Three-dimensional numerical simulations of hydrodynamics with algae transport and its biological behaviors in surface water systems

Algal blooms pose severe ecological and economical threats to estuaries and marine systems. In this study, a three-dimensional model coupling nonhydrostatic free surface flow with algae transport and its biological behaviors is presented. The hydrodynamic model solves the Reynolds-averaged Navier-Stokes equations using a semi-implicit, fractional time-step finite difference method on a staggered Cartesian grid. The algorithm is locally and globally mass conservative and can be applied to different free surface problems ranging from hydrostatic to fully nonhydrostatic. The scheme is verified and validated by comparing simulation results with analytical solutions and measurements. The hydrodynamic model is coupled with an algae transport and biological model. The biological model simulates the buoyancy, vertical migration, and biological behaviors of blue-green algae based on different environmental factors such as nutrients, irradiance, temperature and salinity. The model is used to analyze transport of blue-green algae in Milford Lake, which is the largest man-made lake in Kansas suffering from algal blooms. The results of this study provide useful guidance for water quality management and predicting algal blooms in Milford Lake. For the first time, nonhydrostatic free surface flow, algae transport, buoyancy, migration, and biological production are included in one three-dimensional computational model, which can be used to study other estuaries and marine systems efficiently.