The effect of P and Si additions or. P fluxes and microbial activity i
n sediment were examined using P-33-abeeed surface sediment samples wh
ich were enriched with P-32 or P-32 + Si. The distribution of both P-i
sotopes between the interstitial water and operationally defined solid
-phase P fractions was followed for 15 days. The bulk of the P-33 Sedi
ment label was adsorbed to particles, since only 0.02% of the activity
was recovered in the interstitial water after the 4-day pre-equilibra
tion before the enrichment treatments. The Si addition promoted the de
sorption of P-33 to the interstitial water and, accordingly, retarded
the adsorption of P-32 from solution to solid-phase. The increase in l
abile P, measured with anion exchange resin-impregnated membranes, ind
icated that the availability of P was enhanced immediately after the S
i enrichment as well as at the end of the experiment. As a result of t
he Si addition, the production of organic P compounds by bacteria incr
eased (mainly bound to bacterial cells) and the phosphatase activity d
ecreased, demonstrating increased bioavailability of P. The chemical c
ompetition for sorption sites between P and Si, observed for soils, se
ems to be valid also for sediments. (C) 1998 Elsevier Science Ltd. All
rights reserved.