Environmental Engineering Reference
In-Depth Information
Fig. 10
Relationship
between DOC concentration
and DIC (Fig. a) or CO (Fig.
b) photoproducts generated in
photo experiments conducted
on different sources of natural
waters.
Data source
Table 4
and references therein
Miller
2010
; Liu et al.
2010
; Lohrenz et al.
2010
). It is shown that gaseous CO
2
is
rapidly dissolved in waters, which can be presented as (Eq.
5.1
) (Liu et al.
2010
):
CO
2
+
H
2
O
↔
H
2
CO
2
↔
H
+
+
HCO
3
−
↔
2H
+
+
CO
3
2
−
(5.1)
where the reaction (Eq.
5.1
) is an equilibrium mixture of dissolved carbondiox-
ide, carbonic acid, bicarbonate and carbonate ions. The proportion of each species
depends on pH whereas at high pH the reaction shifts to the right hand side of
(Eq.
5.1
) and bicarbonate
(HCO
3
−
) at pH between 7 and 9 dominates, approximately 95 % of the carbon
in the water. At high pH > 0.5, carbonate predominates (Dreybrodt
1988
). DIC is
also derived remarkably by carbonate dissolution with uptake of CO
2
in soil water
(Eq. 5.2), and weathering as well as dissolution of silicate minerals (Eq. 5.3) (Liu
et al.
2010
; Dupré et al.
2003
; Mortatti and Probst
2003
).
CaCO
3
+
CO
2
+
H
2
O
=
Ca
2
+
+
2HCO
3
(5.2)
(5.3)
2CO
2
+
3H
2
O
+
CaSiO
3
+
2HCO
3
+
H
4
SiO
4
The concentration levels of carbon-gas photoproducts are highly variable
