WETLAND ELEVATIONS AT SUB-CENTIMETER PRECISION: A COMPARISON OF A NEW DIGITAL BARCODE LEVELING TECHNIQUE WITH THE SURFACE ELEVATION TABLE

To estimate wetland sustainability and support sound management strategies in the face of changing water levels and wetland loss, precise measurements of sediment elevations are required to establish long-term rates of elevation change. The Surface Elevation Table (SET) is a portable leveling device that provides a relatively nondestructive method for measuring relative elevation change of wetland sediments. For several decades, the SET has been a critical tool to understand processes controlling marsh vertical dynamics. Recently, however, the SET is used for monitoring long-term elevation change across wetland landscapes spanning thousands of hectares. Due to instrumental constraints as well as the labor intensive nature of the SET method, estimates of marsh accretion and elevation change are often derived from data collected from very few, often spatially clustered, small sample areas. The generalizations derived from these plots may not be representative of the greater marsh.

This study investigates an alternative method for obtaining repeated, high precision measurements of wetland elevation over a hectare-sized area. We examine and compare the precision and accuracy of the SET with a new technique using an inexpensive digital barcode level. We also investigate how precision varies across different wetland types in the greater Chesapeake Bay area: a tidal freshwater marsh with highly organic soils (Jug Bay Wetlands Sanctuary), brackish marsh with highly organic soils (Smithsonian Environmental Research Center), a brackish marsh with mineral soils (Chesapeake Bay Environmental Center), and a salt marsh with mineral soils (Assateague Island National Seashore). Results indicate that in most soils, leveling is very comparable to the SET in both precision and accuracy, suggesting that it has the potential to vastly improve estimates of elevation change over larger spatial scales than are currently available with the SET. Further investigation includes laboratory analyses of soil characteristics and a comparison of inter-operator error between methodologies.