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Greenhouse gas emissions (CO2 and CH4) and inorganic carbon behavior in an urban highly polluted tropical coastal lagoon (SE, Brazil)

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Increasing eutrophication of coastal waters generates disturbances in greenhouse gas (GHG) concentrations and emissions to the atmosphere that are still poorly documented, particularly in the tropics. Here, we investigated the concentrations and diffusive fluxes of carbon dioxide (CO2) and methane (CH4) in the urban-dominated Jacarepagua Lagoon Complex (JLC) in Southeastern Brazil. This lagoonal complex receives highly polluted freshwater and shows frequent occurrences of anoxia and hypoxia and dense phytoplankton blooms. Between 2017 and 2018, four spatial surveys were performed (dry and wet conditions), with sampling in the river waters that drain the urban watershed and in the lagoon waters with increasing salinities. Strong oxygen depletion was found in the rivers, associated with extremely high values of partial pressure of CO2 (pCO2; up to 20,417 ppmv) and CH4 concentrations (up to 288,572 nmol L−1). These high GHG concentrations are attributed to organic matter degradation from untreated domestic effluents mediated by aerobic and anaerobic processes, with concomitant production of total alkalinity (TA) and dissolved inorganic carbon (DIC). In the lagoon, GHG concentrations decreased mainly due to dilution with seawater and degassing. In addition, the phytoplankton growth and CH4 oxidation apparently consumed some CO2 and CH4, respectively. TA concentrations showed a marked minimum at salinity of ~20 compared to the two freshwater and marine end members, indicating processes of re-oxidation of inorganic reduced species from the low-salinity region, such as ammonia, iron, and/or sulfides. Diffusive emissions of gases from the entire lagoon ranged from 22 to 48 mmol C m−2 d−1 for CO2 and from 2.2 to 16.5 mmol C m−2 d−1 for CH4. This later value is among the highest documented in coastal waters. In terms of global warming potential (GWP) and CO2 equivalent emissions (CO2-eq), the diffusive emissions of CH4 were higher than those of CO2. These results highlight that highly polluted coastal ecosystems are hotspots of GHG emissions to the atmosphere, which may become increasingly significant in future global carbon budgets.

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The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.


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This study was supported by the Carlos Chagas Foundation for Research Support of the State of Rio de Janeiro (FAPERJ; proc. no. E- 26202.785/2016) and by the Coordination for the Improvement of Higher Education Personnel (CAPES). Luiz C. Cotovicz Jr. thanks the Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico (FUNCAP; Proc. No. INT-00159-00009.01.00/19) and UFC-PRPPG for a visiting professor grant at the Marine Sciences Institute (LABOMAR). This work is also a contribution to the International Research Project Vulnérabilité des Ecosystèmes Littoraux Tropicaux face à l’Eutrophisation funded by the French National Centre for Scientific Research (CNRS-INEE); and a scientific contribution for the Red Latinoamericana de Acidificación del Océano (LAOCA).


Carlos Chagas Foundation for Research Support of the State of Rio de Janeiro (FAPERJ; proc. no. E- 26202.785/2016).

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LCCJr: Conceptualization, Coordination, Execution, Data curation, Formal analysis, Methodology, Writing – original draft. RPR: Laboratorial Analysis, Writing – review. LOV, CRR, DT, LG: Execution, Laboratorial Analysis. MB, RS: Conceptualization, Execution, Writing – review. BAK: Conceptualization, Funding acquisition, Supervision, Writing – review. GA: Conceptualization, Data curation, Formal analysis, Methodology, Supervision, Writing – original draft.

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Correspondence to Luiz C. Cotovicz Jr.

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Responsible editor: V. V.S.S. Sarma

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• Oxygen-depleted river waters were associated with high concentrations of TA and DIC.

• TA and DIC decreased in the mixing region due to re-oxidation processes.

• Extreme high concentrations and emissions of CO2 and CH4 were found in hypoxic/anoxic polluted river waters.

• Concentrations and emissions of GHGs decreased seaward as a result of mixing, degassing, and biological uptake.

• The diffusive CH4 emissions were more important than CO2 emissions in terms of global warming potential.

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Cotovicz, L.C., Ribeiro, R.P., Régis, C.R. et al. Greenhouse gas emissions (CO2 and CH4) and inorganic carbon behavior in an urban highly polluted tropical coastal lagoon (SE, Brazil). Environ Sci Pollut Res 28, 38173–38192 (2021).

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