Estuarine and Marine Geology (2011-2015)

  • V PURNACHANDRA RAO CSIR-National Institute of Oceanography, Dona Paula 403 004, Goa

Abstract

The estuaries of the Mandovi and Zuari (Ma-Zu) Rivers and Godavari River have been investigated extensively for
understanding the sedimentary and bio-geochemical processes during the last 5 years. Estuarine turbidity maximum is a
characteristic feature at the mouth of Ma-Zu estuaries, formed by the interaction between tidal currents and river flows
during monsoon, and by the re-suspension of bottom sediments by tidal and wind-induced currents during pre-monsoon.
Kaolinite and illite, followed by minor goethite, gibbsite and chlorite are present in SPM and sediment of the estuaries.
Smectite occurs in traces at river end stations but its contents increased downstream. The 87Sr/86Sr ratios of SPM are higher
than those in hinterland rocks and laterite soil The Nd isotopic compositions of Ma-Zu estuaries are influenced by the
lateritization of source rocks and anthropogenic contribution of ore materials. The major and trace elements in sediments of
Ma-Zu estuaries indicate the metals contribution of metals from lateritic formations as well as iron ore. Shale-normalized
REE patterns exhibit MREE- and HREE enrichment with positive Ce and Eu anomalies indicative of contamination from
iron ore. Stable isotopes of organic matter indicate at least ~20% terrestrial organic carbon (TOC) to the coastal system
during wet season. Chemical speciations studies indicate that the concentrations of non-residual and dynamic metalsediment
complexes (which are good indicators of bioavailability) of toxic metals gradually increase with increasing total
metal loading in estuarine sediments. Quality and quantity of sedimentary organic matter (SOM) is one of the key factors
which play a crucial role in controlling speciation of trace/toxic metal in sediments. The distribution and sources of
particulate organic carbon and particulate nitrogen in 27 Indian estuaries during the monsoon indicate higher phytoplankton
biomass with deeper photic zone than other estuaries receiving higher suspended matter. Detailed studies on rock-magnetic
properties and 13Corg in sediments off the Krishna-Godavari provide evidence of reductive diagenesis, formation of
authigenic sulfides and occurrence of methane in these estuarine sediments and also episodic methane expulsion events.

Published
2017-02-09