Stable isotopes of carbon and nitrogen in suspended matter and sediments from the Godavari estuary |
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| Authors: | V V S S Sarma J Arya Ch V Subbaiah S A Naidu L Gawade P Praveen Kumar N P C Reddy |
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| Institution: | (1) National Institute of Oceanography, Regional Centre, Council of Scientific and Industrial Research (CSIR), 176 Lawsons Bay Colony, Visakhapatnam, 530 017, India |
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| Abstract: | Spatial distribution of the carbon and nitrogen content and their isotopic enrichment in suspended matter and sediments were
measured in the Godavari estuary to identify the sources and transformation mechanism of organic matter. Significant variability
in isotopic distribution was found over the entire length of the Godavari estuary, suggesting multiple sources of organic
matter. The mean isotopic ratios (δ13Csed −25.1 ± 0.9, δ13Csus −24.9 ± 1, δ15Nsed 8.0 ± 2 and δ15Nsus 6.5 ± 0.9‰) and elemental concentrations (Csed 0.45 ± 0.2%, Csus 0.9 ± 0.7%, Nsed 0.07 ± 0.05% and Nsus 0.16 ± 0.1%) support a predominantly terrigenous source. Significant enrichment in the isotopic ratios of δ13C from the upper to lower estuary in both suspended (−27.5 and −24.3‰, respectively) and sedimentary (−26.2 and −24.9‰, respectively)
phases indicates a decrease in the influence of terrigeneous material toward the mouth of the estuary. A significant positive
relationship exists between the δ13C of suspended and sediment, which indicates that these two organic carbon pools are likely coupled in the form of a significant
exchange between the two phases. A positive relationship exists between chlorophyll a and suspended organic matter, which may mean that a significant source of organic carbon is the in situ produced phytoplankton.
But, applying a simple mixing model to our isotopes, data yielded about 46% as the contribution of the terrestrial source
to suspended matter, which may support the excessive heterotrophic activity in the Godavari estuary reported earlier. |
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