Applying the core-satellite species concept: Characteristics of rare and common riverine dissolved organic matter
jats:secjats:titleIntroduction</jats:title>jats:pDissolved organic matter (DOM) composition varies over space and time, with a multitude of factors driving the presence or absence of each compound found in the complex DOM mixture. Compounds ubiquitously present across a wide range of river systems (hereafter termed core compounds) may differ in chemical composition and reactivity from compounds present in only a few settings (hereafter termed satellite compounds). Here, we investigated the spatial patterns in DOM molecular formulae presence (occupancy) in surface water and sediments across 97 river corridors at a continental scale using the “Worldwide Hydrobiogeochemical Observation Network for Dynamic River Systems—WHONDRS” research consortium.</jats:p></jats:sec>jats:secjats:titleMethods</jats:title>jats:pWe used a novel data-driven approach to identify core and satellite compounds and compared their molecular properties identified with Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS).</jats:p></jats:sec>jats:secjats:titleResults</jats:title>jats:pWe found that core compounds clustered around intermediate hydrogen/carbon and oxygen/carbon ratios across both sediment and surface water samples, whereas the satellite compounds varied widely in their elemental composition. Within surface water samples, core compounds were dominated by lignin-like formulae, whereas protein-like formulae dominated the core pool in sediment samples. In contrast, satellite molecular formulae were more evenly distributed between compound classes in both sediment and water molecules. Core compounds found in both sediment and water exhibited lower molecular mass, lower oxidation state, and a higher degree of aromaticity, and were inferred to be more persistent than global satellite compounds. Higher putative biochemical transformations were found in core than satellite compounds, suggesting that the core pool was more processed.</jats:p></jats:sec>jats:secjats:titleDiscussion</jats:title>jats:pThe observed differences in chemical properties of core and satellite compounds point to potential differences in their sources and contribution to DOM processing in river corridors. Overall, our work points to the potential of data-driven approaches separating rare and common compounds to reduce some of the complexity inherent in studying riverine DOM.</jats:p></jats:sec>
Peer reviewed: True
Acknowledgements: We thank the WHONDRS consortium for facilitating generation of data used in this manuscript, including study design, crowdsourced sample collection, sample analysis, and public data publishing. We also thank the organizers and participants of the virtual crowdsourced workshop (Borton et al., 2022) where the initial scientific questions and hypotheses were developed.