Wetland Biogeochemistry Techniques - Wetland Techniques - page 376

Table 7.1 Selected UV and fluorescence metrics that have been commonly used to characterize
the composition of dissolved organic matter (DOM)
UV and fluorescence
indices Reference Definition and significance

Specific UV absorbance
(SUVA 254 )
[L mg C 1 m 1 ]

Weishaar
et al. ( 2003 )

UV absorbance at 254 nm divided by DOC
concentration in mg C/L; provides a measure
of aromaticity of DOM. High values of SUVA
indicate more aromatic material

Absorption coefficient
a 254 [m 1 ]

Green and
Blough
( 1994 )

(UV absorbance at 254 nm) 2.303 100

Measure of aromaticity of DOM

Slope ratio S R Helms

et al. ( 2008 )

Ratio of the slope of the shorter UV wavelength
region (275-295 nm) to that of the longer UV
wavelength region (350-400 nm); Can be used
as a proxy for molecular weight (MW)
S R decreases with increasing MW

Fluorescence Index (FI) McKnight
et al. ( 2003 )

Ratio of fluorescence intensities at 470 and 520 nm
at excitation of 370 nm;
Used to distinguish between terrestrial and micro-
bial sources of DOM;
Terrestrial or allochthonous DOM: 1.2-1.5; Micro-
bial or autochthonous DOM: 1.7-2.0

Humification Index (HIX) Ohno ( 2002 ) HIX ¼ aI 435 480 = ð aI 300 345 þ aI 435 480 Þ

Used to characterize humification status of DOM;
Ranges from 0 to 1 and increases with increasing
degree of humification

Freshness Index ( β : α ) Wilson and

Xenopoulos
( 2009 )

Ratio of emission fluorescence intensity at 380 nm
by the maximum emission fluorescence intensity
observed between 420 and 435 nm, calculated at
excitation wavelength of 310 nm. A measure
of recently produced DOM, where β represents

DOM of recent origin and α represents more

decomposed DOM

Redox Index (RI) Miller

et al. ( 2006 )

Q red /(Q red +Q ox ), where Q red is the sum of the
reduced components and Q ox is the sum of the
oxidized components; provide a measure of the
redox state of DOM

Humic-like fluorescence Coble

et al. ( 1998 )

Excitation < 260; Emission 448-480
Indicates DOM from vascular plant sources, high
molecular weight and humic in nature

Protein-like fluorescence Coble

et al. ( 1998 )

Tyrosine-like: Excitation < 270-275; Emission
304-312;
Tryptophan-like: Excitation < 270-280; Emission
330-368;
Indicates protein-like DOM moieties, bioavailable
DOM (Fellman et al. ( 2009 )), and DOM
of microbial origin