Seasonal freshwater flux estimation using mollusc from the tropical Mandovi Zuari estuary, Goa, India

Ghosh, P and Ramdas, L and Banerjee, Y and Thamizharasan, S and Banerjee, S (2021) Seasonal freshwater flux estimation using mollusc from the tropical Mandovi Zuari estuary, Goa, India. In: Journal of Earth System Science, 130 (2).

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Abstract

Abstract: Seawater incursion and freshwater discharges into the tropical Mandovi Zuari (MZ) estuary is investigated here using stable oxygen isotope data on monthly water samples from locations spatially separated within the estuary. Surface water samples were analysed for δ18O and salinity relationship, δ18O= 0.0843 � S- 2.1 , where freshwater end member is designated as �2.1�; similar to the composition recorded for the rain water. We have estimated percentage of monthly freshwater fluxes into the estuary using mass balance equation adopting an isotopic value of seawater end member. Our estimates showed freshwater contribution to the estuary water during monsoon time was 63, while in the post-monsoon season the fraction drops to 34.7. The contribution of the freshwater registered a minimum value of 6.8 during the pre-monsoon season. Further, we analysed the seasonal growth band secreted by the mollusc from the same estuary to understand the potential of mollusc as a recorder of seasonal water composition. The δ18O of mollusc shell growth layers varied over a range between �4.3� and �2.1�. We interpreted this as seasonal signal assuming the growth rate from the culture experiment. The δ18O of estuary water and observed temperature are used to simulate the isotopic composition of seasonal growth bands. The lighter δ18O value of �4.3� precipitated during the month of July 2010, which coincides with the time of low productivity (δ13C = �3.5�). While the heavier δ18O (�2.1�) is recorded in the growth layer generated during November 2010 defining the period of post-monsoon growth. Research Highlights: 1.Here we presented our observation on the spatiotemporal variability of salinity and δ18Owater across a tropical estuary, Mandovi Zuary located at the western coast of India and fed by rivers originating from the peninsular region which receives rainfall during period of Indian summer monsoon.2.We designed a two-component mixing model for the estimation of freshwater fluxes at monthly time intervals and demonstrated its efficacy with the tide gauge data.3.The study highlighted the scope of isotope mass balance approach in estimating freshwater fluxes at seasonal time domain.4.Further, we demonstrated that the isotopic signature preserved in the growth bands of the bivalve shell can be useful proxy for the reconstruction of freshwater fluxes in an estuary and thus add a new tool for reconstruction of seasonal runoff.5.The isotope approach used here can also be extended to other estuaries in the peninsular India and also in other tropical continental settings where hydrological process is driven by seasonal reversal of wind direction. © 2021, Indian Academy of Sciences.

Item Type:	Journal Article
Publication:	Journal of Earth System Science
Publisher:	Springer
Additional Information:	The copyright for this article belongs to Springer
Keywords:	Bivalvia; Mollusca
Department/Centre:	Division of Mechanical Sciences > Centre for Earth Sciences Division of Mechanical Sciences > Divecha Centre for Climate Change Division of Interdisciplinary Sciences > Interdisciplinary Centre for Water Research
Date Deposited:	26 Aug 2021 09:24
Last Modified:	26 Aug 2021 09:24
URI:	http://eprints.iisc.ac.in/id/eprint/69333

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