Salinity:
the quantity of salts dissolved in a certain volume of water. The average salinity of the Adriatic is about 37 parts per thousand (37 grams of salt per litre of water); for the sea in general it is 35 per thousand. Water with salinity below that of the sea is referred to as hypohaline (or hyposaline) and water that contains more salt than the sea is referred to as hyperhaline (or hypersaline).

Saltmarsh (Barena):
one of the most characteristic physical structures of the Lagoonal environment. The “barene” are low, flat stretches of ground, made up of silty-clay sediments, generally covered by halophile vegetation. In altimetric terms, the barene are at an intermediate level between the islands and the velme (mudbanks). They are normally submerged only during spring tide. The saltmarshes have a functional relationship with other characteristic structures: the ghebi, the velme, the channels and the shallows. According to Boerio (1856), the name Barena derives from “baro”, meaning a dense covering of bushes or overgrown marshland.

Sedge:
plant association in which species of the genus Carex (family Cyperaceae) are predominant and/or characteristic. In general, an association characteristic of ponds and marshes. Cf. Plate 65.

Sediment (sedimentation):
deposition, on the Lagoon bed, of solid particles suspended in fluvial and marine waters. Accumulation of mineral detritus and material originating from the weathering and erosion of pre-existing rocks. Cf. Plates 8 and 9. Self-purification:
capacity of a given environment to metabolise substances from outside sources which would otherwise become pollutants.

Septic tank:
cistern or vat, usually underground, into which the waste waters from buildings or settlements not connected to the sewer network are channelled, and in which they are treated via a spontaneous fermentation process.

Silicate:
crystalline mineral making up a large part of sedimentary, metamorphic and igneous rocks. Cf. Plate 10.

Sluice, sluice gate:
passage for water to flow through, with a special gate which can be opened or closed to control it. In the Lagoon of Venice, sluices are commonly used to regulate the flow of water between the valli da pesca and the rest of the Lagoon, allowing fish to enter the valli and facilitating the catch. See valli da pesca.

Soil:
soil may be defined as a layer covering the lithosphere, through which exchanges with the atmosphere, the hydrosphere and the biosphere take place. It is a natural formation of variable thickness and surface area, derived from the physical disintegration and chemical and biological decomposition of the (sub-pedogenetic) parent material and vegetal residues (litter). The weathering of the rocks by the elements is the key factor in the first stage of soil formation: it encompasses all the processes of chemico-physical breakdown to which exposed rocks are normally subject and which vary with the climate and the composition of the rock itself. Specifically, physical weathering processes prevail in regions with arid climates, while chemical weathering dominates above all in wet regions. Biological activity contributes to the disintegration of the rock, especially via so-called “pioneer” organisms, which in turn constitute degradable biomass for other types of micro-organism. The biocoenoses present in soil are among the most diverse and complex on the planet, and it is precisely this complexity and the presence of important feedback mechanisms (retroaction) which ensure stability and the possibility of evolutionary processes. The biocoenoses present in soil are an index of its “health”. (see also pedogenesis).

Spring:
a place where water comes up naturally from the ground, fed by the phreatic groundwaters. Springs usually occur at the point of contact between different areas (plains and hills, plains at different heights) due to the difference in permeability between the highly permeable sediments (generally gravel/sand) of the higher area and the poorly permeable silt or clay of the lower area.

Spring tide:
tide produced around new and full moon, when the Sun, Moon and Earth are in alignment (a condition known as syzygy). At this time, the tidal forces due to the Sun reinforce those of the Moon and the tidal range is thus maximum.

Subsidence:
gradual lowering of the soil in an area or, on a larger scale, lowering of the continental plate or of the sea bed, which tends to sink because of the weight of accumulating sediments and the continuous movement of the Earth’s crust. It may be due to natural causes such the tectonic deformation of the deeper strata of the Earth’s crust, the compacting of alluvial soils or of geologically recent sediments, the collapse of subterranean cavities, or settling linked to seismic events. It may also be due to anthropic causes such as the extraction of fluids from the subsoil, generally the pumping of water from aquifers and the pumping of hydrocarbons.

Sub-tidal:
lying below the level of the water even at the lowest tides.

Sustainability:
see sustainable development.

Sustainable development:
the concept of Sustainable Development was coined in 1987 by the World Commission on Environment and Development, known as the Brundtland Commission from the name of its President. The concept was defined as follows in its final report, “Our Common Future”: Sustainable Development is “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” (World Commission on Environment and Development, 1987). The concept of Sustainable Development grew out of the recognition that the problems of environmental, economic and social policy cannot be tackled separately. The concept of development according to which environmental problems should be tackled only after achieving economic and social development has failed, and the need for these to be integrated has become clear. The various currents of thought all insist on two key points: the ecological management of the environmental space – i.e., the conservation of nature, maintenance of the quality of ecosystems and geosystems and management of environmental resources within the limits of their capacity for regeneration; the social justice of environmental management – i.e., the defence of future generations, which is based on ethical principles of equity among all human beings, both living and future.

Synanthropic:
living in close contact with human beings.

Symbiosis:
relationship in which two organisms live in close contact with reciprocal advantages.

Taxon (plural taxa):
term indicating a systematic category at whatever level (e.g., genus, species, family), considered within the hierarchical classification system (taxonomy) of living things.

Texture:
in geology, the properties of the particles that make up a sedimentary rock, including their size, morphology, surface type and spatial arrangement. (see Granulometry). Cf. Plates 8 and 9.

Thanatocoenosis:
all of the non-decomposable remains of organisms which have accumulated in the same place after their death in a given layer of rock or sediment. Unlike a biocoenosis, a thanatocoenosis may contain remains of organisms of different habitats, buried by the same event. The study of thanatocoenoses provides useful information on the environmental conditions which existed at the time when those organisms lived.

Transitional waters:
in a general sense, all brackish water bodies, such as lagoons, coastal pools and river mouths. The Water Framework Directive of the European Union (2000) sets out a simplified definition of transitional waters which includes only those bodies of water that are influenced by fresh waters, thus excluding hyperhaline coastal pools. We hold that rather than transitional “waters” it is more useful to refer to transitional “environments”, by which is meant environments between land and sea.

Tributary:
a river or stream that flows into a larger river or lake or lagoon.

Trophic level:
the trophic level of an aquatic environment is given by the quantity of nutrients that are found in it. An environment may be oligotrophic if it has few nutrients, mesotrophic, eutrophic, hypertrophic or distrophic.

Trophic migration:
migration in search of food.

Troposphere:
layer of atmosphere stretching from the Earth’s surface up to the tropopause, the height of which varies from a minimum of 8 km (at the poles) to a maximum of 15 km (at the equator). The layer in which the atmospheric phenomena constituting the weather (fronts, clouds, storms etc.) occur.