Climate Change and the European Water Dimension - Agri ...

Concerning the flora of the lagoon bed, there are four species of eelgrass native to
the lagoon. Until recently, eelgrass was an important element of lagoon bed
vegetation. Vast meadows of eelgrass covered the lagoon beds, consolidating them
with its complex system of roots. The growth of this plant has now greatly diminished,
and algae (in some cases invasive, exotic species) have spread throughout the
lagoon.
For fisheries the Northern lagoon basin (with a good presence of salt marshes) and
the freshwater inlets attract large numbers of juveniles of many fish species, as well
as the role of salt marsh creeks and sea-grass meadows in supporting the
endangered species included in the Habitat and Species Directive (92/43/EEC). The
lagoon acts as a fish nursery for an important part of the fish present in the North
Adriatic Sea (Mainardi et al., 2004).
Some interesting transitional environments such as swamps, wetland meadows and
woods, and backwaters that were once part of the lagoon are now reclaimed lands.
The clay quarries in the inland territory behind the lagoon have been spontaneously
re-colonised by the fauna which once lived in these original transitional
environments: small molluscs, insects, reptiles, and amphibians. During the migratory
season, birds find a needed temporary habitat and feeding grounds in these areas.
These environments are the only areas where fresh fluvial waters and brackish
waters meet in the lagoon. Almost all of the coot and the ducks in the lagoon region
are concentrated in fish farm areas during the winter months and during the
migratory season. The reed bed environments offer nesting areas for numerous
species. Plants adapted for fresh water environments grow around waterways and
swamps. Typical plants that can be found in these areas are the common reed and
the cattail. Following the waterways, the reeds make their way into the lagoon along
the channels. In the northern part of the lagoon, fresh water marsh vegetation thrive
in brackish water environments which are rich in species that can adapt and live in
brackish habitat.
VI.B.3 Measurable Climate Change Effects
Sea level rise
Venice is considered the world test-case city for sea level rise (SLR). Even if the
journalistic description is occasionally exaggerated, the frequency of flooding
increased dramatically in the second half of last century, both due to land subsidence
and SLR. The present natural subsidence is limited to less than 0.4 mm/yr, while in
the period 1950-1970 the actual rate of subsidence was as high as 7 mm/yr due to
freshwater extraction from wells for industrial use. Since 1896, of the 23 cm of
relative sea level loss, approximately 12 cm is attributed to anthropogenic land
subsidence.
Figure VI.B.1 shows the mean sea level of Venice and Trieste (Pirazzoli and Taroni,
1999) where good agreement is observed in the initial and in the final part of the
period Carbognin and Taroni (1996). In the period between 1920 and 1970 the strong
extraction of underground water caused Venice to sink giving an apparent SLR
signal. The presence of long historical data series and the use of state-of-the art
techniques (as InSAR Satellite Interferometer), allows distinguishing between
different causes of relative sea level rise.
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