Arc h . Hydrobiol.
139
3
347-378
Stuttgart, May
1 997
Phosphate mobilization in iron-rich anaerobic
sediments: microbial Fe (l I l) oxide reduction versus
iron-sulfide formation
Eric E. Roden
and
Jennifer W. Edmonds 1
With 1 1 figures and 3 tables in the text
Abstract: Mechanisms of phosphate (P04 3 - ) mobilization and retention were exam­
ined in iron-rich anaerobic freshwater wetland, lake, and coastal marine sediments .
Direct microbial Fe (III) oxide reduction solubilized only 3 - 25 % of initial solid-phase
P04 3 - during sulfate-free sediment incubation experi ments . Experiments with re­
duced, non-sulfidic solid-phase Fe (II)-rich sediment demonstrated pol - sorption by
the solid-phase, and chemical equilibrium calculations indicated that conditions were
favorable for precipitation of Fe (II)-P04 minerals [e.g. Fe 3 (P04hl in such sediments.
These results suggested that much of the P04 3 - released from Fe (III) oxides during
microbial Fe (III) reduction was captured by solid-phase reduced iron compounds
(Fe(II) hydroxide-P04 complexes and/or Fe (II)-P04 minerals). Enhanced liberation of
P04 3 - to sediment porewaters (33 - 1 00 % of initial solid-phase P04 3 - ) occurred dur­
ing anaerobic incubation in the presence of abundant sulfate and was directly corre­
lated with sulfate reduction and iron-sulfide mi neral formation. Incubation of P04 3 - ­
amended sediment with different amounts o f sulfate demonstrated a linear correlation
between pol- release and sulfate reduction. Release of P04 3 - to sediment porewaters
during decomposition of fresh organic matter (freeze-dried cyanobacteria) was more ex­
tensive in sulfate-amended (67 % of added organic P) than in sulfate-free sediment ( 1 7 %
o f added organic P), and the ratio o f di ssolved P04 3 - released to organic carbon oxi­
dized was seven-fold higher in sulfate-amended sediment despite a common level of
overall organic C and P mineral ization in the two treatments. Our results demonstrate
that iron-rich anaerobic sediments can immobilize substantial amounts of P04 3 - under
Fe (III) oxide-reducing conditions, but that extensive pol- release will take place if
sediment Fe compounds are converted to iron-sulfides via bacterial sulfate reduction .
I ntroduction
Traditional models of aquatic sediment P biogeochemi stry ascribe P mobiliza­
tion to release of P04 3 - (e.g. deri ved from microbial degradation of deposited
I Authors ' address: Department of Biological Sciences, The Uni versity of Alabama,
Tuscaloosa, AL 35487-0206, USA.
DOI: 10.1127/archiv-hydrobiol/139/1997/347
© 1 997 E.
0003-91 36/97/01 39-0347 $ 8 .00
Schweizerbart ' sche Verlagsbuchhandlung,
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