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:

Francesco Scarton1, Daniele Are1, Andrea Rismondo1 and John Day2

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 email:scarton@selc.it

2Coastal Ecology Institute and Department of Oceanography and coastal Sciences,Louisiana State University, Baton Rouge, LA 7080, USA, email: johnday@lsu.edu

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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 ofVenice:

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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 in1993-1997, 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.

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Reedbeds in

Venice lagoon

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Lost salt marshes

Remaining salt marshes

•Lack of sediment inputs

•Natural and man-induced

subsidence

•Wave erosion

FACTORS OF SALT MARSHES FACTORS OF SALT MARSHES

DISAPPEARINGDISAPPEARING

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Most common saltmarsh species

and their elevation

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MHW

Map of saltmarsh vegetation(for about 50% of the lagoon)

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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 higherDifferent age (oldest: 14 years)

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PART TO BE REMOVED

WOODEN PILEWOODEN PILE

1.00 m a.s.l.

0.60 m a.s.l.

m.s.l.

1.00 m

1.00 m a.s.l.

0.60 m a.s.l.

m.s.l.

- 1.00 m a.s.l.

Hydraulic net

Hydraulic net

DREDGED MATERIAL

Reconstruction of eroded salt marshes with dredged sediment

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Reconstruction of a

disappeared salt marsh

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The network of Venice stations

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012345678

1 2 3 4 5 6 7 8 9 10 11

years

no

. of

stat

ion

s

The Sedimentation Erosion Table (SET)

9 pinsbubble level

pipe benchmark

ca -4 m

From Cahoon et al., 2002

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Conceptual diagram for elevation change/accretion

from Cahoon et al., 1995

Details of a SET station:C e ll A C e ll B

S E T s u p p o rtin g p ip e

S e c to r o f m e a s u re m e n ts

F e ld p s a r m a rk e r

SET re m o va b le a rm

4 m

9 readings in each sector, 36 readings per cell, 72 per station.Accuracy estimated at + 2.0 mm

length of thepin above the arm

marker

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Kaolin markers

1994

2004

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New field data

Dese 1 (reedbed)

0

1

2

3

4

5

6

7

8

Jan

-93

Jun

-94

Oct

-95

Mar

-97

Jul-

98

Dec

-99

Ap

r-01

Sep

-02

Jan

-04

May

-05

cm

elevation change (SET)

accretiony = 0.0446x - 0.407, R2 = 0.95, p<0.001(X= months since beginning)

Accretion: 0.6 cm/yrElev. ch.: 0.5, 11 ys.

Dese 2

-1

-0,5

0

0,5

1

1,5

2

2,5

3

Ma9

3

No9

3

Fe9

4

Ju94

Oc9

4

Ja95

Ap9

5

Ju95

Oc9

5

Ja96

Ap9

6

Oc9

6

Fe9

7

Ju97

Oc9

7

cm MARKERS

SET

Accretion: 0.6 cm/yrElev. ch.: 0.5, 4 ys.

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Laghi (saltmarsh with Juncus )

0

1

2

3

4

5

6

7

8

Ja

n-9

3

Ju

n-9

4

Oc

t-9

5

Ma

r-9

7

Ju

l-9

8

De

c-9

9

Ap

r-0

1

Se

p-0

2

Ja

n-0

4

Ma

y-0

5

cm

elevation change (SET)

accretion

y= 0.0013 x -43.4, r2=0.85, p<

y = 0.0409x + 0.0038, R2 = 0.8736

Accretion: 0.5 cm/yrElev. ch.: 0.5 cm/yr, 11 ys.

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S. Felice 1 (saltmarsh with Sarcocornia )

0

1

2

3

4

5

6

7

8

Jan

-93

Jun

-94

Oct

-95

Mar

-97

Jul-

98

Dec

-99

Ap

r-01

Sep

-02

Jan

-04

May

-05

cm

elevation change (SET)

accretion

y = 0.0235x - 0.2941, R2 = 0.87, p<0.001

Accretion: 0.3 cm/yrElev. ch.: 0.3, 11 ys.

SF1SF2

creekpond 5 m

S. Felice 2 (saltmarsh with Spartina )

0

1

2

3

4

5

6

7

8

Jan

-93

Jun

-94

Oct

-95

Mar

-97

Jul-

98

Dec

-99

Ap

r-01

Sep

-02

Jan

-04

May

-05

cm

elevation change (SET)

accretion

y = 0.0381x - 0.2485, R2 = 0.87, p<0.001

Accretion: 0.4 cm/yrElev. ch.: 0.4 cm/yr, 11 ys.

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Torson 1 (saltmarsh with Puccinellia -Limonium )

-1

0

1

2

3

4

5

6

7

No

v-93

Ap

r-95

Au

g-9

6

Jan

-98

May

-99

Oct

-00

Feb

-02

Jun

-03

No

v-04

Mar

-06

cm

elevation change (SET)

accretion

y = 0.0327x - 0.7039, R2 = 0.84, p<0.001

Accretion: 0.4 cm/yrElev. ch.: 0.4, 11 ys.

T1

T2

Torson 2 (dredge island)

-8

-7

-6

-5

-4

-3

-2

-1

0D

ec-9

3

May

-95

Sep

-96

Feb-

98

Jun-

99

Oct

-00

Mar

-02

Jul-0

3

Dec

-04

cm

elevation change (SET)

Elev. ch: - 1.8 cm/yr, 4 ys + 0.3 cm/yr, 7 ys

June 1997

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P. Cane 1(saltmarsh with frontal erosion)

-1

1

3

5

7

9

11

13

No

v-93

Ap

r-95

Au

g-9

6

Jan

-98

May

-99

Oct

-00

Feb

-02

cm

elevation change (SET)

accretion

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

Observed rates at 14 stations

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Accretion Elevation Shallow Years Elevation Dominantchange Subsidence above s.l. species

cm/yr cm/yr cm/yr m

Dese 1 0.6 0.50 -0.10 11 0.28 PhragmitesDese 2 0.6 0.5 -0.10 11 0.36 PhragmitesLaghi 0.5 0.5 0.00 11 0.29 JuncusSan Felice 1 0.3 0.3 0.00 11 0.35 SarcocorniaSan Felice 2 0.4 0.4 0.00 11 0.29 SpartinaTorson 1 0.4 0.4 0.00 11 0.39 PuccinelliaTorson 2 11 dredge islandFossei nat 0.4 0.4 0.00 8 0.42 LimoniumP. Cane 1* 1.70 0.70 -1.00 8 0.43 SarcocorniaEx Salina 0.45 0.3 -0.15 8 SpartinaBuello 0.9 0.8 -0.10 7 0.23 JuncusP. Vecia 0.9 0.8 -0.10 7 0.35 PuccinelliaChioggia 0.4 0.5 0.10 5 0.35 SarcocorniaTessera 1 0.4 0.4 0.00 4 0.39 SarcocorniaTessera 3 0.3 0.1 -0.20 4 0.36 SarcocorniaP. Cane 2* n.a. -4.7 4 -0.26 tidal flatTessera 2* n.a. 0.8 3 -0.23 tidal flatTessera 4* n.a. -1.5 3 -0.35 tidal flatFossei art* 0 -0.6 -0.60 1 0.31 dredge islandCampalto* 0.3 -0.1 -0.40 1 0.28 Limonium

Mean (excluding *) 0.50 0.45 -0.05

two trends

Elevation change vs accretion(12 st.)

y = 0,8597x + 0,0297

R2 = 0,8526

0

0,2

0,4

0,6

0,8

1

0 0,2 0,4 0,6 0,8 1

Accretion (cm/yr)

Ele

va

tio

nc

ha

ng

e (

cm

/yr)

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4 st.

2 st.

Accretion vs elevation(12 st.)

y = -1,9246x + 1,1595

R2 = 0,2619

0,0

0,2

0,4

0,6

0,8

1,0

0,00 0,10 0,20 0,30 0,40 0,50

Elevation above s.l. (m)

Ac

cr.

(cm

/yr)

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Accretion vs. Elevation Linear Trajectories at 49 Saltmarsh SettingsGrouped by Regional Setting

0

2

4

6

8

10

12

14

16

18

-3 -1 1 3 5 7 9 11

Linear Elevation Trend (mm/yr)

Line

ar A

ccre

tion

Tre

nd (

mm

/yr)

US Atlantic - NE (Can) US Atlantic - SE U.S. Gulf Coast US Pacific

New South Wales Victoria Mediterranean

SELC biologia e geologia applicate Courtesy of Tom Spencer,Cambridge University

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