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Francesco Scarton 1, Daniele Are 1, Andrea Rismondo 1 and John Day 2 Accretion and elevation changes on salt marshes and reedbeds of the lagoon of Venice:

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Presentation on theme: "Francesco Scarton 1, Daniele Are 1, Andrea Rismondo 1 and John Day 2 Accretion and elevation changes on salt marshes and reedbeds of the lagoon of Venice:"— Presentation transcript:

1 Francesco Scarton 1, Daniele Are 1, Andrea Rismondo 1 and John Day 2 Accretion and elevation changes on salt marshes and reedbeds of the lagoon of Venice: ten years of data 1 SELC soc. coop., Via dell’Elettricità 5/d, Marghera (VE), Italy 2 Coastal Ecology Institute and Department of Oceanography and coastal Sciences, Louisiana State University, Baton Rouge, LA 7080, USA, SELC biologia e geologia applicate

2 a total area of 550 sq. km, with about 37 sq. km of salt marshes, 3.5 sq. km of reedbeds and 50 sq. km of tidal flats. Mean tidal range is 0.6 m (1.1 m spring tide), three hydraulic basins. The largest lagoon in the Mediterranean, hosts endemic species, and vegetation communities with restricted distribution in southern Europe. The lagoon of Venice: SELC biologia e geologia applicate

3 Field stations in four habitat types: Saltmarshes (N and S basin): 13 st. Reedbeds (in the NW corner of the lagoon): 2 st. Dredge islands (artificial sites): 2 st. Tidal flat: 3 st. Installed in , most of them were part of monitoring projects performed until 1999 on behalf of the Italian Ministry of Public Works- Water Authority in Venice and its concessionaire Consorzio Venezia Nuova. After that, we did new measurements in 2001 and summer 2004 (11 stations): 4 st. still to be measured, 5 st. destroyed. SELC biologia e geologia applicate

4 Reedbeds in Venice lagoon SELC biologia e geologia applicate

5 Lost salt marshes Remaining salt marshes Lack of sediment inputs Natural and man-induced subsidence Wave erosion FACTORS OF SALT MARSHES DISAPPEARING SELC biologia e geologia applicate

6 Most common saltmarsh species and their elevation SELC biologia e geologia applicate MHW

7 Map of saltmarsh vegetation (for about 50% of the lagoon) SELC biologia e geologia applicate

8 Distribution (in red) of dredge islands in 2004 Ranging in size from 0.3 to 30 ha, mean of 10 ha. Most are made of silty sediments, the remaining are sandier. Mean elevation of the former close or below mean high water level; the latter are usually higher Different age (oldest: 14 years) SELC biologia e geologia applicate

9 PART TO BE REMOVED WOODEN PILE 1.00 m a.s.l m a.s.l. m.s.l m 1.00 m a.s.l m a.s.l. m.s.l m a.s.l. Hydraulic net DREDGED MATERIAL Reconstruction of eroded salt marshes with dredged sediment SELC biologia e geologia applicate

10 Reconstruction of a disappeared salt marsh SELC biologia e geologia applicate

11 The network of Venice stations SELC biologia e geologia applicate

12 The Sedimentation Erosion Table (SET) 9 pinsbubble level pipe bench mark ca -4 m From Cahoon et al., 2002 SELC biologia e geologia applicate

13 Conceptual diagram for elevation change/accretion from Cahoon et al., 1995

14 Details of a SET station: 9 readings in each sector, 36 readings per cell, 72 per station. Accuracy estimated at mm length of the pin above the arm marker SELC biologia e geologia applicate

15 Kaolin markers SELC biologia e geologia applicate

16 New field data Accretion: 0.6 cm/yr Elev. ch.: 0.5, 11 ys. Accretion: 0.6 cm/yr Elev. ch.: 0.5, 4 ys. SELC biologia e geologia applicate

17 Accretion: 0.5 cm/yr Elev. ch.: 0.5 cm/yr, 11 ys. SELC biologia e geologia applicate

18 Accretion: 0.3 cm/yr Elev. ch.: 0.3, 11 ys. SF1 SF2 creek pond 5 m

19 Accretion: 0.4 cm/yr Elev. ch.: 0.4 cm/yr, 11 ys. SELC biologia e geologia applicate

20 Accretion: 0.4 cm/yr Elev. ch.: 0.4, 11 ys. T1 T2

21 Elev. ch: cm/yr, 4 ys cm/yr, 7 ys June 1997 SELC biologia e geologia applicate

22 Elev. ch: 0.7 cm/yr, Acc: : 1.7 cm/yr

23 Observed rates at 14 stations SELC biologia e geologia applicate

24 Elevation change vs accretion (12 st.) SELC biologia e geologia applicate 4 st. 2 st.

25 Accretion vs elevation (12 st.) SELC biologia e geologia applicate

26 Courtesy of Tom Spencer, Cambridge University

27 SELC biologia e geologia applicate


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