Emma Marris, Nature magazine
Part of the show Your Questions, Infectious Cancer and Louisiana Wetlands
Chris - now it's time to take a trip down to New Orleans and the Louisiana wetlands. This area is a very important economic resource for the local population because it supplies enormous amounts of sea food, oil and gas. But they're also disappearing into the sea at the rate of something like the area of a football pitch every thirty minutes. Unfortunately, experts down there seem to be getting bogged down in trying to decide what to do about the problem. Emma Marris has been down there to look at the scale of it, especially in the wake of Hurricane Katrina's visit late last year.
Emma - The major problem has been going on since humans began there. The whole place is sinking and normally what would happen is that the Mississippi river would tumble down sediment from the rest of the country and that would make up the difference. But in order to live in Southern Louisiana they had to cordon off the Mississippi river so that it wouldn't flood them out every year. As a result, all the sediment goes shooting out into the Gulf of Mexico and none of it ends up on the plain. This makes the plain turn into the Gulf of Mexico, and we're losing about 62 square kilometres a year.
Chris - 62 square kilometres a year? That's a significant amount: a football field a day or so.
Emma - In fact it's a football field every thirty minutes.
Chris - A staggering amount of loss. Is there any way to offset that?
Emma - There are various approaches but scientists tend to disagree about which is the best. One is that you can let a little bit of the river out of its levees so that it can bring some natural sediment onto the marsh. Another option is that you can actually build land, islands or terraces and set them up to stop the waves eroding the shore. You can even pipe sediment from one place to another with pipes like the ones used in the oil industry.
Chris - Have any of these strategies been shown to be effective?
Emma - It depends on what time scale you're looking for. The Caernarvon Diversion, which is one of the largest fresh water diversions in the world, is only saving something like 61 square kilometres over 50 years, which is less than the average yearly loss. But it is pushing out some of the salt water, which is another great problem. When the salt water penetrates up these marshes, it changes the whole ecosystem.
Chris - What was the effect of the hurricane? Did it speed up the inevitable?
Emma - Yes, the USGS has suggested that perhaps we lost a 161 square kilometres just due to the hurricane. It ripped up the marsh and threw marsh balls around everywhere, tumbled the trees back and killed animals. I saw alligators lying upside down, and complete sections were just completely destroyed.
Chris - Here in the UK, there's a strategy called Managed Retreat. The idea is to give in to nature and let the sea come back to a certain extent. Is this something that people have considered doing, and just sacrificing a bit of economic output for this area in order to let nature take its course?
Emma - Yes. A lot of the researchers that I spoke to were very much in favour of this. If you only have a certain amount of money you have to prioritise and there are a lot of people who suggest we just depopulate certain parts of Louisiana and focus our energies on protecting places like New Orleans that have the most economic value. This is, of course, politically dicey and difficult.
Chris - So in your view, who's going to win in the long term?
Emma - I think in the long term unless very large amounts of money are thrown at this problem, the winner in the end will be the Gulf of Mexico.