Journal
WATER RESEARCH
Volume 59, Issue -, Pages 198-206Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.watres.2014.04.010
Keywords
Phosphorus bioavailability; Phosphorus uptake; Ferrihydrite; Colloidal phosphorus; Free phosphorus; Phosphorus sorption
Funding
- Research Foundation Flanders (FWO)
- Swedish Research Council
- Knut and Alice Wallenberg Foundation
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Phosphorus (P) is a limiting nutrient in many aquatic systems. The bioavailability of P in natural waters strongly depends on its speciation. In this study, structural properties of iron colloids were determined and related to their effect on P sorption and P bioavailability. The freshwater green alga Raphidocelis subcapitata was exposed to media spiked with radiolabelled (PO4)-P-33, and the uptake of P-33 was monitored for 1 h. The media contained various concentrations of synthetic iron colloids with a size between 10 kDa and 0.45 mu m. The iron colloids were stabilised by natural organic matter. EXAFS spectroscopy showed that these colloids predominantly consisted of ferrihydrite with small amounts of organically complexed Fe. In colloid-free treatments, the P uptake flux by the algae obeyed Michaelis-Menten kinetics. In the presence of iron colloids at 9 or 90 mu M Fe, corresponding to molar P:Fe ratios between 0.02 and 0.17, the truly dissolved P (<10 kDa) was between 4 and 60% of the total dissolved P (<0.45 mu m). These colloids reduced the P uptake flux by R. subcapitata compared to colloid-free treatments at the same total dissolved P concentration. However, the P uptake flux from colloid containing solutions equalled that from colloid-free ones when expressed as truly dissolved P. This demonstrates that colloidal P did not contribute to the P uptake flux. It is concluded that, on the short term, phosphate adsorbed to ferrihydrite colloids is not available to the green alga R. subcapitata. (C) 2014 Elsevier Ltd. All rights reserved.
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