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How Surface Elevation Tables Help Track Salt Marsh Health at Rachel Carson National Wildlife Refuge, Maine
Northeast Region, August 2, 2013
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A surface elevation table deployed in the salt marsh and ready for reading.
A surface elevation table deployed in the salt marsh and ready for reading. - Photo Credit: Rachel Carson NWR
This graph shows the results of SET readings at the same location for over 10 years. After a brief subsidence event in 2009, the marsh surface elevation continued to increase.
This graph shows the results of SET readings at the same location for over 10 years. After a brief subsidence event in 2009, the marsh surface elevation continued to increase. - Photo Credit: Toni Mikula

At Rachel Carson NWR we are working to find out how our salt marshes are changing over time, by monitoring changes in elevation. Rising elevation indicates that sediment is being deposited, a healthy root mass is growing, and marsh peat is getting thicker (accreting). Decreasing elevation means that the marsh surface is sinking (subsiding). To get accurate measurements we use an instrument called a Surface Elevation Table or SET. The underground portion of a SET consists of a stainless steel rod driven 30-80 feet deep into the marsh peat until it meets a point of resistance. A receiver head is mounted on this rod and the unit is cemented in place to prevent any kind of movement. When it's time to take a measurement, a SET "reader arm" is brought into the marsh and mounted on the receiver head. We compare each reading to the previous one so we can document long-term trends.

 

If a marsh is healthy, we expect about a 4mm gain in marsh elevation from year to year. If we find that a marsh is subsiding, this could be due to man-made or natural effects that impound water, reduce sediment supplies, or add excess nutrients. In this time of climate change, we want to find out if salt marsh growth can keep pace with accelerated sea level rise.

We have been taking SET measurements at just two Rachel Carson marshes for a decade. During 2012-2013, the Land Management Research and Demonstration program at Rachel Carson NWR expanded our coverage to include 7 more marsh units. To do this we installed 17 SETs and reclaimed 14 "legacy" SETs used by previous researchers. This work has become an integral part of the United States Fish and Wildlife Services northeast region-wide salt marsh integrity assessment. The data we gather from these new and "legacy" SETs will guide future management of salt marshes, aid in conservation efforts, and provide important information on how marshes react to rising seas.

For more information, please contact:
Susan C. Adamowicz, Ph.D.
LMRD Biologist
Rachel Carson NWR
321 Port Rd.
Wells, ME 04090
Susan_adamowicz@fws.gov
207-646-9226 x31


Land Management Research and Demonstration website
http://www.fws.gov/northeast/rachelcarson/lmrd.html
Contact Info: Stephanie Petrus, 207-646-9226, stephanie_petrus@fws.gov



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