  We develop and analyze a spatial temporal model of light driven
ecotoxicological processes, motivated by an aquatic predator-prey system of
algae and \textsl{Daphnia} subject to a contaminant. Population dynamics are
driven by light, which is periodic in time and varies with spatial depth. The
existence and uniqueness of spatial and temporal dependent periodic solutions
are shown and analytical functions of the solutions under parameter constraints
are presented. We conduct Turing stability analyses of solutions with respect
to perturbations of initial conditions. Given a perturbation to a periodic
equilibrium state, we show the system will return to this equilibrium state as
long as motility is fast enough and/or the reservoir depth is shallow enough.
Analytical results assume some Dirichlet boundary conditions that match the
periodic equilibrium state, however numerical simulations with more relaxed
boundary conditions capture similar periodic solutions. The work sheds light
onto spatially dependent population dynamics that are driven by periodic
forces, such as light levels.
