[Influence of intermittent sediment disturbance-sedimentation process on the bioavailable phosphorus in standing water].

The course of intermittent sediment disturbance-sedimentation, that sediment disturbance was for 10 min and succeeding sedimentation was for 1430 min each day over a 17-day period, was simulated to investigate the variation of bioavailable phosphorus (BAP) in overlying water. The results showed that the concentrations of BAP increased obviously at Oh after each disturbance, and the maximum concentration of BAP was reached up to 2.82 mg x L(-1) after 1 d (the first disturbance). However, the BAP gradually decreased with the sedimentation time increase (1 h, 6 h, 24 h). Moreover, at 0, 1, 6, 24 h after disturbance, the BAP gradually declined with the number of sediment disturbance increase, but the BAP at Oh after each disturbance was higher than that at 1 h, 6 h, 24 h. This may be attributed to the immediate release of bioavailable particulate phosphorus ( BAPP), as a result of sediment disturbance. The average BAPP/BAP was up to 95.0% at Oh after disturbance over a 17-day period, but this value gradually decreased with the sedimentation time increase (1 h, 6 h, 24 h). At 0 h, 1 h, 6 h, 24 h after each disturbance, the equilibrium concentrations of total dissolved phosphorus (TDP) were reached after 5 d (0.053, 0.062, 0.051, 0.045 mg x L(-1)), and the percentage of TDP in BAP also decreased gradually. Therefore, it is considered that sediment intermittent disturbance can accelerate the transformation from TDP to PP and hinder the development process of eutrophication in standing water. Sequential fractionation also indicates that the percentage of refractory phosphorus in Tot-P increased from 72.8% (raw sediments) to 77.3% (sediments after disturbance), attributable to the increase of concentrations of occluded Fe/Al-P. It is hopefully suggested an acceleration of transformation of phosphorus from mobile fractions to refractory fractions.