Environmental Engineering Reference
In-Depth Information
increases production of DOC. Increases in temperature can also induce higher
drawdown of water tables in summer, increasing the depth of the zone where oxi-
dation and production of DOC take place (Evans et al.
1999
). In the UK, the latter
effects would probably be exacerbated by the decreased summer rainfall over the
last 40 years (Burt et al.
1998
). It is suggested that the effect of increased tempera-
ture on water tables can account for between 10 and 20 % of the increase in DOC
concentration (Worrall et al.
2004b
,
2007
; Cole et al.
2002
).
6.4 Microbial Processes
Microbial processes have two important effects on OM (DOM and POM). First
microbial respiration or assimilation of OM into algal or phytoplankton bio-
mass or bacterial biomass can release autochthonous DOM in deep water (Mostofa
et al.
2009a
,
b
,
2011
; Zhang et al.
2009
; Yamashita and Jaffé
2008
; Fu et al.
2010
;
Rochelle-Newall and Fisher
2002a
; Yamashita and Tanoue
2004
; Aoki et al.
2008
;
Stedmon and Markager
2005a
; Stedmon et al.
2007a
). This process can give an
important contribution to autochthonous DOM in natural waters. Second, microbial
processes can change the molecular structure of DOM components and their opti-
cal properties, either absorption properties of CDOM or fluorescence properties of
FDOM (Moran et al.
2000
; Mostofa et al.
2007a
; Hur
2011
). Such properties will
be discussed in chapters
“
Photoinduced and Microbial Degradation of Dissolved
Waters
”. Microbial degradation can mineralize DOC by approximately 0-85 % in
natural waters (see chapter
“
Colored and Chromophoric Dissolved Organic Matter in
Natural Water
”
). High molecular weight protein-like structures in plant-derived DOM
are degraded primarily through physical-chemical and microbial processes (Scully
et al.
2004
). Microbial activity is significantly stimulated by the photoproducts of read-
ily assimilable nitrogen compounds such as ammonium and amino acids (Bushaw
et al.
1996
; Jørgensen et al.
1998
). Under N-limiting conditions, nitrogenous photo-
products can significantly increase the rates of bacterial growth in natural waters
(Bushaw et al.
1996
). Microbial degradation depends on several key factors, such as
occurrence and nature of microbes; sources of DOM and the quantity of its fermenta-
tion products; temperature; pH; and sediment depth (see chapter
“
Photoinduced and
6.5 Photoinduced Processes
Photoinduced processes have two effects on OM (DOM and POM): First, photo-res-
piration or assimilation of POM can release autochthonous DOM in surface waters
(Mostofa et al.
2009b
,
2011
; Harvey et al.
1995
; Fu et al.
2010
; Rochelle-Newall
