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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
1930 Aerial Photo of Nehalem Bay; UO Areal Photograph Collection
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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
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
44.0
45.0
46.0
-124.2 -123.4
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
high sediment supply
no sea level rise
low sediment supply
high sea level rise
expansion of intertidal marsh
End member of salt marsh accretion
Mississippi deltaVenice lagoon
19th century New England
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drowning of marsh
surface
high sediment supply
no sea level rise
low sediment supply
high sea level rise
expansion of intertidal marsh
End member of salt marsh accretion
Oregon? Mississippi deltaVenice lagoon
19th century New England
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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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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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Methods: Sediment Core Collection
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Methods: Sediment Core Collection
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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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 Tsunami deposit
Vegetation at surface
Sediment layers
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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
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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Methods: Sediment Core Collection
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
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ge Techn
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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
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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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
(Cox Analytical Systems)
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Have salt marshes been surviving RSLR?
43.0
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46.0
-124.2 -123.4
Longitude
La
titu
de
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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Have salt marshes been surviving RSLR?
43.0
44.0
45.0
46.0
-124.2 -123.4
Longitude
La
titu
de
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
• All estuaries have been accreting at RSLR, except Salmon River and Alsea
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Have salt marshes been surviving RSLR?
43.0
44.0
45.0
46.0
-124.2 -123.4
Longitude
La
titu
de
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
• 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
43.0
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46.0
-124.2 -123.4
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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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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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
226Ra 210PbDecay Within 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
226Ra 210PbDecay Within Sediment
214Pb
Supported
238U
230Th
226Ra
210Pb Activity
De
pth
222Rn 210Pb
Fal
lout
Washed Out From Catchment
210Pb
Decay Within Atmosphere
Excess (aka Unsupported 210Pb)
Total 210Pb - Supported 210Pb = Excess 210Pb
Eroded Sediment
226Ra 210PbDecay Within Sediment
214Pb
Supported
238U
230Th
226Ra
210Pb Activity
De
pth
222Rn 210Pb
Fal
lout
Washed Out From Catchment
210Pb
Decay Within Atmosphere
Excess (aka Unsupported 210Pb)
Total 210Pb - Supported 210Pb = Excess 210Pb
Eroded Sediment
226Ra 210PbDecay Within 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
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
12
Slide fro
m O
SU research
er Erin Peck’s P
resentatio
n to
the Sitka Sed
ge Techn
ical Team 1
0/2
4/1
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
Relative Sea Level Rise (mm y-1)
Se
dim
en
t A
ccu
mu
lation
(m
m y
-1)
0
4
8
-2
2
6
10
1 2 3-1