Ultrahigh-resolution mass spectrometry of dissolved organic matter from a tar oil contaminated aquifer along biogeochemical gradients

Sabine Dvorski1, Jenny Westphal1, Claudia Kellermann2, Hubert Müller2, Michael Größbacher2, Mourad Harir1, Norbert Hertkorn1, Christian Griebler2, Philippe Schmitt-Kopplin1
1 Analytical BioGeoChemistry, Helmholtz Zentrum München
2 Institute of Groundwater Ecology, Helmholtz Zentrum München

P 7.5 in Controls of dissolved organic matter fluxes in ecosystems

Poster Session 1 on Monday, 16:30-18:30

For the assessment of natural attenuation of organic contaminants in porous aquifers a detailed knowledge on biogeochemical gradients, distribution of individual redox species, and microorganisms is essential. In a tar oil contaminated sandy aquifer at a former gas works site we thus installed a high-resolution multi-level well (HR-MLW) that allows groundwater sampling in high spatial resolution across a thin BTEX plume. Former studies at this test site demonstrated that sampling in the centimeter and decimeter scale is required to capture the prevailing steep and distinct biogeochemical gradients. As a result, the plume fringes were identified as hot spots of biodegradation and sulfate reduction was found to be the dominant redox process.

Our current study links on-site high resolution spatial sampling with high resolution molecular characterization of dissolved organic matter (DOM) from tar oil contaminated groundwater.  DOM, a major player in the global carbon cycle, is a highly complex and abundant mixture of organic compounds that is specific for all aquatic environmental compartments. It interacts continuously with its environment and its formation and decomposition is driven by a multitude of abiotic and biotic reactions. Thus the unique DOM signature reflects several key ecosystem characteristics.

Solid phase extracted DOM from groundwater was analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS), which has been proven to be a powerful tool to unravel the diverse characteristics of abiotic and biotic complexity of DOM. This technique benefits from ultrahigh mass accuracy and resolution that enable its unique capacity to unambiguously distinguish between CHO and sulfur organic compounds (CHOS).

The mass spectra of DOM sampled along vertical gradients of inorganic sulfur species show an increased abundance of CHOS compounds compared to a non-contaminated groundwater sample. The pronounced variance of CHOS compounds observed along the HR-MLW reflects the importance of CHOS compounds for the chemistry and biology of DOM at the sampling site.

The distinct sulfur signature of DOM provides new insights into important biogeochemical processes, like microbial sulfate reduction, metal complexation and pyrite precipitation. This demonstrates the pivotal role of environmental sulfur chemistry for microbial life and its coupling to abiotic redox cycles. 

Letzte Änderung 19.06.2014