Fluorescent Dissolved Organic Matter in Natural Waters - Photobiogeochemistry of Organic Matter - page 524

in Natural Waters ”) (Ma and Green 2004 ; Mostofa and Sakugawa 2009 ; Palenik
and Morel 1988 ; Conrad 1999 ; Lovley et al. 1996 ). Secondly, methanogenesis
caused by microorganisms (methanogens and acetogens) is an important anaerobic
process that can produce CH 4 and CO 2 by converting either acetate (and formate)
or H 2 /CO 2 in anaerobic environments (Conrad 1999 ; Lovley et al. 1996 ; Zinder
1993 ; Kotsyurbenko et al. 2001 ). It is presumably considered that the carbohy-
drate fraction or aliphatic carbon bound in macromolecules (allochthonous fulvic
and humic acids) (Malcolm 1985 ; Peuravuori and Pihlaja 1999 ) may alter by the
methanogenesis. This process can change the molecular structure either by modi-
fying the existing functional groups in the macromolecules or by creating a new
π -electron bonding system in the molecule.
3.3.2 Factors Affecting the Microbial Degradation of FDOM in Waters
An increase in fulvic acid-like or humic-like fluorescence at peak C- and
A-regions as well as a decrease in fluorescence of aromatic amino acids either
in deeper waters of lakes and ocean or in dark incubated water samples is an
effect of the microbial degradation of organic matter and the related functional
groups (Hayase and Shinozuka 1995 ; Coble 1996 , 2007 ; Mostofa et al. 2010 ,
2007a , 2007b , 2011 ; Ma and Green 2004 ; Moran et al. 2000 ). Microbial degra-
dation of DOM thus depends on several key factors that can be distinguished as:
(1) Occurrence and nature of microbes in waters; (2) Sources of DOM and the
quantity of their fermentation products; (3) Temperature; (4) pH; and (5) Sediment
depths in pore waters.
3.4 Complex Formation of Trace Elements with FDOM
Trace elements can significantly affect the fluorescence properties of FDOM in
natural waters (Mostofa et al. 2009a ; Wu et al. 2004a , 2004b ; Fu et al. 2007 ; Lu
and Jaffé 2001 ). The trace elements or metals (M) can generally form complexes
with the fluorophores or functional groups in fluorescent dissolved organic matter
(FDOM), which are termed as M-DOM or M-FDOM. The relevant trace elements
are transition metals such as Fe, V, Ce, Th, U, Mo, Cu, Mn, Ni, Co, Cr, Zn, Pb,
Cd, Hg and UO 2 (II), metal/metalloid such as Sb(III) and Al, as well as the alka-
line earth elements (see also chapter “ Complexation of Dissolved Organic Matter
with Trace Metal Ions in Natural Waters ” ) (Mostofa et al. 2009a , 2011 ; Wu et al.
2004a , 2004b , 2004c ; Zhang et al. 2010 ; Yamashita and Jaffé 2008 ; Lu and Jaffé
2001 ). The relevant organic substances in M-DOM complexation are fulvic acid,
humic acid, tryptophan, cysteine, selenoprotein P, extracellular polymeric sub-
stances (EPS), the Schiff base 2-[4-dimethylaminocinnamalamino]—benzoic acid,
phenols and polyphenols (Mostofa et al. 2009a , 2011 ; Wu et al. 2004a , 2004b ;
Lu and Jaffé 2001 ). The fluorophores in FDOM or functional groups in DOM