Role of sediment size in the distribution and abundance of metals in a tropical (Sharavati) estuary, west coast of India
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ORIGINAL PAPER
Role of sediment size in the distribution and abundance of metals in a tropical (Sharavati) estuary, west coast of India Maria C. Fernandes 1 & G. N. Nayak 1
Received: 9 April 2015 / Accepted: 10 September 2015 # Saudi Society for Geosciences 2015
Abstract Two sediment cores representing adjacent mudflat and mangrove sub-environments from the middle region of Sharavati estuary were analyzed for sand, silt, clay and organic carbon at 2-cm interval. Metal concentration was also analyzed for all bulk sediment samples and selected samples for different sediment size fractions (sand (4Ø), medium silt (6Ø) and clay (8Ø) of both the cores for Aluminium (Al), Iron (Fe), Manganese (Mn), Nickel (Ni), Zinc (Zn), Copper (Cu), Cobalt (Co), and Chromium (Cr). The sediments of mudflat environment are found to be enriched with metals, organic carbon (OC) associated with finer sediments. However, the core collected from the mangrove environment showed higher coarser material. The association and degradation of organic matter played important role in distribution of metals in silt and clay fractions in mudflat core. The paper also discusses on source of sediments and process involved with time. Higher enrichment factor (EF) values of Zn in silt and clay fraction and Co in sand and silt fraction are observed in the mangrove core as compared to mudflat core, whereas, Cu is enriched in the silt and clay fraction of mudflat core. However, Cr was enriched in all the fractions of both the cores. Pollution load index (PLI) indicated higher metal enrichment in the clay fraction of both the cores.
Keywords Estuary . Sediment core . Metals . Sediment size fractions
* G. N. Nayak [email protected]; [email protected]
1
Marine Sciences Department, Goa University, Goa 403206, India
Introduction Estuaries are the interfacial mixing zones where river input to the ocean is modified. Mudflats and mangroves are adjacent sub-environments along estuarine tidal flats that provide habitat to diverse range of marine fauna (Cuong et al. 2005). Mudflats cover large unvegetated areas that are exposed during low tide and submerged during high tide (Reineek 1972), whereas mangroves are salt-tolerant plants associated with a unique horizontal root network (Soto-Jimenez and PaezOsuna 2001; Kumaran et al. 2004). Estuarine mudflats are preferential sites for deposition and accumulation of sediments (Singh and Nayak 2009), and mangrove sediments are generally known to retain large amount of organic matter which are from various sources viz. terrestrial, marine and atmospheric (Wu et al. 2011). The organic matter associated with the finer sediments provides favourable conditions for the accumulation of metals (Spencer et al. 2003). Sediments are composed of different size classes which act as potential binding phases for metals to accumulate in the estuarine system. In addition, Fe-Mn oxide and organic matter are considered important phases which influence the metal transport and its distribution (Tribovillard et al. 2006). Metals acc
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