Spectrofluorometric characterization of dissolved organic matter for indication of precursor organic material and aromaticity

Abstract

We studied the fluorescence properties of fulvic acids isolated from streams and rivers receiving predominantly terrestrial sources of organic material and from lakes with microbial sources of organic material. Microbially derived fulvic acids have fluorophores with a more sharply defined emission peak occurring at lower wavelengths than fluorophores in terrestrially derived fulvic acids. We show that the ratio of the emission intensity at a wavelength of 450 nm to that at 500 nm, obtained with an excitation of 370 nm, can serve as a simple index to distinguish sources of isolated aquatic fulvic acids. In our study, this index has a value of ϳ1.9 for microbially derived fulvic acids and a value of ϳ1.4 for terrestrially derived fulvic acids. Fulvic acids isolated from four large rivers in the United States have fluorescence index values of 1.4-1.5, consistent with predominantly terrestrial sources. For fulvic acid samples isolated from a river, lakes, and groundwaters in a forested watershed, the fluorescence index varied in a manner suggesting different sources for the seepage and streamfed lakes. Furthermore, we identified these distinctive fluorophores in filtered whole water samples from lakes in a desert oasis in Antarctica and in filtered whole water samples collected during snowmelt from a Rocky Mountain stream. The fluorescence index measurement in filtered whole water samples in field studies may augment the interpretation of dissolved organic carbon sources for understanding carbon cycling in aquatic ecosystems.Aquatic fulvic acid is a major fraction of dissolved organic matter (DOM) in natural waters. Aquatic fulvic acids are heterogeneous, moderate molecular weight, yellow-colored organic acids. Examples of processes controlled by fulvic acid are (1) chemical speciation and transport of trace metals through complexation reactions (e.g., Breault et al. 1996); (2) formation of trihalomethanes in drinking water by interactions between chlorine and fulvic acid during water AcknowledgmentsWe thank K. Cunningham for help with spectroscopic methods and G. Aiken, J. Debroux, P. Coble, and four anonymous reviewers for valuable comments on the manuscript.

Evaluating the triplet state photoreactivity of dissolved organic matter isolated by chromatography and ultrafiltration using an alkylphenol probe molecule

“…FI values use the ratio of the emission intensities at 470/520 nm when the sample is excited at 370 nm (Cory and McKnight 2005). These ratios were shown to correlate well to the DOM precursor material as reported by McKnight et al (2001), who found respective larger and smaller FI values for autochthonous derived DOM (~1.9) and allochthonous DOM (~1.4). The samples were run using a SPEX spectrofluorometer at the University of Colorado in Boulder.…”

“…The limited amounts of DOM isolated for this study prevented us from using more robust analytical methods capable of elucidating structure, e.g., 2-D NMR, FTICR-MS. Our parameters of choice, the fluorescence index values, are correlated to DOM source material and to a lesser extent aromaticity (McKnight et al 2001), whereas ε 280nm values are used to estimate aromaticity (Chin et al 1994). The DOM FI values do not show any significant trend related to a specific isolation technique (coefficient of error ±0.02) but do show that all the OWC isolates have a larger proportion of autochthonous material, as indicated by their overall higher FI values relative to the OKS samples (Table 1).…”

Longitudinal discontinuities in riverine greenhouse gas dynamics generated by dams and urban wastewater

“…Scan speed was 2400 nm min -1 and the bandwidth was set to 5 nm for both excitation and emission. UV absorbance and fluorescence data were used to calculate specific UV absorbance at 254 nm (SUVA 254 ) (Weishaar et al, 2003), fluorescence index (FI) (McKnight et al, 2001), humification index (HI) (Zsolnay et al, 1999), and common fluorescence EEM components (Fellman et al 2010). Three fluorescent EEM 185 components termed C1 (excitation/emission peaks at 325/467 nm), C2 (315/404 nm), and C3 (275/354 nm) were used to represent humic-like, microbial humic-like, and protein-like fluorescence, respectively (Fellman et al, 2010).…”

Disinfection byproduct precursor removal by enhanced coagulation and their distribution in chemical fractions

“…According to the results of McKnight (2001), the ratio of the emission intensity at a wavelength of 450 nm to that at 500 nm (I 450 /I 500 = 35.2/21.5 = 1.6), obtained with an excitation of 370 nm, may reflect both terrestrial and microbial inputs in the Songhua River. According to the linear regression equation (McKnight et al, 2001): y = −0.027x + 2.1, r 2 = 0.85, the raw water DOM should have 18% aromatic content.…”