As regional groundwater flow systems arise to the surface as a reductive thermal spring with high TDS, CO2 and often also high trace element and 226Ra content, complex biogeochemical processes begin. Buda Thermal Karst system (Hungary) is a regional discharge area, where these processes can be studied near the surface. The surface of carbonate rocks where the reductive thermal water and the oxidative air interacts (redox environment change), provide a good inhabitation for biofilm-forming bacteria. Escaping CO2 increases the water’s saturation with respect to calcite, resulting in calcite precipitation. These two major driving forces lead to the formation of biogeochemical precipitates (BGPs). BGPs have a high absorption capacity, accumulating large amount of trace elements and radionuclides from the water. The simultaneous examination of the parent fluid and the forming precipitates with comprehensive analytical methods, such as scanning electron microscopy, stereo microscopy, X-ray powder diffraction, inductively coupled plasma mass spectrometry, gamma spectroscopy, give a chance to better understand the ongoing processes. The results of the nature-based experiences were used in the analysis of scales, formed in geothermal plants, as the same processes act also in man-made systems. Furthermore, we could use the purchased information during the comparison of recent and paleo spring cave precipitates of the Buda Thermal Karst, to find indicators for similar paleo processes.
This study is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980.