A numerical study of plankton population dynamics in a deep lake during the passage of the Spring thermal bar

An N–P–Z plankton model has been included in a finite volume formulation of the Navier–Stokes equations and has been used to predict the effect of the spring warming and the thermal bar on the plankton ecosystem of a section of the Central Basin of Lake Baikal. The results presented show that the currents converging towards the thermal bar generate a maximum in the phytoplankton population at the location of the thermal bar, while the boundary between the unstable near-surface region and the stably stratified lower part of the lake acts as a barrier to the diffusion of the plankton population towards deeper regions. The enlargement of the unstable area during the warming of the lake has been found to have a major effect on the distribution of the phytoplankton, with enhanced vertical diffusion balancing the growth near the surface and preventing the phytoplankton population from reaching bloom values, and consequently inhibiting any development of the zooplankton population. It has also been found that the vertical component of the Coriolis force could allow the currents generated by the thermal bar to reach the deeper part of the lake