The chemical properties of dissolved organic matter as a function of seasonal and microbiological factors

Vallette Viallard, Antoine (2022) The chemical properties of dissolved organic matter as a function of seasonal and microbiological factors. Masters thesis, Memorial University of Newfoundland.

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Abstract

Dissolved organic matter (DOM) is the pool of molecules predominantly produced from cellular growth in both terrestrial and aquatic systems and forms a reservoir of 662 Pg of carbon in the ocean. With as many as 10⁵ to 10⁷ different chemicals held in a single sample, the chemical diversity typically outstrips the capability of analytical techniques and the human capacity to effectively monitor the effects of environmental factors on their individual abundance. To address this issue, we adopted a “fingerprinting” approach and performed two sets of experiments to monitor the behavior of co-clustered compounds. In the first experiment, the change of DOM under seasonal, spatial, and reactivity variables was delineated using a size-exclusion chromatography approach applying multiple detectors and a computing technique called PARAFAC. The model showed how the molar mass and fluorescent properties of DOM change with the impact of biological activity and photodegradation in terrestrial aquatic systems, as well as leaching from different soil and sediment profiles. The second experiment analyzed the production of DOM moieties during the growth of several mixed diatom assemblages. Various patterns in fluorescent molecules and NMR bands were observed characterizing better the deep biological imprint of primary producers on DOM in estuaries. These two experiments, both performed in boreal regions, were complementary both in processes (i.e., production vs degradation) and in techniques (e.g., mass spectrometry vs NMR). It also enabled us to map those effects across the aquatic gradient (i.e., rivers and coasts). Interesting findings were yielded, and each time a limited number of factors were able to explain most of the data variance which allowed me to situate and discuss my results within the context of various DOM studies.

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