The Influence of Currents and Bathymetry on the Phytoplankton Growth Dynamics in a Deep Lake: An Application of the Lattice Boltzmann Method

Abstract

The invasive species, the quagga mussel, infiltrated Lake Michigan in the early 2000s and immediately began depleting the base of the aquatic food system: the lake's phytoplankton population. Today the quagga mussel covers 80% of the lake floor deeper than 10 meters, can be concentrated at 35,000 mussels per square meter, and is efficient at filtering throughout the depth of the water column. This thesis aims to contribute to the difficult task of describing the impact these mussels have on the size and preferred depth of the phytoplankton population in Lake Michigan. In a simplified model, two species of phytoplankton competing for nutrients (one preferred) with bottom boundary mussel consumption were simulated using the lattice Boltzmann method. Four lake-bottom boundary condition scenarios, the Mid Lake Plateau, an open channel, a small hill, and a steep drop-off, were considered in order to test the viability and flexibility of the lattice Boltzmann method and to explore how the bathymetry of Lake Michigan influences the phytoplankton population. In addition, slow and fast currents were tested and the varying distributions of the phytoplankton were analyzed. The results of this thesis can be used to evaluate the viability of a modeling and computational tool for quantitatively evaluating the impacts bathymetry and currents have on an aquatic system.