ANDRADE, C., CRUZ, J.V., VIVEIROS, F., COUTINHO, R. (2019) – CO₂ flux from volcanic lakes in the Western Group of the Azores Archipelago (Portugal). Water, 11(3): 599, doi: 10.3390/w11030599.

​Here, we present the first detailed study on diffuse CO₂ degassing in the lakes in the Western Group (Corvo and Flores islands) of the Azores archipelago. This research is of interest in order to determine (1) the overall CO₂ emission from such lakes, as volcanic lakes are often underrepresented in the databases of these water bodies, and (2) the diffuse CO₂ degassing estimates in active volcanic areas such as the Azores. The lake waters on Corvo and Flores islands are mainly of the Na-Cl type, which is likely caused by the lakes’ sea salt signatures, arising from nearby seawater spraying; however, a few samples show evidence of slight alkali earth metal and bicarbonate enrichments in the lake waters, suggesting a contribution of water-rock interaction. In this study, diffuse CO₂ flux measurements were taken using the accumulation chamber method, and statistical analyses utilizing the graphical statistical approach (GSA) and sequential Gaussian simulation (sGs) were conducted on the CO₂ flux data, showing that the CO₂ flux values measured in these lakes were relatively low (0.0-18.6 g m⁻² d⁻¹). The results seem to indicate that there is a single source of CO₂ (a biogenic source), which is also supported by the waters’ δ¹³C isotopic signatures. Significant differences in the final CO₂ output values were verified between surveys (e.g., 0.16 t d⁻¹ in R1; 0.32 t d⁻¹ in R2), and these differences are probably associated with the monomictic character of the lakes. CO₂ emissions ranged between 0.18 t d⁻¹ (CE1) and 0.50 t d⁻¹ (CW1) for the Corvo lakes and between 0.03 t d⁻¹ (P1) and 0.32 t d⁻¹ (R2) for the seven lakes studied on Flores Island. The presence of a dense macrophyte mass in a few of the lakes appears to enhance the CO₂ flux in these lakes.