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Conceptual Diagrams
Visualize coastal wetland assessment methods, processes, and concepts used and studied as a part of the Mid Atlantic Coastal Wetlands Assessment Program.
| Surface Elevation Tables & Surface Elevation Tables (SET) are installed in marshes to study precise changes in surface elevation. Each SSIM station has three deep rod SETs and nine feldspar marker horizons (MH).1-5 An in depth review of methodologies and theories of SET-MHs can be found on the USGS Patuxent Wildlife Research Center’s website. Surface Elevation Tables track precise cumulative elevation changes. Marker horizons are used in conjunction to monitor short term accretion on the marsh platform. MH measure surface elevation changes while SETs capture shallow subsidence. Shallow subsidence (SS) is the reduction in elevation, or sinking, of the wetland surface between the bottom of the SET benchmark and the bottom of the marker horizon. Subsidence dynamics are controlled by subsurface processes and hydrology. SS is equivalent to the difference between cumulative elevation change and the rate of accretion.5 A marsh platform is considered to be “keeping pace,” or vertically stable, when the cumulative elevation change is greater than or equal to the local rate of sea level rise. Understanding minute changes in wetland accretion and erosion over time is valuable to scientists studying marsh response sediment delivery and ultimately to sea level rise. The SET is a portable and nondestructive, making it ideal for scientists to use in marshes. Scientists will measures SETs multiple times a year. |
Graphic created by LeeAnn Haaf | Marsh Elevation The resilience of coastal tidal marshes to sea level rise is governed by dynamic processes that consist of several interconnected positive and negative feedbacks.6-17 In the simplest sense, marsh elevation is controlled by sediment subsidies18 and plant productivity. These processes work together and are co-dependent, maintaining the processes that allow the marsh to avoid drowning.6-17 Sedimentation, in addition to plant productivity, comprises net surface accretion. This is a critical component of each marsh’s natural ability to keep pace with rising sea levels.12 Changes to the rate of surface accretion might influence the degree of impact that subsurface processes have on elevation maintenance. If shallow subsidence out-paces surface accretion, elevation is lost regardless of sea level. This process may take years to have discernible signs of degradation, but is expedited as sea level rises.19 The amount of sediment needed to sustain natural elevation maintenance and keep plants in their optimal growth ranges is site specific and complex.7, 11, 12, 13, 14 Any alteration to the marsh’s sediment subsidy and/or impacts to plant productivity would have consequences for resilience. Reduced resilience or poor condition (degradation) are not exclusive of the amount of sediment a marsh receives as there are many other factors that contribute to plant productivity. |
 Graphic created by LeeAnn Haaf | Marsh Transgression Given their position at the nexus of land and sea, coastal wetlands fall vulnerable to human disturbance from the landward edge but are also at the mercy of sea level rise and destructive oceanic storms. Most coastal wetlands in the Mid Atlantic have been anthropogenically disturbed to some degree, thereby reducing overall condition and enhancing vulnerability to drowning as sea levels rise. Sustaining coastal wetlands through these disturbances and vulnerabilities has been a key focus of coastal management in recent decades. Although coastal wetland responses to sea level rise are well studied, landward processes, specifically the inland movement of coastal wetland grasses into forests, are less understood. Landward migration of coastal wetlands, or transgression, will likely be one of the major strategies to sustaining coastal wetland acreage into the future. Spatial and temporal variability exists in the degree of opportunity to manage areas for transgression as the potential for coastal wetlands to migrate can be dictated by a suite of factors 20. Better understandings of landward transgression processes and management tactics are needed to ensure that guidance tools for practitioners are robust for all predicted situations which may evolve with rising sea levels. |
 Wetland Productivity Graphic created by the Coastwide Reference Monitoring System in Louisiana. | Wetland Productivity This Wetland Productivity graphic was created by the Coastwide Reference Monitoring System21 in Louisiana. It represents information from the Louisiana coast, but it summarizes the various relationships and processes within coastal wetlands very well. We encourage you to follow this link to discover the interactive component of this graphic |
