BOOK OF ABSTRACTS 105 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C NOM and Aquatic Systems SL49 A Novel Fluorescence Index for Predicting DOM Aromaticity in Aquatic Systems Kathleen R. Murphy1 1 Chalmers University of Technology, Department of Architecture and Civil Engineering, Sven Hultins gata 6, murphyk@chalmers.se A new fluorescence index has been developed that predicts DOC aromaticity and molecular size and enables improved predictions of DOC concentrations from optical measurements. The aromaticity index (ARIX) predicts specific UV absorbance (SUVA) in bulk and extracted DOM. It also predicts important molecular-scale features, including ratios of FT ICR MS molecular formulas and LC OCD–derived fractions. Although derived from modelling using parallel factor analysis [1,2], ARIX is a ratio based on a single emission scan [3]. A study of ARIX in global DOM was performed by reanalysing published data sets spanning the continents and river to ocean continuum and encompassing bulk DOM and DOM extracts [3]. Despite that samples were measured by many analytical labs using 14 different instruments, a single linear regression connected SUVA with ARIX in bulk aquatic DOM across eight diverse data sets. In freshwater systems, it is often observed that absorbance measured at 254 nm (A254) is strongly linearly correlated to DOC, allowing the simple prediction of DOC concentrations from absorbance measurements [4]. However weak correlations are frequently observed in systems that have low hydrological connectivity, since long retention times promote the in-situ biogeochemical processing of DOM which causes the divergence of absorption and DOC measurements [4, 5]. Among the eight bulk DOM datasets, weaker correlations were associated with datasets encompassing a wider range of SUVA values. Extending the linear regression between DOC and A254 by using ARIX to account for interactions between absorption efficiencies and aromaticity produced significantly better DOC predictions. Overall, these findings enhance our understanding of how different simple and advanced measurement techniques converge to charactise DOM composition in aquatic systems. ARIX offers a promising new pathway for water-quality monitoring, particularly in field studies relying on optical sensors. Because the structural features of dissolved organic compounds - especially their aromatic character - govern their physical, chemical, and biological behaviour, ARIX offers a valuable new tool for a variety of purposes, including probing carbon cycling in natural aquatic systems and improving operations and outcomes in water treatment plants.
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