Effects of elevated CO2 concentrations on the vegetation and microbial populations at a terrestrial CO2 vent at Laacher See, Germany

CO2 capture and geological storage offers an option for reducing man-made greenhouse gas emissions. But one major concern related to geological CO2 storage is the possibility of leakage from the reservoir and subsequent effects on the environment, which cannot completely be excluded. This study aims at investigating the environmental impact of CO2 release from reservoirs into near surface terrestrial environments. To understand the effect of CO2 leakage on such an ecosystem, detailed knowledge on the abundance and diversity of plants and microorganisms is essential. Therefore, an ecosystem study has been conducted within the Network of Excellence "CO2GeoNet" on a natural CO2 vent at the Laacher See, Germany. Near surface CO2 conditions and CO2 fluxes of the venting area were described by means of conventional soil gas measurement equipment, and brought up the difference between the CO2 anomalies and their surroundings. A comparison of the soil columns between control sites and the centre of the venting area showed a small but significant change in the soil pH below 10 cm. The botanical survey revealed vegetation changes which, like the investigation of important soil microbial communities, showed significant differences between the CO2-rich sites (up to 90% and more of soil gas), medium CO2 sites (∼20%), and control locations with background CO2 concentrations. The ecosystem appears to be adapted to the different conditions through species substitution or adaptation, showing a shift towards anaerobic and acidotolerant to acidophilic species under elevated CO2 concentrations. It is hoped that the final outcome of this ongoing study will be the identification of possible botanical and microbial indicators, whose presence or absence provides easily detectable evidence for leakage of CO2 from deep reservoirs into near surface terrestrial ecosystems.