title: Fluorescence characteristics of size-fractionated dissolved organic matter: implications for a molecular assembly based structure?
abstract: Surface freshwater samples from Everglades National Park, Florida, were used to investigate the size distributions of natural dissolved organic matter (DOM) and associated fluorescence characteristics along the molecular weight continuum. Samples were fractionated using size exclusion chromatography (SEC) and characterized by spectroscopic means, in particular Excitation-Emission Matrix fluorescence modeled with parallel factor analysis (EEM-PARAFAC). Most of the eight components obtained from PARAFAC modeling were broadly distributed across the DOM molecular weight range, and the optical properties of the eight size fractions for all samples studied were quite consistent among each other. Humic-like components presented a similar distribution in all the samples, with enrichment in the middle molecular weight range. Some variability in the relative distribution of the different humic-like components was observed among the different size fractions and among samples. The protein like fluorescence, although also generally present in all fractions, was more variable but generally enriched in the highest and lowest molecular weight fractions. These observations are in agreement with the hypothesis of a supramolecular structure for DOM, and suggest that DOM fluorescence characteristics may be controlled by molecular assemblies with similar optical properties, distributed along the molecular weight continuum. This study highlights the importance of studying the molecular structure of DOM on a molecular size distribution perspective, which may have important implications in understanding the environmental dynamics such materials.
authors.affiliation: Southeast Environmental Research Center, Florida International University, 11200 SW 8th Street, Miami, FL 33199, USA.
authors.forename: Cristina
authors.initials: C
authors.lastname: Romera-Castillo
authors.affiliation: Southeast Environmental Research Center, Florida International University, 11200 SW 8th Street, Miami, FL 33199, USA; Marine Science Program, Department of Chemistry and Biochemistry, Florida International University, MSB 250C, 3000 NE 151 Street, North Miami, FL 33181, USA.
authors.forename: Meilian
authors.initials: M
authors.lastname: Chen
authors.affiliation: Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan.
authors.forename: Youhei
authors.initials: Y
authors.lastname: Yamashita
authors.affiliation: Southeast Environmental Research Center, Florida International University, 11200 SW 8th Street, Miami, FL 33199, USA; Marine Science Program, Department of Chemistry and Biochemistry, Florida International University, MSB 250C, 3000 NE 151 Street, North Miami, FL 33181, USA. Electronic address: jaffer@fiu.edu.
authors.forename: Rudolf
authors.initials: R
authors.lastname: Jaffé
mesh_terms: D002850:Chromatography, Gel; D005618:Fresh Water / Q000032:analysis; D008970:Molecular Weight; D009930:Organic Chemicals / Q000032:analysis* / Q000737:chemistry; D013050:Spectrometry, Fluorescence
chemical_list: D009930:Organic Chemicals
keywords: EEM-PARAFAC; Everglades; Fluorescent DOM; Molecular assemblies; Size exclusion chromatography