A global fluorescence index for predicting dissolved organic carbon abundance and aromaticity

The chemical structures of dissolved organic compounds in natural waters, including degree of aromaticity, affect their physical, chemical, and biological properties and ultimately the fate of carbon in aquatic systems and during water treatment. Herein, a new fluorescence-based aromaticity index named ARIX is shown to link the composition of aquatic dissolved organic matter to its relative aromaticity across diverse aquatic systems. ARIX predicts SUVA, a widely used proxy of aromaticity, as well as the percentage of polycyclic aromatic and polyphenolic molecular formulas determined by FT-ICR MS and the ratio of “humic substances” to “building blocks” fractions determined by LC-OCD. A meta-analysis of nine datasets spanning all seven continents suggests that a single linear relationship predicts SUVA from ARIX in both bulk and extracted DOM. In impounded waterbodies exhibiting decoupling between DOC and absorbance linked to extensive biogeochemical processing, linearity can be restored by accounting for the interaction between absorbance and ARIX. The results deliver new insights on widely discussed trends in DOM optical properties and on the molecular structures underlying optical measurements in aquatic milieu. They further pave the way for new optical technologies capable of real-time predictions of DOC concentration, reactivity and fate.