How is Delaware tackling Sudden Wetland Dieback?

Measuring tape being used to establish a sightline during a sudden wetland dieback study

DNREC’s Wetland Monitoring and Assessment Program and the Center for the Inland Bays are leading The Delaware Sudden Wetland Dieback Task Group, which is made up of government and private organizations to determine the distribution, management implications, and possible causes of SWD.

An aerial survey conducted in September, 2006 found that sudden wetland dieback (SWD) was present in all three of the Inland Bays. The survey demonstrated that dieback varies greatly in intensity, and may be present in a majority of the marshes at low levels. It was severe in a few locations. Because this was an aerial survey taking place in the autumn, end-of-season natural changes may have partially obscured some instances of SWD. A survey taken in June, 2007 showed 47 percent of ‘06 dieback sites still exhibited effects. In 2008 aerial surveys were conducted for all estuarine marshes in Delaware and determined that no new occurrences of SWD had occurred.

The task group secured funding to intensively study a marsh known to have suffered from SWD in 2006. The sample marsh has been outfitted with three Surface Elevation Tables (SETs) which can determine the accretion and subsidence of the marsh. Water level meters have been  installed at shallow and deep placements within the marsh to determine the amount, frequency, duration, and entry path of water to the marsh. Meters will soon be installed to capture data on chemical transformations associated with extended drought conditions. Additional sites will be outfitted with similar equipment as funding becomes available.

Installation of Surface Elevation Table

Data collected at sites in Delaware will be compared to other wetlands in Delaware as well as wetlands worldwide. Elevation data will be used to determine if current accretion rates will allow local marshes to sustain themselves due to increasing sea level rise rates. This data will also allow the workgroup to monitor the site’s recovery and document associated conditions. Additionally, if another SWD event occurs we will better understand the site specific effects of SWD and gain insight into the causes.

Within the Delaware Estuary, tidal wetland condition and change will also be assessed from 1993 to 2006. The assessment will be conducted using a method developed by Kearney et al. (2002) which documents the condition of tidal marshes based on satellite imagery. Analysis of the changes in marsh condition will determine the trends in wetland condition over the past decade and the rates of marsh degradation and loss. This information will be used to focus future field monitoring and restoration and protection activities of these valuable resources.

 Additional Resources

To learn more about the magnitude of the challenges SWD poses, particularly in areas where our saltmarshes are close to sea level, click on the links below:

White Paper on the Status of Sudden Wetland Dieback in Saltmarshes of the Delaware Inland Bays

Uncertain Threats to Saltmarshes of the Delaware Inland Bays

Salt Marsh Dieback - A Literature Review

Inland Bays Marsh Dieback - Weather and Climate Data

Center for the Inland Bays - Salt Marsh Dieback

Coastal Wetland Dieback: the Phenomenon of Marsh Browning & Marsh Dieback, by Leah Stetson, Association of State Wetland Managers (ASWM)

Coastal Marsh Dieback - U.S. Geological Survey