This paper describes the oxygen dynamics in the Orbetello coastal lagoon (central Italy), a highly trophic environment monitored by ENEA during 1993-94. The study is based on both the analysis of in situ field data and mathematical modelling. We briefly summarize the results of the analysis performed on the time series of meteorological and hydrological data collected in the lagoon. It follows that the oxygen time evolution can be described in terms of a first order autoregressive process with periodical forcing. This process is the discrete analogue of an oxygen global mass balance in water. This allows the estimation, for both summer and winter periods, of production, consumption and transfer rate of oxygen. A more detailed description of the oxygen dynamics takes into account the interaction processes between some chemical species (POM, DOM, O2, H2S). A simplified representation of the main processes affecting the oxygen dynamics in a horizontal homogenous environment, and for time periods no longer than a few weeks, is presented. As these processes depend on depth, in particular on the compartments sediments and waters, the vertical dimension has been considered in modelling oxygen dynamics. Results of numerical simulations are shown.

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