  In this paper, we establish a reaction-diffusion-advection partial
differential equation model to describe the growth of algae depending on both
nutrients and inorganic carbon in a poorly mixed water column. Nutrients from
the water bottom and inorganic carbon from the water surface form an asymmetric
resource supply mechanism on the algal growth. The existence and stability of
semi-trivial steady state and coexistence steady state of the model are proved,
and a threshold condition for the regime shift from extinction to survival of
algae is established. The influence of environmental parameters on the vertical
distribution of algae is investigated in the water column. It is shown that the
vertical distribution of algae can exhibit many different profiles under the
joint limitation of nutrients and inorganic carbon.
