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 £ 10 7 cells L ¡1 on 15 July and 18 August. The maximum D 50 (the particle size value when the percentage volumes are 50%) of Microcystis colonies (524 mm) occurred on 1 September. The differences in D 50 values in different areas were not significant most of the time. … Show more
“…The size frequency distribution measured by microscopy on samples collected at stations WE 2, 4, 6, and 8 in July to October 2013 and June to July 2014 gave a similar size distribution to that of the 4 August 2014 sample (Figure a). It is likely that the colony size distribution varies to some extent spatially and temporally [e.g., Lin et al ., ], and our estimate could be refined through additional measurements. Even so, the consistency between our two estimated size distributions gives some indication of representativeness.…”
Cyanobacterial harmful algal blooms (CHABs) are a problem in western Lake Erie, and in eutrophic fresh waters worldwide. Western Lake Erie is a large (3000 km2), shallow (8 m mean depth), freshwater system. CHABs occur from July to October, when stratification is intermittent in response to wind and surface heating or cooling (polymictic). Existing forecast models give the present location and extent of CHABs from satellite imagery, then predict two‐dimensional (surface) CHAB movement in response to meteorology. In this study, we simulated vertical distribution of buoyant Microcystis colonies, and 3‐D advection, using a Lagrangian particle model forced by currents and turbulent diffusivity from the Finite Volume Community Ocean Model (FVCOM). We estimated the frequency distribution of Microcystis colony buoyant velocity from measured size distributions and buoyant velocities. We evaluated several random‐walk numerical schemes to efficiently minimize particle accumulation artifacts. We selected the Milstein scheme, with linear interpolation of the diffusivity profile in place of cubic splines, and varied the time step at each particle and step based on the curvature of the local diffusivity profile to ensure that the Visser time step criterion was satisfied. Inclusion of vertical mixing with buoyancy significantly improved model skill statistics compared to an advection‐only model, and showed greater skill than a persistence forecast through simulation day 6, in a series of 26 hindcast simulations from 2011. The simulations and in situ observations show the importance of subtle thermal structure, typical of a polymictic lake, along with buoyancy in determining vertical and horizontal distribution of Microcystis.
“…The size frequency distribution measured by microscopy on samples collected at stations WE 2, 4, 6, and 8 in July to October 2013 and June to July 2014 gave a similar size distribution to that of the 4 August 2014 sample (Figure a). It is likely that the colony size distribution varies to some extent spatially and temporally [e.g., Lin et al ., ], and our estimate could be refined through additional measurements. Even so, the consistency between our two estimated size distributions gives some indication of representativeness.…”
Cyanobacterial harmful algal blooms (CHABs) are a problem in western Lake Erie, and in eutrophic fresh waters worldwide. Western Lake Erie is a large (3000 km2), shallow (8 m mean depth), freshwater system. CHABs occur from July to October, when stratification is intermittent in response to wind and surface heating or cooling (polymictic). Existing forecast models give the present location and extent of CHABs from satellite imagery, then predict two‐dimensional (surface) CHAB movement in response to meteorology. In this study, we simulated vertical distribution of buoyant Microcystis colonies, and 3‐D advection, using a Lagrangian particle model forced by currents and turbulent diffusivity from the Finite Volume Community Ocean Model (FVCOM). We estimated the frequency distribution of Microcystis colony buoyant velocity from measured size distributions and buoyant velocities. We evaluated several random‐walk numerical schemes to efficiently minimize particle accumulation artifacts. We selected the Milstein scheme, with linear interpolation of the diffusivity profile in place of cubic splines, and varied the time step at each particle and step based on the curvature of the local diffusivity profile to ensure that the Visser time step criterion was satisfied. Inclusion of vertical mixing with buoyancy significantly improved model skill statistics compared to an advection‐only model, and showed greater skill than a persistence forecast through simulation day 6, in a series of 26 hindcast simulations from 2011. The simulations and in situ observations show the importance of subtle thermal structure, typical of a polymictic lake, along with buoyancy in determining vertical and horizontal distribution of Microcystis.
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