Author(s)

A. Facchini, C.Mocenni, E. Tiezzi & A. Vicino

Abstract

In this paper a nonlinear analysis of time series representing dissolved oxygen, temperature, pH and salinity data, collected in the Lagoon of Orbetello (Grosseto, Italy) is performed. A first biological inspection of the data shows that the coastal area is highly eutrophic and subject to unexpected phenomena, like anoxic and distrofic crises. From a more theoretical point of view, the ecological complexity of this ecosystem suggests the need to consider nonlinear models for understanding the dynamics of the system. The appearance of low dimensional deterministic chaos is demonstrated, using the nonlinear time series analysis approach by means of attractor reconstruction and the computation of the Maximum Lyapunov Exponent. 1 The Lagoon of Orbetello The Orbetello lagoon is located in southern Tuscany, near Grosseto (Italian West Coast). This lagoon is an important ecosystem from environmental and econom-ical point of view. In fact it is very rich in flora and fauna, as well as productive activities. The Orbetello lagoon is divided in two basins (Ponente and Levante) and covers a total area of about 27 2 . The meteorological and environmental situation is strongly influenced by the following data: the annual average tempera-ture is 16 ◦C , the precipitation is scarce, the tides are limited ( ÷45 cm ). Wind intensity is the unique important phenomenon that favors in summer the water movement. As a result of the above ecological status of the lagoon and the inten-sive agriculture, aquaculture and urban activities, a strong eutrophication affects

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