Carbon dioxide sources and sinks in the delta of the Paraíba do Sul River (Southeastern Brazil) modulated by carbonate thermodynamics, gas exchange and ecosystem metabolism during estuarine mixing

Abstract

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

“…Following the seaward direction, the levels of pCO2 decreases exponentially with the increases of salinity. This decrease is associate with degassing, biogeochemical processes and mixing with low-pCO2 waters (Cotovicz et al 2020). The CO2 degassing is strongest at the freshwater stations, taking account that the dissolved concentrations are at the highest in this estuarine region, creating a steep gradient between the pCO2 in the air and in the water.…”

“…In this way, the pCO2 values reflects both the physical mixing, and the biogeochemical processes. For intermediate to high-salinities the low values of pCO2 values are expected due to the mixing with low-pCO2 seawaters (Chen et al 2013;Cotovicz et al 2020), taking account that the adjacent coastal waters present pCO2 averaging 411 ppmv (Cotovicz et al, 2015). The uptake of CO2 by primary producers are likely to occur since that phytoplankton blooms occurred in some stations, and also attributed to this marked decline of pCO2.…”

“…The internal processes of respiration of organic matter in eutrophic aquatic ecosystems modifies not only the CO2 concentrations, but all the parameters of the carbonate chemistry, with influences on the acid-base properties, altering the pH, and concentrations of total alkalinity (TA) and dissolved inorganic carbon (DIC) (Abril and Frankignoulle 2001;Cai et al 2011;Sunda and Cai 2012;Cotovicz et al 2018). However, eutrophication can also contributes to promote CO2 sink by stimulating the primary production with important CO2 uptake in coastal waters that receives important amounts of nutrients (Borges and Gypens 2010;Cotovicz et al 2015Cotovicz et al , 2020Kubo et al 2017). In this regard, eutrophication can both amplify CO2 outgassing (when organic matter is intensely degraded by microbial activities) or CO2 ingassing (when organic matter is intensely produced by primary producers).…”

Coastal Ocean Observing and Modeling Systems in Brazil: Initiatives and Future Perspectives

“…BrOA has identified the most ocean acidification sensitive ecosystems as the coral reefs and rhodolith beds along the eastern and north-eastern Brazilian shelf, as well as inner shelf areas under influence of megacities or riverine freshwater input (Kerr et al, 2016). Ocean acidification is exacerbated by the combination of anthropogenic CO 2 uptake and increased organic matter degradation from human-driven eutrophication, especially at subsurface layers in coastal areas (Jiang et al, 2019;Cotovicz et al, 2020;Marotta et al, 2020). The extension and heterogeneity of the Brazilian coastline and Exclusive Economic Zone are also a challenge.…”

Eutrophication overcoming carbonate precipitation in a tropical hypersaline coastal lagoon acting as a CO2 sink (Araruama Lagoon, SE Brazil)

“…However, many exceptions exist where autotrophic systems are CO2 sources and heterotrophic systems are CO2 sinks (Borges 2005;Cotovicz et al 2020;Abril et al 2021). In addition, the diurnal variability of carbonate chemistry parameters and associated air-water CO2 fluxes are significant in productive ecosystem (Cotovicz et al 2015).…”