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K. M. G. Mostofa et al.
intensity, and S is the integrated solar intensity (MJ m −2 ). Photodegradation of
FI can be clearly understood from the relationship between the S and Ln(FI/FI o )
(Mostofa et al. 2007a).
In river water, the reaction rate constant of fulvic acid-like FI is significantly
higher in the first step of photodegradation (8.9–20 × 10 −3 MJ −1 m 2 ) than in the
second step (5.6–8.5 × 10 −3 MJ −1 m 2 ) (Mostofa et al. 2007a). The photodegradation rate constant of protein-like FI often follows one-step kinetics with respect to
integrated solar radiation. The photodegradation rate constant of tryptophan-like
Fig. 10 Relationships
between the Ln(FI/FI 0 ) and
the integrated solar intensity
and the integrated solar
intensity for upstream waters
(a and b Kago upstream
and Nishi-Mataya upstream,
respectively) and downstream
waters (c Yasu River).
Open circle indicates the
changes in fulvic acid-like
fluorescence intensity (FI)
and open triangle in c shows
the change in the proteinlike FI under the irradiated
condition. Data source
Mostofa et al. (2007a)
Integrated solar intensity (MJ m -2 )
Ln
(a)
(b)
(c)
(FI/FI
0 )