Change of magnetic mineralogy related to groundwater fluctuation and hydrocarbon contamination

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During a pilot study at a former military airbase (in Czech Rep.) we observed a change of magnetic properties due to fluctuations of hydrocarbon (HC) contaminated groundwater in unconsolidated sediments. A systematic increase of magnetite content was observed towards the upper limit of the fluctuation zone, an effect that has not been described before. In the proposed project we therefore want to (a) extend the field studies to localize and quantifiy this effect in more detail and (b) perform laboratory experiments by simulating controlled water level fluctuations (WLF) in order to reveal the character of magnetic changes (concentration, temporal dynamics, spatial extent) and to gain insight into the important driving processes. We assume that there are three key factors for the formation of ferro(i)magnetic minerals: (a) bacterial activity, (b) HC content, (c) water content. In the laboratory we want to study short and long-term (up to >1 year) processes and vary the following parameters: bacterial communities (iron oxidizing/reducing bacteria and sterile conditions), extent and frequency of WLF, type and content of HC. The study shall be jointly conducted by German and Czech groups with sound expertise in environmental magnetism and geomicrobiology. The work has relevance for developing simple methods for detection of HC in the environment, e.g. due to contamination.