Spatio-temporal variation in δ 13 C DIC of a tropical eutrophic estuary (Cochin estuary, India) and adjacent Arabian Sea

Bhavya, P. S.; Kumar, Sanjeev; Gupta, G.V.M.; Sudharma, K. V.; Sudheesh, V.

doi:10.1016/j.csr.2017.12.006

Cited by 16 publications

(7 citation statements)

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“…For the same wind velocity, the parametrization of Liss and Merlivat (1986) provides the lowest k value over other parametrization (Wanninkhof, 1992;Raymond and Cole, 2001;Borges et al, 2004) and therefore the F CO 2 presented during this study may be considered to be a conservative estimate. The wind-velocity-based k estimation for the Hooghly-Sundarbans system has been applied in earlier studies as well (Mukhopadhyay et al, 2002;Biswas et al, 2004). Mean global atmospheric CO 2 mixing ratio in dry air during 2016 (data source: ftp://aftp.cmdl.…”

Section: Computation Of Air-water Co 2 Flux and %Domentioning

confidence: 99%

“…Earlier, the major focus of biogeochemical studies in the Hooghly and the estuaries of the Sundarbans had been on the biogeochemistry of trace gases (Mukhopadhyay et al, 2002;Biswas et al, 2004Biswas et al, , 2007Ganguly et al, 2008Ganguly et al, , 2009Dutta et al, 2013Dutta et al, , 2015Dutta et al, , 2017 with the exception of one comprehensive study on nutrient budgets at the Hooghly estuary (Mukhopadhyay et al, 2006). Recently, attempts have been made to understand different aspects of C cycling in these two estuaries (Samanta et al, 2015;Ray et al, 2015Ray et al, , 2018Akhand et al, 2016).…”

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confidence: 99%

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The post-monsoon carbon biogeochemistry of the Hooghly–Sundarbans estuarine system under different levels of anthropogenic impacts

et al. 2019

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Abstract. The present study focused on understanding differences in the post-monsoon carbon (C) biogeochemistry of two adjacent estuaries undergoing different levels of anthropogenic stresses by investigating anthropogenically influenced Hooghly estuary and mangrove-dominated estuaries of the Sundarbans in the north-eastern India. The salinity of well-oxygenated estuaries of the Sundarbans (DO: 91 %–104 %) varied over a narrow range (12.74–16.69) relative to the Hooghly estuary (0.04–10.37). A mixing model suggested a combination of processes including freshwater intrusion, carbonate precipitation and carbonate dissolution to be a major factor controlling dissolved inorganic C (DIC) dynamics in the freshwater regime of the Hooghly, whereas phytoplankton productivity and CO2 outgassing dominated in the mixing regime. In the Sundarbans, the removal of DIC (via CO2 outgassing, phytoplankton uptake and export to the adjoining continental shelf region) dominated its addition through mineralization of mangrove-derived organic C. The concentration of dissolved organic C (DOC) in the Hooghly was ∼40 % higher than in the Sundarbans, which was largely due to the cumulative effect of anthropogenic inputs, DOC–POC interconversion and groundwater contribution rather than freshwater-mediated input. The measured δ13CPOC in the Hooghly suggested particulate organic matter contributions from different sources (freshwater runoff, terrestrial C3 plants and anthropogenic discharge), whereas the contribution from C3 plants was dominant at the Sundarbans. The significant departure of δ13CPOC from typical mangrove δ13C in the mangrove-dominated Sundarbans suggested significant particulate organic C (POC) modification due to degradation by respiration. The average pCO2 in the Hooghly was higher by ∼1291 µatm compared to the Sundarbans with surface runoff and organic matter degradation by respiration as dominant factors controlling pCO2 in the Hooghly and Sundarbans, respectively. The entire Hooghly–Sundarbans system acted as a source of CO2 to the regional atmosphere with ∼17 times higher emission from the Hooghly compared to the Sundarbans. Taken together, the cycling of C in estuaries with different levels of anthropogenic influences is evidently different, with significantly higher CO2 emission from the anthropogenically influenced estuary than the mangrove-dominated ones.

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Section: Computation Of Air-water Co 2 Flux and %Domentioning

confidence: 99%

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confidence: 99%

The post-monsoon carbon biogeochemistry of the Hooghly–Sundarbans estuarine system under different levels of anthropogenic impacts

et al. 2019

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“…Studies on the sources and export fluxes of DIC from the Indian rivers are very limited. Though DIC measurements were conducted in some Indian estuaries, for example, Mandovi and Zuari (Sarma et al, 2001), Godavari (Sarma et al, 2011), Cochin (Gupta et al, 2009;Bhavya et al, 2018), Hooghly (Mukhopadhyay et al, 2002;Samanta et al, 2015), Mahanadi (Pattanaik et al, 2017) and Chilka (Gupta et al, 2008;Muduli et al, 2013), they were confined only to the internal cycling of DIC and exchange of CO 2 at the airwater interface but were not focused on the sources and export fluxes of DIC. The major sources of DIC in the Indian rivers remain unclear, except only a couple of rivers, Krishna (Das et al, 2005;Laskar et al, 2014) and Ganges (Samanta et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Export fluxes of dissolved inorganic carbon to the northern Indian Ocean from the Indian monsoonal rivers

et al. 2019

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Abstract. Rivers are an important source of dissolved inorganic carbon (DIC) to the adjacent coastal waters. In order to examine the spatial variability in the distribution and major sources of DIC in the Indian monsoonal rivers and to quantify their export flux to the northern Indian Ocean, 27 major and medium-sized rivers were sampled during the discharge period. Significant spatial variability in concentrations of DIC (3.4–73.6 mg L−1) was observed, and it is attributed to spatial variations in the precipitation pattern, the size of rivers, pollution and lithology of the catchments. The stable isotopic composition of DIC (δ13CDIC) also showed strong spatial variability (−13.0 ‰ to −1.4 ‰) in the Indian monsoonal rivers with relatively depleted δ13CDIC values in rivers of the northwest of India (-11.1±2.3 ‰) and enriched values in the southeast of India (-3.5±2.3 ‰). Results of the linear least-squares regression models of Keeling and Miller–Tan's plots indicated that the chemical weathering of carbonate and silicate minerals by soil CO2 is the major source of DIC in the Indian monsoonal rivers. Spatial variability in the deviation of δ13CDIC from the approximated δ13C of the source may probably be due to dominant autotrophic production in rivers of the southeastern region, whereas heterotrophic decomposition of organic matter largely influences the other Indian monsoonal rivers. It is estimated that the Indian monsoonal rivers annually export ∼10.3 Tg of DIC to the northern Indian Ocean, of which the major fraction (75 %) enters into the Bay of Bengal, and the remaining fraction reaches to the Arabian Sea. This is consistent with the freshwater flux, which is 3 times higher for the Bay of Bengal (∼378 km3 yr−1) than for the Arabian Sea (122 km3 yr−1). Despite discharge from the Indian monsoonal rivers accounting for only 1.3 % of the global freshwater discharge, they disproportionately export 2.5 % of the total DIC exported by the world's major rivers. Despite rivers from the region in the southwest (SW) of India exporting DIC that is an order of magnitude lower (0.3 Tg yr−1) than the rivers from other regions of India, the highest yield of DIC was found in the rivers of the SW region of India. It is attributed to intense precipitation (∼3000 mm), favorable natural vegetation of tropical moist deciduous and tropical wet evergreen and semi-evergreen forests, tropical wet climate, high soil organic carbon, and the dominance of red loamy soils in catchments of the rivers of the SW region.

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“…Generally, the stable isotope signature of DIC in estuaries follows mixing process between marine and freshwater end-members (Mook and Tan, 1991), attesting that DIC levels are mainly controlled by physical processes (Wang et al, 2016). However, deviation from mixing curves are frequently reported (Coffin and Cifuentes, 1999;Bouillon et al, 2003;Gillikin et al, 2006;Miyajima et al, 2009;Bouillon et al 2011;Bhavya et al, 2018). The δ 13 C-DIC data below conservative mixing suggest prevalence of respiration that adds depleted δ 13 C-DIC (Bouillon et al, 2003;Bouillon et al 2011).…”

Section: Introductionmentioning

confidence: 98%

“…Therefore, aquatic https://doi.org/10.1016/j.ecss.2019.02.048 Received 27 November 2018; Received in revised form 27 February 2019; Accepted 28 February 2019 primary production tends to leave the water rich in 13 C, increasing δ 13 C-DIC signatures (Zeebe and Wolf-Gladrow, 2001). On the other hand, the degradation of organic carbon by respiring heterotrophic organisms, either in pelagic or in benthic compartments, produces CO 2 with approximately the same isotopic signature of the respired organic matter, decreasing δ 13 C-DIC signatures (Kendall and Doctor, 2004;Miyajima et al, 2009;Bouillon et al 2011;Bhavya et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Sources and sinks of dissolved inorganic carbon in an urban tropical coastal bay revealed by δ13C-DIC signals

Cotovicz

Knoppers

Deirmendjian

et al. 2019

Estuarine, Coastal and Shelf Science

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Dissolved inorganic carbon (DIC), its stable isotope composition (δ 13 C-DIC) and ancillary parameters of the water column were investigated in a eutrophic tropical marine-dominated estuary surrounded by a large urban area (Guanabara Bay, Rio de Janeiro, Brazil). Most negative δ 13 C-DIC signatures (down to −6.1‰) were found in polluted regions affected by direct sewage discharges where net heterotrophy induces high partial pressure of CO 2 (pCO 2) and DIC concentrations. Keeling plot was applied to this polluted region and determined the δ 13 C-DIC sewage signature source of −12.2‰, which is very consistent with isotopic signature found in wastewater treatment plans. These negative δ 13 C-DIC signatures (i.e., DIC depleted in 13 C) were restricted to the vicinity of urban outlets, whereas in the largest area of the bay δ 13 C-DIC signatures were more positive (i.e., DIC enriched in 13 C). The most positive δ 13 C-DIC signatures (up to 4.6‰) were found in surface waters dominated by large phytoplankton blooms, with positive correlation with chlorophyll a (Chl a). In the largest area of the bay, the preferential uptake of the lighter stable carbon isotope (12 C) during photosynthesis followed the Rayleigh distillation, and appeared as the most important driver of δ 13 C-DIC variations. This reveals an important isotopic fractionation (ε) by phytoplankton due to successive algal blooms that has turned the remaining DIC pool enriched with the heavier stable carbon isotope (13 C). The calculated diel apparent ε showed higher values in the morning (18.7‰-21.6‰) and decreasing in the afternoon (6.8‰-11.1‰). ε was positively correlated to the pCO 2 (R 2 = 0.88, p = 0.005) and DIC concentrations (R 2 = 0.73, p = 0.02), suggesting a decline in carbon assimilation efficiency and decreasing uptake of the lighter carbon under CO 2 limiting conditions. The eutrophic coastal waters of Guanabara Bay have δ 13 C-DIC signatures well above that found in estuaries, shelf and ocean waters worldwide.

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Spatio-temporal variation in δ 13 C DIC of a tropical eutrophic estuary (Cochin estuary, India) and adjacent Arabian Sea

Cited by 16 publications

References 29 publications

The post-monsoon carbon biogeochemistry of the Hooghly–Sundarbans estuarine system under different levels of anthropogenic impacts

The post-monsoon carbon biogeochemistry of the Hooghly–Sundarbans estuarine system under different levels of anthropogenic impacts

Export fluxes of dissolved inorganic carbon to the northern Indian Ocean from the Indian monsoonal rivers

Sources and sinks of dissolved inorganic carbon in an urban tropical coastal bay revealed by δ13C-DIC signals

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