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PRI's Environmental News Magazine

Bye-Bye Bayou

Air Date: Week of June 29, 2012

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Massive amounts of oil resulted in this common marsh die-off pattern.

Two years after five million barrels of oil entered the Gulf of Mexico, the marshes off Louisiana’s coast are feeling the blow. These wetlands are changing rapidly, but there may be hope in restoration efforts. Brian Silliman, a marine biologist at the University of Florida, tells host Bruce Gellerman that America’s hardest working wetlands are going to have to work even harder to keep up with the oil spill.

Transcript

GELLERMAN: Even before the BP oil disaster, Louisiana’s delicate marshlands were rapidly disappearing. But now, 2 years after the largest oil spill in US history, the destruction of the marshland has accelerated at an alarming rate.

Marine biologist Brian Silliman, from the University of Florida, traveled to Louisiana’s bayou to study the erosion of the marshlands. They’re known as America’s hardest working wetlands.

SILLIMAN: Well, these salt marshes, in many ways, are the life-blood of the costal communities there in Louisiana. They’re home to the important and valuable fisheries that support the local economies.They also act as sponges and absorb any of the nutrients that come in from the land that run off from the freshwater and thereby protect the open waters from potential harmful algal blooms.

And very importantly, in the case of storms, they can protect the shoreline from incoming waves, because they baffle the waves - they act as a bit of a natural seawall - and at times, they also will decrease the amount of flooding because they absorb the water as the sea level rises during those storms.

GELLERMAN: Well, they weren’t in great shape even before the BP disaster.

SILLIMAN: Yes, these marshes are very stressed both because of what people do and also because of natural phenomenon. They’re also really starved from sediments, part of that being from the channelizations of the Mississippi River. There’s also natural subsidence - there’s sinking marshes there. And without those sediments being sprayed back and forth over the marshes over the years, the marshes tend to sink.

And that creates this unique aspect of Louisiana marshes on their edges. They’re changing and eroding, they’re not sort of gently sloped like in Georgia. And their edges look like a steep face of a small beach dune that’s been cut in half. And so the marshes there are in retreat, we’re losing a lot of those marshes every year.

GELLERMAN: So, the BP disaster pumped, you know, millions of gallons of oil into the Gulf. How did that affect the marshland - how did that destroy the marshland?

SILLIMAN: Theory in marsh ecology predicts that marsh grasses should be very resilient to oil covering them. In studies in the field, they’ve shown to grow back quickly - within one to two years. But what happened, that’s only half of what happened in this case.

The oil came into the marshes and started concentrating around the edges. The grasses in the marsh itself acted like a baffling wall, protecting the interior marshes from the oil coming in. But the oil itself concentrated on the first thirty to forty-five feet of shoreline of the marsh edge. It looked like a thick, black belt along the shoreline.

GELLERMAN: Well, you described them as sponge-like, so it’s not surprising then that it absorbed all this oil.

SILLIMAN: Right. It was almost like a catcher's mitt. And the oil covered the grasses, it covered the ground; about 80 percent of the marsh that I was walking over was covered in a pretty thick amount of oil.

GELLERMAN: So, in terms of the rate of destruction, how much has the oil from the BP disaster affected the destruction of the marshland?

SILLIMAN: Well, when the oil landed on the marsh grasses, what happened after that is the grasses started to die and decay because they were being smothered. Once the grasses above ground started to be lost, their roots started to die as well. And those roots are important because they hold onto the sediments. When they died, they lost their grip on the soil.

Consequently, the erosion rates on those unique steep edges of Louisiana marshes doubled for more than 18 months. The rate, I was astonished, that naturally occurs in this area - without oil - is about five feet of the edge is lost per year. And that is transformed from marsh to Gulf. And that doubled. So, with the oil present, and the oil killing the marsh grasses that hold on to the soil, that doubled to about 10 feet per year.

GELLERMAN: You know, it seems a bit bizarre: you’ve got all this marshland, all the soil washing into the Gulf - then you’ve got the land getting lower and the Gulf getting higher.


An eroding marsh in Bay Jimmy, Louisiana.

SILLIMAN: That’s right. I mean, if you look at the direction at which the sea level is going, and which the marsh is going - is that they’re additive effects. The marsh is sinking away at the same time the sea level is going up. So, it’s a bit of a double-whammy for these marshes to try to keep up with the stresses in the system.

GELLERMAN: Now, the U.S. Army Corps of Engineers has been working on the Mississippi River and removing silt from the channel, since they’ve been working on the Mississippi. Why don’t they just take that silt - instead of just pushing it into the Gulf-why don’t they just make new marshlands?

SILLIMAN: An interesting question. And it’s a conversation that’s now being discussed by many managers, scientists - politicians even, within the Gulf region itself. It will be a massive, massive effort; but it’s being discussed right now, and it’s encouraging that we’re all at the table discussing it.

GELLERMAN: Well, Professor, I want to thank you very much for talking with us about Louisiana’s marshlands and the BP disaster. Appreciate it.

GELLERMAN: Thank you, it’s my pleasure.

GELLERMAN: Brian Silliman is a marine biologist at the University of Florida.

 

Links

Brian Silliman, marine biologist at the University of Florida, conducted the study.

Silliman’s paper highlights the degradation and resilience of the marshes.

 

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