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Woods Hole Coastal and Marine Science Center

Woods Hole Coastal and Marine Science Center > Sea-Level Rise Hazards and Decision Support > Biological Systems > Coastal Wetlands

Coastal Wetlands

Coastal wetlands are among the most productive ecosystems in the world. These wetlands at the land-ocean margin provide many direct benefits to humans, including habitat for commercially important fisheries and wildlife; storm protection; improved water quality through sediment, nutrient, and pollution removal; recreation; and aesthetic values. These valuable ecosystems will be highly vulnerable to future sea level rise.

Wetlands are complex systems that respond to a variety of processes (figure CW1).  A key concern is whether wetlands are able to build vertically to keep pace with increases in sea level.  There are three processes by which marshes build vertically: the accumulation of inorganic sediment (sand and mud) on the marsh surface, accumulation of organic debris (plant material) on the marsh surface, and the subsurface growth and accumulation of marsh plant roots. All processes are controlled by marsh hydrology and both contribute to changes in soil volume, which directly influences marsh surface elevation. In marshes where soil volume decreases due to either insufficient inorganic sediment input or decreases in plant growth, the marshes are less capable of maintaining their elevation as the average water level (mean sea level) increases and consequently they become prone to deterioration.

The loss of wetland habitats and the important ecosystem functions they provide is a critical concern.  Wetlands provide critical habitat for wildlife; trap sediments, nutrients, and pollutants; cycle nutrients and minerals; buffer storm impacts on coastal environments, and exchange materials with adjacent ecosystems.  As wetland habitat is lost, there will be significant impacts to other ecosystems.  To complicate the issue, large portions of the coastal environment have been developed and management practices may affect ecosystem responses to sea level rise as well.  This will exacerbate the vulnerability and impacts to plant and animal species in coastal regions.  Of particular concern are the impacts to environments such as wetlands that are critical to support migratory bird populations and fisheries.

Understanding whether or not marsh systems can tolerate higher sea level requires knowledge of whether the present–day marsh surface is able to maintain elevation with respect to SLR.  To monitor marsh surface elevation trends, USGS scientists have developed tools to measure changes in surface elevation in marshes (Fig CW2, http://www.pwrc.usgs.gov/set/).  This information when collected over time provides an indication of whether the marsh is able to build vertically at a rate sufficient to pace increases in sea level.

As part of our research we are investigating several aspects of coastal wetland systems.  In particular we are assessing the ability of coastal wetlands to keep pace with future sea level rise by monitoring wetland elevation trends and accretion dynamics and coupling these observations with data describing the tidal and sediment concentration characteristics.  We are also using numerical models to evaluate wetland survival (FigCW3).  Both the field observations and information derived from modeling experiments will be integrated into a Bayesian Network which will allow us to evaluate the probability of coastal wetland survival for different sea level rise scenarios.

 

Diagram showing factors affecting wetland development

Figure CW1.  Climate and environmental drivers influencing vertical and horizontal wetland development.  From Cahoon and others (2009).

Photo of scientists using a Surface Elevation Table

Figure CW2.  USGS researchers using a Surface Elevation Table (SET) to monitor changes in the elevation of the marsh surface at Assateague Island (Patrick Brennand, USGS).

Photos showing sea level change in wetlands

Figure CW3.  Figures illustrating the results of marsh survival simulations conducted using a wetlands elevation change model by Kirwan and Guntenspergen (2010).  Each panel illustrates the marsh morphology at sea level rise rates of 1, 3, and 10 mm/yr for tidal ranges of 0.4 (row a), 1 (row b), and 4 m (row c). For example the first row (a) illustrates marsh morphology for the three different sea level rise rates where the tidal range is 0.4 m. Bluer regions indicate low elevations nearer to or below mean low water and progressively greener areas indicate higher bed elevations nearer to mean high water. Figure source: figure 4, Kirwan, M.L. and Guntenspergen, G.R., 2010, Influence of tidal range on the stability of coastal marshland, Journal of Geophysical Research Earth Surface, v. 115, doi:10.1092/2009JF001400.

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Page Last Modified:Tuesday, 07-Jul-2015 13:50:03 EDT (GW)