Acknowledgements The authors wish to express particular appreciation to C.I.G.R.I. (Consorzio Intercomunale Gestione Risorse Idriche) of Venturina (Livorno;
Italy) for cooperation throughout the work. Dr. David Stephenson is also thanked for the revision of this manuscript. This research was supported by a MURST 60% grant to M. Salleolini;