Anoxia: is a lack of oxygen in deep waters. The values that indicate this condition, are set at between 0-1.0 mg/l. Anoxia causes damage and rot to the organisms that live in deep waters.

Autotroph: is an organism capable of feeding on and producing organic substance using inorganic substances. It is a characteristic common to all green plants that perform chlorophyll photosynthesis.

Clorophyll "a": is a pigment present in microalgae. When it is more than 10 ug/l, it indicates an anomalous increase in microalgae (microalgal biomass) and therefore, signals an excess of nourishing substances.

Clorophyll photosynthesis: is a process by which vegetable matter, in the presence of light and with the availability of carbon monoxide and water, is able to form an organic substance. In the process, oxygen is freed into the environment.

Colour: the normal colour of seawater can be defined as 'sui generis', with variations from green to deep blue, and also depends on the configuration of the seabed and the sky. The colour of seawater is determined either visually or photometrically, according to Pt/Co scale standards. The colour is usually subject to changes caused by algal bloom (diatoms, dinoflagellata, etc.).

Diatoms: this class of microalgae is responsible for causing bloom in seawater, usually in winter-spring. A large quantity of diatoms causes cloudy water of an unusual colour.

Dinoflagellata: this class of microalgae is responsible for causing bloom in seawater, usually in summer-autumn. A large quantity of dinoflagellata causes cloudy water of an unusual colour.

Dissolved oxygen: this term refers to the quantity of oxygen in the water. In surface water, levels of more than 10 mg/l (oversaturation) signal an excessive development of microalgae. Average values should be between 6-8 mg/l but are subject to variation and in deep water, values of less than 3 mg/l are normal.

Enterococci (see faecal streptococci)

Eutrophy: euthophication is a condition characterised by an increase of nutrients in water, in particular nitrogen and phosphorous. This causes a proliferation of microalgae (bloom) and macroalgae and alters the quality of the water.

Faecal coliforms: are microorganisms (gram-negative coccobacillary bacteria) that make up the normal intestinal microflora of all human beings and mammals. Their presence in water indicates very recent faecal contamination as they have an average life span of just a few days. In accordance with DPR 470/82, they must not exceed 100/100 ml of seawater.

Faecal streptococci: are round, chain-like bacteria that form the intestinal microflora. Their presence indicates recent faecal contamination. The acceptable limit is 100 colonies per 100ml (DPR 470/82).

Hypoxia: is the reduction of dissolved oxygen in deep water. The values that indicate this condition are between 3.0 and 1.0.

Microalgae: are microscopic single-cell organisms that belong to the phytoplankton family.

Microalgal bloom: is caused by an abnormal development in the number of microalgae present in water, which can even reach up to a million cells per litre. It causes the water to become cloudy and of an unusual colour.

Mineral oils: are oily substances that derive from petrol. Their presence in the sea, caused by discharges from boats or industrial dumping, manifests itself with characteristic films on the surface of the water and the lack of odour.

Nutrients: is a term used, above all, to indicate the compounds of nitrogen and phosphorous, which cause the proliferation of microalgae.

Oversaturation of dissolved oxygen: this is a condition in which the dissolved oxygen in surface water is higher than its saturation value (the balance between dissolved oxygen in the water and atmospheric gaseous oxygen). Oversaturation values indicate processes of a photosynthetic nature and consequently, a high microalgal biomass.

pH: or hydrogenionic concentration, is the unit of measurement for the acidity and basicity of water. In aquatic ecosystems, pH is the result of the quantity of dissolved CO² and is an indicator of the metabolism of the animal and vegetable community (photosynthesis and respiration). In surface seawater the average pH value is 8.2 whereas higher values (for example 8.9) coincide with high levels of chlorophyll and oxygen. In deep water, lower values are the result of the combination of a lack of oxygen and the formation of toxic substances (for example, ammonia or hydrogen sulphide), which are harmful to living species on the seabed. Due to its high buffering ability, seawater is capable of containing these pH variations.

Phenols: are chemical substances derived from aromatic hydrocarbons, which are generally of industrial origin (they are used to manufacture rubber, plastic, pharmaceutical products etc). They smell and taste very unpleasant.

Phytoplankton: is a mix of autotrophic vegetable organisms that includes microalgae (microscopic single-cell algae), which are the first link in the food chain.

Salinity: Seawater contains dissolved "salts" under the form of ions. Salinity is in fact, expressed as the number of grams of dissolved salts per kilo of water. The highest values in the water off our coasts are between 34-36 PSU (Practical Salinity Unit - the standard unit of measurement obtained by measuring conductivity). There is reduced salinity near the mouths of rivers or canal ports.

Salt stratification: is a condition by which, following spillover from rivers (when the sea is calm), a layer of fresh water forms on the surface, with underlying, increasingly salty layers beneath. Salt stratification hinders the gaseous exchange between the surface and the seabed.

Surface-active agents: are additives present in many products and chemical processes and they are commonly used as emulsifying agents in detergents. One of their characteristics is that they react to methylene blue but they are usually checked for by visual inspection.

Temperature stratification: is a condition by which, following a warming of the surface water (when the sea is calm), a warmer surface layer is formed with underlying colder layers beneath (this condition is typical during the summer period). Temperature stratification hinders the gaseous exchange between the surface and the seabed.

Total coliforms: are microorganisms (gram-negative coccobacillary bacteria) that indicate a faecal contamination of water, but not only. These organisms are in fact, naturally present in water and in soil but in accordance with DPR 470/82 (President's executive order) they must not exceed 2,000/100 ml of seawater.

Transparency: is a parameter that is determined by sinking a varnished white disc, which is 3 mm thick with a diameter of 30 cm (Secchi's disc), into the water and assessing the distance when it disappears from view (between 15 cm and 20 m). Transparency is influenced by the presence of particles of sediment, caused by the motion of the waves and bathers, and by the presence of inorganic material and/or microalgal bloom.

Undersaturation of dissolved oxygen: see hypoxia and anoxia.

Upwelling: is the process of the resurfacing of deep water, determined above all by the currents and indirectly, by the wind.