Tracking Estuary Change

Dec 4, 2023

Understanding where our estuaries are, were, and could be will help us protect them for the future. Learn more about this project.

How big is your local estuary? Bigger than you think, according to a research team led by the National Estuarine Research Reserve System. And with strategic investment in conservation and restoration, it could be bigger still. 

Using a novel combination of historical and elevation-based mapping methods and data, the team explored changes in the extent of 30 U.S. estuaries and their habitats. They found that the nation’s estuaries are not only larger than previously thought, there are clear regional differences in how they’ve changed over time.

“To our surprise, we discovered the U.S. Pacific Coast lost much more tidal marsh than other coasts,” says lead investigator Kerstin Wasson, research coordinator at California’s Elkhorn Slough Reserve. “More than 60 percent of Pacific marshes have been lost, while the Atlantic Coast saw an eight percent loss, and the extent of Gulf of Mexico marshes actually increased.”

Climate resilience strategies should be tailored for the region and estuary in question, and the maps generated through this project can help, according to Wasson. “Restoring tidal exchange in areas that are disconnected could help restore lost habitats,” she says, “but in places where wetlands are moving landward, emphasizing the protection of migration corridors may be a better approach.”

This interactive Story Map explores the 30 estuaries studied in this project. You can toggle between maps of past and present estuaries and zoom into areas of interest. Shown here, an elevation-based map of Washington’s Padilla Bay, where more than half of the land potentially within the reach of tides has been disconnected from natural tidal exchange.

“Our communities depend on the healthy natural infrastructure of estuaries to protect people and places,” says Rebecca Roth, executive director of the National Estuarine Research Reserve Association. “Research like this provides the information they need as they decide where to prioritize land and habitat protection.” 

The Reserve-led team collected land elevation and tidal data in a technique known as elevation-based mapping—a powerful way to visualize where the estuary is today, where it was, and where it could be were artificial barriers to tides removed. They combined this with historical mapping using topographic sheets from 1846 to 1920, which helped identify areas for restoration of habitat types that may have once been common, but are now rare. 

At more than three quarters of the tidal estuaries studied, tidal forests identified by elevation-based mapping had been missed by the U.S. Fish and Wildlife National Wetland Inventory, highlighting the need to apply multiple mapping methods to glean a more accurate understanding of true extent of today’s estuaries. 

The approach taken in this study, using elevation and historical mapping to complement current maps based on aerial imagery, led to a more robust understanding of estuary extent and dynamics, and is applicable anywhere in the world.

Difficult to identify with visual surveys, tidal forests like these are more detectable through elevation-based mapping.

This project was sponsored by the National Estuarine Research Reserve System Science Collaborative, which coordinates regular funding opportunities and supports user-driven collaborative research, assessment, and transfer activities that address critical coastal management needs identified by Reserves.

Learn more about this project.

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ReservesElkhorn Slough, CaliforniaTracking Estuary Change