Carbon dioxide emissions from estuaries of northern and northeastern Brazil

The carbon dioxide flux through the air-water interface of coastal estuarine systems must be quantified to understand the regional balance of carbon and its transport through adjacent coastal regions. We estimated and calculated the emissions of carbon dioxide (FCO2) and the partial pressure of CO2 (pCO(2)) values in 28 estuarine environments at a variety of spatial scales in the northern and northeastern regions of Brazil. The results showed a mean FCO2 (water to air) of 55 +/- 45 mmol.m(-2).d(-1). Additionally, a negative correlation between dissolved oxygen saturation and pCO(2) was observed, indicating a control by biological processes and especially by organic matter degradation. This leads to increased dissolved CO2 concentration in estuarine waters which results in a pCO(2) that reached 8,638 mu atm. Our study suggests that northern and northeastern Brazilian estuaries act as sources of atmospheric CO2. The range of pCO(2) observed were similar to those found in inner estuaries in other places around the world, with the exception of a few semi-arid estuaries (Koppen climate classification - BSh) in which record low levels of pCO(2) have been detected.