Agriculture Reference
In-Depth Information
600
with tubificids
without
400
200
0
500
400
300
200
100
0
10
8
6
4
2
0
750
600
450
300
150
0
150
175
200
225
250
Day of year
Figure 5.11
Effects of tubificids on concentrations of N species, P and Fe in the floodwa-
ter of unplanted microplots in ricefields. Species
B. sowerbyi
, density 1000m
−
2
(Kikuchi
and Kurihara, 1982). Reproduced with kind permission of Kluwer Academic Publishers
solid particles constantly cycled between oxic and anoxic zones but typically
spent 10- to 100-times longer under anoxic than oxic conditions. Cyclic redox
patterns were also common within individual burrows and were accompanied
by rapid switching of metabolic processes. Even brief, periodic re-exposure of
organic matter to O
2
resulted in more complete decomposition than under con-
stant conditions or unidirectional redox change. Redox oscillation apparently
results initially in net remineralization of existing microbial biomass followed
by stimulated renewed synthesis. Aller (1994) found that some properties, such
as the accumulation of P in the sediment, were comparable under fully oxic and
oscillating redox conditions but differed under continuously anoxic conditions.
This is another mechanism by which the operation of the floodwater-soil system
as a whole is not a simple sum of its component parts.
