Phosphorus sorption experiments and the potential for internal phosphorus loading in littoral areas of a stratified lake He ´le `ne Cyr a, *, Shelley K. McCabe a,1 , Gertrud K. Nu ¨ rnberg b a Department of Ecology and Evolutionary Biology, Ramsay Wright Zoological Labs, University of Toronto, 25 Harbord Street, Toronto, Ontario, Canada M5S 3G5 b Freshwater Research, 3421 Hwy 117, Baysville, Ontario, Canada P0B 1A0 article info Article history: Received 8 July 2008 Received in revised form 20 November 2008 Accepted 23 December 2008 Published online 14 January 2009 Keywords: Phosphorus Internal loading Sediment resuspension P sorption Oxic Littoral Lake abstract The exchange of phosphorus (P) during the resuspension of sediments into shallow (oxic) waters of deep stratified lakes is regulated by equilibrium dynamics. In this study, we compared the P-sorption characteristics of sediments from 17 shallow and deep littoral sites in an oligo-mesotrophic lake. Zero Equilibrium P Concentration (EPC 0 ) ranged from 0.2 to 5 mgPL 1 . EPC 0 did not vary with sediment characteristics, but increased with increasing sediment-to-water ratios (SWR). Buffering capacity also increased with increasing SWR up to 1gL 1 , at which point P concentrations were buffered almost perfectly. Therefore, internal P loading in littoral areas may depend primarily on the intensity and duration of sediment resuspension instead of sediment composition, and is expected to be spatially and temporally patchy. Maximum P-sorption capacity (S max ) varied with chemical composition of the sediments, but was generally low, indicating a limited capacity of littoral sediments to retain external inputs of P. ª 2009 Elsevier Ltd. All rights reserved. 1. Introduction Internal loading of phosphorus in lakes has been studied most extensively in the anoxic hypolimnion of eutrophic lakes, and models have been developed to predict hypolimnetic loading of phosphorus for lake management purposes (Nu ¨ rnberg, 1984, 1998; Sas, 1989; Nu ¨ rnberg and LaZerte, 2004). Sediment phosphorus can also be released into oxic waters (Søndergaard et al., 2001), and this has been most clearly demonstrated in shallow eutrophic lakes (Søndergaard et al., 1992; Istva ´ novics et al., 2004; Jensen et al., 2006), in rivers and estuaries (Carignan and Vaithiyanathan, 1999; Deborde et al., 2007) and in marine coastal areas (Slomp et al., 1998). Release of phosphorus into oxic waters can be due to diffusion through a very thin oxic layer at the sediment surface, low Fe availability in surface sediments, decompo- sition of recently settled organic matter, physical forcing of sediment porewater (by wave action, convection currents) or sediment resuspension (Søndergaard et al., 2001). Sediment resuspension is an episodic event, but because of the * Corresponding author. Tel.: þ1 416 978 0975. E-mail addresses: helene.cyr@utoronto.ca (H. Cyr), mccabesh@yorku.ca (S.K. McCabe), gkn@fwr.on.ca (G.K. Nu ¨ rnberg). 1 Present address: Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3. Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2008.12.050 water research 43 (2009) 1654–1666