EFFECTS OF EXPOSURE TO AIR AND SUBSEQUENT DRYING ON THE PHOSPHATE SORPTION CHARACTERISTICS OF SEDIMENTS FROM A EUTROPHIC RESERVOIR

The effects of exposure to air and subsequent drying on the phosphate adsorptive characteristics of sediments taken from Chaffey Dam-a small eutrophic water storage reservoir in New South Wales, Australia-were studied. Sediments were sampled along a transect that covered heavily desiccated, wet-littoral, and submerged sediments, both from above and below the oxycline. Phosphate adsorption isotherms showed that there was a definite transition in P affinity along the transect, with sedim ents taken from the driest sites displaying the least adsorptive capac ity for phosphate and samples taken from beneath the oxycline the high est. A similar transition was observed for the kinetics of phosphate u ptake. The order of reaction with respect to phosphate loading decreas ed from approximately first order for anoxic sediments to fractional o rder for desiccated sediments. These effects are mostly the result of sediment oxidation and aging rather than desiccation, variation in ele mental composition, or differences in the amount of native P adsorbed to the sediment.