A dynamic simulation model of the widgeon grass Ruppia maritima and its epiphytes in the estuary of the Patos lagoon, RS, Brazil

The dynamics of the vegetated beds of the estuary of the Patos Lagoon was investigated using a simulation model for two important benthic primary producers (the widgeon grass Ruppia maritima and its epiphytes). The model, of deterministic characteristics, simulated two development cycles of the beds from summer 1992/1993 to 1993/1994. Model validation and calibration were accomplished by using R. maritima biomass collected in shallow bays of the Patos Lagoon estuary during the two simulated cycles. The model simulated the seasonal variations in the biomass of blades, stems, roots plus rhizomes, seeds and fruit of R. maritima, by using the experimental components method, and the epiphytes biomass, by using the compartmental system method, all expressed in g dry wt. (gDW) m super(-2). The model accurately reproduced the processes of building and decay of R. maritima biomass, representing the maximum values observed in the environment. Plant height and its phenological stage were two important attributes included in the model. They were important to control the processes of light attenuation, beginning of the epiphytes installation and the removal of the grass by hydrodynamic action. Bending of the grass and biomass removal were very important to the model results and they seemed to be the primary factors that control the plant decay in late summer. Ecological modeling has proved to be a powerful tool for the proposition of new control mechanisms for the dynamics of the vegetated beds of the estuary of the Patos Lagoon.