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Kouchibouguac National Park, Canada
SET Concepts and Theory:
Surface Elevation Table:

The design of the original SET developed by Boumans and Day (1993) is derived from the Sedi-Eros Table created by Schoot and de Jong (1982). The SET can be used to determine both the influence of a single meteorological event on sediment surface elevation and a long-term trend (i.e., decades) in elevation change.

When attached to a bench mark pipe or rod, the SET provides a constant reference plane in space from which the distance to the sediment surface can be measured by means of pins lowered to the sediment surface. Repeated measurements of elevation can be made with high precision because the orientation of the table in space remains fixed for each sampling.

Elevation change measured by the SET is influenced by both surface and subsurface processes occurring within the soil profile.

SURFACE PROCESSES:
1) Sediment deposition
2) Sediment erosion
SUBSURFACE PROCESSES:
3) Root Growth
4) Decomposition
5) Porewater Flux
6) Compaction

NOTE: The SET only provides data on processes that are occurring between the bottom of the benchmark and the sediment surface. The SET cannot provide information on processes occurring below the bottom of the benchmark pipe.

Marker Horizons:

Marker horizons are commonly used in conjunction with the SET. Marker horizons measure vertical accretion which predominantly incorporates Surface Processes.

SURFACE PROCESSES:
1) Sediment deposition
2) Sediment erosion

Numerous materials such as sand, feldspar, brick dust and glitter, can be used as marker horizons. We normally use white feldspar clay which is easily distinguishable from surrounding sediments.

Marker Horizon
Marker Horizon

Shallow Subsidence:

When used simultaneously, the SET and Marker Horizon techniques can provide information on below ground processes that influence elevation change. Differences between the rates of Vertical Accretion and Elevation Change can be attributed to processes occurring below the feldspar layer and above the bottom of the SET pipe. This area is called the Zone of Shallow Subsidence.

For example, say the rate of Vertical Accretion measured from your marker horizon is calculated to be 3 mm per year. While the rate of Elevation Change measured from the SET is 2 mm per year. Based on these numbers you would say that the rate of Shallow Subsidence is 1 mm per year (3 mm/yr - 2 mm/yr = 1 mm/yr). In otherwords, the difference between the two measurements is due to processes occurring in the Zone of Shallow Subsidence.

Pond and Marsh SET
Vertical Accretion

ROD SET

Accretion - Elevation = Shallow Subsidence
Vertical Accretion: 3 mm/yr
Elevation Change: 2 mm/yr
Shallow Susidence: 1 mm/yr
 
 
U.S. Department of the Interior, U.S. Geological Survey, Patuxent Wildlife Research Center
URL: http://www.pwrc.usgs.gov/ | Last Updated: 18 February 2010
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