The breath of the Lagoon of Venice EarthCache
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The breath of the Lagoon of Venice
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The site is near the Punta Sabbioni lighthouse (1 m above sea
level), located on an 300 m-long seawall near the Lido inlet. The
cache site is totally public and free of access.
This earthcache is placed in the Lido inlet. This is one of the
three “open doors” between the Adriatic Sea and the
Lagoon of Venice.
The main educational goal of this earthcache is to tell you the
history of the Lagoon, their environmental concerns and the
importance of the inlets. If you love the nature, you may also
visit the nearby natural area “Penisola del Cavallino”,
a Site of Community Importance (SCI). Moreover, in this area you
can see the “remains” of the original Venetian beach
dune system. During the summer, you can also sunbathe on the nearby
beach of Punta Sabbioni, or you can take the ship
“vaporetto” to make an historical tour of Venice,
Murano and Torcello islands.
Figure 1. Image from Wikipedia
"http://en.wikipedia.org/wiki/Venetian_Lagoon"
The Lagoon of Venice is located along the north-western coast of
the Adriatic Sea (approx 45°N; 12°E) and is the largest lagoon in
the Mediterranean Sea. The Lagoon of Venice is today the most
important survivor of a system of estuarine lagoons, which in Roman
times extended from Ravenna to Trieste. It is a complex ecosystem,
controlled by many natural factors and affected by several
centuries of heavy human influence (see Figure 1). Today, the
lagoon covers an area of about 550 km2; it has an
extension of about 50 km along the coast and an average width of 15
km. The average depth is 1.2 m, with only the 5% of total surface
deeper than 5 m and 75% shallower than 2 m [1,2]. About 140
km2 of the total lagoon surface is occupied by mud flats
which form salt marshes (barene), emerging from the water only
during low tide.
Some studies reported that the lagoon of Venice originated nearly
6–7 thousand years ago, during the Flandrian Transgression,
during the last Ice Age. In this geological period, the rising sea
flooded the Upper Adriatic Würmian paleo-plain and outlined the
coast in approximately the present position [3]. The ancient lagoon
was smaller than the present one, principally controlled by two
main factors: i) the continuous sediment supply from several rivers
originally flowing into the lagoon (e.g., Adige, Bacchiglione,
Brenta, Sile and Piave); ii) the noticeable coastal nourishment
coming from southward, due to the Po river, that led to a gradual
silting-up of the tidal inlets. In this geological system, the
sediments transported from the rivers compensated for the sinking
coastal plain, and coastwise drift from the mouth of the Po tended
to close tidal inlets. These two natural processes started
unavoidably to the disappearing of the lagoon basin [3], however,
in the subsequent centuries, the Venetians contributed
significantly to modify the lagoon system with some hydraulic
interventions. During the age of the Serenissima Republic (XV-XVI
centuries), the Venetians, considering the lagoon a source of
security against enemies, carried out several hydraulic works to
preserve it.
Today, the lagoon appears as a salt-water estuary, protected from
the Northern Adriatic Sea by some sandbars (Cavallino, Lido and
Pellestrina) which are interrupted by three tidal inlets (Lido,
Malamocco and Chioggia). The three inlets are not very wide, but
they are extremely important, allowing the matter and energy
exchange between sea and lagoon, driven by the tidal cycle. The
tidal cycles can be considered as the “breath”
of the lagoon, a fundamental process of water renewal between
Adriatic Sea and lagoon, that is essential for the lagoon’s
metabolism, i.e., salinity control, exchange of dissolved oxygen,
nutrients and oligo-elements and… unfortunately, also the
pollution.
At the present time, the Lagoon of Venice suffers from a series of
environmental problems directly linked to: i) the presence of the
city of Venice, with about 63,000 inhabitants; ii) the industrial
zone of Porto Marghera, perturbing the air, the water and the
sediments with heavy metal and organic pollution; iii) the
commercial–industrial and private shipping, with some fishing
vessels carrying out an intense -and in many cases illegal- clam
harvesting and mechanical dredging of channels.
However, one of the most serious environmental problems affecting
the Lagoon is the increasing of the high waters
(“AcquaAlta”), due to the exceptional tide
events. Venice is afflicted by high waters since ancient times,
predominantly in autumn, winter and spring. Although the tide in
the lagoon basin is lower than in other areas of the world where it
may reach as high as 20 m, the phenomenon may become significant if
associated with atmospheric and micro-meteorological factors, such
as pressure and the action of the Bora wind blowing from Trieste or
Sirocco wind coming from south-east, which push the waves into the
gulf of Venice [4]. The recent increase in the frequency and
intensity of high waters was associated with natural and artificial
causes. The main “natural (?)” causes are the
subsidence (sinking of the Earth’s surface in response to
geologic or anthropogenic causes) and the eustatism (rise of the
sea-level). In this way, during the 20th century, land in the
lagoon dropped by 23 cm with respect to mean sea level. The main
“human-made” cause is the erosive action of the water
flows as a result of some of the measures taken by man to
facilitate port activities (jetties, artificial canals) [2].
The MOSE Project (Italian acronym for Experimental
Electromechanical Module) is a project started to protect the city
of Venice from extreme events such as the high floods (see
earthcache “AcquaAlta”) and from morphological
degradation. It consists of some rows of submarine mobile gates,
built to isolate the Venetian Lagoon from the Adriatic Sea when the
tide reaches above the level of 110 cm. The construction of these
mobile barriers was started on 2003, together with other
complementary measures, i.e., coastal reinforcement, the raising of
quaysides and paving and improvement of the lagoon environment.
Today, you can see the works to build the barriers near the Lido
inlet. You can read more information about the MOSE project from
Wikipedia.
Near the earthcache site you can see the natural area called
“Penisola del Cavallino”. This is a Site of Community
Importance (SCI), defined by the European Commission Habitats
Directive (92/43/EEC) as a site contributing significantly to the
maintenance or restoration at a favourable conservation status of a
natural habitat type, and contributing significantly to the
maintenance of biological diversity… a great place to make
pictures of birds (birdwatching). Moreover, near the beach you can
see the “remains” of the ancient dune system. Today,
the dune system is almost-totally destroyed by human activities and
urban/touristic infrastructures.
New question added!
To log this Cache you must go at the coordinates, in front of
the Punta Sabbioni lighthouse (see Figure 2), and you have to
answer four questions: 1) The lighthouse has 3 wall faces to the
open sea. What is their color?; 2) How many doors have the
lighthouse on the ground-floor? 3) How many inlets have the Lagoon
of Venice? 4) In the 20th century, the land in the lagoon dropped
some centimeters, with respect to mean sea level… How many
centimeters?
Send me the correct answers using the geocaching mail (mauro78). If
you want, you can make a photo of you, your GPS device and the
Punta Sabbioni lighthouse!
Logs without correct answers will be extinguished by the owner
regularly.
Figure 2. Another lighthouse, near the cache.
References
[1] Ravera O., 2000. The Lagoon of Venice : the result of both
natural factors and human influence. J. Limnol., 59(1):
19-30.
[2] Molinaroli E., Guerzoni S., Sarretta A., Masiol M., Pistolato
M., 2009. Thirty-year changes (1970 to 2000) in bathymetry and
sediment texture recorded in the Lagoon of Venice sub-basins,
Italy. Mar. Geol., 258: 115–125.
[3] Brambati A., Carbognin L., Quaia T., Teatini P., Tosi L., 2003.
The Lagoon of Venice: geological setting, evolution and land
subsidence. Episodes, 26(3): 264-268.
[4] Wikipedia, http://en.wikipedia.org/wiki/MOSE_Project
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The lighthouse seawall and the earthcache location are accessible
from 0 to 24h (all the day!). The area is totally public and free
of access.
Reaching the cache location by foot: you may reach the final
coordinates directly from the beach, or from the surrounding
campings (e.g., Marina di Venezia, Miramare).
Reaching the cache location by car: you may park at the
waypoint 1 coordinates. There is a big parking open 24h per day.
Warning: since May 2009, parking costs 1 euro per hour. You have to
pay from 0 to 24h.
See parking fee by clicking here (tnx to Herp of Many Colours to
this advice).
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Be careful in case of adverse weather: e.g., thunderstorms,
seastorm, heavy seas, windy days.
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Additional Hints
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