materials induced by catastrophic events such as cyclone, heavy rainfall and landslides. The variation and accumulation of heavy metals in core sediment mainly revealed the natural variations of sediment sources, the anthropogenic inputs of heavy metal enhanced due to rapid heavy human activities, such as urbanization and industrialization of Chittagong area. In general, the heavy metal accumulation after normalized by Al in the Karnafuli River estuary indicated the urbanization and industrialization intensity in recent years, and also revealed the influence of catastrophic event on estuarine environment.

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