Estuaries: interface between land and sea a complex interaction between morphology, hydrodynamics and ecology

Patrick Meire & Eric De Deckere

University of Antwerp, Dep. of Biology, Ecosystem management research group,

2

Content

• Introduction• The Schelde estuary• Impact of present and past management• Conclusions

3

1) Introduction

RIVER catchment SEAESTUARY

Urban and industrial development

Human developmentIn the whole catchment

2) The Schelde estuary

5

Antwerpen

Gent

Vlissingen

BELGIUM

THE NETHERLANDS

WESTERSCHELDE

ZEESCHELDE

The Schelde estuary:•160 km long and macro- mesotidal•Entire salinty gradient from fresh to salt

6

0 20 40 60 80 100 120 140 0

500

1,000

2,000

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

50,000Dec 98

Dec 97

Dec 96

Dec 95

7

3) Impact of past and present management

8

Geomorphology

habitats

dredging

embankments

Physical structure

9

10

35853

42341

28,4

20,3

32000

34000

36000

38000

40000

42000

44000

1900 1990

Year

Surf

ace

(ha)

0

5

10

15

20

25

30

% in

tert

idal

are

a

total surface % intertidal

Habitat loss embankment of silted up areas

11

-150

-130

-110

-90

-70

-501940 1950 1960 1970 1980 1990 2000 2010

Year

Dep

th (d

m G

LLW

S)

Borssele Hansweert Bath Zandvliet

DREDGING

Westerschelde Mouth

Maintenance 8 à 9 mio 5 à 6 mio

Deepening year 1

17 mio

16 mio

year 2 19 mio 16 mio

Present maintenance

15 mio 10 mio

12

Geomorphology

habitats Hydrodynamics

Sea levelrise

Changes inthe basin

dredging

embankments

13

14

40 km

Van Braeckel

et al. 2006

15

33,5

44,5

55,5

66,5

0 50 100 150 200

Km from river mouth

Dur

atio

n of

ris

ing

tide

(hrs

)Tidal asymmetry increases

16

1895 1925 1955 1985Vlissingen - Hansweert 71 70 63 56Vlissingen - Antwerpen 144 133 120 104

Time of flood wave (min)

17

• Increased discharges from the catchment

• Less buffering of peak discharges upstream

Van Braeckel

et al. 2006

18

Import from the catchment: erosion

Sediment input in the estuary, average 670.000 ton drymatter, is largely anthropogenic

Erosionfactor:Forest: 0.001Meadow: 0.01Field: 0.37(Govers, KUL)

19

Suspended matter (mg.L-1)

1996

1997

1998

1999

2000

2001

2002

Vlissingen

Gent

Antwerpen

B-Nl border

Dis

tanc

efr

omth

e ri

ver

mou

th(k

m)

0

20

40

60

80

100

120

140

050100150200250300350400450500550600650700

Flocs

20

Geomorphology

habitats Hydrodynamics

Sea levelrise

Changes inThe basin

dredging

embankments

21

• Can habitats cope with this changing hydrdynamic conditions?

22

Tidal asymmetry Tidal pumping

23

Can habitats cope with the changing tidal amplitude?

old

marshes

young

marshes

Data Stijn Temmerman

24

VlissingenAntwerpen

DendermondeGentSaeftinge

1931

old

marshesyoung

marshes

Temmerman et al., 2003; 2004, Marine GeologyData from

aerial

photgraphs

and topographic

maps

25

VlissingenAntwerpen

DendermondeGentSaeftinge

1999/2001/ 2002

old

marshesyoung

marshes

Field data

Temmerman et al., 2003; 2004, Marine Geology

26

4

5

6

7

8

0 20 40 60 80 100 120 140 160

4

5

6

7

8

0 20 40 60 80 100 120 140 160

gem. hoogwaterpeil 2000

hoog

telig

g ing

(m T

.A. W

.)

afstand tot de monding (km)

2100

4

5

6

7

8

0 20 40 60 80 100 120 140 160

Modeling

future developments

Gepubliceerd in:

Temmerman et al., 2003;

2004, Marine Geology

27

Sediment management in catchment

2000 2005

28Total sedimentexport = +/- 1385 m³

export = 705 m³

data=: Karel Van Daele

29

4

5

6

7

8

0 20 40 60 80 100 120 140 160

gem. hoogwaterpeil 2000

hoog

telig

g ing

(m T

.A. W

.)

afstand tot de monding (km)

2100

4

5

6

7

8

0 20 40 60 80 100 120 140 1604

5

6

7

8

0 20 40 60 80 100 120 140 160

Modellering

Temmerman et al., 2003; 2004, Marine Geology

If

SS Conc

decreases: marshes disappear

?Ti

dal h

eigh

t

Distance along estuary

30

Slope ↑, current speed ↑ marsh erosion ↑

31

Increase high dynamic flats

0

20

40

60

80

1920 1940 1960 1980 2000 2020

% High dynamic% Low dynamic

Courtesy Dick de Jong, RIKZ

32

Geomorphology

habitats Hydrodynamics

Sealevelrise

Changesin the basin

dredging

embankments

Ecological

Structure/functioning

33

• Pelagic and benthic habitats

34

0

5000

10000

15000

20000

0 20000 40000 60000 80000

macrobenthos biomass * surface intertidal flats

num

ber

Birds and their food

Data Tom Ysebaert NIOO- CEMO

35

1E-1

1E0

1E1

1E2

1E3

biom

ass

0.1 1 10 100 % Silt50

L.Springer Everingen Molenplaat Valkenisse

Benthos biomass depends on sediment characteristics

Data Tom YsebaertData Tom Ysebaert NIOO- CEMO

36

Benthos and its food

System primary

production

(gC.m-2.y-1)0 100 200 300 400 500 600 700

Sys

tem

-ave

rage

dm

acro

faun

a bi

omas

sg

AFD

W m

-2

0

10

20

30

40

50

60

70

B=-1.5 + 0.105 Pr2=0.77

GR

OS

VM

WS

B1

B2

ED

EWCBSFB

LISLY

COL

YT

BF

Source: P. Herman NIOO-CEMO

37

Light climate phytoplankton

Zm

Zp Photic depth

Mixing depth Survival chance~ Zp/Zm

38

Benthos is dependent on primary production in pelagic

Zm

Zp

North Sea

Schelde estuaryWesterschelde

freshwater

tidal estuary(Reid et al. 1990)

(Soetaert

et al. 1994)

(this study)

200 g C m-2

year-1

41 g C m-2

year-1

260 g C m-2

year-1

Kromkamp & Peene (1995) Mar. Ecol. Progr. Ser. 121: 249-259 and this study

0

2

4

6

8

10

12

14

Z m/Z

p

Westerschelde freshwater tidal estuaryNorth Sea

39

Zm

Zp

Photic depth Zp~ suspended matter

mixing depth Zm~ embankments/ deepening

40

Log 10 of mean

spring tidal

rangeUncles

et al., 2002

Van der Spek et al., 1997

Linking

tidal

range history with

the relation

between

tidal

range, tidal

lenght

and SPM

1 meter less

mean

spring tidal

range

would

give

for

an

estuary

of 160 km longan

SPM concentration

of about

ten times

less

41Major changes

in foodwebfytoplankton

zooplankton

fish

zoobenthos

Microbes CO2

epibenthos

42

• Suspended sediments:• decrease is benefical for primary production• possibly a problem for survival of marshes

under global change scenario’s

• Are marshes important?

43

Marsh

HT

LT

Role of marshes

Tidalflat

Exchange betweenmarsh and pelagic

44• Based on a whole ecosystem labeling experiment (N15) we were able to show that about 15% of DIN is retained in the tidal marshes each tide! (Gribsholt et al. Lim & Ocean)

45

HT

LT

Role of marshes

Tidalflat

Exchange betweenmarsh and pelagic

150 –

300 ton BSi

46

HT

LT

Role of marshes

Tidalflat

3) Exchange betweenmarsh and pelagic

150 –

300 ton BSi

100 –

200 ton Si

47

Does marsh Si recycling matter?

• Marshes significantly affect yearly flux of BSi and DSi to the ocean (7%)

• In summer months, 43 % of Si load in the estuary is recycled trhough the marshes

• In summer months, marshes are essential DSi suppliers to estuarine ecosystem

48

Marshes import N and P in inorganic

form

Stimulation

of biological

production

Marshes export Si and high energy

organic

C, both

as living organisms

and as plant detritus

Outwelling

hypothesisMARSHES PROVIDE THE COASTAL SYSTEM WITH AN

EXTREMELY HIGH LIFE ENERGY

49

Conclusion 1

• Complex interaction between human activity, hydrodynamics and sediment dynamics led to a significant loss of habitats

• Loss of habitat and changing characteristics of habitats led to changes in the structure and function of the biodiversity

• This led to a decrease of ecosystem services• Restoration is necessary

50

• Based on modelling- 1500 ha of marsh extra is needed to take away Si

limitation for diatoms- 500 ha of tidal flats extra is needed for stabilizing

the estuarine food chain and water quality improvement

51

Spatial distribution of restoration sites

52

Restoring raised sites

53Managed realignment

1990 1998

54The Sigmaplan

1800 ha of Flood Control Areas (FCA) needed to reach required safety against inundations

Ring Dike Lowered CIA dike

FCA estuary

Outlet

polder area

55

• Is there a combination possible with the area needed for safety?

56

Ring Dike Lowered CIA dike

FCA estuary

Outlet

polder area

Ring Dike Lowered CIA dike

CRTestuary

Outlet

Inlet

polder area

Flood Control Areas (FCA) Controlled Reduced Tide (CRT)

57

-2

0

2

4

6

8

10

hoog

te(m

TA

W)

springtijgemiddelddoodtij

GOG - GGG

Scheldepolder

58

Lippenbroek

1: Ring Dike

2: FCA dike

3: Inlet sluice

4: Outlet sluice1

231

4

1

1

Management scenario Lippenbroek

Pilot project Lippenbroek

10 ha of tidal

nature developping

since

March

2006

59

60

61

Pilootproject Lippenbroek

Sedimen-

tatie

(g/m²/tij)

0

150

UA -

KUL

Lippenbroek inwateringen 13u-metingen: Sediment vs debiet

y = 30,129e0,7478x

0

50

100

150

200

250

0 0,5 1 1,5 2 2,5

debiet (m3/s)

sedi

men

tcon

cent

ratie

(mg/

l)

Reeks1Exponentieel (Reeks1)

WL

R2 = 0.6866

0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100 120 140

sediment load (g/l)

Zn c

onte

nt

63

A: non contaminated + reed

C: non contaminated blanco

B: contaminated + reed

D: contaminated blanco

Mesocosm experiment

Historical versus actual pollution

64

Waterregime

65

66

0123456789

10

aug/03 sep/03 okt/03 nov/03 dec/03

months

mg

Cd/

kg

susp solnon contamcontam

67Impact of heavy metal contamination on the development of controlled inundation areas along the Scheldt-estuary

Cd (Bed A)

-80-70-60-50-40-30-20-10

010

0 1 2 3 4mg Cd kg DM-1

dept

h (c

m)

aug/03okt/03dec/03feb/04apr/04jun/04

Cd (Bed B)

-80-70-60-50-40-30-20-10

010

0 2 4 6 8 10mg Cd kg DM-1

dept

h (c

m)

aug/03okt/03dec/03feb/04apr/04jun/04

Cd (Bed D)

-80-70-60-50-40-30-20-10

010

0 2 4 6 8 10mg Cd kg DM-1

dept

h (c

m)

aug/03okt/03dec/03feb/04apr/04jun/04

Cd (Bed C)

-80-70-60-50-40-30-20-10

010

0 1 2 3 4 5mg Cd kg DM-1

dept

h (c

m)

aug/03okt/03dec/03feb/04apr/04jun/04

A: non contam + reed B: contam. + reed C: non contam. D: contam.

68

Vegetation: metal concentration 2003

contamination reed

0

0.1

0.2

0.3

0.4

0.5

0.6

1

Cd

(µg/

g)Blad AStengel APluim ABlad BStengel Bpluim B

unpollutedpolluted

No effect on pore water concentrations

No effect on performance of reed

69

Site A

Site B

H o o gte van het gro ndwater van 5/ 07 to t 18/ 08

-60

-50

-40

-30

-20

-10

0

tijd

Site A

Site B

70

Concentratie Cd in het sediment

0 10 20 30 40

50-6040-5030-40

20-3010-200-10

diep

te (c

m)

concentratie (mg/kg droge massa)

site A, ↑

inundatie

site B, ↓

inundatie

71

Concentratie Cd in het poriënwater (rhizons)

0,000 0,002 0,004 0,006 0,008

40-50

30-40

20-30

10-20

0-10

diep

te (c

m)

concentratie (mg/l)

site A, ↑

inundatie

site B, ↓

inundatie

72

•Gehalten hoger dan in sediment: oxidatie van de rhizosfeer.

→ vorming van een ijzerplaque.

•Diepteprofielen: redoxpotentiaal?

•Verschil sites:Op grotere diepte: hogere gehalten bij minder frequente inundatie (meestal significant).

Gehalte aan zware metalen in de wortels.Concentratie Cd in de wortels

0 200 400 600

50-60

40-50

30-40

20-30

10-20

0-10

diep

te (c

m)

concentratie (mg/kg droge massa)

site A, ↑

inundation

site B, ↓

inundation

73

bGehalte cadmium (site A)

0102030405060708090

100

sediment (g) wortels (mg) rhizomen (mg)

geha

lte /

m²

Gehalte cadmium (site B)

0102030405060708090

100

sediment (g) w ortels (mg) rhizomen (mg)

geha

lte /

m²

But all above ground biomass is under detection limitLocal conditions strongly impact availabilityWill local conditions change?

74

No young marshes in estuary anymoreOne of the aims of managed retreat is to restore the dynamicsof the marshes

75

Dike

Wave erosion ++

Silt/Clay

PlantsSchematic cross-section through a salt marsh

Flow erosion high Flow erosion low

Salt marsh: natural dynamics between sedimentation and eriosion

after Van de Koppel et al 2005 Am. Natur.

Natural marshes are very dynamic: an equilibrium betweenSedimentation and erosion

76

Simulated salt marsh development

Development of clat thickness and vegetation density along a transect(MP3-movie not included in this ppt)

77

Geomorphology

habitatsHydrodynamics

Ecological

functioning

The System

Habitat and BirdDirective

Water frameworkDirective

Economicdevelopment

Sedimentmanagement

78

RIVER catchment SEAESTUARY

Management

River-estuary-sea continuüm

LAST CHANCE TO REDUCE LOAD TOWARDS THE NORTH SEA

79

Conclusion

• Sediment management is a crucial part of integrated water management taking into account spatial relations

• Sediments have both very negative and very positive impacts on the ecosystems:- Too much impact on productivity and habitat

characteristics- Too little habitat sustainability

• Sediment quality is a major problem for habitat development and dynamics

• An integration of several EU directives is necessary to achieve an true integrated water management

80

81

Pore water: Cd,

Cd: not contaminated+ reed

-60

-50

-40

-30

-20

-10

00 0.005 0.01 0.015 0.02

mg/l

dept

h (c

m)

Cd: contaminated+ reed

-60

-50

-40

-30

-20

-10

00 0.005 0.01 0.015 0.02

mg/l

dept

h (c

m)

Cd: not contaminated

-60

-50

-40

-30

-20

-10

00 0.005 0.01 0.015 0.02

mg/l

dept

h (c

m)

Cd: contaminated

-60

-50

-40

-30

-20

-10

00 0.005 0.01 0.015 0.02

mg/l

dept

h (c

m)

82M e s o c o s m e x p e rim e n t: to ta l b io m a s s

0

50

100

150

200

250

300

350

DG

W (g

/m2)

bak Abak B

A: non contam + reed B: contam. + reed C: non contam. D: contam.

Average length and diameter/shoot

0

10

20

30

40

50

60

70

80

90

leng

te (c

m)/

diam

eter

(mm

)

lengte bak Alengte bak Bdiameter bak Adiameter bak B