Real-time monitoring of CO2-rich mineral waters and mofettes in the Eifel volcanic fields

Real-time fluid monitoring began in late 2020 in the East Eifel and currently includes 12 sites, such as abandoned CO₂ wells, mofettes, CO₂-rich springs, CO₂-rich soil, and a cold-water geyser in the West Eifel. For the first time, fluid data are being recorded continuously with a high temporal resolution of up to 1 Hz. Depending on the local site conditions, the following parameters are being monitored: instrument temperature and battery voltage; barometric pressure and temperature; meteorological parameters; water level, wellhead pressure, water temperature; radon in free gas phase; CO2 concentration and CO2 flux in soil gas. Data are transmitted hourly via FTP to GFZ. While we generally observe small seasonal variations, short-term transients related to heavy rain or local and distant earthquakes are indicated. Over longer periods, we observe trend changes in helium isotope ratios, radon concentration, and water temperature. For example, two sites exhibited significant helium isotope changes from 2021 to 2025, which appear to correlate with earthquake swarms at depth. These examples demonstrate the necessity of jointly interpreting meteorological, hydrogeological, geophysical, and geodetic data.