G. Bendoricchio

Description of the three shallow estuaries: Mondego River (Portugal), Roskilde Fjord (Denmark) and the Lagoon of Venice (Italy)

The paper describes three European estuaries which were compared with respect to the dynamics between autotrophic components under the MUST-project: The Mondego River (M) (Portugal), Roskilde Fjord (R) (Denmark) and Venice Lagoon (V) (Italy). The areas of the three estuaries are (M) 3.4, (R) 125 and (V) 540 km2 and their maximum tidal ranges are (M) 3.3, (R) 0.2 and (V) 2.2 m. They are all eutrophic with high loadings of nitrogen (M) 126 t N/yr, (R) 2500 t N/yr and (V) 7000 t N/yr and high loadings of phosphorus (M) 1 t P/yr, (R) 180 t P/yr and (V) 1000 t P/yr. The dominating phytoplankton species are (M) diatoms and dinoflagellates, (R) Skeletonema sp. and (V) Amphora sp. and Chaetocerus sp. and the dominating macrophytes are (M) Enteromorpha sp., Gracilaria sp. and Zostera noltii, (R) Zostera marina and Ulva lactuca and (V) Ulva rigida and Zostera noltii. All three estuaries are frequently exposed to collapses caused by severe oxygen depletion.

Exergy as goal function of ecosystems dynamic

Abstract The need for models with dynamic structure is discussed. The differences between traditional models and models with dynamic structure is reviewed. Several goal functions have been briefly reviewed, while exergy, most widely used up to now in structural dynamic models, is presented and used for the case studies of the projects discussed in this special issue. The theoretical background of the application of exergy as goal function is presented.

Application of structural dynamic approach to estimate space variability of primary producers in shallow marine water

Structural dynamic models attempt to simulate ecosystem dynamic interms of species composition by using flexible state variable parameters that are allowed to change in order to optimize a given ecological goal function. In the present paper, this modelling approach has been applied to the two main groups of primary producers in shallow water of the Lagoon of Venice, namely free floating macroalgae and seagrass. Differences in macroalgae species considered (Ulva rigida, Chaetomorfa aerea, Gracilaria confervoides) have been characterized by expressing the main physiological parameters as function of one morphological parameter: surface/volume ratio. This latter parameter has been used as unique flexible parameters of the state variable representing macroalgae and its actual value s found by optimizing exergy under a given scenario. This corresponds to find the best adapted macroalgae species in a given environmental condition. The same concept is applied to seagrass by stressing different capacities of the three species observed (Zostera marina, Z. noltii and Cymodocea nodosa) to react to self shading and erosion processes. The application was able to explain in a satisfactory way the observed distributions of both macroalgae and seagrass in the Lagoon of Venice.

A trophic model for Ulva rigida in the Lagoon of Venice

Abstract This paper focuses on a model of the life cycle of the macroalgae which can be considered one of the most important and earliest steps of a more general environmental modelling activity for the Lagoon of Venice. The variables considered by the model are the algal biomass, and the intracellular quota of nutrients (nitrogen and phosphorus). The model simulates a point in the Lagoon. Because of this, other factors, such as external nutrients and dissolved oxygen concentrations, are considered as input data and evaluated by monitoring the water quality. The model is calibrated with a time series of weekly data collected during the years 1985 and 1986. The model allows for a deep knowledge of the macroalgae life cycle in the Lagoon and points out the relevance of some processes or factors like: nitrogen limitation; control of algal decay due to oxygen depletion; relevance of the combination of photosynthesis, temperature and nutrient effects.

Modelling the fate of dioxins in a trophic network by coupling an ecotoxicological and an Ecopath model

This paper shows the possibility to combine a trophic network model and an ecotoxicological food web model to calculate toxic concentrations of area-specific aquatic species. The trophic network model was derived from an Ecopath application made for a shallow water area (Palude della Rosa), situated in the northern part of the Lagoon of Venice. The organisms-specific output data from the energy model, such as metabolic rates, diet composition and structural characteristics were used as input to the ecotoxicological food chain model. The toxic substance model estimated bioaccumulation (pg/g lipid) of dioxins (e.g. 2378-TCDD, 12378-PeCDD, 123478-HxCDD, 123789-HxCDD, 1234678-HpCDD and 12346789-OCDD) and dibenzofurans (e.g. 2378-TCDF, 12378-PeCDF, 123478-HxCDF, 123678-HxCDF, 123789-HxCDF, 234678-HxCDF, 1234678-HpCDF, 1234789-HpCDF and 12346789-OCDF) for all groups in the trophic network. A sensitivity analysis showed that the toxic concentration in the aquatic species was highly affected by the following parameters: Kow, fraction of organic carbon in the sediment, lipid fraction, and fraction of unassimilated food. The coupling of the two models was validated with data from four sites in the Lagoon (two in the industrial zone, and two in the southern basin). Calibration and comparisons with measured data were conducted for a clam (Tapes philippinarum), a mussel (Mytilus edulis) and a fish (Scardinius eritrophtalamus). Model output showed that the discrepancy between chemical analysis and model estimations were in the range of one order of magnitude for T. philippinarum and M. edulis (except for tetra- and penta-furans, where the overestimation reached two order of magnitude). It was also shown that more monitoring efforts should be made on fish species, to have a set of data useful for the validation of the model.

Modelling biomass and nutrient dynamics in eelgrass (Zostera marina L.): applications to the Lagoon of Venice (italy) and Øresund (Denmark)

Abstract A model to describe the seasonal cycle of eelgrass biomass and to quantify the presence of Zostera marina in coastal areas, depending upon environmental conditions, is presented in this paper. This model is characterised by a simple structure and it can easily be coupled with other models considering other compartments of the ecosystem. The simulation of internal nutrient dynamics, peculiar to this model, allows a more comprehensive description of eelgrass physiology. The first goal of this study is the understanding of the growth cycle of Zostera marina in the Lagoon of Venice and the comparison with other environmental situations. Secondly, this work aims to provide a tool to study the competition between marine phanerogams and floating macroalgae in the Lagoon of Venice. The model is calibrated with a set of experimental data collected ad hoc in the Lagoon of Venice and quantitatively tested with another set of data reported in literature for a Danish shallow water area. A sensitivity analysis was carried out, the most sensitive parameter, accounting for shoots respiration, was used to tune the model for both environmental situations. A statistical analysis of the results is finally shown.