Environmental Engineering Reference
In-Depth Information
(a)
(b)
Peak A
Peak C
Peak A
(c)
Peak A
Peak M
Fig. 3
The fluorescent components of allochthonous fulvic acid (C-like) (
a
) and allochthonous fulvic
acid (A-like) (
b
) of standard Suwannee River Fulvic Acid's aqueous samples and of allochthonous
fulvic acid (M-like) (
c
) of upstream waters (Yellow River, China) identified using PARAFAC modeling
on their respective EEM spectra. Allochthonous fulvic acids (C-like and A-like) are similar to those
of stream allocthonous fulvic acid (C-like and A-like) (Fig.
2
a, b) of upstream water samples (Nishi-
Mataya upstream). PARAFAC analysis is conducted on earlier published and their respective a.u. data
(
Data source
Mostofa et al.
2005a
; Mostofa KMG et al., unpublished data).
and 240/417 nm in water extracted from sugar maple leaves (Fig.
3
c; Table
2
)
(Mostofa KMG et al., unpublished data; Hunt et al.
2008
; Baghoth et al.
2010
;
Chen et al.
2010
; Fellman et al.
2010
; Holbrook et al.
2006
; Yamashita and Jaffé
2008
). The origin of this component is presumably located in the terrestrial soil
ecosystem. Experimental results show that allochthonous fulvic acid (M-like) is
entirely decomposed photolytically in the upstream waters and in the main chan-
nel waters of the Yellow River, because this component is minor (~5 %) compared
to the major component (~89 %) of allochthonous fulvic acid (C-like) in the total
Yellow River DOM (Mostofa KMG et al., unpublished data). On the other hand,
the allochthonous fulvic acid (M-like) undergoes complete microbial degradation
after 12 days of dark incubation in both upstream and main channel filtered waters
of the Yellow River at room temperature. This indicates that the allochthonous ful-
vic acid (M-like) is both photolytically and microbially labile in natural waters.
The molecular structure of fulvic acid is not yet known because of the com-
plicated chemical composition and relatively large molecular size. The molecular
weight of fulvic acid is approximately 2310 Da (Chin et al.
1994
); it is generally
composed of relatively few aromatic groups, which yield 14-20 % of aromatic
carbon compared to 30-51 % for humic acid (Malcolm
1985
; Steelink
2002
; Gron
et al.
1996
). The fluorophores associated with the low molecular weight fraction of
