Decomposition of organic matter: from details to the big picture

Large volumes of greenhouse gases are emitted to the atmosphere as a result of natural organic matter (OM) decomposition. Accordingly, the mechanisms, driving forces, and quantitative outcomes of OM decay attract considerable attention. Even the core aspects of OM decay still require clarification, not the least due to extreme complexity of OM as a substrate.

A recent study published in Environmental Science and Technology addresses the fundamentals of OM decay and provides particularly detailed, yet comprehensive insights into kinetics of OM decomposition. Taking decomposition of lake dissolved organic matter (DOM) as a case and using ultrahigh resolution mass spectrometry the authors traced the decay of hundreds of molecular formulas within bulk DOM. Further analysis demonstrated that decay coefficients associated with molecular formulas formed a continuous distribution, or a continuous spectrum of reactivities within bulk DOM. In such a way, the study shows that the overall OM decomposition pattern is a result of integrated behavior of a large number of OM constituents. This has important implications for the realistic modeling of OM decomposition and highlights a conceptual superiority of the continuous models of OM decay over their predecessors based on limited number of reactivity pools.

The study takes advantage of the cutting-edge 15-Tesla Fourier transform ion cyclotron resonance mass spectrometer and can be of great value to those interested in characterization of organic matter and its behavior. The authors suggest that their approach of combining ultrahigh resolution mass spectrometry with the kinetic modeling of OM decomposition has a promising potential, and emphasize the need for thoughtful interpretation of the data.

The work was conducted by the researchers from Uppsala University and the University of Oldenburg, Germany, with the financial support from the Swedish Research Council.

Reference: Mostovaya, A., Hawkes, J. A., Koehler, B., Dittmar, T., and Tranvik, L. J. (2017). Emergence of the reactivity continuum of organic matter from kinetics of a multitude of individual molecular constituents. Environ. Sci. Technol., 51 (20), 11571-11579. DOI: 10.1021/acs.est.7b02876.