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 sediments taken from the driest sites displaying the least adsorptive capacity for phosphate and samples taken from beneath the oxycline the highest. A similar transition was observed for the kinetics of phosphate uptake. The order of reaction with respect to phosphate loading decreased from approximately first order for anoxic sediments to fractional order for desiccated sediments. These effects are mostly the result of sediment oxidation and aging rather than desiccation, variation in elemental composition, or differences in the amount of native P adsorbed to the sediment.