One of the strategic aims in SFB 1313's second funding period is to foster collaboration and synergy between its four different project areas in order to achieve an integrated research programme that simultaneously bridges Project Areas A to C with support from Project Area D and the entire range of scales addressed in this Collaborative Research Centre. To emphasise this strategic development two “vision topics” were formulated:
- Salt precipitation, e.g. occurring due to evaporation in the unsaturated zone and driven by wind or solar radiation in the atmosphere and by capillary pumping from the saturated zone.
- Calcite dissolution in the subsurface which is relevant, e.g. during karstification where fluctuations in CO2 partial pressure are caused by atmospheric pressure fluctuations that can lead to increased dissolution potential due to induced convective mixing in the saturated zone.
- Fractures in porous media are of huge research interest. During SFB 1313's second funding period we will develop ideas for a third vision topic on fractures.
The vision topics illustrate how the commonalities of environmental engineering applications and their corresponding processes are planned to be handled, and how the structure of SFB 1313 reflects this approach in the coming years. Projects from different areas will contribute to the vision topics, so that area-spanning models will be developed that integrate the capabilities of the models from the individual areas.
Vision Topic "Salt Precipitation"
The primary focus of this vision topic is on soil salinisation with particular attention on the interactions between salt precipitation and evaporation. Results from SFB 1313's first funding period have shown that accurately modelling the evaporation of saline water from porous media in the presence of salt precipitation remains challenging on the REV scale. This is attributed to the complexity of salt precipitation that can range from efflorescent crusts at the top of the soil (e.g. NaCl) to subflorescent precipitation within the porous medium (e.g. MgSO4). In addition, it is evident that salt crusts formed on top of the soil must have their own porous structure to allow evaporation. However, the properties of this newly formed medium have not yet been adequately investigated experimentally.
The SFB 1313 research will focus on pore and REV-scale experiments and modelling, respectively. In particular, there will be executed REV-scale experiments that will be investigated with XRCT, NMR, and MRI measurements in collaboration with the Porous Media Lab (PML) and the expertise of our external partners at the Oregon State University. Furthermore, numerical simulations with DuMux shall confirm and verify the experimental data. This vision topic has already been worked on during the first funding period of SFB 1313. There is existing a scientific overlap with various SFB 1313 research projects.
Vision Topic "Calcite Dissolution"
The subject of calcite dissolution is a new research object within SFB 1313 and shall be investigated as vision topic, starting with the second funding period of SFB 1313 in January 2022.
Density-driven dissolution of carbon dioxide in water is a well-known and much described mechanism in geological sequestration of this greenhouse gas. It is remarkable that such enhanced dissolution does not receive attention in karst hydrology and speleology. Models and hypotheses on karst development are complex and consider many different processes. E.g. Seasonal variations of microbial soil activity and root respiration or barometric-pressure changes cause fluctuations in CO2 partial pressures. Dependent on the existence and strength of a karst-water background flow, fingering regimes might be triggered causing enhanced dissolution of CO2. This allows replenishment of CO2, and, thus, dissolutional power even deep in the water body without the need for percolating water to transport dissolved CO2.