NCER 2004

Wetland and tidal channel evolution affecting critical habitats at Cape Sable

Everglades National ParkEverglades National Park

Wetland and tidal channel evolution affecting critical habitats at Cape Sable

Brigitte VlaswinkelBrigitte Vlaswinkel

Harold WanlessHarold Wanless

NCER 2004

NCER 2004

Wetland and tidal channel evolution affecting critical habitats at Cape SableWetland and tidal channel evolution affecting critical habitats at Cape Sable

10 km

Study areaStudy area

Southwest FloridaSouthwest Florida

Everglades National ParkEverglades National Park

NCER 2004

What is happening?

3) Major hurricanes

Rapid ecosystem changes in past 80 years, due to…

1) Human modifications

(canals)

2) Sea level rise

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Major land- and seascape changes

1)Alteration of vegetation communities: freshwater marsh mangrove wetland

mangrove

freshwatermarsh

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Major land- and seascape changes

2) Small canals become large tidal inlets…

and new creeks evolve

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Major land- and seascape changes

3) Lagoons fill up with muddy sediments

N

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Take Home Message

Man-made canals acted as catalysts for interior freshwater marsh collapse (but with sea level rise, this would now be happening in any case)

Large amounts of organic material are released from collapsed freshwater marsh and redistributed within the system

Complicated connectivity of processes and products. Cape Sable may serve as an analog for other sensitive channeled saline-to-freshwater wetland complexes

NCER 2004

Main question is…

What are the sediment dynamics of

the system?

Sediment from where?Sediment from where?Where to?Where to?How fast?How fast?

MARL RIDGE

LAGOON

COLLAPSEDFRESHWATERMARSH

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1928

500 m

2002

Aerial photographs (1928, 1935, 1953, 1964, 1973, 1990, 1999) Ikonos high resolution satellite images (2002, 2004)

Geomorphologic changes (± 80 yrs)

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Geomorphologic changes (± 80 yrs)

1928 2002

pond

pond

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Collapse of interior freshwater marsh

and

redistribution of the released organic

material

Focus of talk

Marl ridgeMarl ridge

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Narrow canals were dredged across the interior of Cape Sable in the 1920s to drain the wetland

1973

Marl Ridge

Marl Ridge

Homestead Canal

East Cape Canal

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Remaining fresh (to brackish) water marsh

Saline water, collapsed former freshwater marsh

Mangrove wetland 1 km

Ikonos 2002

SALINE INTRUSION

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Lake IngrahamLake Ingraham

Coastal RidgeCoastal Ridge

NE

SWNE

SW

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2002

~1995

1953

Since canal has been connected to lagoon mud and organics have been deposited. ± 75% of surface area lagoon is exposed with low tide.

1 cm /year accumulation

Rate of infill is increasing!

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Extremely high!

5 cm5 cm

40 cm 40 cm40 cm

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Remaining fresh (to brackish) water marsh

Saline water, collapsed former freshwater marsh

Mangrove wetland

WATER MASS 1

WATER MASS 1

WATER MASS 2WATER MASS 2

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0

20

40

60

80

100

120

140

160

8:00 9:57 11:54 13:50 15:47 17:44 19:40

Time (hour)

SS

C (

mg

/l) station A

station B

station C

ebb

flood

ebb

Station A

250m

Station C

Station B

April 2004

Suspended sediment concentrations – 1 daySuspended sediment concentrations – 1 day

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Year Day

Suspended sediment concentrations – 2 weeksSuspended sediment concentrations – 2 weeks

Station A

250m

Station C

Station A

Station C

SSC(mg/l)

ebbpeak

August 2004 Year Day

floodpeak

IMPORTANT

Station A: Not much sediment during flood

Station C: A lot of sediment during flood!

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SedSedOMOM

+ SedSedCARBCARB

SedSedCARBCARB

SedSedCARBCARB

Collapsed freshwater marsh

SedSedOMOM

SedSedOMOM = organic matter sediments

SedSedCARBCARB = carbonate sediments

Geochemical analyses:Geochemical analyses:70% organics70% organics30% carbonate30% carbonate

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10,000 Islands10,000 IslandsDegradation of mangroveDegradation of mangrove and transitional marshand transitional marsh

Gopher CreekGopher CreekCollapse of interior Collapse of interior mangrove wetlandmangrove wetland

Expansion of ‘White Zone’Expansion of ‘White Zone’ Collapse of transitional and freshwater marshes Collapse of transitional and freshwater marshes

North Cape Sable North Cape Sable loss of interior loss of interior

mangrove wetlandmangrove wetland

Rapid loss of saline and freshwater wetlands is also occurring in other areas in South Florida

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Impact of released organic matter ?

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Conclusions The Cape Sable geomorphic system is out of equilibrium and has evolved dramatically and rapidly

Man-made canals acted as catalysts for interior freshwater marsh collapse (but with sea level rise, this would now be happening in any case)

Large amounts of organic material are released from interior freshwater marshes and redistributed within the system

• The results illustrate the complicated connectivity of processes and products on this coast. Cape Sable area may serve as an analog for other sensitive channeled mangrove-to-freshwater wetland complexes

NCER 2004

AcknowledgementsEverglades National ParkStable Isotope Lab at RSMASMany field assistantsCape Sable Seaside Sparrow

With water, water everywhere, and no time left to think,Your battle will wage on

Among cash and good intentions.Slowly flying, slowly dying,

While the lifeblood of the River drainsPast the sawgrass bent in discontent.

Tom Fucigna

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1928• A narrow drainage

ditch was cut across the freshwater marsh in the 1920s

• It also cut across the marl ridge to the west

Mar

l Rid

ge

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1953• By 1953 the marsh

adjacent to the marl ridge had collapsed

Mar

l Rid

ge

1953

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1928

1999

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Sediment dynamic patterns on decadal scale

Soft sediment cores• Sediment constituents• Depositional processes (grain size, storm layers)• Average sedimentation rate through time

Geochemical analyses• Ratio carbonate/organic matter/insolubles• Organic carbon isotopic composition (δ13C )

Source of sediment

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Sediment dynamic patterns on short time scale

Sediment dynamicsIn situ sedimentationShoreline dynamics

HydrodynamicsWind dataWater levelCurrent flowDischargeSediment in suspension