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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.

21This paper provides an overview of regional geochemical mapping using stream 22 sediments from central and south-western Nigeria. A total of 1569 stream sediment 23 samples were collected and 54 major and trace elements determined by ICP-MS and 24Au, Pd and Pt by fire assay. Geostatistical techniques (e.g. correlation analysis and 25 principal factor analysis) were used to explore the data, following appropriate data 26 transformation, to understand the data structure, investigate underlying processes 27 controlling spatial geochemical variability and identify element associations.

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