Abstract
Chemically reducing humic (HA) and fulvic acids (FA) provides insight into spectroscopically identifiable structural moieties generating the optical properties of HA/FA from aquatic, microbial and terrestrial sources. Sodium borohydride reduction provides targeted reduction of carbonyl groups. The contrast between the pH induced optical changes of untreated, reduced and reoxidized HA/FA highlights differences in the quantity, and physicality of structural components generating optical properties associated with HA/FA. Because borohydride reactions alter pH, pH re-adjustment to the original pH is required. Careful titrations of selected HA/FA provided the mmole H+ g-1 HA/FA required to titrate reduced and reoxidized HA/FA from pH 2-11; and the pH dependent spectral slope (S) at low (pH 2-3), neutral (pH 7-7.5) and high (pH 11.0). Molar extinction coefficients (e) (Lmg-1cm-1) at pH 7.6 and 350 nm provide a point of consistency linking intrinsic pH dependent optical properties to the concentration of material used for titrations. Soil derived humic acids differ from aquatic humic acids in the heterogeneity of optically identifiable group as well as the overall concentration of those groups. The microbial source of FA has a limited concentration of homogeneous titratable groups when compared to aquatic FA generated terrestrially. Microbial FA exhibits pH linked optical recovery upon reoxidation when compared to aquatic FA which is consistent with the presence of quinones in microbial FA.
Highlights
Humic substances (HS) and chromophoric dissolved organic matter (CDOM) are related and dynamic parts of the global carbon cycle (Hernes & Benner, 2003)
Optical titration and fluorescence difference spectra ( F) indicate that quinones may act as acceptor moieties in Pony Lake fulvic acid (PLFA)
The optical properties of terrestrially based sources of humic and fulvic acid have been attributed to partial oxidation of land based plant materials, lignin phenols
Summary
Humic substances (HS) and chromophoric dissolved organic matter (CDOM) are related and dynamic parts of the global carbon cycle (Hernes & Benner, 2003). Analysis and comparison of untreated and borohydride reduced model humic compounds at short wavelength (< 350) using potentiometric and optical titrations, spectral slope values (S), difference plots ( A) (Dryer et al, 2008), fluorescence emission spectra, (Jørgensen et al, 2011), and fluorescence difference spectra ( F) (Del Vecchio & Blough, 2004) provide insight into how electronic interactions work universally in the environment as well as how differences that exist between sources humic materials can potentially augment existing knowledge about the fate and transport of humic substances in the environment (Hernes & Ronald Benner, 2002)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
