Vertical distribution of buoyant Microcystis blooms in a Lagrangian particle tracking model for short‐term forecasts in Lake Erie

Abstract

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.

Alternative Methods for Analysis of Cyanobacterial Populations in Drinking Water Supplies: Fluorometric and Toxicological Applications Using Phycocyanin

“…Selection of a 53 µm mesh plankton net for the initial separation of BFC's by filtration preferentially collected the portion of the cyanobacterial population that would not be subject to grazing [44] [45] [46] and tend to be buoyant [8] [47] [48]. Floatation has previously been used to isolate Microcystis to calculate weight specific toxicity [49] and biomass [23].…”

Removal of the algal toxin microcystin‐LR in permeable coastal sediments: Physical and numerical models

“…In practice, the removal rate would decline over time as the surface water concentration and supply rate to the benthic zone decreased, though we held the surface water concentration constant in our numerical sensitivity study. These benthic removal rates are still relevant, as HAB events can persist for days to weeks, exhibited by a do‐not‐drink order issued for 500,000 people in Toledo, Ohio over the span of 2 d in 2014 (Rowe et al ).…”

“…Real‐time microcystin concentration data and transport forecasts could easily be coupled with our benthic attenuation model in order to better assess HAB hazards in coastal areas of Lake Erie. Both seasonal and short‐term models for HABs in Lake Erie have been developed: seasonal models are used to predict annual variance in bloom severity, while short‐term models use particle‐tracking to focus on the importance of physical controls on bloom variability (Rowe et al ). Our modeling framework presented here could be used in conjunction with short‐term physical models aimed to predict MC‐LR fate and transport in coastal settings.…”

Lateral dispersion of dye and drifters in the center of a very large lake

“…Accurate predictions of lateral dispersion in large enclosed and semi‐enclosed waterbodies are important for a wide range of applications including contaminant spills (Olascoaga and Haller ), algal blooms (Rowe et al ), larval fish advection (Beletsky et al ), invasive species (Beletsky et al ), and microplastics (Hoffman and Hittinger ). With the increasing application of particle‐tracking models to simulate dispersion, direct measurements of dispersion in aquatic systems are becoming essential because the data provide a baseline against which these simulations can be compared, in turn allowing for model validation, calibration, and improvement.…”