Dissolution of CaCo3 in calcareous soils is mainly governed by CO2 which forms a weak but ubiquitous acid in the aqueous phase. It is generally assumed, that it is mainly the CO2 concentration and the discharge control the re-location of CaCO3, and thus the further formation of soil and karst. In most cases soil and karst systems are considered to be static and that the CaCO3 dissolution process is a steady state process, that can be derived from the amount of water infiltrating into the deeper soil or karst system, and the mean CO2 concentration in the deeper soil (Williams 1983). Soil CO2 measurements in a calcareous soil showed, however, a strange phenomenon. Low intensity precipitation and following slow infiltration only resulted in a increase in soil CO2 concentration, since the rain water blocks the soil pores. Intense precipitation followed by fast infiltration and probably preferential flow, however, resulted in temporary drops in soil CO2 (Maier et al 2010).These drops can be explained by a relative undersaturation of the soil solution with CO2 and are probably associate with a much stronger dissolution of CaCO3 followed by the transport of the dissoluted CaCO3.

Since the intensity of this phenomenon seems to depend on rain intensity , we hypothesize that rain intensity affects dissolution and re-location of CaCO3. This might mean that on the long term relocation of CaCO3, soil formation and karst formation depend possibly more on the precipitation regimes or individual events more than on the groundwater seepage.

We want to test the effect of different precipitation regimes on CaCO3 re-location using soil samples from different sites (e.g. Schönberg, Vogtsburg, Hartheim).The sites will have different characteristics regarding, saturated and unsaturated conductivity, pore structure (preferential flow?), and soil aeration. Soil CO2 will be monitored during the measurements. Re–located CaCO3 seeping from the samples will be quantified. Different precipitation events will be simulated. All technical equipment necessary for construction of the set-up is available.

Andreas Hartmann, Martin Maier (Bodenkunde)

none.

Andreas Hartmann andreas.hartmann@hydrology.uni-freiburg.de Martin Maier martin.maier@bodenkunde.uni-freiburg.de

Good technical skills required and accurate manual field and lab work is essential for the successful implementation of the MSc. Topic. Interest in geochemical prcesses is essential and interest in developing modelling approaches to explain the observed results are welcome and will be supported but are not essential.

English or German

Maier, M., Schack-Kirchner, H., Hildebrand, E.E., Holst, J., 2010. Pore-space CO2 dynamics in a deep, well-aerated soil. Eur. J. Soil Sci. 61, 877–887 Williams, P.W., 1983. The role of the subcutaneous zone in karst hydrology. Journal of Hydrology 61, 45–67