Role of sediment size in the distribution and abundance of metals in a tropical (Sharavati) estuary, west coast of India

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 (4 theta), medium silt (6 theta) and clay (8 theta) 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.