THE EFFECT OF PROTOZOA ON THE REDUCTION OF SOLID PHASE FE(III)

The role of protozoa in the microbial ecology of aquifers is not well understood. Following the injection of bacteria into the oxic and suboxic zones of the shallow, sandy, Columbia aquifer in Oyster, VA, a substantial increase in the concentration of protists was observed. Microcosms simulating this aquifer were constructed to investigate the effect of protozoa on Fe(III) reduction. The bacterium, Shewanella putrefaciens strain CN32 isolated from the Morrison Formation in Northwestern New Mexico, the protist, Spumella sp. isolated from the Columbia Aquifer in Oyster, VA and an artificial groundwater medium were utilized. It was shown that in aquifer sediments the addition of protozoa to microcosms containing CN32 and lactate dramatically decreased the rate and total amount of Fe(III) reduction. After 15 days, in microcosms containing ferrihydrite coated quartz sands and sediments from the Columbia aquifer, the addition of protists decreased the amount of soluble Fe(II) produced by 69% and 64%, respectively, when compared to microcosms without protists. These results may help to increase our understanding of bacterial diversity and biogeochemical processes in aquifers. In addition, they may have important implications for bioaugmentation as a remedial scheme at metal contaminated sites.