New insights into the degassing dynamics of Lago Albano (Colli Albani volcano, Rome, Italy) during the last three decades (1989-2019)

With this study a nine-year hiatus (May 2010-April 2019) in thequantification of the CO2 content of Lago Albano by our working grouphas been resolved through the acquisition and analysis from two newfield campaigns. Based on a CO2 budget analysis the dynamics of CO2degassing throughout the past thirty years (1989-2019) is detailedand quantified. The decreasing CO2 content (expressed as dissolvedinorganic carbon, DIC) in the lake, since the co-seismic CO2 inputduring the 1989-1990 seismic swarm beneath Colli Albani volcano, wasaccelerated at lake bottom layers (-140 m to bottom, near -160 m) in the4-5 years after the swarm, continued afterwards at lower depths (-125to -95 m), and seems to have reached steady-state conditions duringrecent years. The peculiar lake basin morphology has control on thedegassing dynamics. The low chemical gradients detected during theApril 2019 survey have induced near-zero degassing conditions, andarguably stopped the gas-self lifting process: Lago Albano might notbecome CO2-free in the future. This finding has implications for gashazard when the next seismic swarm will hit the area. The updateddegassing model also takes into account the lake level drop, andhence the volume decrease of Lago Albano, caused by excessive wellpumping for anthropic purposes. This volume decrease appears to havea destabilizing effect on the degassing dynamics, which renders LagoAlbano's gas release less predictable in the future. Enhanced gas surveys(high-frequency and fine-scale spatial measurements) are needed toshed light on how Lago Albano degasses in this quiescent stage duringthe Anthropocene. A submersible infra-red detector to directly measurein-lake dissolved CO2 concentrations, applied satisfactorily during thisstudy, is an adapted instrument to do so.