Environmental Engineering Reference
In-Depth Information
which is the strong evidence of significant in situ biological production of CDOM
in natural waters (Chen and Gardner
2004
).
Incubation of coastal seawater in the presence of model (DON: amino sug-
ars and amino acids) and DIN compounds shows that net biological DOM for-
mation occurs upon addition of amino sugars (formation of fluorescent, mostly
labile DOM) and tryptophan (formation of non-fluorescent, refractory DOM)
(Biers et al.
2007
). Similarly, natural assemblages of marine bacteria can rap-
idly produce refractory material (in <48 h) utilizing labile compounds (glucose,
glutamate), as observed in a laboratory experiment (Ogawa et al.
2001
). On the
other hand, photoinduced formation of DOM is only detected when tryptophan
is added to the water (Biers et al.
2007
). This CDOM is highly fluorescent, with
excitation-emission matrices (EEMs) resembling those of terrestrial, humic-like
fluorophores (Biers et al.
2007
). The bulk particulate organic carbon (POC) dur-
ing the decomposition process of freshwater or marine algae and phytoplank-
ton is significantly decreased during the first few days. It subsequently remains
almost constant (Zhang et al.
2009
; Hanamachi et al.
2008
; Matsunaga
1981
;
Fukami et al.
1985
; Osinga et al.
1997
; Fujii et al.
2002
). The carbohydrate con-
tents of both the particulate and dissolved pools are increased during the phy-
toplankton growth cycle, accounting for 18-45 % and 26-80 % of total organic
carbon (TOC), respectively, in natural waters (Biddanda and Benner
1997
).
Photoreactions driven by UV-B can reduce the microbial availability of certain
organic substrates such as peptone and algal exudates (Morris and Hargreaves
1997
; Thomas and Lara
1995
; Naganuma et al.
1996
). This phenomenon can be
caused by light-induced cross-linking between DOM and algal exudates (Morris
and Hargreaves
1997
).
LMW organic acids are presumably formed by four major processes (Lovley
et al.
1996
; Xiao and Wu
2011
; Wetzel et al.
1995
; Smith and Oremland
1983
;
Kieber et al.
1990
; Corin et al.
1996
; Janczarek et al.
1997
; Evans
1998
; Bertilsson
et al.
1999
; Tedetti et al.
2006
; Lu et al.
2007
; Xiao et al.
2009
,
2011
): first, pho-
toinduced decomposition of allochthonous and autochthonous DOM in surface
waters; second, photoinduced and microbial respiration or assimilation of algae or
phytoplankton biomass in natural waters; third, conversion of anaerobic organic
substances (carbohydrates, fats, proteins, etc.) into CH
4
and CO
2
in pore waters or
soil ecosystems; and fourth, root exudations of plants or plant-microbe associa-
tions (e.g. Rhizobium symbiosis with leguminous roots).
A number of factors can influence the DOC release by algae or phytoplank-
ton and bacteria in waters, which can be distinguished as: (i) occurrence of the
phytoplankton species and their contents; (ii) water quality; (iii) presence of
nutrients; (iv) effect of UV and PAR; (v) water temperature; (vi) occurrence of
microbes; (vii) metabolic abilities or inabilities and so on (Norrman et al.
1995
;
Mostofa KMG et al., unpublished data; Lancelot
1979
; Fogg
1983
; Nelson et al.
1998
,
2004
; Rochelle-Newall and Fisher
2002a
,
b
; Cammack et al.
2004
; Biers
et al.
2007
; Ortega-Retuerta et al.
2009
; Hulatt et al.
2009
; Zhao et al.
2006a
,
2009
; Williams
1990
,
1995
; Obernosterer and Herndl
1995
; Anderson and
Williams
1998
; McCallister et al.
2004
).
