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Geophysical Research Abstracts
Vol. 21, EGU2019-8052, 2019
EGU General Assembly 2019
© Author(s) 2019. CC Attribution 4.0 license.
In situ experimental study of the formation and physicochemical
circumstances of thermal water-related biogeochemical precipitates and
calcites
Petra Kovács-Bodor (1), Dóra Anda (2), Judit Makk (3), Mihály Óvári (2), Árpád Bihari (4), Mihály Braun (4),
István Futó (4), and Judit Mádl-Sz˝
onyi (1)
(1) József and Erzsébet Tóth Endowed Hydrogeology Chair, Department of Physical and Applied Geology, Eötvös Loránd
University, Budapest, Hungary (petra.bodor28@gmail.com), (2) MTA Centre for Ecological Research, Danube Research
Institute, Budapest, Hungary, (3) Department of Microbiology, Eötvös Loránd University, Budapest, Hungary, (4) Isotope
Climatology and Environmental Research Centre, Institute for Nuclear Research, Hungarian Academy of Sciences, Debrecen,
Hungary
The formation and evolution (and so the age) of biogeochemical precipitate and calcite of thermal springs are diffi-
cult to study in their natural environment and in laboratory. In situ experiments are useful tools to better understand
the physicochemical circumstances, growth and the role of microbes in mineral formation.
A 12-week-long in situ experiment was conducted in a 37◦C warm flowing water (with a ∼1.5*10-4 m3/s volume
discharge) in a 130-m-long trapezoid-shaped channel. Physicochemical parameters (temperature, specific electrical
conductivity, pH, dissolved oxygen content) of the water was measured continuously. The concentration of major
ions, trace elements (in filtered and unfiltered water), and the specific activity of 226Ra and 222Rn were followed
along the flow path three times during the experiment. The formation of precipitates was followed on glass slides
(put perpendicular to the water flow into the channel at 1, 8, 20, 40, 60, 80, 100 and 120 m far from the source of
the water) under stereo, transmitted light and scanning electron microscopes.
The attachment of rod-shaped bacteria to the surface of the slides could be seen after one day along the whole
flow path. After two days, calcite crystals formed after 80 m. By the 6th week, there was enough precipitate for
analytical measurements. At the first 15 m, red, amorphous iron-oxyhydroxide formed. Around 20 m, light red
calcite formed, built-up by rhombohedral crystals. Between 30 and 120 m, yellowish grey calcite could be seen,
composed by dendritic crystals with trapped microbial filaments inside them. These precipitates were sampled
again for detailed analysis after 12 weeks.
The analysis (gamma spectroscopy, ICP-MS) of the six and twelve-week-old precipitates suggests that the iron-
oxyhydroxides have high adsorption capacity, resulted in elevated trace element (e.g. As, Fe, Mn, P, S) and ra-
dionuclide (226Ra) content. The effect of calcite precipitation and evaporation of water can be detected in the
changing stable isotope (δD, δ18O) composition of the precipitates along the flow path. Mössbauer spectroscopy
proved that the concentration of Fe(III) (in the form of ferrihydrite/goethite) is decreasing along the flow path until
20 m, then it is undetectable.
The simultaneous study of the physicochemical parameters of the water and the forming precipitates during an in
situ experiment can help to improve our understanding of the circumstances and processes of mineral formation.
The research was supported by the NK 101356 OTKA research grant, the European Union and the State of Hun-
gary, co-[U+FB01]nanced by the European Regional Development Fund in the project of GINOP-2.3.2.-15-2016-
00009 ‘ICER’. 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.