Using a laser particle analyzer to demonstrate relationships between wind strength and Microcystis colony size distribution in Lake Taihu, China

Abstract

Cell density and colony size distribution of Microcystis spp. at 14 sites in Meiliang Bay and Gonghu Bay of Lake Taihu, China, were determined using a laser particle analyzer. Cell density increased from 1 July to 18 August 2010 and exceeded 20 × 107 cells L-1 on 15 July and 18 August. The maximum D50 (the particle size value when the percentage volumes are 50%) of Microcystis colonies (524 μm) occurred on 1 September. The differences in D50 values in different areas were not significant most of the time. However, the differences in colony size distribution in different areas were mostly significant. It was also found that colony size distribution of samples with similar D50 values differed significantly with each other. These results suggested that a mean value (such as D50 and mean colony diameter) would not reveal complete information on Microcystis colony size under natural conditions. Our study also revealed that spatial variation was caused by wind-driven transport when wind speed was lower but by disaggregation induced by wind shear when the wind was strong enough.