Sedimentary phosphorus fractions and bioavailability as influenced by repeated sediment resuspension

Concentrations of phosphorus (P) fractions and changes in their bioavailability in the sediments as influenced by repeated resuspension were determined by sequential fractionation in laboratory experiments. The water and sediment samples used were taken from the campus canal. Sequential fractionation indicated that the concentrations of the iron bound P (BD–P) were predominant, consisting of over 50% of total P (Tot-P) in the sediments that did and did not undergo resuspension. BD–P mobility was reduced due to resuspension resulting from the decline of the proportion ratio of non-occluded Fe–P and occluded Fe–P from 0.53 to 0.29. Therefore, under sediment resuspension conditions, using the sum of loosely sorbed P (NH4Cl–P), BD–P, aluminium bound P (Al–P), and organic-P (NaOH–nrP) to estimate bio-available P (BAP) might be problematic. However, BAP could be accurately estimated by the sum of NH4Cl–P, % BD–P (bio-available, non-occluded Fe–P), and NaOH–nrP. By this estimation, the amount of BAP in the sediments as influenced by repeated resuspension decreased by about 10% of Tot-P, compared with the initial state (raw sediments). The results suggest that repeated resuspension could accelerate the transformation of P from mobile fractions to refractory fractions, which can be attributed to the increase of occluded Fe–P, Al–P, and calcium bound P (HCl–P).