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

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