Environmental Engineering Reference
In-Depth Information
deeper lake or oceanic environments. The study shows that the global annual rate
of photoinduced production of DIC (10
14
-10
15
mol DIC per year) (Johannessen
2000
) might be on the same order of magnitude as that of sequestration of DIC
by new production (~10
15
mol DIC per year) (Liu et al.
2000
).
CO production upon photoinduced degradation of DOM is highly variable for
a variety of waters (Table
3
). Production rates are 0.004-1.5
μ
M h
−
1
in rivers,
0.26
μ
M h
−
1
in lakes, 0.004-1.0
μ
M h
−
1
in seawaters, and 1.5-3.3
μ
M h
−
1
in
standard dissolved fulvic and humic acids (Table
3
). It is estimated that >95 %
of the total water-column CO photoproduction occurs within the mixed layer on
a global, yearly basis (Fichot and Miller
2010
). It has been shown that the pro-
duction rates of CO are almost linearly correlated with the concentration of
DOC and of standard organic substances (Fig.
10
b). The photoproduction of CO
in the ocean is induced mainly by the UV component of solar radiation (Zepp
et al.
1998
; Atlas et al.
1994
). Quantum yields (the quantum yield is the fraction of
absorbed radiation that results in photoreaction) for CO production at wavelengths
greater than 297 nm are highest in the UV-B region (Zepp et al.
1998
). Turnover
times for CO are in the order of hours, and they are generally lower (3-98 h) in
fall and higher (2-108 h) in spring samples in the Caribbean Sea (Jones
1991
;
Jones and Amador
1993
). The CO oxidation rate is lower in spring samples
(20-340 pmol L
−
1
h
−
1
except one sample, 980 pmol L
−
1
h
−
1
) than in fall samples
(20-660 pmol L
−
1
h
−
1
except one sample, 810 pmol L
−
1
h
−
1
). The concentra-
tion levels of CO are variable: 1-6 nM in spring and 0.6-32 nM in fall. The vari-
ations in the oxidation rates appear to be linked with two important phenomena.
First, nitrifying and carboxydobacteria are both thought to have a role in oxidizing
CO in the oceans (Conrad and Seiler
1980
). Second, high concentrations of CO
are able to inhibit marine nitrifying bacteria in natural waters (Jones and Amador
1993
; Jones and Morita
1984
).
In the estuary of River Ohta, the concentration of carbonyl sulfide (COS) was
highest (54.4 ng L
−
1
) in the late afternoon (17:00) during the summer season
(July), and lowest (23.9 ng L
−
1
) soon after noontime (14:00) during the winter
season (December) (Table
3
) (Fujiwara et al.
1995
). In Seto Inland Sea the COS
concentration was higher (~5-17 ng L
−
1
) in the surface layer (0-5 m), whilst it
was lower (~3-5 ng L
−
1
) in the deeper layer (20 m) (Fujiwara et al.
1995
). An
increase in COS concentrations is often linked with an increase of solar radia-
tion, lower concentrations being detected at night time and in the early morning.
Moreover, higher concentrations are found in surface seawater than in the deeper
layers, suggesting that COS is photolytically produced in natural waters.
Photo products such as H
2
O
2
, ROOH and CO
2
, simultaneously generated dur-
ing the photoinduced degradation of DOM, can be photosynthetically transformed
into carbohydrates during the summer season in natural surface waters. The rel-
evant processes can be depicted as follows (Eqs.
5.4
,
5.5
) (Mostofa et al.
2009a
;
Komissarov
1994
,
1995
,
2003
):
(5.4)
DOM
+
h
υ →
H
2
O
2
+
CO
2
/
CO
/
DIC
+
LOWDOM
+
E
(±)
x CO
2
(
air
)
+
yH
2
O
2
(
H
2
O
)
+
h
υ →
C
x
(
H
2
O
)
y
+ (
x
+
y
/
2
)
O
2
+
E
(±)
(5.5)
