529
Fluorescent Dissolved Organic Matter in Natural Waters
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 significantly 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 μm), colloidal 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(Mostofa KMG et al., unpublished data).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: compared 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
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)
Fluorescence intensity (a.u.)
pH
Peak A
Peak C
Fluorescent Dissolved Organic Matter in Natural Waters
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 significantly 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 μm), colloidal 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: compared 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
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)
Fluorescence intensity (a.u.)
pH
Peak A
Peak C