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

Abstract

CO 2 capture and geological storage offers an option for reducing man-made greenhouse gas emissions. But one major concern related to geological CO 2 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 CO 2 release from reservoirs into near surface terrestrial environments. To understand the effect of CO 2 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 "CO 2 GeoNet" on a natural CO 2 vent at the Laacher See, Germany. Near surface CO 2 conditions and CO 2 fluxes of the venting area were described by means of conventional soil gas measurement equipment, and brought up the difference between the CO 2 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 some remarkable vegetation changes like the investigation of important soil microbial communities showed significant differences between the CO 2 -rich sites (up to 90% and more of soil gas), medium CO 2 sites (~20%), and control locations with background CO 2 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 CO 2 concentrations. At the end, this ongoing study should identify possible candidates in the botanical and microbial kingdoms, whose presence or absence provide easily detectable indicators for the leakage of CO 2 from deep reservoirs into near surface terrestrial ecosystems.

Comparison of the impacts of elevated CO 2 soil gas concentrations on selected European terrestrial environments

“…Zone 3) was also seen as a consequence of long-term exposure of the soil environment to elevated CO 2 (plus trace H 2 S) concentrations and the associated drop in pH. A similar shift in community composition was also seen within the vent area at Laacher See (Frerichs et al, 2013;Krüger et al, 2011) and Florina (Ziogou et al, 2013). Additionally, at Laacher See, the archaeal community composition changed along the transect, with a predominance of Crenarchaeota-and Thaumarchaeota-associated genetic sequences in the vent area.…”

“…Release is typically from gas vents, characterised by a small core of elevated gas flux (Möller, 2009). One defined gas vent has been studied on the western side of the lake, the age of which is estimated to be less than 150 years (Krüger et al, 2011). The vent is in a large field used for cattle pasture.…”

“…Surveys near the Laacher See were conducted in September 2007 and July 2008 along a 60 m transect across the vent (Figure 1) which provided a range of different CO 2 soil gas concentrations and fluxes (Krüger et al, 2011). Detailed botanical, microbiological, mineralogical and geochemical analyses were performed at the site in addition to the gas measurements.…”

“…Consequently, the impact of elevated CO 2 soil gas concentrations and fluxes on near-surface ecosystems and soils (to a depth of ~1 m) has been an area of active research, particularly where there are naturally occurring CO 2 releases from volcanic or geothermal areas. These include studies in California, USA (Bergfield et al, 2006;Biondi and Fessenden, 1999;McFarland et al, 2013;Stephens and Hering, 2004); Germany (Frerichs et al, 2013;Krüger et al, 2011, Oppermann et al, 2010; Greece (Ziogou et al, 2013); Italy Donders et al, 2013;) and Slovenia (e.g. Maček et al, 2005;Pfanz et al, 2007;Šibanc et al, 2014).…”

“…It evaluates all these results and presents, for the first time, general unified conclusions from these studies, providing CO 2 thresholds where effects on plants and soil microbiology are observed and making recommendations on how this information can be used when planning CO 2 storage projects. The sites include those where CO 2 is being naturally released to the atmosphere from deep geological formations (Florina, Greece (Ziogou et al, 2013); Laacher See, Germany (Krüger et al, 2011); and Latera, Italy; ) and a nonadapted site, with no previous history of CO 2 seepage, where CO 2 has been injected into the unsaturated soil horizon (Artificial Soil Gassing and Response Detection (ASGARD) field site, England) (Smith et al, 2013;West et al, 2009). …”