Background

The IEAGHG workshop on Natural Releases of CO₂: Building Knowledge for CO₂ Storage Environmental Impact Assessments was held in Maria Laach, Germany, in November 2010 and hosted by CO2GeoNet and BGR.  The workshop was well attended, with forty seven participants from over ten different countries.

Sessions included: Setting the Scene; Releases, Magnitudes and Impacts: Marine Environments and Terrestrial Environments; Mobilisation of Brine and Metals; Near Surface vs. Deep Subsurface Mechanisms and, Monitoring Challenges in Light of Natural Systems.  Due to considerable interest in the workshop and an overly prescribed agenda, poster sessions were included within coffee and lunch breaks, with eight presented posters during the workshop.

Presentations showed there are now regulations in place specifying the need to monitor and detect leakage and impacts, both in the EU CCS Directive to detect and measure impact, and in the ETS Directive to quantify leakage; however uncertainty remains  and the research community are asked to provide information to move this forward.  There have been various studies on natural and controlled release sites, which can be used to learn where CO₂ leakage is more likely to occur; the structural or geological controls on leakage should any occur; potential rates; spatial-temporal scale and transport processes; how humans, plants and animals are impacted; mitigation strategies and, the most cost effective design of monitoring techniques.  Though much can be learnt it was noted it is important to recognise limitations as well as the benefits and maintain the context ensuring experimental programmes are created to understand key processes and responses to changing conditions.

Research to-date has shown decreased biodiversity in environments of enriched CO₂, and changes in species (particularly calcareous organisms); however species can cope if there is sufficient energy from other sources e.g. methane.  Particularly noteworthy was the presentation on mofettes by Hardy Pfanz, which showed CO₂ terrestrial release sites can be mapped by plant and soil-animal species (introducing the terms ‘mofettophilic’ and ‘mofettophobic’), and concentrations may even be determined by understanding the impact on specific species, with research highlighting the possibility of global indicator species.

A portfolio of technologies is recommended for detection, quantification and system understanding, and shallow monitoring strategies should be iterative based upon deep monitoring tools.  There are various monitoring technologies available, and they are seen to be sufficient to detect CO₂ bubbles streams and to monitor chemical effects (such as pH and pCO₂) in the marine environment, including hydroacoustical methods; though technologies to assess impacts are still being developed or are currently being applied e.g. ROVs (see section 2.1).  Various tools are required to determine the effects of CO₂ injection and to ascertain what is being mobilised new sensors need to be developed and, existing sensors improved (see section 3).  Additionally, there is a need for more site investigations to understand CO₂ processes and their natural variability, as baseline monitoring is crucial to meet political and public perception challenges (see section 5).  Research indicates it is important to monitor gases other than CO₂, such as nitrogen and oxygen, to aid understanding of site-specific processes (see section 5.2.1), and in terms of microbiological impacts, there is a systematic response to high CO₂ concentrations: understanding this response is critical to the implementation of CCS .