The effects of drying on phosphorus sorption and speciation in subtropical river sediments
Jason G. Kerr A C D , Michele Burford A , Jon Olley A and James Udy BA Australian Rivers Institute, Griffith University, Nathan, Qld 4111, Australia.
B Seqwater, 240 Margaret Street, Brisbane, Qld 4000, Australia.
C Department of Geography, Trent University, 1600 West Bank Drive Peterborough, Ontario, Canada K9J 7B8.
D Corresponding author. Email: jasonkerr@trentu.ca
Marine and Freshwater Research 61(8) 928-935 https://doi.org/10.1071/MF09124
Submitted: 28 May 2009 Accepted: 2 December 2009 Published: 13 August 2010
Abstract
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 (0–2 cm) 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 (P < 0.05) in partially dried and desiccated sediments than in wet sediments, suggesting that a substantial transformation from a relatively unavailable organic form to a readily available inorganic form of P had occurred with drying. The equilibrium phosphate concentration (EPC0), which is a measure of the potential for sediments to function as a source or a sink of phosphate (PO43–), 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.
Additional Keywords: desiccation, sediment, soluble P.
Acknowledgements
We thank the Australian Research Council, the South-east Queensland Healthy Waterways Partnership and Seqwater for their financial support.
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