Environmental Engineering Reference
In-Depth Information
Table 4. Total alkalinity (A T ) and the increases over depth of total alkalinity ( A T ) and its
components in the anoxic zone of the Black Sea (see text for details).
Depth or
Total alkalinity and its components (µM)
depth
A T
A C
A S
A N
A P
A Si
A B
interval, m
100
3306
3283
0
0.21
1.26
2.10
19
200
4457
4117
312
1.10
7.64
5.00
14
A T
100-2000
1151
834
312
0.89
6.38
2.90
-5.0
%ofA T
100
100
99.30
0
< 0.01
0.04
0.06
0.57
2000
100
92.37
7.00
0.02
0.17
0.11
0.31
%of A T
100-2000
100
72.46
27.11
0.08
0.55
0.25
-0.43
on
going complex biogeochemical and physiochemical mineralization processes
in seawater [101]. Among factors that complicate the application of “Richard's
stoichiometry” for describing the aerobic and anaerobic mineralization of or-
ganic matter are seasonal changes in the composition of plankton communities
and non-stoichiometric composition of the total organic carbon and its compo-
nents.
Given that
A T
≈ ∆
A C +
A S
and pH changes with depth, the ratios
C T cannot be constant with depth accord-
ing to Richards' equation. If C T = 1 and C T /S T = 2 in the pH range of 6.6-8.2,
A C /
C T ,
A S /
C T , and
A T /
A C /C T must increase from 0.8 to 1.08,
A S /C T from 0.21 to 0.48.
A T /C T
and
A T /S T ratios must change from 1.01 to 1.56 and from 2.02 to 3.12, re-
spectively [103]. Theoretical Richardsian
A T /S T = 2.32
will occur when pH is 6.8-6.9, which is the pH range observed in the bottom
water of the Framvaren Fjord below 100 m. In the Black Sea anoxic zone with
pH=7.5-7.7,
A T /C T = 1.16 and
A T /C T is in the range of 1.40-1.46, whereas it is equal to 1.48-
1.50 in the anoxic water of the Cariaco Trench with pH=7.8-7.9. In sum, fixed
Richards' stoichiometry in equation (2) can not be used to describe alkalinity
changes during anaerobic mineralization of the organic matter under different
pH conditions.
Volkov et al. [103] have undertaken a systematic analysis of the alkalinity
variations and its composition in different anoxic basins using own and pub-
lished data [109, 110]. These results showed that the increase in total alkalinity
with depth and its compositional changes in anoxic waters are determined by the
scale (depth) of the organic matter mineralization process and pH that is itself a
function of the anaerobic mineralization. Carbonate and sulfide alkalinities are
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