4 1
a. Neckar River
0
Ol
40
60
E
80
o
1(
r
. ~
.~ 0
~a
1.1
20
,
0
tu~on
10
20
Elsenz
30
0 I0 20 30 40 50
0
I0
20
b. tributaries
8ot_____2L_ _A
10
20
30 0
10
20
30
Carbonate (%)
30
Fig. 4.15. Carbonate concentrations in the sediments of the Neckar River and its tributaries
The mineralization of organic matter releases CO2 and NH3 into porewater of
anoxic sediments. This process can change the chemical equilibrium (e.q.
precipitation/dissolution, adsorption/desorpdon of Ca and Mg), and consequently
control the distribution of these elements between sediments and water:
CaCO3 + CO2 + H20 ~ CaliCO3 + + HCO3
MgCO3 + CO2 + H20 --~ MgHCO3 § + HCO3"
NH 3 + CO 2 + H20 ~ NH4 + + HCO 3"
Me§
+ NH3 + CO2 + H20 ~ NI-I4+-clay + Me + + HCO3
where Me§ 0.5 Ca 2§ 0.5 Mg 2§