Comparing discrimination capabilities of fluorescence spectroscopy versus FT-ICR-MS for sources and hydrophobicity of sediment organic matter

Abstract

Characterizing the chemical and molecular composition of sediment organic matter (SeOM) provides critical information for a complete picture of global carbon and nutrient cycles, and helps to track the sources and the fate of organic carbon in aquatic environments. In this study, we examined fluorescence properties and the molecular composition of the alkaline-extractable organic matter (AEOM) of sediments in a coastal lake (Lake Sihwa) and its surrounding creeks (rural, urban, wetland, and industrial areas). Five fluorescence-based indices and 20 molecular parameters were selected from fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICRMS), respectively, and utilized to discriminate the AEOM among five different sources as well as the chemical composition of hydrophobic acid (HoA) and hydrophilic (Hi) fractions. Ordination based on Bray-Curtis dissimilarity matrices showed that the fluorescence-based indices distinguished among urban, lake, and the three other sources, while the molecular parameters from FT-ICR-MS performed better in discriminating among the sources of rural, wetland, and industrial areas. Irrespective of the sources, the two different chemical fractions were statistically distinguished by their relative distributions of the UVA-humic-like fluorescent component and the carbohydrate molecular group. However, a rigorous test based on percent dissimilarities indicated no superior capability of either of the two tools in discriminating the sources or their two chemical fractions, which might be attributed to the inherent structural heterogeneity of SeOM and the limited analytical window of FT-ICR-MS for relatively large-sized molecules.