Measuring the resilience of salt marshes used in Living ... C/Thurs… · • Wave energy reduction...
Transcript of Measuring the resilience of salt marshes used in Living ... C/Thurs… · • Wave energy reduction...
Measuring the resilience of salt marshes used in Living Shorelines and other nature-based efforts to protect
coastal infrastructureCarolyn Currin & Jenny DavisNOAA NCCOS, Beaufort, NC
NOAA Beaufort Lab Harkers Island, NC
• 50% of wave energy reduced within 5 m (15’) of marsh edge; >90% over 25 m of marsh (S. alterniflora)
• Belowground biomass binds sediments (and stores carbon)
• Wave energy reduction increases with plant biomass
• Linear Relationship between wave energy or wave power and marsh erosion over large scales, other factors important locally and regionally
• Wave energy reduction decreases as inundation depth exceeds canopy height
Salt marshes effectively attenuate wave energy and reduce erosion
Research reviewed in Currin et al. 2017 Response of salt marshes to wave energy provides guidance for successful living shoreline implementation.. In CRC Press The Science and Management of Nature-based Coastal Protection
Modified from: Cahoon, DR., J.W. Day, Jr., and D. J. Reed. 1999.
Oyster Reefs Can Keep Up with SLR in some settings
Worldwide 58% of salt marshes were adding elevation at rate > local SLR (Cahoon 2015)
Rodriguez et al (2014) showed NC oyster reefs can grow >1 cm yr-1
Cahoon, D. 2015 Estuaries & Coasts 38:1077-1084 ; Rodriguez, A. et al. 2014. Nature Climate Change DOI: 10.1038/NCLIMATE2216
Sediment supply is crucial parameter
Salt marshes and oyster reefs are resilient ….. and vulnerable… to sea level rise
Marsh transgression in response to SLRMove LANDWARD
• Landward transgression of salt marsh determined by topography and absence of development
• May preserve marsh habitat acreage even with accelerated SLR
Kirwan et al. 2016
New Marsh Drowned
Marsh
SLR
(a) Landward migration
Wave Energy, Cost, Permitting Time
Hard
enin
g
NWP 54-compliant LS
NOAA Defined LS
NNBF
Living Shorelines
Living Shoreline
• What are LS design impacts on resilience?• Does increasing resilience to SLR and erosion alter
ecosystem services provided by marsh habitats?
Measuring marsh elevation change in NC Living Shoreline Sites
Digital Elevation ModelsSurface Elevation Table
8 mGainLoss
10 m
0 NAVD88SET
•Surface elevation increase greater in Sill marshes than Natural at both upper and lower edges (p<0.025)
•Surface elevation change in Natural marshes significantly different at Upper marsh than Lower marsh edge
RTK GPS
4 Marsh-Sill and 4 Natural Fringing Marsh Sites
Date
1/04 1/05 1/06 1/07 1/08 1/09 1/10 1/11 1/12 1/13 1/14 1/15 -40
-20
0
20
40
60
80
-40
-20
0
20
40
60
80
100
PINCMMPKSHI
Sill Lower
Sill Upper
Natural Lower
Date1/04 1/05 1/06 1/07 1/08 1/09 1/10 1/11 1/12 1/13 1/14 1/15
-140-120-100-80-60-40-20
020
Natural Upper
Surfa
ce e
levat
ion ch
ange
(mm
)
-140-120-100-80-60-40-20
020
PINCMMPKSHI
SET Results Fringing Salt Marshes Carteret County, NCSurface elevation change mm / year
Surface elevation change in Living Shorelines is dynamic
Long-term SET data collection is difficult to maintain
aa
b
b
Sill sediment accretion results in increased Spartina biomass at lower edge, loss of Spartina habitat at upper edge
Marsh vegetation in Living Shoreline Sites
(m) landward of shoreline
S. a
ltern
iflor
aBi
omas
s (g/
m) 2011
20 m510
15-1 0
20 m510
15-1 0
PLOT -1 m PLOT 0 m PLOT 5 m
Loss of vegetation at lower edgeMaintained interior vegetation
Increase in vegetation at lower edgeMaintained interior vegetation
Permanent Vegetation Plots 2006 -2016
Mean S. alterniflora Stem Density
Live
stem
s m-2
Marsh transgression in response to SLR
SLOPE
2 4 6 8 10 12 14-505
1015
Sea Level Rise Rate (mm yr-1)
Mar
sh e
xpan
sion
rate
(m y
r-1)
0.00050.0010.0021.0
Scenario with human barriers to
migration
Slope and SLR rate determine marsh area expansion
Kirwan et al. 2016 GRL
Habitat Changeleads toChanges in Ecosystem Services
Stone Sills
• Reduce/eliminate shallow subtidal
• Reflect wave energy• Non-native hard substrate;
Invasives
• Fish habitat• Oyster settlement• Increase sediment trapping
Low Marsh
• Less SLR resiliency• Lower plant diversity
• Absorb wave energy• Faunal utilization• Denitrification• Sediment trapping• C sequestration
High Marsh
• Less faunal utilization• Reduced denitrification• Reduced Sediment trapping• Lower C sequestration
• Greater SLR resiliency• Greater plant biodiversity
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+++
New Marsh
Accumulated Sediment
SLR
New Marsh
Drowned Marsh
SLR
(a) Landward migration
Drowned Marsh
SLR
(b) Coastal squeeze
New Marsh
Accumulated Sediment
SLR
(c) Delayed squeeze
A longer view…
Using Living Shorelines to protect property and Infrastructure
Thin Layer Application of Dredged Sediment to Vulnerable Salt MarshesTwo pilot projects on Marine Corps Base Camp Lejeune, North Caroline
Raising elevation of low-lying salt marshDredged sediment added to ponded areas in fragmented marsh, Spartina
planted
Spartina alterniflora biomass : elevation distribution
Resilience to Sea Level Rise
Fishery Habitat, Denitrification,
Biom
ass
Elevation
Thin LayerAddition
Thin Layer application and Ecosystem Services
Will thin layer addition impact C burial?
Greater input?Greater turnover?
Can we quantifyhabitat trade offs?
Long-term Monitoring is needed to understand ecosystem impacts of Living Shorelines and TLA• Choose parameters wisely (easy, cheap, meaningful)• Use control and reference sites• Form partnerships• Use citizen scientists
Landward migration is crucial for maintaining future salt marsh habitat. • Living Shoreline placement and design need to accommodate this function• Avoid ‘Delayed Squeeze’
Adding marsh resiliency by increasing surface elevation alters habitats and ecosystem services• Be clear about temporal and spatial scales when measuring ecosystem service changes
SUMMARY