Environmental Engineering Reference
In-Depth Information
Vermilyea et al.
2010
).Variations in production rates of H
2
O
2
are likely to be caused
by the amount and the molecular nature of DOM (Table
2
). This fact can be easily
understood from a significant difference in the production rates of H
2
O
2
estimated
in the presence of various standard organic substances (Table
2
). The major source
of H
2
O
2
in river water is fulvic acid, which contributed 23-61 % in upstream riv-
ers, 28-63 % in polluted Kurose waters, and 67-70 % in clean Ohta river waters
(Mostofa and Sakugawa
2009
). Tryptophan-like substances are a minor source of
H
2
O
2
(~1 %) in all river waters. The contribution of the fluorescent whitening agents
(DAS
+
DSBP) to H
2
O
2
production was minor (2 %), although they were dominant
FDOM components in the downstream waters of the Kurose river. The 4-biphenyl
carboxaldehyde (4BCA), one photoproduct of DSBP, showed that the percent con-
tribution to total H
2
O
2
production was 2.0-5.0 % in the downstream waters of the
Kurose river (Mostofa and Sakugawa
2009
). Unknown sources of H
2
O
2
(other than
fulvic acid-like and tryptophan-like substances or FWAs) accounted for 34-68 % of
H
2
O
2
in the upstream waters of the Kurose, 35-67 % in the upstream areas of the
Ohta, 14-15 % in the downstream sites of the Ohta, and 51-70 % in the downstream
sites of the Kurose (Mostofa and Sakugawa
2009
). The unknown sources of H
2
O
2
may be other fluorescent and non-fluorescent substances (Kramer et al.
1996
), which
can originate from forest ecosystems in the upstream regions of a river and from vari-
ous anthropogenic sources affecting the downstream regions. The production rate
of H
2
O
2
for Suwannee River Fulvic Acid (SRFA) is relatively low (344 nM h
−
1
)
compared to DSBP (1073 nM h
−
1
), tryptophan (648 nM h
−
1
), and Suwannee River
Humic Acid, SRHA, (644 nM h
−
1
, Table
2
). However, fulvic acids may be impor-
tant H
2
O
2
sources due to their significant occurrence (30-80 % of total DOM) in the
aquatic environments (Mostofa et al.
2009
; Malcolm
1985
; Peuravuori and Pihlaja
1999
).
1.8 Diurnal Cycle or Diel Variation of H
2
O
2
and its Controlling Factors in Natural Waters
A diurnal cycle is a regular and ubiquitous phenomenon of H
2
O
2
production
and decay. H
2
O
2
concentration in natural waters gradually increases as incident
solar radiation increases during the period from dawn to noon. The solar radia-
tion reaches a peak at noon time and then the concentration gradually decreases
with the decrease of sunlight intensity (Fig.
6
). The amplitude of the H
2
O
2
diurnal cycle (highest concentration at noon time minus concentration during
the period before sunrise) was 35 nM in upstream and 65 nM in Kurose River
(Fig.
6
) (Mostofa and Sakugawa
2009
), 790 nM in Jacks Lake (Cooper and
Lean
1989
), 36 nM (February), 173 nM (August), 183 nM (September), and
56 nM (November) in Patuxent Estuary (Kieber and Heltz
1995
), 187 nM in
Seto Inland Sea (Sakugawa et al.
1995
), 305 nM in Hiroshima Bay (Akane et
al.
2004
), 120 nM in Taira Bay and 80 nM in Sesoko Island Bay (Arakaki et al.
2005
), 70 nM in Mediterranean (Israeli) coastal waters, 92 nM in Red Sea in Gulf
