The effects of drying on phosphorus sorption and speciation in subtropical river sediments

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.

Effects of pretreatment on the sequential phosphorus fractionation of anaerobic sediment

“…Goedkoop and Pettersson (2000) however, have reported that freeze-drying increased the loosely adsorbed inorganic P of surface sediment (0-5 mm) by 20%. Kerr et al (2010) also found drying increased loosely adsorbed P with surficial sediment (0-2 cm) (Tab. 5).…”

“…Drying and desiccation have been found to increase or decrease P bound to ferric J. Limnol., 2014;73(2): 274-281 ORIGINAL ARTICLE DOI: 10.4081/jlimnol.2014.871 Effects of pretreatment on the sequential phosphorus fractionation of anaerobic sediment Lei (Fabre, 1992;De Groot and Fabre, 1993;Kerr et al, 2010). In addition, drying decreases or has no influence on calcium bound P (De Groot and Fabre, 1993;Kerr et al, 2010).…”

“…Goedkoop and Pettersson (2000) demonstrated that freeze-drying resulted in higher estimates for loosely adsorbed P, whereas P extracted by NaOH solution was decreased. Drying accelerates the mineralization of acid soluble organic P and decreases organic P in sediment (De Groot and Fabre, 1993;Kerr et al, 2010). The present study was designed specifically to test the hypothesis that pretreatment would influence P fractionation of anaerobic sediment.…”

Science to Support Management of Receiving Waters in an Event-Driven Ecosystem: From Land to River to Sea

“…Sources, forms and transformation of phosphorus, for example, have been identified in the catchment of Wivenhoe reservoir, the major source of drinking water in SEQ. Contrary to common belief, much of the phosphorus running off the catchment is in the dissolved inorganic form or loosely bound to soils owing to release from soil during wetting events [28][29][30]. As a result, the phosphorus can directly stimulate phytoplankton blooms, although the spatial and temporal scales over which this occurs depends on the turbidity of inflowing waters (which alters light availability) and the size, timing and source of those waters [19].…”

Sequential extraction procedures for the determination of phosphorus forms in sediment

“…In the later versions of the scheme, a 1 M NH 4 C1 extraction was used, instead of water for extraction of loosely adsorbed P in the first step . Kerr et al (2010) proposed a modification of scheme and applied this to a subtropical river sediment in Australia. A subsample of extract was digested with 1 M NaOH using the persulfate digestion before analysis, leading to the determination of non-reactive NaOH-extractable P (NaOH-NRP), which is thought to represent labile organic and bacterial P.…”