ANDRADE, C., CRUZ, J.V., VIVEIROS, F., COUTINHO, R. (2019) - Estudo hidrogeoquímico nos lagos vulcânicos dos Açores. Hydrogeochemistry study in volcanic lakes of Azores. In: Nogueira, P. Moreira, N., Roseiro, J., Maia, M. (Eds.), Extended Abstracts, XII Congresso Ibérico de Geoquímica - XX Semana da Geoquímica, Évora: 323-326.

​In the Azores archipelago there is a significant number of volcanic lakes, distributed along some islands of the archipelago. Thus, in order to better characterize the dynamics and hydrogeochemical processes occurring in these water bodies, samples were collected along the water column, according to vertical profiles carried out 44 lakes selected for the present study. Results shown that some lakes present a monomictic character, with the water column stratified during summer, while the remaining, usually of low depth, present permanent mixture along the year. Waters are mainly cold, low mineralized and are mainly of the Na-Cl type due to the deposition of salts of marine origin. Bicarbonate is another anion that is present in a significant content in some lakes due to the absorption of volcanic volatiles, contamination by fluids of volcanic origin, and water-rock interaction. In a large number of studied lakes, especially in the small lakes occurring in São Miguel island, dissolved carbon dioxide is associated to the gas exchanges that occur on the surface of the water bodies and to the decomposition of organic matter, enhanced by the ongoing eutrophication process. The main findings of the present research enable the definition of the lake geochemical baseline, which is of interest for ​the ongoing sismo-volcanic monitoring in the Azores.