Hindcasting and Forecasting
GOM Coastal Wetlands
James Morris
U South Carolina, Baruch Institute
How does the marsh maintain equilibrium with sea level?
Distribution of S. alteniflora across the
intertidal zone at North Inlet.
Standing
biomass of
Spartina
alterniflora
Standing Biomass (g/m2)
1400
Bioassay Data
Polynomial Fit
1200
When elevation is super-optimal.
1000
800
600
400
200
MSL
0
-40
-20
0
20
40
60
80
100 120
Elevation of Marsh Surface Relative to MSL (cm)
Marsh Elevation (cm)
Rising sea level stimulates growth and sedimentation
Increased sedimentation raises the elevation of the marsh
Juncus roemerianus
Root Weight (g/m2)
Leaf Weight (g/m2)
Bioassays (marsh organs) are
used to define growth range
and response to relative
elevation.
Elevation (cm NAVD88)
Apalachicola Hindcast
Apalachicola + 100 cm/century
Apalachicola Forecast with Enhanced Biologicals and 2x TSS
Sensitivity Analysis of Apalachicola MEM Model
Sea Level + 100 cm/century
Hindcast Sea Level
+30 cm +50 cm/cent
& peak & refrac
& BG
per
Default
Default biomass + fraction turnover
century Parameters Parameters 20%
+20%
+20%
At Year 50
Biomass (g/m2)
Rel Elevation (cm)
At Year 100
Biomass
Rel Elevation
& Drag
Coef.
+20%
All
All Biology
& TSS Biological & 2 x TSS
x2
Combined Combined
1365
28
1294
23
940
13
1274
16
1033
15
1013
15
977
14
1101
17
1533
23
1536
23
1232
25
621
12
0
-26
0
-24
0
-25
0
-25
0
-26
0
-12
0
-19
0
2
Hypsometric Projections Based on Current LiDAR DEMS and Tides
Intertidal Wetland Areas (km2) Current and Future
Current
Following a 1 m Rise in Sea Level
No Survival of 100% Survival of
Existing Marsh Existing Marsh
117
46
473
116
173
1126
Mississippi
FL Panhandle
MHHW
MHHW
MSL
MSL + 1m
MHHW
MSL + 1m + survival
Conclusions
The forecast for a 50 cm rise in sea level by year 2100 is for a rapid decline in
the relative elevation of the marsh in the latter half of the century,
culminating in marsh collapse and a relative elevation below mean sea level.
A rise in sea level to 100 cm by year 2100 results in marsh collapse by about
2060. Carbon sequestration follows the same path.
The survival of extant wetlands could be improved by breeding and
introducing plant varieties that possess a higher lignin content, greater
belowground biomass productivity, and higher drag coefficients.
Aboveground biomass production is especially important for trapping
sediment, belowground biomass for accretion of organic carbon. Both are
important to marshes for maintaining equilibrium with sea level.
Rising sea level could increase intertidal wetland area, depending on barriers
to transgression (migration).