ANDRADE, C., CRUZ, J.V., VIVEIROS, F., COUTINHO, R. (2019) - Emissão de CO₂ na Lagoa das Sete Cidades (São Miguel, Açores). CO₂ emission from Sete Cidades Lake (São Miguel Island, Azores). In: Nogueira, P. Moreira, N., Roseiro, J., Maia, M. (Eds.), Extended Abstracts, XII Congresso Ibérico de Geoquímica - XX Semana da Geoquímica, Évora: 307-310.

​Sete Cidades Lake is located in the Sete Cidades volcano caldera, São Miguel Island, the biggest of the Azores archipelago. This lake is the biggest volcanic lake of the Azores, with a total area of 4.41 km², and it is composed by two connected lakes, Lagoa Azul and Lagoa Verde. Hydrogeochemical profiles were carried out in both lakes in different sampling sites. Waters are cold (mean=14.0 ºC), weakly mineralized (mean=116 µS/cm) and with neutral pH (mean=7.7). In what concerns the CO₂ fluxes at the surface of the lakes a survey was carried out and values are in the range of 0.3 to 17.2 g m^-2 d^-1 (Lagoa Azul) and 2.1 to 17.9 g m^-2 d^-1 (Lagoa Verde). The most significative degassing areas are found associated to the massive presence of macrophytes and algal blooms. The measured values seem to be correlated with one single CO₂ source, which is probably of biogenic nature. The estimated total CO₂ emission varied between 5.8 t d^-1 (Lagoa Verde) and 25.0 t d¹ (Lagoa Azul).