A numerical investigation of the influence time distribution in a shallow coastal lagoon environment of the Gulf of California

The influence time distribution in Santa María La Reforma coastal lagoon, which is one of the most productive ecosystems in Mexico, has been numerically investigated. A depth integrated finite difference hydrodynamic model, coupled with the advection–diffusion equation and an approach known as remnant function, have been used to predict the influence time distributions. Prescribed values of tidal harmonics were used to force the model at the two open boundaries of the model domain. The numerical experiments performed consisted of the instantaneous injection, of a passive hypothetical tracer at 100% concentration, to the whole coastal lagoon which was subject to the wind action and tidal forcing. The results indicate that influence time fluctuated between a few days and 4.0 months. The longest values were predicted close to the Talchichitle Island in the eastern part of the lagoon while the shortest were found close to the inlets where the relatively deep channels and high speed tidal currents favor the discharge of the tracer into the ocean. Knowledge of the influence time distribution is very useful to assess the environmental impacts of contaminants and to establish management plans for coastal lagoons conservation.