Reconstruction of depositional environment of a tropical estuary and response of delta C-13(org) and TOC/TN signatures to changing environmental conditions

Abstract

The distribution of sediment components, organic carbon, aluminium normalized metals, bulk sedimentary organic stable carbon isotope ratios i.e. deltasup13/sup csuborg/sub 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, deltasup13/sup csuborg/sub and TOC/TN ratios. The narrow range (-22.9 ppt to -22.0 ppt) and absence of distinct trend for deltasup13/sup csuborg/sub 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. deltasup13/sup csuborg/sub values in this core increased from -28.4 ppt at the bottom to -20.7 ppt 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.