Geochemistry of mudflat and mangrove sedimentary environments, within tropical (Sharavati) estuary, Karnataka coast, India

Abstract

Five sediment cores from Sharavati estuary were analysed for sediment components, organic carbon and selected metals with 2 cm interval. Progressive sorting of sediments was noted in the Sharavati estuary from the mouth to middle estuarine region. Sand in the vertical section showed overall decreasing trend which is compensated by increase in the finer sediments and organic carbon in recent years except in core F1. The data revealed prevalence of relatively higher and varying hydrodynamic energy conditions facilitating greater deposition of sand particles in the past, while, lower and stable hydrodynamic conditions in recent years seemed to have resulted in deposition of finer particles towards the surface. Metals in different sediment size fractions indicated their association with finer sediments. In addition Fe-Mn oxides played a major role in distribution of metals in sediments. Cobalt showed value almost equal to Apparent Effects Threshold (AET) in core G2 of upper middle region, suggesting risk of toxicity and high bioavailability of Co to sediment dwelling organisms. Risk Assessment Code (RAC) criteria also indicated high risk of Co in core G1 and shows medium risk in the other cores.