Dissolved Organic Matter in Natural Waters - Photobiogeochemistry of Organic Matter - page 12

discussed extensively in the FDOM chapter (see chapter “ Fluorescent Dissolved
Organic Matter in Natural Waters ”). Note that “autochthonous fulvic acids” of
algal or phytoplankton origin are newly termed in this study for mostly two rea-
sons: first, to distinguish and generalize between all freshwaters and marine
waters; second, because of the confusion in different studies that use several
names such as marine humic-like (Coble 1996 , 2007 ), sedimentary fulvic acids
(Hayase and Tsubota 1983 ), microbially derived fulvic acids or marine fulvic
acids (McKnight et al. 1991 , 1994 ; Harvey and Boran 1985 ; Meyers-Schulte and
Hedges 1986 ).
DOM is produced significantly by eleven species of intertidal and sub-tidal
macroalgae when they are illuminated, providing evidence for a light-driven exu-
dation mechanism (Hulatt et al. 2009 ). The contribution of the released DOC
has been detected as 6.4 and 17.3 % of the total organic carbon in cultures of
Chlorella vulgaris and Dunaliella tertiolecta , respectively, upon light exposure
(Hulatt and Thomas 2010 ). DOM can support a significant growth of bacterial bio-
mass, representing a further loss of algal assimilated carbon in water (Hulatt and
Thomas 2010 ). Dissolved combined amino acids, middle-reach peaks of particu-
late amino acids and non-protein amino acids are often decreased in downstream
rivers, which is likely the result of photoinduced degradation of DOM and algae
(Duan and Bianchi 2007 ).
On the other hand, the key processes of autochthonous DOM release by micro-
bial respiration of algae or phytoplankton biomass in waters are presumably the
extracellular release by living cells, cell death and lysis, or herbivore grazing
that may occur in the deeper waters of rivers, lakes and oceans (Mostofa et al.
2009a ; Tanoue 2000 ; Tranvik et al. 2009 ; Hulatt et al. 2009 ). In fact, bacteria play
a specific role in subsequent processing of the DOM released by algae in natu-
ral water (Nelson et al. 1998 , 2004 ; Rochelle-Newall and Fisher 2002a ; Cammack
et al. 2004 ; Biers et al. 2007 ; Ortega-Retuerta et al. 2009 ). Cultivation of three
kinds of phytoplankton (green algae Microcystis aeruginosa and Staurastrum dor-
cidentiferum and dark-brown whip-hair algae Cryptomonas ovata collected from
lake waters) shows that fulvic acid-like and protein-like fluorescent components
are released when they are cultivated under a 12:12 h light/dark cycle in a MA
medium and an improved VT medium at 20 °C (Aoki et al. 2008 ). This study
implies that the increase of the refractory organic matter in lake waters may be
attributed to a change of the predominant phytoplankton. Similarly, cultivation of
three kinds of phytoplankton ( Prorocentrum donghaiense, Heterosigma akashiwo
and Skeletonema costatum collected from sea water) can produce visible humic-
like (C-like and M-like) and protein-like or tyrosine-like components in waters
(Zhao et al. 2006a , 2009 ).
Releases of DOM by eleven species of intertidal and sub-tidal macroal-
gae in the dark account for 63.7 % of that in the light in the UV-B band (Hulatt
et al. 2009 ). Some brown algae can produce considerably less DOM (e.g. Pelvetia
canaliculata ), which are more comparable to the green and red species (Hulatt
et al. 2009 ). It is shown that thin, subsurface DOM maxima are observed below
the plume during the highly stratified summer period but are absent in the spring,