Soils contain enough organic matter to intensify climate change, if these organics are converted to carbon dioxide and released into the atmosphere. Minerals in soils may interact with the organic carbon, preventing it from being released, but it is unclear which organics are stabilized by different minerals. Many studies have simulated these interactions in the laboratory, reacting key soil minerals with dissolved organic matter (DOM) from stream water. However, different experimental approaches have led to conflicting results, and most studies do not compare findings to in-situ soil samples. This study seeks to address this gap in the literature, combining new spectroscopic analysis of experimentally simulated organo-mineral interactions with analysis of soil samples from diverse climates. In laboratory experiments, DOM has been reacted with five of the most abundant and reactive soil minerals: kaolinite, montmorillonite, calcite (CaCO3), boehmite (γ-AlOOH), and goethite (α-FeOOH). The DOM comes from an uncontaminated stream water source in the Pine Barrens, New Jersey. To determine which organic molecules have reacted with different minerals, the post-reaction DOM is analyzed with infrared spectroscopy (FTIR), high-resolution mass spectrometry (FTICR-MS), and nuclear magnetic resonance spectroscopy (1H NMR). To complement this analysis of post-reaction DOM, the post-reaction mineral surfaces are investigated with X-ray absorption spectroscopy (XAS). For comparison, soil samples are studied from diverse environments, including tropical, temperate, and boreal forests in North America. Organic molecule extracts from these soils are analyzed with FTICR-MS and 1H NMR, while in-situ soils are investigated with XAS. These spectroscopic methods show that organics with different functional groups are preferentially stabilized by different minerals. Clays may engage in van der Waals interactions with hydrocarbon-rich structures such as lipids and proteins. However, calcite reacts more with negatively-charged oxygen groups, and oxides show mixed preferences. We hypothesize that the surface chemistry of soil minerals may be the key controlling parameter for these interactions. By linking simulated organo-mineral interactions with analysis of in-situ soils, this work investigates how the cycling of soil carbon is affecting present and future climate change.

Integrating laboratory and field studies of organo-mineral interactions using multiple spectroscopic methods

255th National Meeting (2018)

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