BOOK OF ABSTRACTS 119 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C NOM and Aquatic Systems SL56 Physico-Chemical and Molecular Properties of DOM in Peat Pore Water: Effect of Seasonality, Vertical Stratification, and Catchment Connectivity Miroslav Jonas1, Lukas Vlcek1, Martin Pivokonsky1 1 Institute of Hydrology of the Czech Academy of Sciences, Pod Paťankou 30/5, 160 00, Prague, jonas@ih.cas.cz Peatland ecosystems are major terrestrial sources of dissolved organic matter (DOM). While compositional changes in DOM along the acrotelmcatotelm gradient are well documented, their spatiotemporal variability remains less understood. In this study, we investigated physico-chemical and molecular changes in DOM in the Rokytka peat bog (Bohemian Forest, Czechia) at four depths (0.5, 2, 3, and 3.7 m) over a single vegetation period. Both pH and acid neutralization capacity increased with depth and shifted toward higher values as the vegetation period progressed. Dissolved organic carbon (DOC) exhibited the greatest seasonal variability in the upper acrotelm and stabilized with depth. The contribution of very hydrophobic acids (VHA) to DOC was highest in the upper peat layers and decreased with depth, whereas slightly hydrophobic acids (SHA) and neutral hydrophilic fraction (NEU) showed the reversed dynamics. These patterns were consistent with observed decrease in aromaticity and molecular weight along the vertical gradient. Additionally, DOM properties were evaluated as tracers for runoff formation by analysing a surface-draining stream using identical sampling and analytical methods. In general, the stream showed the highest similarities with the upper acrotelm; however, during summer, its molecular characteristics shifted toward those of deeper catotelm layers. This suggests that qualitative DOM indices may potentially provide a useful tool for tracing runoff sources in peatland ecosystems. Acknowledgement The authors acknowledge the institutional support of the Czech Academy of Sciences [RVO: 67985874] and the Czech Academy of Sciences Premium Academiae.
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