Environmental Engineering Reference
In-Depth Information
2.6 Kinetics of Photoinduced Degradation of DOM
Photoinduced degradation can decrease the concentration of dissolved organic car-
bon (DOC) as a function of the integrated solar intensity (Fig.
7
) (Mostofa et al.
2005
,
2007
). The changes in the DOC concentration can be best fit with a first
order reaction as reported below (Eq.
2.47
):
Ln
(
DOC
/
DOC
o
)
=−
k
1
S
(2.47)
where
k
1
is the reaction rate constant for the photoinduced degradation of DOC,
DOC
is organic carbon concentration after irradiation and
DOC
o
the initial
one, and
S
is the integrated solar intensity or photon energy (MJ m
−
2
) (Fig.
7
a)
(Mostofa et al.
2007
).
Kinetics studies on the photoinduced degradation of DOM can explain several
important phenomena in waters (Mostofa et al.
2007
). First, stream DOM under-
goes rapid photoinduced degradation (1.8-2.6
×
10
−
3
MJ
−
1
m
2
in waters of the
Kago and Nishi-Mataya upstreams) (Mostofa et al.
2007
). Second, microbial
degradation under dark incubation is quite low or negligible for upstream DOM
(0.7-4.6
×
10
−
4
MJ
−
1
m
2
for the same upstreams). Third, in rivers that include
various sources of DOM the latter can be uniformly degraded both photolytically
(9.5
×
10
−
4
MJ
−
1
m
2
) and microbiologically (11
×
10
−
4
MJ
−
1
m
2
) (Fig.
1
c and d).
3 Factors Controlling the Photoinduced Degradation
of DOM in Natural Waters
Photoinduced degradation of DOM depends on the sources of waters, concentra-
tion level and optical-chemical nature of DOM, time and space. Photoinduced
degradation of DOM is an important phenomenon that plays a significant role
in the biogeochemistry of the carbon cycle, biological activity and primary and
secondary productions in natural waters (Mostofa et al.
2009a
; Ma and Green
(a)
(b)
(c)
Integrated solar intensity (MJm
-2
)
−
2
) in
the Kago upstream (
a
), Nishi-Mataya upstream (
b
), and in the downstream waters of Yasu River
(
c
).
Data source
Mostofa et al. (
2007
)
Fig. 7
Relationship between the
Ln
(
DOC
/
DOC
0
) and the integrated solar intensity (MJm
