Francois Guillemette David C. Podgorski George R. Aiken Kenna D. Butler Robert G. M. Spencer Anne M. Kellerman 2018 <p><span>The link between composition and reactivity of dissolved organic matter (DOM) is central to understanding the role aquatic systems play in the global carbon cycle; yet, unifying concepts driving molecular composition have yet to be established. We characterized 37 DOM isolates from diverse aquatic ecosystems, including their stable and radiocarbon isotopes (δ</span>¹³<span>C-dissolved organic carbon (DOC) and Δ</span>¹⁴<span>C-DOC), optical properties (absorbance and fluorescence), and molecular composition (ultrahigh resolution mass spectrometry). Isolates encompassed end-members of allochthonous and autochthonous DOM from sites across the United States, the Pacific Ocean, and Antarctic lakes. Modern Δ</span>¹⁴<span>C-DOC and optical properties reflecting increased aromaticity, such as carbon specific UV absorbance at 254 nm (SUVA</span>₂₅₄<span>), were directly related to polyphenolic and polycyclic aromatic compounds, whereas enriched δ</span>¹³<span>C-DOC and optical properties reflecting autochthonous end-members were positively correlated to more aliphatic compounds. Furthermore, the two sets of autochthonous end-members (Pacific Ocean and Antarctic lakes) exhibited distinct molecular composition due to differences in extent of degradation. Across all sites and end-members studied, we find a consistent shift in composition with aging, highlighting the persistence of certain biomolecules concurrent with degradation time.</span></p> application/pdf 10.1021/acs.est.7b05513 en ACS Unifying concepts linking dissolved organic matter composition to persistence in aquatic ecosystems article