Agriculture Reference
In-Depth Information
Concentration of P in solution (
µ
M)
0
100
200
300
400
500
600
0.0
0.5
N
30 000
1.0
15 000
1.5
5000
2.0
2.5
1000
3.0
Figure 2.13
Effect of mixing of pore water by tubificid worms on profiles of P concen-
tration in submerged soil calculated with Equations (2.37) and (2.40). Numbers on curves
are densities of tubificids
1.0
0.8
0.8
L
=
5 cm
0.6
0.6
3
1.5
0.4
0.4
1.5
3
0.2
0.2
5
0.0
0.0
0
10 000
20 000
30 000
0
10 000
20 000
30 000
N (m
−
2
)
N (m
−
2
)
Figure 2.14
Effect of mixing by tubificids on flux of P between soil and floodwater
calculated with Equations (2.37) and (2.40). Numbers on curves are depths of mixing
soil and overlying floodwater. The primary productivity of the floodwater, includ-
ing the fixation of N by photosynthetic aquatic organisms, is often limited by the
supply of P from the soil. So enhanced P transport resulting from tubificid activ-
ities can be important. Figure 2.13 shows calculated concentration profiles of P
in the soil near the floodwater for realistic densities of tubificids (see Chapter 5)
and other parameters, and Figure 2.14 shows the corresponding fluxes from the
soil into the floodwater. Following Aller (1980b) for Si desorption in marine
sediments, the rate of P desorption from the soil is calculated with the formula
R
=
k(C
eq
−
C)
(
2
.
40
)
