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K. M. G. Mostofa et al.
2.6 Kinetics of Photoinduced Degradation of DOM
Photoinduced degradation can decrease the concentration of dissolved organic carbon (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):
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. 7a)
(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 undergoes 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. 1c and d).
3 Factors Controlling the Photoinduced Degradation
of DOM in Natural Waters
Photoinduced degradation of DOM depends on the sources of waters, concentration 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
(2.47)
Ln (DOC/DOC o ) = −k 1 S
Integrated solar intensity (MJm
(a)
(b)
(c)
-2 )
Ln(DOC/DOC
0 )
Fig. 7 Relationship between the Ln(DOC/DOC 0 ) and the integrated solar intensity (MJm −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)
K. M. G. Mostofa et al.
2.6 Kinetics of Photoinduced Degradation of DOM
Photoinduced degradation can decrease the concentration of dissolved organic carbon (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):
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. 7a)
(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 undergoes 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. 1c and d).
3 Factors Controlling the Photoinduced Degradation
of DOM in Natural Waters
Photoinduced degradation of DOM depends on the sources of waters, concentration 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
(2.47)
Ln (DOC/DOC o ) = −k 1 S
Integrated solar intensity (MJm
(a)
(b)
(c)
-2 )
Ln(DOC/DOC
0 )
Fig. 7 Relationship between the Ln(DOC/DOC 0 ) and the integrated solar intensity (MJm −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)