Reconstruction of depositional environment of a tropical estuary and response of δ13Corg and TOC/TN signatures to changing environmental conditions

The distribution of sediment components, organic carbon, aluminium normalized metals, bulk sedimentary organic stable carbon isotope ratios i.e. δ13Corg and elemental TOC/TN ratios were studied within the sediment of Vaitarna estuary. Deposition of coarser sediment was favored under higher energy conditions prevailing in the past. Prevalence of relatively calm environment in recent years favored deposition of finer particles. Changes in depositional environment of Vaitarna estuary were very well reflected in distribution pattern of metals, δ13Corg and TOC/TN ratios. The narrow range (−22.9‰ to −22.0‰) and absence of distinct trend for δ13Corg in core collected towards the mouth (core S4) was attributed to prevalence of higher hydrodynamic energy conditions at this location. While protected environment of core S9 indicated a gradual change in the proportion of organic matter input to the estuary over a period of time. δ13Corg values in this core increased from −28.4‰ at the bottom to −20.7‰ at the surface and showed a corresponding decrease in TOC/TN ratio. All these changes will significantly alter the biogeochemical processes within the Vaitarna estuary and adjoining coastal waters.