Extreme Rainfall and Flooding Contributes to Sudden Vegetation Dieback in Texas Salt Marsh

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Sudden vegetation dieback events in salt marshes have historically been linked to severe drought, but a new U.S. Geological Survey study reports the first documented example of such an event being triggered by extreme rainfall and flooding.

Coastal wetlands with a white quadrat and blue sky in background

Coastal wetlands in Texas before Hurricane Harvey, Spring 2017

Widespread, rapid mortality of smooth cordgrass, the predominant plant species in salt marshes, was observed in parts of coastal Texas after Hurricane Harvey brought intense rainfall and catastrophic flooding in 2017.

 

Largescale diebacks can turn healthy salt marshes into mudflats or open water. The degradation or loss of these productive ecosystems impacts their ability to protect coastlines from storm surge and flooding, filter toxins from the water, and provide habitat to important fish and wildlife.

 

Scientists from the USGS Wetland and Aquatic Research Center and the U.S. Fish and Wildlife Service collected and analyzed Landsat imagery and field data to investigate the role rainfall and flooding played in the large-scale salt marsh vegetation dieback. The team focused their efforts within San Bernard National Wildlife Refuge, where large areas of smooth cordgrass dieback were observed post-hurricane.

Browned coastal wetlands with a white quadrat and blue sky in background

Coastal wetlands in Texas after Hurricane Harvey, Fall 2017

 

Hydrology plays an essential role in salt marshes and other coastal wetland types, helping to control ecosystem function and structure, as well as the plant community composition. Smooth cordgrass and other salt marsh plants can tolerate some flooding. However, as noted by the USGS study, the significant amount of rainfall and flooding associated with Hurricane Harvey exceeded the threshold for plant survival.

 

As storms are expected to increase in frequency and intensity, bringing heavier rainfall in shorter periods, more vegetation dieback events may occur. Understanding the factors that contribute to sudden vegetation dieback and how these stressors might interact is necessary to accurately assess and prepare for future climate impacts along the Nation’s coasts. 

Mud with field sampling gear in forefront, and coastal wetlands and blue sky in background

Coastal wetlands in Texas after Hurricane Harvey, Fall 2019

 

 

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