502
K. M. G. Mostofa et al.
any macromolecule (e.g., fulvic acids and humic acids) at any peak C- or peak
A-regions can be referred to as ‘fluorochrome’. Any changes of the fluorochrome
by photoinduced or microbial degradation can cause changes in the fluorescence
properties of that molecule. Conversely, any DOM fraction that does not show fluorescence and is mostly composed of aliphatic C chain, which is photolytically
inactive, is termed as ‘non-fluorochrome’. On the basis of fluorescence characteristics, DOM can be separated into two major parts: fluorochrome and non-fluorochrome. They allow the photolytically sensitive fractions of DOM in waters to
be distinguished. Therefore, any changes in the chemical composition of DOM
by photoinduced processes can be examined by the determination of fluorescence
characteristics in the asquatic environments (Mostofa et al. 2007a; Ma and Green
2004; Moran et al. 2000; Wu et al. 2007).
3 Factors Affecting the Fluorescence Properties of FDOM
in Natural Waters
The fluorescence properties of FDOM are significantly affected by several
factors in natural waters. They are: (i) Autochthonous origin of FDOM;
(ii) Photodegradation of FDOM; (iii) Microbial degradation of FDOM;
(iv) Complex formation between trace elements and FDOM; (v) Salinity; (vi) pH,
and (vii) Temperature.
3.1 Autochthonous Origin of FDOM in Natural Waters
Photorespiration or photoinduced assimilation of organic matter (e.g. algal or
phytoplankton biomass) can produce new DOM or FDOM in the aquatic environments (Fig. 3i, j) (Mostofa et al. 2009b; Fu et al. 2010; Aoki et al. 2008; Thomas
and Lara 1995; Rochelle-Newall and Fisher 2002; Hiriart-Baer and Smiith 2005).
It has been shown that the fluorescence intensity of FDOM is gradually increased
upon 6 h sunlight irradiation in the presence of re-suspended algal biomass, collected by filtration of water (~0 m depth) from Lake Hongfeng (China) using
GF/F filters during the summer season (Mostofa et al. 2009b). These results
imply that photoinduced processes play an important role both in the decomposition of FDOM and in its production. They also play a key role in the biogeochemical cycles in the aquatic environments. Also the microbial degradation or
assimilation of organic matter (e.g. algal or phytoplankton biomass) in in vitro
experiments or under dark incubation may produce new DOM or FDOM in natural waters (Fig. 3h, j–l) (Mostofa et al. 2009b; Stedmon and Markager 2005a;
Fu et al. 2010; Zhao et al. 2009; Aoki et al. 2008; Zhang et al. 2009b; RochelleNewall and Fisher 2002; Yamashita and Tanoue 2004, 2008; Miller et al. 2009).
The fluorescence intensity of microbiologically produced FDOM was gradually
increased after 20 days dark incubation at room temperature or upon resuspension
K. M. G. Mostofa et al.
any macromolecule (e.g., fulvic acids and humic acids) at any peak C- or peak
A-regions can be referred to as ‘fluorochrome’. Any changes of the fluorochrome
by photoinduced or microbial degradation can cause changes in the fluorescence
properties of that molecule. Conversely, any DOM fraction that does not show fluorescence and is mostly composed of aliphatic C chain, which is photolytically
inactive, is termed as ‘non-fluorochrome’. On the basis of fluorescence characteristics, DOM can be separated into two major parts: fluorochrome and non-fluorochrome. They allow the photolytically sensitive fractions of DOM in waters to
be distinguished. Therefore, any changes in the chemical composition of DOM
by photoinduced processes can be examined by the determination of fluorescence
characteristics in the asquatic environments (Mostofa et al. 2007a; Ma and Green
2004; Moran et al. 2000; Wu et al. 2007).
3 Factors Affecting the Fluorescence Properties of FDOM
in Natural Waters
The fluorescence properties of FDOM are significantly affected by several
factors in natural waters. They are: (i) Autochthonous origin of FDOM;
(ii) Photodegradation of FDOM; (iii) Microbial degradation of FDOM;
(iv) Complex formation between trace elements and FDOM; (v) Salinity; (vi) pH,
and (vii) Temperature.
3.1 Autochthonous Origin of FDOM in Natural Waters
Photorespiration or photoinduced assimilation of organic matter (e.g. algal or
phytoplankton biomass) can produce new DOM or FDOM in the aquatic environments (Fig. 3i, j) (Mostofa et al. 2009b; Fu et al. 2010; Aoki et al. 2008; Thomas
and Lara 1995; Rochelle-Newall and Fisher 2002; Hiriart-Baer and Smiith 2005).
It has been shown that the fluorescence intensity of FDOM is gradually increased
upon 6 h sunlight irradiation in the presence of re-suspended algal biomass, collected by filtration of water (~0 m depth) from Lake Hongfeng (China) using
GF/F filters during the summer season (Mostofa et al. 2009b). These results
imply that photoinduced processes play an important role both in the decomposition of FDOM and in its production. They also play a key role in the biogeochemical cycles in the aquatic environments. Also the microbial degradation or
assimilation of organic matter (e.g. algal or phytoplankton biomass) in in vitro
experiments or under dark incubation may produce new DOM or FDOM in natural waters (Fig. 3h, j–l) (Mostofa et al. 2009b; Stedmon and Markager 2005a;
Fu et al. 2010; Zhao et al. 2009; Aoki et al. 2008; Zhang et al. 2009b; RochelleNewall and Fisher 2002; Yamashita and Tanoue 2004, 2008; Miller et al. 2009).
The fluorescence intensity of microbiologically produced FDOM was gradually
increased after 20 days dark incubation at room temperature or upon resuspension