Correlation between molecular absorption spectral slope ratios and fluorescence humification indices in characterizing CDOM

Abstract

Ultraviolet-visible absorption spectral slope ratios S R (slope in 275-295 nm divided by slope in 350-400 nm) and humification index (HIX, integrated fluorescence emission in 435-480 nm divided by that in 435-480 and 300-345 nm) were compared when characterizing chromophoric dissolved organic matter (CDOM) in three humic acids and 44 whole water samples. HIX increased with increasing pH for humic acids, while their S R showed much more complicated dependencies on pH. There was a negative correlation between S R and HIX. S R increased in the order terrestrial coal/peat \ terrestrial soil/ river \ seawater, while HIX increased in the order seawater \ terrestrial soil/river \ terrestrial coal/peat. The comparative study in this work indicates that terrestrially derived CDOM has higher HIX and lower S R than marine CDOM. Investigators may potentially use these two indices to compare qualitatively the character of CDOM in different sources (e.g., terrestrial vs. marine).

Study on organic matter fractions in the surface microlayer in the Baltic Sea by spectrophotometric and spectrofluorometric methods

“…The HIX index is sensitive to the humification and condensation processes, focused on large, high-weighted organic molecules, that mainly reflect the changes in a longwavelength range (above 330 nm). However, the photochemical degradation processes, resulting in a decrease in the mass of molecules and an increase in the concentration of low molecular weighted molecules, are much more pronounced in the lower-wavelength range and are held primarily in the surface microlayer (Chin et al, 1994;Fuentes et al, 2006). For the same reason mentioned above, the relation between the ratio E 2 : E 3 and S R is better correlated in SML than SS water (Helms et al, 2008).…”

“…, and at 450 to 650 nm, a CDOM (450) /a CDOM (650) (called E 4 : E 5 ), are used to track changes in the relative size and the aromaticity of CDOM molecules (De Haan and De Boer, 1987;Peuravuori and Pihlaja, 1997;Chin et al, 1994). When molecular size and aromaticity increase, the values of the ratios E 2 : E 3 and E 4 : E 5 decrease.…”

“…9 (Helms at al., 2008;Chen et al, 2011;Vähätalo and Wentzel, 2004;Zhang et al, 2013). High values of the HIX index of ca.…”

“…1-1.2 (Zsolnay et al, 1999;Chari et al, 2012). While S 275−295 < S 350−400 indicates the occurrence and predominance of highly condensed matter, as a dominance of and/or terrestrial DOM, with HMW molecules absorbing in a long-wavelength range (Helms et al, 2008;Chen et al, 2011), the lower HIX and higher S R values (S 275−295 > S 350−400 ) indicate the predominance of marinederived low molecular weighted LMW molecules absorbing in a short-wavelength range (Chen et al, 2011). The relation between the HIX index and S R shows a simple linear relation in subsurface waters.…”

Relationships between molecular weight and fluorescence properties for size-fractionated dissolved organic matter from fresh and aged sources

“…At the same time, increasing signal in the 'humic-like' fluorescence region has been associated with increases in relatively aromatic, humic materials and shifts to longer wavelengths via the humification index (HIX; Zsolnay et al, 1999). Correlations between HIX and the spectral slope, and between HIX and both molecular weight and specific UV absorbance (SUVA) have also been noted, where SUVA is a strong indicator of aromaticity (Weishaar et al, 2003;Hur and Kim, 2009;Chen et al, 2011).…”