398
K. M. G. Mostofa et al.
Alteration of autochthonous fulvic acids (C-like) changes their fluorescence
intensity during a long incubation period in the dark (120 days) at room temperature, possibly because of microbial assimilation of lake algae (Mostofa KMG et
al., unpublished data). The autochthonous fulvic acid (C-like) of algal origin is
identified using the PARAFAC model on the EEM spectra of the samples. The aerobic microbial incubation in the dark results in a statistically significant decrease
of S over timescales of days to weeks, due to microbial production or to selective
preservation of long-wavelength absorbing substances (Helms et al. 2008).
Microbial degradation typically alters S in natural waters (Fig. 8) (Helms et al.
2008; Mostofa KMG et al., unpublished data; Brown 1977). It has been observed a
decrease in S of 1–13 % at both 275–295 nm (S 275–295 ) and 350–400 nm (S 350–400 )
for upstream and downstream DOM, with the esception of 350–400 nm (S 350–400 )
in downstream DOM where S has been found to increase (~5 %) after 13 days of
dark incubation (Fig. 8). Because of significant variations in CDOM composition
between upstream and downstream samples, it is suggested that microbial degradation of CDOM depends on its chemical nature and on its sources.
4.4.1 Factors Controlling the Microbial Degradation of CDOM
Absorbance
Microbial degradation of DOM depends on several key factors that can be listed
as: (1) Occurrence and nature of microbes in waters; (2) Sources of DOM and
amount of bacterial fermentation products; (3) Temperature; (4) pH; and (5)
Sediment depths in pore waters. These factors are discussed in detail in chapter
“Photoinduced and Microbial Degradation of Dissolved Organic Matter in Natural
Waters”.
4.5 Salinity
The absorption properties of CDOM are modified when the terrestrial riverine input of CDOM is mixed with costal seawaters (Singh et al. 2010; Hernes and
Benner 2003; del Vecchio and Blough 2004; Blough and del Vecchio 2002; Fournier
2007; Nieke et al. 1997; Twardowski and Donaghay 2001; del Castillo et al.
1999; Gonsior et al. 2008; Uher et al. 2001; Blough et al. 1993; Sholkovitz 1976).
A recent study shows that the addition of various salts, which are present in seawater, gives rise to an extra absorption in the far UV and to an increase of the amount
of scattering because small variation in salt concentration can cause refractive
index fluctuations (Fournier 2007). A linear inverse relationship of CDOM absorption to salinity could be a useful indicator of salinity in coastal waters strongly
affected by river input (Singh et al. 2010; del Vecchio and Blough 2004; Nieke
et al. 1997; Blough et al. 1993). However, at lower salinity minor deviations from
linearity may result from consumption or production of CDOM in coastal waters
K. M. G. Mostofa et al.
Alteration of autochthonous fulvic acids (C-like) changes their fluorescence
intensity during a long incubation period in the dark (120 days) at room temperature, possibly because of microbial assimilation of lake algae (Mostofa KMG et
al., unpublished data). The autochthonous fulvic acid (C-like) of algal origin is
identified using the PARAFAC model on the EEM spectra of the samples. The aerobic microbial incubation in the dark results in a statistically significant decrease
of S over timescales of days to weeks, due to microbial production or to selective
preservation of long-wavelength absorbing substances (Helms et al. 2008).
Microbial degradation typically alters S in natural waters (Fig. 8) (Helms et al.
2008; Mostofa KMG et al., unpublished data; Brown 1977). It has been observed a
decrease in S of 1–13 % at both 275–295 nm (S 275–295 ) and 350–400 nm (S 350–400 )
for upstream and downstream DOM, with the esception of 350–400 nm (S 350–400 )
in downstream DOM where S has been found to increase (~5 %) after 13 days of
dark incubation (Fig. 8). Because of significant variations in CDOM composition
between upstream and downstream samples, it is suggested that microbial degradation of CDOM depends on its chemical nature and on its sources.
4.4.1 Factors Controlling the Microbial Degradation of CDOM
Absorbance
Microbial degradation of DOM depends on several key factors that can be listed
as: (1) Occurrence and nature of microbes in waters; (2) Sources of DOM and
amount of bacterial fermentation products; (3) Temperature; (4) pH; and (5)
Sediment depths in pore waters. These factors are discussed in detail in chapter
“Photoinduced and Microbial Degradation of Dissolved Organic Matter in Natural
Waters”.
4.5 Salinity
The absorption properties of CDOM are modified when the terrestrial riverine input of CDOM is mixed with costal seawaters (Singh et al. 2010; Hernes and
Benner 2003; del Vecchio and Blough 2004; Blough and del Vecchio 2002; Fournier
2007; Nieke et al. 1997; Twardowski and Donaghay 2001; del Castillo et al.
1999; Gonsior et al. 2008; Uher et al. 2001; Blough et al. 1993; Sholkovitz 1976).
A recent study shows that the addition of various salts, which are present in seawater, gives rise to an extra absorption in the far UV and to an increase of the amount
of scattering because small variation in salt concentration can cause refractive
index fluctuations (Fournier 2007). A linear inverse relationship of CDOM absorption to salinity could be a useful indicator of salinity in coastal waters strongly
affected by river input (Singh et al. 2010; del Vecchio and Blough 2004; Nieke
et al. 1997; Blough et al. 1993). However, at lower salinity minor deviations from
linearity may result from consumption or production of CDOM in coastal waters