Standardizzazione per lo studio dell'effetto Broensted della reazione di Co(NH3)5Cl++Co(NH_3)_5Cl++ con Hg++ e HgCl++

A kinetic study of the Hg(II)X catalyzed acquation of the complex $RCIY_2$ $(R = Co(NH_3)_5; X, Y = ClO_4-, NO_3-)$ has been carried out. A reaction mechanism involving two consecutive and competitive reactions RCI++ + Hg++ -> $RH_2O+++$ + HgCl+; RCI++ + HgCl+ -> $RH_2O+++$ + $HgCl_2$, with velocities of the same order, and the equilibrium 2HgCl++ $\rightleftharpoons \$ Hg++ + $HgCl_2$ is proposed. A method of evaluation of the relative rate constants is developed: the expression of the ratio complex transformed/time is obtained as a polynomial of 8th order in time by series integgration of the differential equation rapresenting the reaction system and the kinetic constants are determined, that give the best fitting of the polynomial to experimental data. The difference in the values of the constants for the reactionas with X = Y = $ClO_4-$, X = Y = $NO_3-$, X = $ClO_4-$ and Y = $NO_3-$ is significant, and trying a first interpretation of this phenomenon it is shown that, for the study of the kinetic salt effect, the reaction with perclorates of the cations (reagents and of the added salts) are the most suitable

Global sensitivity analysis of a shallow-water 3D eutrophication model

The dynamic of a shallow water system has been studied using a 3D transport-water-quality model. This model was originally designed to study the eutrophication in the central part of the Venice lagoon. Four model outputs and six input factors are considered in this paper. Sensitivity analysis is performed using the Sobol' method:and linear regression based methods. Results of this study suggest that nitrogen load, the main controllable factor, plays a major role in governing the primary production of the whole system. However, the "history" of the system, represented by the initial density of benthic algae, is even more important in determining the occurrence of dramatic events, such as anoxic crisis, which may happen in particular areas

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

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

Global Sensitivity Analysis of a Shallow-Water 3D Eutrophication Model.

The dynamic of a shallow water system has been studied using a 3-D transport-water-quality model. This model was originally designed to study the eutrophication in the central part of the venice lagoon. Four model outputs and six input factors are considered in this paper. Sensitivity analysis is performed using the Sobol' method and linear regression based methods. Results of this study suggest that nitrogen load, the main controllable factor, plays a major role in governing the primary production of the whole system. However, the "history" of the system, represented by the initial density of benthic algae, is even more important in determining the occurrence of dramatic events, such as anoxic crisis, which may happen in particular areas.JRC.(ISIS)-Institute For Systems, Informatics And Safet

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

An informational approach to model time series of environmental data through negentropy estimation

A methodology based on the minimum negentropy criterion (minimum cross-entropy) is proposed, which enables one to determine the optimal order of a model candidate to reproduce the behaviour of time series of environmental data. The procedure, which involves the computation of the prediction error, represents a unifying approach of conventional and inferential statistics and permits at the same time to account for all informational content embodied in the data and it avoids both underfitting and overfitting of experimental observations, thus guaranteeing the principle of model's parameter parsimony and balanced accuracy. Following the theoretical derivation of the approach, the method is verified through harmonic analysis of data sets collected in the lagoon of Venice and exhibiting high variability: surface data temperature, exceptional tidal observations, chlorophyll a and ammonia concentrations. Extensions of the procedure to other type of data and of class of model, are also prospected. © 1993