Modelling the distribution of Anabaena and Melosira in a stratified river weir pool

Abstract

We have developed a model to predict the stratification dynamics and its influence on the distribution of algal species in a river with strong diurnal changes in temperature stratification. While the phytoplankton concentrations vary in response to buoyancy and light limited growth, the populations are also redistributed vertically due to diurnal mixing caused by surface evaporation and night time cooling. The parameterization of the vertical eddy diffusivity coefficient within the model takes into account the generation of mixing by heat losses at the surface and the suppression of mixing by thermal stratification. The model is successfully tested against extensive temperature and algal concentration data in Maude weir pool on the Murrumbidgee River, Australia. Given literature values of floating/sinking rates and maximum growth rates for the cyanobacterium Anabaena and the diatom Melosira, we were able to reproduce extremely well the time evolution of concentrations of each species over long periods of low flow.