EFFECTS OF DESICCATION OXIDATION ON THE POTENTIAL FOR BACTERIALLY MEDIATED P RELEASE FROM SEDIMENTS/

The effect of desiccation/oxidation on the potential for phosphorus re lease from reservoir sediments under anoxic conditions was studied. Wh en sediments were exposed to the air and subsequently dried, their abi lity to release P under anaerobic conditions was severely limited rela tive to sediments that were not exposed. Anaerobic P release in respon se to the addition of a toxicant (formaldehyde), bioavailable carbon s ources (acetate or glucose), available sulfur (sulfate), and sulfide w ere used to infer possible causes for the decrease in anaerobic P rele ase as a function of desiccation/oxidation. A substantial reduction in P release occurred in sediments that had not been exposed when formal dehyde was added. This suggests that anaerobic P release may be microb ially driven. Addition of acetate and sulfate slightly enhanced P rele ase from nondesiccated sediments, suggesting some C and(or) S limitati on of the bacterial processes occurring in these sediments. Substantia l P was released when sulfide was added to the nonexposed sediments, i ndicating that there is a significant amount of P associated with sulf ide-reducible minerals (e.g. iron oxyhydroxides). Sulfide addition to exposed sediments released only about one-fourth of the P compared wit h nonexposed sediments. Furthermore, no additional P was released when sulfate was added to exposed sediments, but P was released in the pre sence of either glucose or acetate. Together these results indicate th at the decrease in potential for P release from exposed sediments was caused by a shift in bacterial community structure (specifically the l oss of viable sulfate-reducing bacteria), carbon limitation as a resul t of drying, and aging of minerals with which P is associated.