Developing standardized geospatial metrics for salt marsh management and restoration

South Atlantic Third Thursday Web Forum

Developing standardized geospatial metrics for salt marsh management and restoration

Neil K. Ganju, U.S. Geological Survey

Effective management and restoration of salt marshes and other vegetated intertidal habitats requires objective and spatially integrated metrics of geomorphic status and vulnerability. The unvegetated-vegetated marsh ratio (UVVR), a recently developed metric, is essential for establishing present-day vegetative cover, identifying stability thresholds, and quantifying vulnerability to open-water conversion over a range of spatial scales. We developed a Landsat-based approach to quantify the vegetated fraction and UVVR for coastal wetlands of the contiguous United States. We will demonstrate multiple applications of the data across varying spatial scales: first, we aggregate the UVVR across individual states and estuaries to quantify total vegetated wetland area; secondly, we present cases where this dataset can be used to track wetland change (i.e., expansion due to restoration and loss due to stressors). Lastly, we propose a classification methodology that delineates areas vulnerable to open-water expansion based on the five-year mean and standard deviation of the UVVR.

The UVVR is an essential lateral stability metric, and is enhanced by integration with vertical metrics such as elevation and elevation change. We compare the UVVR with vertical elevation trends from surface elevation tables across coastal refuges in the southeast US: refuges with a low UVVR, indicating intact marsh plains and lateral resilience, are gaining elevation at a rate exceeding sea-level rise, while areas with a high UVVR (degraded wetland plains) are not keeping up vertically with sea-level rise. We also present a lifespan methodology which integrates the UVVR, elevation, and local sea-level rise rate to provide actionable information for coastal managers seeking restoration targets and approaches. Ultimately, these standardized metrics are a step forward for coastal wetland management and provide an objective basis for decision making with regards to restoration and management.

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