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Rising sea levels and ongoing anthropogenic development continue to threaten estuaries worldwide. New research conducted by USGS alongside state, federal, and tribal partners in Puget Sound provides crucial support for sediment management strategies to preserve these invaluable habitats.

Map of surface elevation tables in Puget Sound, Washington
Map of surface elevation tables in Puget Sound, Washington.

Puget Sound, the second-largest estuary in the contiguous United States, has seen a significant loss of estuarine habitat since the 1800s. Up to 70–80% of historical estuarine areas have vanished due to human activities, with further losses projected as sea levels continue to rise throughout the twenty-first century.

To assess the dynamics of sedimentation and elevation change within Puget Sound's estuaries, researchers assessed vertical rates of elevation change from a regional network of surface elevation tables and marker horizons. Sites studied included estuarine areas that underwent complete or partial restoration measures, such as the removal of anthropogenic barriers like dikes and levees and the replanting of native vegetation. Removal of these barriers effectively reconnects the flow of water and sediment to previously disconnected systems, while restoring vegetation prevents erosion and can help trap sediment.

The study found varying rates of sedimentation across different estuarine sites. Restoration sites with regular sediment input, particularly in the Stillaguamish and Skagit estuaries, exhibited the highest rates of elevation gain. Conversely, low-elevation sites in sediment-starved estuaries such as Padilla Bay consistently experienced negative rates of elevation change (e.g., erosion).

"This research underscores the importance of sediment delivery for sustaining the health and resilience of Puget Sound's estuarine habitats,” said Melanie Davis, USGS Research Ecologist and lead author of the study. "Sites with adequate sediment supply show promising signs of keeping pace with current rates of sea-level rise.”

The findings suggest that targeted sediment management strategies could strengthen the resilience of Puget Sound's estuarine habitats against rising sea levels. By ensuring the continued delivery of sediment to these critical areas, policymakers and resource managers may help safeguard the Sound’s rich biodiversity and vital ecosystem services.

"Determining estuarine resilience to rising tidal levels, and identifying the factors that reduce their vulnerability, are critical to estuary conservation and restoration efforts within Puget Sound and the greater U.S. west coast, where sediment, particularly from the region’s steep, young watersheds, is the dominant source of material to support marsh and estuary stability," said Eric Grossman, USGS Research Geologist and co-author of the study. “Strategic sediment management guided by new sediment transport models and sediment budget assessments can bolster the resilience of these estuaries and ensure that they continue providing essential habitat and ecosystem services as sea level rises.”

The team’s findings are published in the Estuaries and Coasts Special Issue: Wetland Elevation Dynamics

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