The effects of drying on phosphorus sorption and speciation in subtropical river sediments
2010
Kerr, Jason G. | Burford, Michele | Olley, Jon | Udy, James
The present study investigated whether drying and desiccation substantially increase the biologically available phosphorus (P) in riverbed sediments from a dry subtropical river. Sequential extraction and batch equilibrium experiments were undertaken on sediments with contrasting organic matter content, percentage fines and P content. The response of sediments to drying differed predominately as a result of drying time rather than as a result of the different physiochemical properties and total P content of the sediments. For both in situ and laboratory drying, major changes in P speciation occurred in the surface-layer sediment (0-2cm) where NH₄Cl-P (loosely sorbed P) was higher in partially dried and desiccated sediments than in wet sediments. Conversely, NaOH-nrP (labile organic and poly-P) was significantly lower (P3-), was higher in sediments desiccated in situ and in the laboratory than in submerged and partially dried sediments. Together with the speciation results, the higher EPC₀ indicates that the potential for sediments to release P during the next flow event is substantially increased as a result of desiccation. The lower EPC₀ in partially dried sediments suggested that the degree of drying may be an important factor in terms of the long-term potential for sediments to act as a source or a sink of PO₄3- after rewetting. The results from the present study have important implications because natural or anthropogenic processes which lead to riverbed drying may increase the flux of bioavailable P from bed sediments when flow returns.
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