INCREASED BIOAVAILABILITY OF SEDIMENT PHOSPHORUS DUE TO SILICATE ENRICHMENT

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.