Dynamic behaviour of lagoon ecosystems

An analysis of coastal lagoon ecosystem dynamics is proposed the aim is to achieve a better understanding of mechanisms responsible of vegetal species substitution and water anoxia phenomena occurring in lagoons as a consequence of eutrophication such a understanding is fundamental to individuate more effective management strategies for the control of eutrophication processes. The analysis is carried out by using a eutrophication model which allows the simulation of the temporal evolution of the concentration in the water column and into sediments of the significant species affecting eutrophication phenomena. The dynamic behaviour of the lagoon ecosystem state, for an assigned parameter space, is analysed by simulations carried out varying both the phosphorous external load and the maximum tidal flow rate at the inlet connecting the lagoon to the sea , which were assumed as control parameters. The response diagram, obtained by simulations, varying the value of control parameters, shows the existence of different ranges of stability of the ecosystem, characterized by the dominance of a specific group of primary producers and by a different ecosystem vulnerability to summer water anoxia. A catastrophic bifurcation, which manifests as an abrupt change of the dominant species from eelgrass to macro algae, occurs for some critical values of the control parameters.