Algae blooms in turbulence
Algae Blooms in natural water environments can be toxic to both humans and animals. Natural waters like lakes are usually turbulent. Here we aim to understand the dynamics of algae migration in such environment as to improve future water management models. Vertical migration of algae is strongly influenced by their ability to regulate their density on a daily basis in search for optimal nutrient and light conditions.
The effect of small scale turbulence on vertical trajectories of algae is studied by using Direct Numerical Simulations with Lagrangian Particle Tracking. Via simultaneous biological modeling, also time-dependent density variations of the algae are taken into account. We apply our methodology to study the vertical migration of a particular cyanobacteria species: Microcystis Aeruginosa.
In general, biological time scales are much longer than the flow time scales that are simulated in a typical computer simulation. Therefore we artificially speed up the biological reactions, but such that the key character of the problem remains the same.
Under low turbulent conditions, the vertical migration of Microcystis depends mainly on its buoyant status (left figure). Higher turbulent environments suppress the buoyant ability of the algae and distribute them more uniformly within the domain (right figure).