Environmental Engineering Reference
In-Depth Information
Fig. 7.1 Fluorescence excitation-emission matrices (EEMs) for dissolved organic matter (DOM)
from two mid-Atlantic, USA watershed sources (forest floor litter leachate and groundwater seeps)
illustrating humic-like and protein-like fluorescence peaks (Modified from Inamdar et al. (
2012
).
Published with kind permission of
Springer Science + Business Media B.V 2012. All Rights
©
Reserved)
relative contribution of each component to the total DOM fluorescence (Cory and
McKnight
2005
).
Some of the more common fluorescence metrics and PARAFAC components
that have been used in recent studies are reported in Table
7.1
. The fluorescence
index (FI) is calculated using the ratio of fluorescence emission intensities at
470 and 520 nm at an excitation wavelength of 370 nm (Cory and McKnight
2005
). McKnight et al. (
2003
) have used the FI to differentiate between DOM
derived from vascular plants (FI: 1.3-1.4) versus microbial or planktonic sources
(FI: 1.7-2.0). Another fluorescence metric, the humification index (HIX) was
defined (Zsolnay et al.
1999
) as a ratio of the peak integrated area under
the emission spectra 435-480 nm by the peak integrated area under the emission
spectra 300-445 nm; obtained at excitation wavelength 254 nm. This definition was
later modified by Ohno (
2002
) to the integrated areas under the emission spectra
435-480 nm divided by the peak integrated area (300-345 nm + 435-480 nm);
again obtained at excitation wavelength 254 nm. The revised equation of Ohno
(
2002
) constrained HIX values to the range of 0-1 with higher values indicating
more humified material. Another metric referred to as the freshness index (
;
Wilson and Xenopoulos
2009
) is computed as the 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. The
freshness index is a measure of recently produced DOM where
β
:
α
β
represents DOM
of recent origin and
represents more decomposed DOM. Miller et al. (
2006
)
proposed the redox index (RI) to explain the oxidation states of DOM fluorescence
α
