Environmental Engineering Reference
In-Depth Information
Fig. 7
Changes in the
fluorescence intensities of the
fluorophores regarding peak
A- (
a
) and C-(
b
) regions with
solution pH for bulk sample
collected from Rio Solimoes
in Amazon basin rivers. The
error bar
indicates their
standard deviation.
Data
source
Patel-Sorrentino et al.
(
2002
)
Peak A
Peak C
pH
3.6 pH
The fluorescence properties of various FDOM components are significantly
changed by pH variations (2-12) in aqueous solution (Figs.
6
,
7
,
8
) (Gosh and
Schnitzer
1980
; Henderson et al.
2009
; Zhang et al.
2010
; Laane
1982
; Vodacek
and Philpot
1987
; Pullin and Cabaniss
1995
; Mobed et al.
1996
; Patel-Sorrentino
et al.
2002
; Baker et al.
2007
; Spencer et al.
2007
). The fluorescence intensities
at peak C- and peak A-regions for fulvic acid in Amazon basin rivers are signifi-
cantly increased up to pH 11, and then decrease in the pH interval 11-12 (Fig.
7
)
(Patel-Sorrentino et al.
2002
). The ratios of fluorescence intensities of peak A and
peak C are independent of the molecular fractions of particulate (>0.22
μ
m), col-
loidal and dissolved (<5 kDa) organic matter in natural waters (Patel-Sorrentino et
al.
2002
). The fluorescence intensity of peak C (Ex/Em
=
320-340/410-430 nm,
presumably caused by fulvic acid) is increased markedly between pH 2 and 6 and
then decreases at pH 8-10. In contrast, the fluorescence of peak C (Ex/Em
=
370-
390/460-480 nm, possibly caused by humic acid) is unaltered at higher pH
(Henderson et al.
2009
; Spencer et al.
2007
).
In the case of bulk lake DOM, the autochthonous fulvic acids (C-like and
M-like, respectively, of algal origin) identified by PARAFAC modeling are
detected at pH 8-10, but the C-like component is absent at pH 2-4 (Fig.
8
)
(Mostofa KMG et al., unpublished data). The fluorescence intensities of the
M-like component are significantly influenced by pH in the peak A-region: com-
pared to the initial lake-water pH (7.5), a 79 % increase is observed at pH 2, it
decreases to 59 % at pH 4 and then gradually increases to 88 % at pH 10. The
