Unraveling the size‐dependent optical properties of dissolved organic matter

Abstract

The size‐dependent optical properties of dissolved organic matter (DOM) from four Swedish lakes were investigated using High Performance Size Exclusion Chromatography (HPSEC) in conjunction with online characterization of absorbance (240–600 nm) and fluorescence (excitation: 275 nm, emission: 300–600 nm). The molecular size of chromophoric DOM (CDOM) was consistently higher than that of fluorescent DOM (FDOM), with an average difference of 0.37 kDa. The relative abundance of FDOM vs. CDOM ranged from 0.3 to 0.7 across lakes, and increased with decreasing average molecular size. Across sites, the CDOM spectral slopes of the large molecular size fraction were highly similar while the low molecular size fraction differed and contributed to different bulk spectral slopes. Our results indicate structural congruence of high molecular size DOM across systems while lake trophic status determined the characteristics of the low size range. Furthermore, the combination of HPSEC and parallel factor analysis (HPSEC‐PARAFAC2) allowed the decomposition of DOM fluorescence chromatograms. Three humic‐like components and one protein‐like component with broadly overlapping molecular size distributions were identified. This overlap provides further evidence for the supramolecular assembly hypothesis since fluorophores, as revealed by PARAFAC2, occur in aggregates of overlapping molecular size. Our results further suggest a link between the molecular size of these fluorophores and the associated supramolecular assemblies. This study demonstrates the potential for HPSEC and novel mathematical approaches to provide unprecedented insights into the relationship between optical and chemical properties of DOM in aquatic systems.

Dissolved organic matter variations in coastal plain wetland watersheds: The integrated role of hydrological connectivity, land use, and seasonality

“…The spectral slope ratio ( S R ) was calculated from UV–Vis spectra by taking the ratio of log‐transformed absorbance slopes at 275–295 and 350–400 nm. This metric decreases with increasing DOM average molecular weight (Wünsch, Stedmon, Tranvik, & Guillemette, ) and is positively correlated with DOM photodegradation (Helms et al, ). UV–Vis absorbance metrics can be sensitive to iron and nitrate interference.…”

The influence of dissolved organic matter on the marine production of carbonyl sulfide (OCS) and carbon disulfide (CS<sub>2</sub>) in the Peruvian upwelling

“…The method favors the retention of polar molecules, which comprise approximately 40 % of the total dissolved organic carbon (DOC) in marine waters (Dittmar et al, 2008). Due to the operational definition, no direct comparison to the CDOM and FDOM pools is possible (Wünsch et al, 2018).…”

The influence of dissolved organic matter on the marine production of carbonyl sulfide (OCS) and carbon disulfide (CS<sub>2</sub>) in the Eastern Tropical South Pacific

“…The method favors the retention of polar molecules, which comprise approximately 40 % of the total dissolved organic carbon (DOC) in marine waters. Due to the operational definition, no direct comparison to the CDOM and FDOM pools is possible (Wünsch et al, 2018).…”