MARSH VULNERABILITY INDEX: IMPACTS OF RISING SEA LEVEL ON DELAWARE'S MARSHES

An index is needed to allow assessment of the long-term viability of Delaware’s marshes under differing sea level rise scenarios and to target areas for conservation, restoration and monitoring. Salt marsh sediment can be composed of up to or greater than fifty percent organic matter, and, therefore, the productivity of flora in a salt marsh plays a key role when determining the marsh’s response to rising sea levels (“Storms as agents of wetland elevation”. Cahoon, 2003.). The Marsh Vulnerability Index (MVI) is based upon the positive correlation between mean tidal range, productivity and elevational growth range of Spartina alterniflora.

The MVI will classify marshes as healthy, degrading or severely degrading. Degraded and severely threatened marshes are more prone to catastrophic losses due to sea-level rise due to a rate of sea level rise that is greater than sediment accretion. These classifications will be utilized to select areas to conduct detailed sediment accretion rate and other sediment monitoring. Understanding the current and historic sedimentation accretion rates of these marshes can help to better predict the longevity and the sediment deficits of these areas and possible management practices that might be implemented to prevent marsh elevation losses.

The MVI will be essential for evaluating wetland vulnerability on a watershed or statewide basis, while enabling the strategic placement of monitoring resources to enhance efforts to understand the future evolution potential of Delaware’s tidal wetlands and its response to rising sea levels. Marsh Vulnerability Index classification optimizes the monitoring efforts and resources to the highest levels possible, so the broadest extent of Delaware’s tidal wetlands may be evaluated and managed.