Molecular signatures of dissolved organic matter in a tropical karst system

Lechleitner, Franziska A.; Dittmar, Thorsten; Baldini, James U. L.; Prufer, Keith M.; Eglinton, Timothy I.

doi:10.1016/j.orggeochem.2017.07.015

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Molecular signatures of dissolved organic matter in a tropical karst system

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Dittmar, Thorsten
Marine Geochemistry Group, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Lechleitner, F. A., Dittmar, T., Baldini, J. U. L., Prufer, K. M., & Eglinton, T. I. (2017). Molecular signatures of dissolved organic matter in a tropical karst system. ORGANIC GEOCHEMISTRY, 113, 141-149. doi:10.1016/j.orggeochem.2017.07.015.

Cite as: https://hdl.handle.net/21.11116/0000-0001-C16E-A

Abstract

Karst areas are widespread landforms present on all continents, formed by the dissolution of carbonate or evaporite host rock. Little is known about the composition and nature of dissolved organic matter (DOM) as it moves through karst systems, although karst DOM has been recognized as important for a range of natural processes. Microbial communities living in karst systems are some of the most diverse and intriguing on the planet, and their metabolism and life cycle can give clues related to the development of a host of different life forms. Karst areas are also of interest due to their mostly subterranean hydrology, and the repercussions of these processes on local carbon cycles.
We illustrate some of the processes acting on DOM in karst waters through the analysis of soil, drip and cave pool waters at the tropical site of Yok Balum Cave, in southern Belize. Water samples were analyzed using ultra-high resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS), a technique that enables the resolution of single molecular formulae within a DOM spectrum. We perform multivariate statistics to detect trends in the data and identify provenance of detected molecular components. In addition to karst waters, four aliquots of a powdered stalagmite sample from the same cave system are analyzed. Our results show a clear gradient between the soil and the cave system. We hypothesize that both sorption on mineral surfaces and microbial reworking are responsible for the observed trend in DOM composition. The stalagmite extracts show an anomalous DOM pattern, which may be due to a variety of factors, including microbial activity on the stalagmite surface and different affinities of compounds to incorporation in the carbonate. The goal of this study was to follow the molecular transformations of DOM on its journey from the surface to the cave, and to provide a molecular basis for the establishment of stalagmite DOM proxies in karst systems. (C) 2017 Elsevier Ltd. All rights reserved.