controls on sediment accretion and blue carbon burial in ... processes peck 2019.pdf · surface...

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Controls on sediment accretion and blue carbon burial in tidal saline

wetlands: Insights from the Oregon coast

Erin Peck, Rob Wheatcroft, & Laura Brophy

Oregon State University

College of Earth, Ocean, & Atmospheric Sciences

[email protected]

1930 Aerial Photo of Nehalem Bay; UO Areal Photograph Collection

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Disclaimer:

My research has not focused on Sand Lake salt marshes specifically

My research focuses on ”least disturbed” salt marshes

43.0

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Longitude

La

titu

de

Youngs Bay

Nehalem

Coquille

Tillamook

Netarts

Salmon River

Alsea

50 100 1500

Carbon Accumulation Rate

(g Corg

m-2 y-1)

Global Average91 ± 19 g C

org m-2 y-1

(IPCC 2014)

Sand Lake

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Outline• Background – salt marsh sediment

dynamics

• Motivating questions

• Sediment core collection & methods

• Results & conclusions

• Applications to Sand Lake?

• Ongoing questions

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Motivation: Oregon marshes are important

• Ecosystem services • Understudied • Particularly resilient to sea level rise (?)

(610kona.com) (HMSC)(bethzaiken.com)

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Recent Publications: Brophy et al. 2019

Key Finding: ~85% of US West Coast vegetated tidal wetlands have been lost

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Recent Publications: Thorne et al. 2018

Key Finding: under high sea level rise rates, ~83% of US West Coast tidal saline wetlands are projected to be fully submerged by 2110

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Anatomy of a Salt Marsh (Tidal Saline Wetland)

subtidalintertidal

high marsh

low marsh

scrub-shrub

mud flat

mean tide level

mean lower low water

mean higher high water

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Sea Level Rise

Hydroperiod

SedimentElevation

Salinity

BiomassAccumulation

Decomposition

Tidal Range

Sedimentation

Erosion

Subsidence (Deep & Shallow)

Tectonic Uplift

Plant Growth & Turnover

Fluvial Water & Sediment

Supply

+

+

+

+

-

+

-

+

+

-

+

+

++

+/-

-

Salt marsh feedbacks

(Adapted from Cahoon et al. 2009 and Reed 1990)

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Salt marsh feedbacks

(Adapted from Cahoon et al. 2009 and Reed 1990)

Sea Level Rise

Hydroperiod

SedimentElevation

Salinity

BiomassAccumulation

Decomposition

Tidal Range

Sedimentation

Erosion

Subsidence (Deep & Shallow)

Tectonic Uplift

Plant Growth & Turnover

Fluvial Water & Sediment

Supply

+

+

+

+

-

+

-

+

+

-

+

+

++

+/-

-

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End member of salt marsh accretionhigh sediment supply

no sea level rise

low sediment supply

high sea level rise

• Sediment is needed for the marsh to accrete upward• Rising sea level provides accommodation space for that accretion to occur

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high sediment supply

no sea level rise

low sediment supply

high sea level rise

expansion of intertidal marsh

End member of salt marsh accretion

19th century New England

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drowning of marsh

surface


no sea level rise

low sediment supply

high sea level rise



Mississippi deltaVenice lagoon


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drowning of marsh

surface


no sea level rise

low sediment supply

high sea level rise



Oregon? Mississippi deltaVenice lagoon


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subtidalintertidal

high marsh

low marsh

scrub-shrub

mud flat

mean tide level

low tide

high tide

good indication of future resiliency to sea level rise

good indication of current resiliency to sea level rise

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subtidalintertidal

high marsh

low marsh

scrub-shrub

mud flat

mean tide level

low tide

high tide

good indication of current resiliency to sea level rise

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Motivating Questions• Are Oregon salt marshes drowning or accreting?

• What controls marsh carbon burial and vertical accretion?• Relative sea level rise (RSLR)

• Sediment load relative to tidal area

• Elevation

• How has mass accumulation changed over time?• Changes in carbon burial

• Changes in sediment source

• Related to changing climate and human impacts

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Methods: Estuary Selection

(dat

a fr

om

Maz

zott

iet

al. 2

00

8 &

Bu

rget

teet

al.

20

09

)

• RLSR= eustatic SLR – uplift rate

• Sediment load relative to salt marsh area • USGS discharge & suspended

sediment data

• USGS SPARROW model (Wise &

O’Connor 2016)

• Literature (Karlin 1980; Hatten et al. 2012;

Wheatcroft and Sommerfield 2005; Goñi et al. 2013)

• Suspended sediment concentration would be ideal

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Methods: Sediment Core Collection

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Estuary Scrub-Shrub & High Marsh Low Marsh Mudflat Total

Youngs Bay 4 1 - 5

Nehalem 7 3 2 12

Tillamook 4 2 - 6

Netarts 15 - 3 18

Salmon River 8 - - 8

Alsea 7 3 3 13

Coquille 5 3 2 10

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Methods: Sediment Analysis

• X-ray CT scan (downcore density)

• Excess 210Pb (& 137Cs)

• Downcore organic matter (OM) by loss on ignition (LOI)

• Downcore organic C and N by elemental analysis

• Downcore element ratios by X-ray fluorescence (XRF) core scan

• Downcore ẟ13C & ẟ15N

(OSU Vet Med)

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• Downcore ẟ13C & ẟ15N Tsunami deposit

Vegetation at surface

Sediment layers

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gamma spectrometers

De

pth

(cm

)

-50

-40

-30

-20

-10

01 10 100 1000

CS02

r2 = 0.91

SAR = 2.2 mm yr-1

Excess 210Pb (Bq kg-1)

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Estuary Scrub-Shrub & High Marsh Low Marsh Mudflat Total

Youngs Bay 4 1 - 5

Nehalem 7 3 2 12

Tillamook 4 2 - 6

Netarts 15 - 3 18

Salmon River 8 - - 8

Alsea 7 3 3 13

Coquille 5 3 2 10

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Organic Matter (%)

0

10

20

30

40

50

Org

anic

Carb

on (

%)

AlseaCoquille

Netarts

NehalemYoungs

Tillamook

Salmon

0 40 60 80 10020

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(Cox Analytical Systems)

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Have salt marshes been surviving RSLR?

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Longitude

La

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Youngs Bay

Nehalem

Coquille River

Tillamook

Netarts

Salmon River

Alsea

= Sediment Accumulation Rate (mm y-1)= Relative Sea Level Rise (mm y-1)

-2 0 2 4-4

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Longitude

La

titu

de

Youngs Bay

Nehalem

Coquille River

Tillamook

Netarts

Salmon River

Alsea


-2 0 2 4-4

• All estuaries have been accreting at RSLR, except Salmon River and Alsea

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Longitude

La

titu

de

Youngs Bay

Nehalem

Coquille River

Tillamook

Netarts

Salmon River

Alsea


-2 0 2 4-4

• All estuaries have been accreting at RSLR, except Salmon River and Alsea

• Some estuaries are accreting faster than RSLR

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Carbon Burial Rates

Global C burial (IPCC 2014) = 91 ± 19 g Corg m-2 y-1

California C burial (Ouyand & Lee 2014) = 174 ± 45 g Corg m-2 y-1

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Longitude

La

titu

de

Youngs Bay

Nehalem

Coquille

Tillamook

Netarts

Salmon River

Alsea

50 100 1500

Carbon Accumulation Rate

(g Corg

m-2 y-1)

Global Average91 ± 19 g C

org m-2 y-1

(IPCC 2014)

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Youngs

Nehalem

Tillamook

Netarts

Salmon River

Alsea

Bandon

Sediment Accumulation Rate (mm y-1)

Ca

rbon

Accum

ula

tio

n R

ate

(g

Corg m

-2 y

-1)

0 51 2 3 4

160

0

80

40

120

R2 = 0.62

What’s controlling carbon burial?

0 0.5 1.0 1.5

z*

10

20

0

Me

an %

Co

rg

R2 = 0.59

Youngs

Nehalem

Tillamook

Netarts

Salmon River

Alsea

Bandon

Z* = Elevation – MTLMHHW – MTL

Relative Elevation

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Kirwan et al. 2016n = 179

US, Canada, UK, France, Spain

Crosby et al. 2016n = 142

US, Canada, Europe, Australia

What’s controlling sediment accumulation? RSLR?

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High Marsh Low Marsh

Relative Sea Level Rise (mm y-1)

Se

dim

ent A

ccu

mu

latio

n (

mm

y-1)

0

4

8

-2

2

6

10

1 2 3-1

Global Accretion Rates (Kirwan et al. 2016)Oregon Data

What’s controlling sediment accumulation? RSLR?

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Youngs

Nehalem

Tillamook

Netarts

Salmon River

Alsea

Bandon

Se

dim

en

t A

ccu

mu

latio

n R

ate

(m

m y

-1)

0

2

0.4 0.8 1.0 1.2

z*

0

4

6

Z* = Elevation – MTLMHHW - MTL

What’s controlling sediment accumulation? Elevation?

Relative Elevation

Coquille

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What’s controlling sediment accumulation? Sediment flux?

Sediment Supply

(Relative to Wetland Area; ton km-2 y-1)

Accre

tio

na

ry B

ala

nce

=

Se

dim

en

t A

ccu

mu

latio

n R

ate

- S

ea

Le

ve

l R

ise

-1

0

1

2

3

0 5 10 15 20-2

Youngs

Netarts

Alsea

Tillamook

Salmon

Coquille

Nehalem

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Conclusions

• Most Oregon salt marshes have been surviving RSLR over the last century• Except Salmon River & Alsea

• Both sediment accumulation and elevation are controlling carbon burial

• Sediment accumulation is controlled by both RSLR and sediment supply

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Conclusions

• Most Oregon salt marshes have been surviving RSLR over the last century• Except Salmon River & Alsea

• Both sediment accumulation and elevation are controlling carbon burial

• Sediment accumulation is controlled by both RSLR and sediment supply

What does this mean for Sand Lake?

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Sand Lake• We don’t know whether sediment accretion in

least disturbed marshes is keeping pace with sea level rise…

• We don’t know sediment accretion rates behind the dike…

• We don’t know how removing the dike would impact sediment accretion rates on the disturbed marshes or on the least disturbed marshes.

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Sand Lake

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Ongoing work

• Analyze more XRF data• Complete more ẟ13C & ẟ15N analysis • Georeference, digitize, and analyze historical aerial

photography

1930 Aerial Photo of Nehalem Bay; UO Aerial Photograph Collection

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[email protected]

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Excess 210Pb & 137Cs

238U

230Th

226Ra

210Pb Activity

De

pth

238U

230Th

226Ra

210Pb Activity

De

pth

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Eroded Sediment

226Ra 210PbDecay Within Sediment

214Pb

Supported

238U

230Th

226Ra

210Pb Activity

De

pth

Eroded Sediment


214Pb

Supported

238U

230Th

226Ra

210Pb Activity

De

pth

Excess 210Pb

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222Rn 210Pb

Fal

lout

Washed Out From Catchment

210Pb

Decay Within Atmosphere

Excess (aka Unsupported 210Pb)

Total 210Pb - Supported 210Pb = Excess 210Pb

Eroded Sediment


214Pb

Supported

238U

230Th

226Ra

210Pb Activity

De

pth

222Rn 210Pb

Fal

lout


210Pb




Eroded Sediment


214Pb

Supported

238U

230Th

226Ra

210Pb Activity

De

pth

222Rn 210Pb

Fal

lout


210Pb




Eroded Sediment


214Pb

Supported

238U

230Th

226Ra

210Pb Activity

De

pth

Excess 210Pb

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De

pth

137Cs Activity

137Cs

Eroded From Catchment

1963

1954

De

pth

137Cs Activity

137Cs

Eroded From Catchment

1963

1954

137Cs

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137Cs Post depositional remobilization

-50

-40

-30

-20

-10

0

0 100 200 300 400

Dep

th (

cm

)

137Cs (Bq kg-1)

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De

pth

(cm

)

-50

-40

-30

-20

-10

01 10 100 1000

CS02

r2 = 0.91

SAR = 2.2 mm yr-1

Excess 210Pb (Bq kg-1)

-50

-40

-30

-20

-10

01 10 100 1000

BM01

detection limit

non-steady state sediment

accumulation

steady state sediment accumulation

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High Marsh Low Marsh


Se

dim

ent A

ccu

mu

latio

n (

mm

y-1)

0

4

8

-2

2

6

10

1 2 3-1

12

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9 Relative Sea Level Rise (mm y-1)S

ed

ime

nt A

ccu

mu

latio

n (

mm

y-1)

0

4

8

-2

2

6

10

1 2 3-1

Bandon

Alsea

Youngs Bay

Nehalem

Tillamook

Salmon River

Netarts

High Marsh

Low Marsh

Mudflat


Se

dim

en

t A

ccu

mu

lation

(m

m y

-1)

0

4

8

-2

2

6

10

1 2 3-1

controls on sediment accretion and blue carbon burial in ... processes peck 2019.pdf · surface...

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