Spatial and temporal variability of CO2 fluxes in tropical estuarine systems near areas of high population density in Brazil

Quantifications of CO2 fluxes across the air–water interface of estuarine ecosystems are needed to understand regional carbon balances. In this study, we estimate the amount of carbon emitted from tropical estuaries of the State of Pernambuco, Brazil, using measurements of temperature, alkalinity, salinity and pH at stations located in the estuaries. The results showed that the average CO2 fluxes (+51 ± 32 mmol m−2 day−1) were mainly a product of the input of aloctone organic matter from urban centers with high population densities (~1,000 inhabitants.km−2) adjacent to the estuarine systems. This organic material increased the amount of aqueous CO2, which increased the pCO2 to 8,900 μatm. October, November and December had the highest monthly averages of the parameters associated with the carbonate system (HCO3−, dissolved inorganic carbon, aqueous carbon dioxide, CO32−, total alkalinity, temperature and pH), whereas the averages in July correlated with the CO2 fluxes. Multivariate analysis revealed that estuarine areas near the most densely populated areas (Beberibe—9,000 inhabitants.km−2 and Paratibe—3,000 inhabitants.km−2) were positively correlated with high CO2 fluxes and high pCO2.