Osservazioni sulla distribuzione superficiale di parametri idrologici e batteriolgici nello Stagnone di Marsala (Sicilia)

The Marsala Sound undergoes wide temperature and salinity variations especially in the central part where the salinity ranges from < 36 psu in winter to > 41 psu in late spring and summer. During the spring survey minimal rain waters inputs and elevated evaporation caused the formation of dense waters (t> 29 kg m-3) in the central part of the lagoon. Low nutrients and chlorophyll a concentrations characterise as oligotrophic the main part of the Marsala Sound waters though elevated ammonium and chlorophyll a concentrations (up to 2-3 μg dm-3) and oxygen oversaturation were observed near the northern mouth of the sound. The bacteriological parameters distribution showed that the Marsala town waste waters constituted a localised source of faecal contamination, whereas water outflows from an acquiculture plant are responsible for the more elevated concentrations of ammonium, chlorophyll a and heterotrophic bacteria near the northern mouth of the Sound. The progressive burying of the Tramontana mouth, caused by the southwards displacement of the Birgi creek mouth, and the settlement of an aquaculture plant near the northern mouth at the beginning of the eighties, seem to be the main causes of the outspreading of dystrophic conditions which endanger the Marsala Sound ecosystems, particularly in the northern and central zones.