West Coast
Michelle Cordrey, TJNERR.

National Centers for Coastal Ocean Science News: Wetlands in Intermittently Closed Estuaries Can Build Elevation to Keep Pace With Sea Level Rise

Along the U.S. Pacific Coast, many estuaries are not permanently open to the ocean, but shift between open and closed states. A NCCOS-supported study tested the hypothesis that intermittently-closed estuary marshes are more resilient to sea-level rise than open-estuary marshes.

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Along the U.S. Pacific Coast, many estuaries are not permanently open to the ocean, but shift between open and closed states. A NCCOS-supported study tested the hypothesis that intermittently-closed estuary marshes are more resilient to sea-level rise than open-estuary marshes.

Estuaries are brackish water environments traditionally thought of as open to the ocean with one or more freshwater rivers or streams flowing into them mingling with waves and tides from the sea. However, in some estuaries the entrance is not permanently open to the ocean but shifts between open and closed states. These bar-built intermittently-closed estuaries (ICEs) may take many forms but are typically found on wave dominated coasts with high sediment loads and variable river or creek inflow that allow waves to build a sand barrier across the mouth. There is a range of closure from the ocean ranging from days or even years with a single seasonal closure being most common.

Using California as a case study, the NCCOS-sponsored researchers from USGS and U.C. Davis conducted a spatial analysis comparison showing that marshes in ICEs had significantly greater elevations than marshes in permanently open estuaries. Using a model, they determined marsh elevation change under 840 simulated responses to sea-level rise to 2100. The closure-scenario modeling showed that regular annual ICE closure can promote sediment accretion rates and increase marsh elevations fast enough to match even high rates of sea-level rise. Also, estuaries that have a closed mouth phase contain marshes with higher elevations than in perennially open estuaries.

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