Resuspended particulate matter in shallow lakes contributes remarkable phosphorus (P) concentrations to the water column that potentially support algal/cyanobacterial growth. However, only fine particulate matter can be retained in the water column for a long time after sediment resuspension events. The size at which fine particulate matter has ecological implications remains undefined. This research defined suspended particulate matter with a median grain size <2.5 μm (SPM2.5) in shallow lakes, which resists sedimentation and enriches bioavailable P. The relationship between the size of suspended particulate matter (SPM) and water disturbance was characterized by conducting a lab-scale jar test with sediments in a shallow lake. The sedimentation of completely resuspended particulate matter occurred under a series of turbulence shear rates (G) ranging from 0 to 50 s-1. When G was larger than 20 s-1, the SPM had a median grain size (D50) ranging from 9 μm to 11 μm for the three samples. When G was <10 s-1, only SPM <2.5 μm remained in suspension. The SPM larger than 2.5 μm settled when G was between 10 s-1 and 20 s-1, and the SPM remained in complete suspension when G was larger than 20 s-1. Furthermore, P fractionation was conducted on different size-grouped particles that were sorted using gravity sedimentation. The concentration of iron/aluminium bound-P (Fe/Al-P) decreased exponentially as the particle size increased. The concentration of Fe/Al-P in SPM2.5 ranged from 902.8 mg/kg to 1212.1 mg/kg, accounting for over 80 % of extractable total phosphorus. SPM2.5 contributed a remarkable amount of bioavailable P to the algal/cyanobacterial biomass in the shallow lake with frequent sediment resuspension.
Keywords: Fine particles; Particle size distribution; SPM(2.5); Sediment resuspension.
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