Elemental geochemistry of surface sediments from Manakudy estuary, south-west coast of India: Inferences to sources of elements and their accumulation

Manakudy estuary is located in the southernmost tip of the Indian sub-continent, which is essential to study the sediment geochemistry as it receives limited input of sediments during the rainy season from its catchment zones. The elemental geochemical variation of sediments is to understand the mechanism influencing the estuarine environment, and it becomes baseline data to assess the environmental impact in the near future. Twenty surface sediments samples were collected at different seasons, and the grain size results showed that the estuary sediments were carpeted by the mixture of sand, silt, clay, organic matter (OM), and CaCO3. The seasonal variation of elements is slightly more in the pre-monsoon than in the post-monsoon season. Fe showed maximum variation, while Cd showed minimum variation in total heavy metal concentrations of detrital sediments. The order of abundance of metals based on their mean values is as Fe > Mn > Cr > Zn > Cu > Pb > Ni > Co > Cd in pre-monsoon and Fe > Mn > Zn > Cr > Ni > Co > Cu > Pb > Cd > in post-monsoon, respectively. Different elemental ratios and enrichment factors were used to assess the abundance of major and trace elements in both seasons. The ecological risk assessment clearly shows the higher concentration of a few metals in the estuarine sediments during post- monsoon. Correlation and factor analysis show that from geogenic along with the anthropogenic input of industrial effluents, agriculture, urban, municipal wastes and slum sewage are the major sources for derived metals in the estuarine sediments.