Environmental Engineering Reference
In-Depth Information
shows an entirely opposite behavior (maximum fluorescence at peak C and low
fluorescence at peak A) (Fig.
3
k, l).
2.6 Relationship Between FDOM and DOM
Fulvic acid-like fluorescence intensity (FI) is significantly correlated with DOC
concentration both linearly and non-linearly as a consequence of the effects of
sunlight on river water. However, non-linear correlation is more significant than
the linear one (Fig.
5
). The extrapolation of the linear relationship suggests that
fulvic acid contributes approximately 45-63 % of the total DOM in Kago (KG)
upstream, approximately 53 % in Nishi-Mataya (NM) upstream and approx-
imately 73 % in the downstream waters of the Yasu River (YR) (Mostofa et al.
2007a
). The fulvic acid contribution in Japanese rivers estimated from DOC
and fulvic acid-like FI is similar to that reported in other studies of river water
(40-80 %) (Mostofa et al.
2009a
; Malcolm
1985
; Peuravuori and Pihlaja
1999
;
Mostofa
2005
). The higher presence of allochthonous fulvic acid and humic acids
in river water is responsible for the good correlations with DOM found in natu-
ral waters (Mostofa et al.
2005a
; Fu et al.
2007
,
2010
; Westerhoff et al.
2001
).
A gradual decrease in fulvic acid-like FI with decreasing DOC concentration
(Fig.
5
) can be explained if losses in FI and DOC are mostly involving the fluoro-
phores in fulvic acid. The latter consist of some repeating functional groups with
highly variable composition, having aromatic rings and highly unsaturated aliphat-
ics with extensive
π
-electron systems (Mostofa et al.
2009b
,
2010
; Senesi
1990a
;
Malcolm
1985
; Corin et al.
1996
; Wu et al.
2005
). The fluorophores present in
Fig. 5
Changes in DOC concentration and fulvic acid (FA)-like fluorescence intensity (FI) dur-
ing photodegradation of DOM modeled by the first-order kinetics. Initial DOC concentration and
FI are presented by the
open circle
(the Nishi-Mataya, NM upstream);
open diamond
(the Kago,
KG upstream); and
open triangle
(Yasu River, YR downstream) for their respective samples col-
lected from Lake Biwa watershed, Japan.
Data source
Mostofa et al. (
2007a
)