479
Fluorescent Dissolved Organic Matter in Natural Waters
shorter wavelengths (Ex/Em = 295–310/443–450 nm) in surface waters (0–20 m)
compared to the deep water layers (40–80 m) (Ex/Em = 300–310/444–464 nm).
Furthermore, maxima are 320–325/422–454 nm in sea waters and 300–305/449
and 250/449 nm in irradiated river waters (Table 2) (Mostofa KMG et al., unpublished data; Mostofa et al. 2005b; Yamashita et al. 2011). The excitation–emission maxima of the fluorescence peak C are shifted in irradiated samples from
longer to shorter wavelength regions, which gives a blue-shift of the peak position
(Mostofa et al. 2005a, 2007a; Moran et al. 2000). Such blue-shift phenomenon is
the photoinduced result of the mineralization of fluorophores that are present in
the molecular structure of fulvic acids. Irradiation decomposes the allochthonous
fulvic acid (A-like and M-like) entirely (Table 2) (Mostofa KMG et al., unpublished data). Photobleached fulvic acid is generally detected in the surface waters
of rivers, lakes, estuaries and oceans (Table 2) (Brooks et al. 2007; Mostofa et al.
2007a, 2005b; Garcia et al. 2005; Skoog et al. 1996; Moran et al. 2000; Osburn
et al. 2009; Lepane et al. 2003; Abboudi et al. 2008; Poiger et al. 1999; Zhang
et al. 2009b).
Allochthonous Humic Acids (C-like, A-like and M-like)
The standard Suwannee River Humic Acid (SRHA) has three fluorescent components, namely allochthonous humic acid (C-like), humic acid (A-like) and
humic acid (M-like). They can be identified using PARAFAC modeling of EEM
spectra in a variety of waters (Fig. 3f, g; Table 2). The allochthonous humic acid
(C-like) shows three fluorescence peaks, of which two are at Ex/Em = 285–340/
460–480 nm (shorter wavelength) and at 350–405/480–508 nm (longer wavelength,
peak C-region). The third peak is located at Ex/Em = 240–270/460–508 nm in
the peak A-region (Fig. 3f; Table 2). Allochthonous humic acid (C-like) has been
detected at Ex/Em = 320–350/461–498 and 300/461 nm (peak C-region) and
at 255/461 nm (peak A-region) in standard SRFA dissolved in Milli-Q water; at
295–310/423–464 and 255/464 nm in extracted humic acid; at 330/456–480 and
<250/450–460 nm in river and soil waters; at 385/>500 and 256/>500 nm in estuaries; at 300–340/>500–510, 290–405/>500–510 and <260–270/>508 nm in bay
and marine waters; at 370–380/490–498 and <260/490–498 nm in the north Pacific
and Atlantic ocean; at 360/458–480, 300/458 and 250–260/458–480 nm in drinking
water treatment plants and municipal wastes; at 370/440 and <250/440 nm in soil;
at 351/459 and 240/459 nm in water extracted from sugar maple leaves; finally, at
350–360/460–480 nm in plant biomass, manure and soil (Fig. 3f; Table 2) (Coble
1996; Mostofa et al. 2005a; Ohno and Bro 2006; Baker 2005; Hunt et al. 2008;
Kowalczuk et al. 2009; Baghoth et al. 2010; Chen et al. 2010; Fellman et al.
2008, 2010; Guo et al. 2010; Yu et al. 2010; Wu et al. 2011; Yamashita et al. 2011;
Balcarczyk et al. 2009; Santín et al. 2009; Murphy et al. 2008; Yamashita and Jaffé
2008).
The allochthonous humic acid (A-like) can exhibit a strong shoulder (not
often a clear peak) at peak A-region in a wide range of emission wavelengths.
Fluorescent Dissolved Organic Matter in Natural Waters
shorter wavelengths (Ex/Em = 295–310/443–450 nm) in surface waters (0–20 m)
compared to the deep water layers (40–80 m) (Ex/Em = 300–310/444–464 nm).
Furthermore, maxima are 320–325/422–454 nm in sea waters and 300–305/449
and 250/449 nm in irradiated river waters (Table 2) (Mostofa KMG et al., unpublished data; Mostofa et al. 2005b; Yamashita et al. 2011). The excitation–emission maxima of the fluorescence peak C are shifted in irradiated samples from
longer to shorter wavelength regions, which gives a blue-shift of the peak position
(Mostofa et al. 2005a, 2007a; Moran et al. 2000). Such blue-shift phenomenon is
the photoinduced result of the mineralization of fluorophores that are present in
the molecular structure of fulvic acids. Irradiation decomposes the allochthonous
fulvic acid (A-like and M-like) entirely (Table 2) (Mostofa KMG et al., unpublished data). Photobleached fulvic acid is generally detected in the surface waters
of rivers, lakes, estuaries and oceans (Table 2) (Brooks et al. 2007; Mostofa et al.
2007a, 2005b; Garcia et al. 2005; Skoog et al. 1996; Moran et al. 2000; Osburn
et al. 2009; Lepane et al. 2003; Abboudi et al. 2008; Poiger et al. 1999; Zhang
et al. 2009b).
Allochthonous Humic Acids (C-like, A-like and M-like)
The standard Suwannee River Humic Acid (SRHA) has three fluorescent components, namely allochthonous humic acid (C-like), humic acid (A-like) and
humic acid (M-like). They can be identified using PARAFAC modeling of EEM
spectra in a variety of waters (Fig. 3f, g; Table 2). The allochthonous humic acid
(C-like) shows three fluorescence peaks, of which two are at Ex/Em = 285–340/
460–480 nm (shorter wavelength) and at 350–405/480–508 nm (longer wavelength,
peak C-region). The third peak is located at Ex/Em = 240–270/460–508 nm in
the peak A-region (Fig. 3f; Table 2). Allochthonous humic acid (C-like) has been
detected at Ex/Em = 320–350/461–498 and 300/461 nm (peak C-region) and
at 255/461 nm (peak A-region) in standard SRFA dissolved in Milli-Q water; at
295–310/423–464 and 255/464 nm in extracted humic acid; at 330/456–480 and
<250/450–460 nm in river and soil waters; at 385/>500 and 256/>500 nm in estuaries; at 300–340/>500–510, 290–405/>500–510 and <260–270/>508 nm in bay
and marine waters; at 370–380/490–498 and <260/490–498 nm in the north Pacific
and Atlantic ocean; at 360/458–480, 300/458 and 250–260/458–480 nm in drinking
water treatment plants and municipal wastes; at 370/440 and <250/440 nm in soil;
at 351/459 and 240/459 nm in water extracted from sugar maple leaves; finally, at
350–360/460–480 nm in plant biomass, manure and soil (Fig. 3f; Table 2) (Coble
1996; Mostofa et al. 2005a; Ohno and Bro 2006; Baker 2005; Hunt et al. 2008;
Kowalczuk et al. 2009; Baghoth et al. 2010; Chen et al. 2010; Fellman et al.
2008, 2010; Guo et al. 2010; Yu et al. 2010; Wu et al. 2011; Yamashita et al. 2011;
Balcarczyk et al. 2009; Santín et al. 2009; Murphy et al. 2008; Yamashita and Jaffé
2008).
The allochthonous humic acid (A-like) can exhibit a strong shoulder (not
often a clear peak) at peak A-region in a wide range of emission wavelengths.