Resuming volcanic surveillance at Lago Albano: updates on the dissolved gas content and vertical temperature profiles

In April 2019, in the framework of the FISR-2016 CALAPA project, Lake Albano (Colli Albani volcanic complex, Rome, Italy) was the target of a geochemical sampling and measurement campaign, the first one of this kind since May 2010 (Chiodini et al., 2012). Conductivity, pH, and temperature were measured along the vertical profile of the lake, until a maximum depth of about 160 m. An evident thermocline is observed near 10 m depth, showing a T drop from 13.1°C at the surface to 9.9°C near 20 m depth. This thermocline has remained stable with respect to May 2010: a T drop from 16 to 10°C in May 2010 for the same depth interval. Temperature further dropped till 9.2°C between 20 m depth and the bottom. The 95 m thermocline, as observed in May 2010, was less evident in April 2019, probably due to the fact that a lower bottom temperature was detected in May 2010 (8.7°C). pH dropped from 9.1 at the surface to 7.6 near the bottom. These pH values fit the increasing pH trend as observed between 1989 and 2010. Alkalinity follows a long-term decreasing trend. The degassing model for Lake Albano proposed by Chiodini et al. (2012) is revised based on the full chemical composition (dissolved gases, major, minor and trace elements, He-C isotope systematics of dissolved gases). Apparently, partial CO2 degassing during density driven winter roll-over events is a fact, but not a factor to explain the alkalinity drop on the long-term. Temperature loggers were installed at six different depths (at 2, 8, 23, 43, 73 and 153 m depth) to track seasonal variations in lake water temperatures. This will enable to better understand thermal lake stratification, lake stability and its relation to CO2degassing from Lake Albano, and to better constrain the geochemical evolution shown by the lake during the last 30 years.