Geoscience Reference
In-Depth Information
Table 9.1.
Fluorescence indices highlighted in this chapter, with relevant papers, and their definitions
Fluorescence Index
Parameters
Comments
Humification Index (HIX
SYN
)
Kalbitz et al. (
1999
,
2000
)
Calculated using synchronous scans with 18 nm offset.
(ex 470 nm/em 488 nm)/(ex 360 nm/em 378 nm) or (ex
400 nm/em 418 nm)/(ex 360 nm/em 378 nm) for fulvic
acids. (ex 390 nm/em 408 nm)/(ex 355 nm/em 373 nm)
for whole water.
Correlated with C/N ratio, aromaticity, and
polycondensation for soil extracted and groundwater
OM. Higher numbers indicate more polycondensation
and lower C/N.
Humification Index (HIX
EM
)
Zsolnay et al. (
1999
)
Ohno (
2002a
)
At ex 254 nm, area of peak under em 435-480 nm
divided by peak area under em 300-345 nm. Ohno later
suggested modification for concentrated samples of
area under em 435-480 nm divided by area under em
300-345 nm + 435-480 nm.
Indicates degree of humification of soil extracts, with
higher numbers indicative of lower H/C ratios shifting
the emission to longer wavelengths, attributed to a
greater degree of humification.
Freshness Index (
β
/
α
) (BIX)
Parlanti et al. (2000)
Huguet et al. (2009)
Wilson and Xenopoulos (
2009
)
Originally calculated as the ratio of the
β
peak (max
intensity within ex 310-320 nm/em 380-420 nm) and
α
peak (max intensity within ex 330-350 nm/em 420-
480 nm). Modified to intensity at em 380 nm divided by
max intensity between em 420 nm and em 435 nm at ex
310 nm.
Indicates proportion of recently produced DOM. The
β
peak represents recently created (likely microbial)
OM while the
α
peak is older, more decomposed
OM. Developed for and mostly used in estuarine
environments.
Fluorescence Index (FI)
McKnight et al. (2001)
Cory and McKnight (
2005
)
Originally calculated as the ratio of em 450 nm and em
500 nm at ex 370 nm for non-instrument corrected
spectra. Modified, for instrument-corrected spectra, to
em 470 nm/em 520 nm at ex 370 nm.
Indicates if precursor material for DOM is of a more
microbial (FI ~1.8) in nature or more terrestrially
derived (FI ~1.2).
Peak T/Peak C ratio
Baker (2001)
Ratio of maximum fluorescence at ex 275 nm/em 350 nm
(peak T) to max intensity of the region ex 320-340 nm/
em 410-430 nm (peak C).
Used to identify impact of sewage effluent on a river.
Indicates biochemical oxygen demand relative to
dissolved organic carbon.
Redox Index (RI)
Cory and McKnight (
2005
)
Miller et al. (2006)
Sum of reduced quinone-like input over total quinone-like
input from components of Cory-McKnight PARAFAC
model.
Indicates whether quinone-like components within DOM
are more reduced (closer to 1) or oxidized (closer to
0) in character. Typical values are around 0.42.
Note
: em = emission wavelengths, ex = excitation wavelengths.
