Dissolved organic matter compositions in 0.6–3.4 km deep fracture waters, Kaapvaal Craton, South Africa

Thomas L. Kieft, Clifford C. Walters, Meytal B. Higgins, Anthony S. Mennito, Catherine F.M. Clewett, Verena Heuer, Michael J. Pullin, Sarah Hendrickson, Esta van Heerden, Barbara Sherwood Lollar, Maggie C.Y. Lau, Tullis C. Onstott

Research output: Contribution to journalArticle

6 Scopus citations

Abstract

The composition of dissolved organic matter (DOM) in extremely deep groundwaters has rarely been investigated. Focusing on deep fracture waters in billion year old rocks in South Africa, we hypothesized the DOM would be predominantly derived from in situ microbial sources, consistent with H2-driven lithoautotrophic ecosystems previously documented in these fluids. We collected groundwater from 0.6 to 3.4 km depths via boreholes in mines, and characterized the DOM by a variety of analytical methods. Dissolved organic carbon concentrations ranged from 0.25 to 4.9 mg C/L. Low molecular weight organic acids (formate, acetate, lactate, propanoate) and amino acids (after hydrolysis) accounted for varying fractions of the total dissolved organic carbon. UV spectrophotometry, scanning fluorimetry, and nuclear magnetic resonance (NMR) spectra indicated lower concentrations of aromatic compounds than are commonly found in surface waters and shallow groundwaters. Molecular weights of aromatic compounds measured by size-exclusion chromatography were dominantly 500–1000 Da. Scanning fluorimetry revealed humic substances in two shallow (578 and 1300 m) samples; deeper samples showed peaks indicating aromatic amino acids. Intensive study of one sample from a previously sampled borehole in Beatrix mine resulted in large NMR peaks for aliphatics and carboxyls with lesser aromatics peaks; negative electrospray ion Fourier transform ion cyclotron resonance-mass spectrometry detected protein-, lipid-, and lignin-like compounds. These results are consistent with DOM in the form of microbial metabolites, and modified cell components (membrane lipids and proteins). These findings support previous geomicrobiological reports of chemolithoautotrophic microbial ecosystems functioning in isolation from photosynthetic primary production.

Original languageEnglish (US)
Pages (from-to)116-131
Number of pages16
JournalOrganic Geochemistry
Volume118
DOIs
StatePublished - Apr 2018

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology

Keywords

  • Aliphatics
  • Aromatics
  • Carboxyls
  • Dissolved organic matter
  • Fluorescence
  • Groundwater
  • Negative electrospray ion Fourier transform ion cyclotron resonance-mass spectrometry
  • Proteins
  • Solid state NMR
  • UV–vis spectrophotometry

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    Kieft, T. L., Walters, C. C., Higgins, M. B., Mennito, A. S., Clewett, C. F. M., Heuer, V., Pullin, M. J., Hendrickson, S., van Heerden, E., Sherwood Lollar, B., Lau, M. C. Y., & Onstott, T. C. (2018). Dissolved organic matter compositions in 0.6–3.4 km deep fracture waters, Kaapvaal Craton, South Africa. Organic Geochemistry, 118, 116-131. https://doi.org/10.1016/j.orggeochem.2018.02.003