Watching Salt Marshes from Above: An Intern's Imagery Method for Park Marshes

Salt marshes filter nutrients, harbor a wealth of life and shield the coast from storms. But across the National Park Service's Northeast Coastal and Barrier Network (NCBN), climate change is transforming them fast, and habitat is being lost. The network has monitored marsh vegetation and tidal wetland elevation for decades. In fiscal year 2024, a summer intern gave it a new way to watch: from above.

Eddie Cascella on the water at Cape Cod National Seashore, setting out transects for a seagrass restoration project. Credit: Katie Button, National Park Service.

Two new procedures

Edward Cascella, a Scientists-in-the-Parks (SIP) intern, worked with the Southeast Coast Inventory and Monitoring Network and researchers at the U.S. Geological Survey's Woods Hole Coastal and Marine Science Center to draft two standard operating procedures (SOPs) for using imagery to monitor the vegetated and unvegetated parts of the network's coastal marshes.

How it works

The key measure is the unvegetated-to-vegetated ratio: how much bare area there is compared with plant-covered area in a given part of a marsh.

1. Define areas of interest in each park's marshes.
2. Gather the data: aerial imagery from the National Agriculture Imagery Program (NAIP), downloaded from USGS's EarthExplorer, plus topobathymetric digital elevation models from USGS's Coastal National Elevation Database (CoNED).
3. Classify the pixels: an unsupervised classification sorts every pixel into classes by its spectral characteristics, separating vegetated from unvegetated ground.
4. Compare: with the pixels sorted, the vegetated and unvegetated area of each marsh unit can be measured against each other.
5. Repeat over time: run every five or ten years, the procedure will reveal trends in marsh vegetation to guide each park's management.

What comes next

The work will extend to using imagery to track changes at the marsh edge. Cascella's internship has ended, but he is continuing work on the SOPs while completing a master's degree in environmental science and management at the University of Rhode Island. For the network, the project is part of a push to find new approaches to monitoring that use advanced technology and cooperation with other networks and agencies.

Sources

Based on "SIP, SOPs, and Salt Marshes: Edward Cascella's Work Using Remote Sensing to Analyze Salt Marsh Vegetation," National Park Service Northeast Coastal and Barrier Network, part of the series NCBN Highlights | FY24; a work of the United States government in the public domain.