Indian Journal of Geo-Marine Sciences

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Partial pressure of carbon dioxide (pCO2) and air-water CO2 exchange in the tropical semidiurnal estuarine system


Affiliations
1 Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai ‒ 608 502,Tamil Nadu, India
2 National Remote sensing Centre, Balanagar, Hyderabad ‒ 500 625, Andhra Pradesh, India

Time-series observations of the Vellar estuary between May 2013 and December 2019 showed clear variability with respect to space and time in the distribution of nutrients, partial pressure of carbon dioxide (pCO2) and air-water CO2 exchange. Lower and higher salinities revealed significant seasonality in estuarine pCO2, as well as variations in the seasonal pattern due to the freshwater discharges during monsoon rainfall. The pCO2 attained the highest levels (8457 μatm) during monsoon which coincided with the lowest pH (7.498) and the undersaturation of pCO2 (322 μatm) was observed with maximum pH (8.182) during pre-monsoon. The Principal Component Analysis (PCA) identified four components that accounted for 77.28 % of the total variance and explained the significant influence of nutrients, chlorophyll and temperature on pCO2 distribution. Similarly, the multiple linear regression analysis showed significant influence of environmental variables on pCO2 variability with a R2 of 0.957, SEE±230.816, p < 0.001. The surveyed area of the Vellar estuary had an overall pCO2 of 1068 μatm and was supersaturated with regard to the atmospheric pCO2 throughout the year, with an average CO2 flux of 4.13±5.59 mmol C m-2 d-1 to the atmosphere. During the study period, the Vellar estuary actively supplied 650.2 mol C m-2 Y-1 to the atmosphere. Hence, the metabolic balance of the estuarine ecosystem is aided by land derived organic carbon accompanied with freshwater flows from the Vellar river, constituting the estuary as a substantial source of atmospheric CO2.
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  • Partial pressure of carbon dioxide (pCO2) and air-water CO2 exchange in the tropical semidiurnal estuarine system

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Authors

R Shanthi
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai ‒ 608 502,Tamil Nadu, India
D Poornima
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai ‒ 608 502,Tamil Nadu, India
A Saravanakumar
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai ‒ 608 502,Tamil Nadu, India
T Thangaradjou
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai ‒ 608 502,Tamil Nadu, India
S B Choudhry
National Remote sensing Centre, Balanagar, Hyderabad ‒ 500 625, Andhra Pradesh, India
R Roy
National Remote sensing Centre, Balanagar, Hyderabad ‒ 500 625, Andhra Pradesh, India

Abstract


Time-series observations of the Vellar estuary between May 2013 and December 2019 showed clear variability with respect to space and time in the distribution of nutrients, partial pressure of carbon dioxide (pCO2) and air-water CO2 exchange. Lower and higher salinities revealed significant seasonality in estuarine pCO2, as well as variations in the seasonal pattern due to the freshwater discharges during monsoon rainfall. The pCO2 attained the highest levels (8457 μatm) during monsoon which coincided with the lowest pH (7.498) and the undersaturation of pCO2 (322 μatm) was observed with maximum pH (8.182) during pre-monsoon. The Principal Component Analysis (PCA) identified four components that accounted for 77.28 % of the total variance and explained the significant influence of nutrients, chlorophyll and temperature on pCO2 distribution. Similarly, the multiple linear regression analysis showed significant influence of environmental variables on pCO2 variability with a R2 of 0.957, SEE±230.816, p < 0.001. The surveyed area of the Vellar estuary had an overall pCO2 of 1068 μatm and was supersaturated with regard to the atmospheric pCO2 throughout the year, with an average CO2 flux of 4.13±5.59 mmol C m-2 d-1 to the atmosphere. During the study period, the Vellar estuary actively supplied 650.2 mol C m-2 Y-1 to the atmosphere. Hence, the metabolic balance of the estuarine ecosystem is aided by land derived organic carbon accompanied with freshwater flows from the Vellar river, constituting the estuary as a substantial source of atmospheric CO2.