Dissolved Organic Matter in Natural Waters - Photobiogeochemistry of Organic Matter - page 19

including organic acids (~14-40 %) such as acetic and formic acid, dicarboxylic
acids (~<6 %, including oxalic, succinic, malonic and maleic acids), pyruvic acid
(~<1 %), amino acids (~2 %) including tryptophan-like and tyrosine-like compo-
nents, formaldehyde (~2-8 %), acetaldehyde (~5 %), organic peroxides (ROOHs:
see chapter “ Photoinduced and Microbial Generation of Hydrogen Peroxide and
Organic Peroxides in Natural Waters ” for detailed description) (McDowell and
Likens 1988 ; Hellpointner and Gäb 1989 ; Hewitt and Kok 1991 ; Guggenberger
and Zech 1993 ; Sakugawa et al. 1993 ; Sempéré and Kawamura 1994 ; Chebbi and
Carlier 1996 ; Williams et al. 1997 ; Willey et al. 2000 , 2006 ; Ciglasch et al. 2004 ;
Avery et al. 2006 ; Kieber et al. 2006 ; Muller et al. 2008 ; Miller et al. 2008 , 2009 ;
Santos et al. 2009a , b ; Southwell et al. 2010 ; Zhang et al. 2011 ; Nichols and Espey
1991 ; Brassell et al. 1980 ; Sargent et al. 1981 ). These studies also show that rainwa-
ter mostly consists of low molecular weight organic substances, having MW < 1000
Dalton. Note that factors such as wind speed, storm trajectory and rainwater volume
can influence DOM contents in rainwater. The relative importance of these factors
depends on the sources of the rainwater constituents (Miller et al. 2008 ).
The contribution of allochthonous fulvic and humic acids is significantly high
in source waters (streams and rivers), then their contributions decrease during the
flow into the downward water ecosystem (lakes, estuaries and oceans) because of
three major processes: first, photoinduced and microbial degradation; second, dilu-
tion of the source waters with other water bodies; third, high contents of autoch-
thonous DOM can decrease the relative contribution of allochthonous fulvic and
humic acids in stagnant waters, particularly in lakes, estuaries and oceans.
On the other hand, the contribution of autochthonous DOM including autoch-
thonous fulvic acids of algal or phytoplankton origin, carbohydrates, proteins,
amino acids, lipids, organic acids etc. is relatively low in source waters, but sig-
nificantly high in lakes and oceans. Autochthonous production of DOM is typi-
cally detected in the epilimnion of lake and ocean during the stratification period.
A rough estimate shows that the contribution of autochthonous DOM is 0-102 %
in lakes and 0-194 % in oceans, which has been discussed in earlier section
(Mostofa et al. 2009a ; Wigington et al. 1996 ; Fu et al. 2010 ; Ogawa and Tanoue
2003 ; Ogawa and Ogura 1992 ; Mitra et al. 2000 ; Yoshioka et al. 2002a ; Hayakawa
et al. 2003 , 2004 ; Annual Report 2004 ; Bade 2004 ; Sugiyama et al. 2004 ).
The sterol biomarkers used for identifying DOM sources in water are terrestrial
(b-sitosterol and ergosterol), sewage (5b-coprostanol and epi-coprostanol), phy-
toplankton (cholest-5,22-dien-ol, brassicasterol, dinosterol), and marine markers
(cholesterol) (McCalley et al. 1981 ; Mudge and Bebianno 1997 ; Mudge and Duce
2005 ; Nichols and Espey 1991 ). Long-chain C22-C30 alkanols are generally con-
sidered to originate from terrestrial plants, while short-chain alkanols have unspec-
ified marine, terrestrial and bacterial origins (Brassell et al. 1980 ; Sargent et al.
1981 ). From the above contributions to the DOM composition in various sources
of waters, it is evidenced that, on average, approximately 80-90 % of bulk DOM
in streams, rivers, lakes and oceans is specifically identified as allochthonous ful-
vic and humic acids, autochthonous fulvic acids, carbohydrates, proteins, lipids,
amino acids, fatty acids, sterols, and organic acids.