A geospatially resolved wetland vulnerability index: Synthesis of physical drivers

Assessing wetland vulnerability to chronic and episodic physical drivers is fundamental
for establishing restoration priorities. We synthesized multiple data sets from E.B
Forsythe National Wildlife Refuge, New Jersey, to establish a wetland vulnerability
metric that integrates a range of physical processes, regulatory information and
physical/biophysical features. The geospatial data are based on aerial imagery, remote
sensing, regulatory information, and hydrodynamic modeling, and include elevation,
tidal range, unvegetated to vegetated marsh ratio (UVVR), shoreline erosion, potential
exposure to contaminants, residence time, marsh condition change, change in salinity
and salinity exposure, and sediment concentration. First, we delineated the wetland
complex into individual marsh units based on surface contours and then defined a
wetland vulnerability index that combined contributions from all parameters. We
applied principal component and cluster analyses to explore the interrelations between
the data layers and separate regions that exhibited common characteristics. Our
analysis shows that the spatial variation of vulnerability in this domain cannot be
explained satisfactorily by a smaller subset of the variables. The most influential factor
on the vulnerability index was the combined effect of elevation, tide range, residence
time, and UVVR. Tide range and residence time had the highest correlation, and
similar bay-wide spatial variation. Some variables (e.g., shoreline erosion) had no
significant correlation with the rest of the variables. The aggregated index based on the
complete dataset allows us to assess the overall state of a given marsh unit and quickly
locate the most vulnerable units in a larger marsh complex. The application of
geospatially complete datasets and consideration of chronic and episodic physical drivers
represents an advance over traditional point-based methods for wetland assessment.