Marsh Equilibrium Model – Version 3.4
Abbreviation: MEM
DCERP1 Ecosystem Module: Coastal Wetlands
Lead Researcher: Dr. Jim Morris, University of
South Carolina
Ecosystem Processes: Sedimentation
Objective: Forecast changes in marsh elevation
Inputs: Plant biomass as a function of elevation;
root:shoot quotient; turnover rate of
belowground biomass; fraction of belowground
biomass that is refractory (i.e., insoluble); relative
marsh elevation; tidal range; rate of sea-level rise;
suspended sediment concentration; settling
trapping coefficients.
Outputs: Forecast of marsh productivity and
relative elevation
Figure 1. Factorial Fertilization Experiments with
nitrogen and phosphorus showing enhanced growth of
marsh plants with fertilization.
Background: Coastal wetlands adapt to changes in sea
level and land use by accreting or losing sediment (Morris
Linkage to other models: None
et al., 2002; Kearney et al., 2002) and transgressing across
Benefit to the Base: Tool for forecasting the
the land margin (Gardner and Porter, 2001). Marshes
future lifespan of coastal wetlands in the face of
equilibrate at a relative elevation that depends on the
sea level rise.
rate of sea-level rise and local sediment supply. The
End Product: Report; web-based model that
Marsh Equilibrium Model (MEM) version 3.4 was
produces graphs and tabular results.
developed to forecast changes in the relative elevation of
the marsh surface and marsh response to sea-level rise
(Morris et al., 2002). The model must be calibrated by measuring the response of vegetation to relative
elevation, the change in elevation of the marsh surface as a consequence of changes in the biomass density of
the vegetation, and sea level. During DCERP1, the model was revised to incorporate tidal ranges, the
concentration of suspended sediment, and explicit addition of below ground organic matter.
Type of Model: Numerical/analytical hybrid
Marsh Elevation 100-Year Forecasts: MEM simulations of marsh elevation and biomass were made for different
sea level scenarios (Figure 2). Simulations of control or ambient marsh sites showed that the vegetation survived
100 years only when sea level was assumed to rise either 24 cm or 60 cm by 2100. The 24-cm sea-level rise
scenario is essentially the current rate of relative sea level rise held constant. The marsh was predicted to gain
approximately 55 cm in elevation from a starting elevation of 0 cm, which indicates that at that rate of sea level
rise, the starting elevation was less than the equilibrium elevation. By the end of the 100-year simulation, this
marsh had reached its equilibrium (approximately 31 cm). In simulations, marsh sites fertilized with nitrogen
and phosphorus fared better than control sites (Figure 1). In the case of the constant, current rate of sea level
rise, marsh elevation reached approximately 65 cm by 2100 and its standing biomass approached the maximum.
The 60-cm sea level simulation resulted in a standing biomass and elevation by the 2100 that also were nearly in
equilibrium. Fertilized sites were also predicted to survive a 100-cm rise in sea level, although biomass was
The Defense Coastal/Estuarine Research Program (DCERP), a two-phase ten-year ecological research program, was funded by the
Strategic Environmental Research and Development Program (SERDP) to conduct basic and applied research on the coastal ecosystems at
Marine Corps Base Camp Lejeune, NC. DCERP focuses on an integrative and synthesized understanding of ecosystem function, ecosystem
response to stressors, and the potential impacts of stressors to the military mission. This tool was developed as part of the first 5-year
cycle (DCERP1; 2007-2012). For more information: https://dcerp.rti.org/
beginning to decline rapidly by 2100 (Figure 2). The mean percentage error of the MEM predicted rates of
change of marsh elevation, inclusive of all sites and treatments was 15%. Moreover, the predicted trends among
sites and treatments were consistent with observations.
120
MEM Forecasts of Marsh Elevation
at Different Rates of Sea-Level Rise
100
80
Marsh Elevation (cm)
Marsh Elevation (cm)
100
Controls
60
24 cm
60 cm
100 cm
150 cm
200 cm
40
20
Fertilized
80
24 cm
60 cm
100 cm
150 cm
200 cm
60
40
20
0
0
0
20
40
60
80
0
100
20
MEM Forecasts of Marsh Biomass
at Different Rates of Sea-Level Rise
800
2
600
Controls
400
24 cm
60 cm
100 cm
150 cm
200 cm
200
60
80
100
80
100
2500
Standing Biomass (g/m )
2
Standing Biomass (g/m )
1000
40
Years From Present
Years From Present
2000
1500
Fertilized
1000
24 cm
60 cm
100 cm
150 cm
200 cm
500
0
0
0
20
40
60
80
100
0
20
Years From Present
40
60
Years From Present
Figure 2. MEM forecasts of marsh elevation and standing biomass
for different sea level rise scenarios.
Forecasts were made for ambient (controls) and fertilized marshes. The sea level rise scenarios ranged from a constant rate
equivalent to 24 cm/y to a rapidly accelerating rate that raised mean sea level to 200 cm by the end of a century.
In summary, the MEM predicts a collapse of these marsh sites within 95 years depending upon the rate of sea
level rise and other factors such as sediment supply, tidal amplitude, and biomass.
For More Information: http://129.252.139.114/model/marsh/mem.asp
References:
Gardner, L.R., and D.E. Porter. 2001. Stratigraphy and geologic history of a southeastern salt marsh basin, North Inlet, South Carolina,
USA. Wetlands Ecology and Management. 9:371-382.
Kearney, M.S., A.S. Rogers, J.R.G. Townshend, E. Rizzo, D. Stutzer, J.C. Stevenson, and K. Sundberg. 2002. Landsat imagery shows decline
of coastal marshes in Chesapeake and Delaware Bays. EOS 83:17–178.
Morris, J.T., P.V. Sundareshwar, C.T. Nietch, B. Kjerfve, and D.R. Cahoon. 2002. Responses of coastal wetlands to rising sea level. Ecology
83(10):2869–2877.
August 2013