Vegetation - 7 of 10

Vegetation FAQs - 10 Found

What is the Brown Marsh phenomenon?

Brown Marsh is a term that scientists have given to the unusually extensive and rapidly spreading browning of Louisiana’s normally lush green intertidal saltwater marsh grass Spartina alterniflora, known more commonly as oyster grass or smooth cordgrass.

The phenomenon of brown marsh has been observed along Louisiana's coastline. Hardest hit is the Barataria-Terrebonne estuary extending from the west side of the Mississippi River to the Atchafalaya River. Least affected marshes appear to be those lying east of the Mississippi River.

This marsh browning (or dieback) began during the spring of 2000, long before it would normally occur in the fall. Some areas of marsh having roots, with little or no aboveground vegetation remaining, have been tested and are completely dead. Other affected areas still have the marsh grass standing but are entirely or mostly brown. Experts cannot be sure if the root structures in these areas are dead. Still other affected areas show the browning effects but have some patches or individual plants that are green and still living.

Sudden marsh dieback events have occurred in coastal marshes from the Northern Gulf of Mexico to Maine. One of the most severe events occurred in 2000, where over 100,000 hectares (ha) of salt marsh were impacted throughout Louisiana’s Mississippi River Delta Plain. In 2009 Louisiana experienced another episode of large-scale coastal dieback that rivaled the peak dieback conditions from earlier in the decade.

The cause of sudden marsh dieback is still under debate but may be cyclical depending on interactive climate conditions, sea level anomalies, and other biotic factors. National Wetlands Research Center scientists have been engaged in field and laboratory studies to contribute our best understanding of possible causal mechanisms and management implications of sudden marsh dieback on long-term marsh resiliency and vulnerability to climate change.

While scientists have not completed their investigations, they believe that extreme drought, high salinities, heat, evaporation, combined with extremely low Mississippi and Atchafalaya River discharges have stressed the shallow rooted Spartina alterniflora.

Water management in the Mississippi River delta has focused on preventing flood conditions during the last 100 years. The engineered flood plain of the Mississippi River in Louisiana limits the release of fresh water to wetland areas. The lack of freshwater flow may lead to a more severe response of coastal wetlands under drought conditions.

Many strategies to introduce more freshwater into Louisiana's marshes have been studied. Diversions from the Mississippi River and increased flow from the Atchafalaya River appear most promising. Scientists observed that salt marsh to the east in the vicinity of the Mississippi River diversion at Caernarvon have appeared healthy throughout drought periods. The problem requires short- and long-term solutions. However, rebuilding marshes and ensuring against future die-off can best be accomplished by getting more freshwater flow into the marshes.

Learn more:

Salt Marsh Dieback in Coastal Louisiana: Survey of Plant and Soil Conditions in Barataria and Terrebonne Basins, June 2000-September 2001

Global Change Impacts on Mangrove Ecosystems (USGS Fact Sheet 2004-3125)

Tags: Vegetation, Ecosystems, Marsh, Water, Coasts, Wetlands, Rivers, Streams, Measurement, Analysis, Ecology