Molecular structure and biodegradation kinetics of Linear Alkylbenzene Sulphonates in sea water.

The present paper describes the results of the application of the biodegradation test proposed by the United States Environmental Protection Agency (USEPA) “Biodegradability in sea water” Office of Prevention, Pesticides, and Toxic Substances (OPPTS) 835.3160, to Linear Alkylbenzene Sulphonate (LAS), the synthetic surfactant with the highest consumption volume on a world-wide basis. High performance liquid chromatography (HPLC) has been employed for the separation and quantification of the different homologues and isomers of the surfactant. Water from the Bay of Cádiz (South–West of the Iberian peninsula) has been used as test medium. The results indicate how both lag and t50 time shows a significant linear relationship with the length of the alkyl chain of the homologue; the effect of this is that the homologues of longer chain length not only begin to degrade first but also degrade at a faster rate. Regarding the isomeric composition, it is observed that as the percentage of biodegradation increases, there is an increase in the proportion of internal isomers, in comparison with the isomeric relationships of the original test substanc

A unified approach to the modelling of the Venice Lagoon–Adriatic Sea ecosystem

In this paper, a first attempt at analysing the macronutrients' mass balance between the north Adriatic coastal sea and the lagoon of Venice by means of a nested and coupled model is presented. The hydrodynamic part of the model simulates the evolution of the sea-surface elevation and of the three-dimensional field of velocity, temperature, salinity and density. Tides, winds, river discharges, thermal and evaporative fluxes are included as forcings. Two models are nested in order to handle the correct spatial scales. The first one, with a resolution of about 10 km, is able to describe the basin and sub-basin scale hydrodynamical features; the second one, with a resolution of 1·2 km, describes the interactions between the open sea and the lagoon. This last circulation model has been coupled with a simple primary production submodel, in order to investigate the short-term dynamic of the ecosystem during spring time. Results show that, in some instances, the primary production can be sustained by macronutrients' fluxes coming from the coastal area. 1998 Academic Press Limite

A unified approach to the modelling of the Venice Lagoon–Adriatic Sea ecosystem

In this paper, a first attempt at analysing the macronutrients’ mass balance between the north Adriatic coastal sea and the lagoon of Venice by means of a nested and coupled model is presented. The hydrodynamic part of the model simulates the evolution of the sea-surface elevation and of the three-dimensional field of velocity, temperature, salinity and density. Tides, winds, river discharges, thermal and evaporative fluxes are included as forcings. Two models are nested in order to handle the correct spatial scales. The first one, with a resolution of about 10 km, is able to describe the basin and sub-basin scale hydrodynamical features; the second one, with a resolution of 1·2 km, describes the interactions between the open sea and the lagoon. This last circulation model has been coupled with a simple primary production submodel, in order to investigate the short-term dynamic of the ecosystem during spring time. Results show that, in some instances, the primary production can be sustained by macronutrients’ fluxes coming from the coastal area

Conditions for the application of transport models to problem of analytical and environmental chemistry

INTERNATIONAL JOURNAL OF ENVIRONMENTAL CHIMISTR

Modelling macroalgae (Ulva rigida) in the Venice lagoon: Model structure identification and first parameters estimation

The paper describes the definition and a first parametrization of a dynamic model of macroalgae (Ulva rigida) population. Based on specific literature, a two-step kinetic scheme is selected for modelling growth and uptake of nitrogen and, therefore, the intratissual concentration of nitrogen has been considered as a state variable of the model. Accordingly, Ulva r. growth rate depends on the concentration of phosphorus in the external medium and on the intratissual nitrogen concentration, which influences, in turn, the uptake rates of reduced and oxidized nitrogen. The influences of temperature and light intensity on Ulva r. photosynthetic activity are also discussed. The dynamics of dissolved oxygen has also been modelled and a specific mortality rate, depending on dissoved oxygen, has been adopted. The model has proved to be qualitatively consistent with the available literature, while a first parametrization yields results in quantitative agreement with short term laboratoy experiments, regarding samples collected in the lagoon of Venice. The model has been applied to data sets collected in the lagoon of Venice and is capable of reproducing the main features of the seasonal dynamic of Ulva r. These results prompted its inclusion in a comprehensive 3D transport-water quality model of the Venice lagoon ecosystem

Local sensitivity analysis of a distributed parameters water quality model.

RELIABILITY ENGINEERING AND SYSTEM SAFET

A model for macroalgae and phytoplankton growth in the Venice Lagoon

The definition and a first parameterization of a dynamic model of macroalgal growth is described, aimed at including this species and related physico-chemical variables in a more comprehensive 3-D eutrophication-diffusion, water-quality model of the Venice Lagoon. Relevant physicochemical factors affecting macroalgal and phytoplankton competition and succession have been analyzed as a function of physiological and trophic conditions. Results of simulations show that while phytoplankton response to growth factors is more intense and of shorter duration, internal nutrient storage in macroalgae stabilizes the growth process and makes macroalgal communities relatively more independent of variations of chemical and external forcing functions. The model provides results which appear to be qualitatively and quantitatively consistent with available functional in situ measurements. © 1995

USING PARALLEL COMPUTERS IN ENVIRONMENTAL MODELING - A WORKING EXAMPLE

An application of the utilization of parallel supercomputers for a 3D eutrophication-diffusion macromodel of the Venice lagoon is presented. Problems encountered in program restructuration, in the choice and in the introduction of parallel algorithms for solving the diffusion equation are discussed, together with the approach used to exploit multitasking performances. Results obtained show that, through appropriate coding, execution times for a full year simulation of the model, involving the diffusion and the trophic interactions of eight state variables, with a time step of one hour, have been decreased by about an order of magnitude