Mississippi Delta Marshes in a State of Irreversible Collapse

The researchers found that in the Mississippi Delta, most marshes drown in a few centuries once the rate of sea-level rise exceeds about one-tenth of an inch per year (3 mm/yr).  (Image: via   pixabay  /  CC0 1.0)
The researchers found that in the Mississippi Delta, most marshes drown in a few centuries once the rate of sea-level rise exceeds about one-tenth of an inch per year (3 mm/yr). (Image: via pixabay / CC0 1.0)

Given the present-day rate of global sea-level rise, remaining marshes in the Mississippi Delta are likely to drown, according to a new Tulane University study. A key finding of the study, published in Science Advances, is that coastal marshes experience tipping points, where a small increase in the rate of sea-level rise leads to widespread submergence.

Salt marshes about 30 miles (50 km) southeast of New Orleans are vulnerable to drowning. (Image: Torbjörn Törnqvist)

Salt marshes about 30 miles (50 km) southeast of New Orleans are vulnerable to drowning. (Image: Torbjörn Törnqvist)

The loss of 2,000 square miles (5,000 km²) of wetlands in coastal Louisiana over the past century is well documented, but it has been more challenging to predict the fate of the remaining 6,000 square miles (15,000 km²) of marshland. The study used hundreds of sediment cores collected since the early 1990s to examine how marshes responded to a range of rates of sea-level rise during the past 8,500 years. Torbjörn Törnqvist, lead author and Vokes Geology Professor in the Tulane Department of Earth and Environmental Sciences, said:

The researchers found that in the Mississippi Delta, most marshes drown in a few centuries once the rate of sea-level rise exceeds about one-tenth of an inch per year (3 mm/yr). When the rate exceeds a quarter of an inch per year (7.5 mm/yr), drowning occurs in about half a century. Törnqvist said:

While these findings indicate that the loss of remaining marshes in coastal Louisiana is probably inevitable, there are still meaningful actions that can be taken to prevent the worst possible outcomes. The most important one, Törnqvist said, is to drastically curb greenhouse gas emissions to prevent sea-level rise from ramping up to rates where marshes will drown within a matter of decades.

The other one is to implement major river diversions as quickly as possible, so at least small portions of the Mississippi Delta can survive for a longer time. However, the window of opportunity for these actions to be effective is rapidly closing, he said. Törnqvist conducted the research with Krista Jankowski and Juan González, who received their Ph.D. degrees at Tulane under his supervision, and Yong-Xiang Li, a former postdoc in his group.

Justin Lawrence of the National Science Foundation, which provided funding for the study, added:

Provided by: Barri Bronston, Tulane University [Note: Materials may be edited for content and length.]

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