Persistence By Structure

Life is short for some organic compounds dissolved in lakes and long for others. But what controls their life spans? The answer depends, at least in part, on specific structural motifs found in a lake’s dissolved organic matter, reports a team of researchers led by Anne Kellerman and Lars Tranvik of Uppsala University, in Sweden (Nat. Geosci. 2015, DOI: 10.1038/ngeo2440). The team investigated the persistence of dissolved organic matter in 109 freshwater lakes in Sweden by using ultra-high-resolution mass spectrometry and optical spectroscopy. They found that reduced, aliphatic, and nitrogen-containing compounds are among the most persistent. In contrast, oxidized, aromatic compounds are much less persistent, they say, because degradation processes in the lakes work more quickly on those species. The results challenge a paradigm in geological science that emphasizes extrinsic influences—such as temperature—as primary factors dictating the persistence of organic matter. Instead, the team argues that intrinsic influences, such as molecular structure, play an important role in determining the persistence of organic matter. The team also stresses that the observed persistence patterns are not unique to Swedish lakes but likely found elsewhere as well.