Protecting and restoring the salt marshes and seagrasses in the lagoon of Venice.

The Lagoon of Venice is one of the largest and important Coastal Transitional Ecosystems of the Mediterranean (Tagliapietra et al. 2009). Human presence has constantly modified the original estuarine structure so that the lagoon can be nowadays considered as a human-oriented ecosystem, still maintaining strong natural traits. It is located at the north-western part of the Adriatic Sea between the current mouths of the Sile and Brenta rivers, ranging in latitude between 45,18 - 45,57 N and 12,12 - 12,63 E in Longitude (Fig. 1). The lagoon is connected to the sea by three lagoon-inlets and the physical separation between the lagoon and the Adriatic Sea is constituted by two barrier islands and the two spits. The lagoon is about 50 km long and 10 km wide. accounting for a surface of about 540 km2. Out of them the 36 km2 are saltmarshes, 30 km2 islands (excluding the barrier islands) and the rest is covered by water. The mean depth of the water column is about 1.2 m, with only 5% of the lagoon deeper than 5 m (Molinaroli et al. 2009). The maximum depth is 47 m, at a scour located at the lagoon side of the Malamocco Inlet. The volume of water contained in the lagoon is about 628 million m3. According to Kjerfve (1994), the Lagoon of Venice can be defined as a "restricted" coastal lagoon. The basin is connected to the Adriatic Sea through three inlets (Lido, Malamocco and Chioggia) which allow tidal flushing twice a day. Every day the Venice lagoon exchanges with the Adriatic Sea about 400 million m3 of water while the inflow from the inland through the rivers and subsoil about 3.7 million m3 (Bernstein and Montobbio 2011). Tides are a main factor in shaping the morphology of the lagoon and driving water exchange, dissolved oxygen, salinity, nutrients and sediment distribution. The North Adriatic tides are the largest in the Mediterranean. In the Lagoon of Venice tides are mixed, predominantly semidiurnal, and microtidal (Tagliapietra and Ghirardini 2006) with a mean tidal range of 61 cm , and an intertidal range of 121 cm from the Highest to the Lowest Astronomical Tidal Level (calculated for 1986-2004). The drainage basin is about 1850 km2, 40% of which is reclaimed land laying under the sea level. According to the Koeppen–Geiger–Pohl Climatic Classification (Geiger and Pohl 1953) the lagoon experience a Cfa climate i.e. humid subtropical climate, hot summers. Due to the shallowness of the lagoon, water temperature follows strictly the seasonal trends of air temperature, ranging from zero (seldom freezing) to above 30°C. Precipitations distributed throughout the year contribute to an average freshwater input of about 35.5 m3 s-1 as recorded in 1999 (Zuliani et al. 2005), with the most important tributaries located in the northern basin. Freshwater input and tides produce a salinity gradient, ranging from marine (ca 37 psu) to almost freshwater near the bay-head estuaries and freshwater inlets. The salinity gradient is compressed toward the mainland, due to the preponderant tidal contribution resulting in an average value of ca 30 psu. Therefore the majority of the lagoon can be classified as Mixoeuhaline/(Mixo-)polyhaline according to the Venice System (D’ancona 1959). Some socio-environmental contexts are particularly sensitive to the use of traditional materials or compatible with the landscape in which they are placed. Venice and its lagoon are all about it. Due to the uniqueness and peculiarity of its cultural values, which are made up of an exceptional cultural heritage and, above all, integrated into an extraordinary environmental context, "Venice and its Lagoon" is a UNESCO World Heritage List since 1987. The Venice Lagoon can be considered as a "cultural landscape" where over time the work of man and nature is intertwined under the influence of environmental, social and economic constraints and opportunities (Fig. 2). The lagoon of Venice is one of the most studied coastal sites in the world, both ecologically and culturally, it is a site belonging to the international Long-Term Ecological Research network (https://data.lter-europe.net/deims / site / lter_eu_it_016)