Now on the Naked Scientists we're going to go to Louisiana which is where the Louisiana wetlands are. Robinson Fulweiler is a researcher who works there, she's at Louisiana State University.
Chris - Thanks for joining us. First of all, most people probably don't actually know where the Louisiana wetlands are or what they are so could you give us a bit of an introduction to them?
Robinson - Sure. Louisiana is actually about 7500km away from you all right now. I'm at the very southern part of the United States, right next to Texas. The wetlands here are actually the largest wetlands in the United States and they're actually bigger than the island of Cyprus.
Chris - They're pretty large. What is special about them?
Robinson - I think the vastness is definitely very important. They make up most of the wetlands in the United States and they're twice the size of the Everglades which is often what people think of as big wetlands.
Chris - What's the actual definition of a wetland? What do we expect to see if we go to one?
Robinson - The main thing, in fact the defining part of a wetland is the fact that there's so much water. And so a lot of the soil is full of water too. Then there's a lot of these plants which I heard you mention too that are called hydrophytes and that's vegetation that's specifically adapted to live in this environment. You can have environments that are freshwater, saltwater or some sort of mix like a brackish wetland.
Chris - How did they get created in the case of the Louisiana? Where did they come from?
Robinson - It's really interesting. The Mississippi river which is one of the largest rivers in the world has been flooding this region for over six thousand years and as it does that it sort of switches its path as it overflows. As the water overflows it brings with it sediments and nutrients and that kinda builds land off to the side of the river. That's how Louisiana was built so it 's been six thousand years in the making basically and it's all from the river system.
Chris - So it's a bit like the same sort of delta system that you would see on, say, the Nile: running past Egypt and Cairo.
Robinson - Yep, exactly and in fact Louisiana is the seventh largest delta in the world.
Chris - Given that people have started to fiddle with the course of the Mississippi because dykes have been built, barrages and it's being diverted does that have a consequence for the growth of these wetlands or their maintenance even?
Robinson - Yes it does. In fact it has a really important negative consequence. That is that since the river is no longer allowed to overflow its banks and bring with it that freshwater sediment and nutrients that the wetlands need the river is instead made into a pipe that now discharges directly into the Gulf of Mexico. Without that rejuvenating resource every year the wetlands are slowly disappearing.
Chris - I should think there's another major consequence which I mentioned at the beginning of the programme which is that the Mississippi is draining right through the heartland of the USA. There's a lot of agriculture going on along its banks and invariably that means nutrients like nitrogen and fertiliser getting into that water. What's the consequence for the ocean then of having what you call a pipe going straight out to sea?
Robinson - One of the main things that we really like about wetlands that provides a really important ecosystem service and that is that it can filter out sediments and nutrients, right. Instead of letting the water flow through wetlands we made this pipe and so all of the nutrients and sediments don't get filtered. It's a direct discharge into the Gulf of Mexico. In fact, I did a little math[s] here and if you think about the amount of nitrogen coming into the Mississippi river and the Gulf of Mexico, it's equivalent to dumping 314,000 elephants each year. There's a lot of nitrogen coming in.
Chris - That's a lot of fertiliser isn't it?
Robinson - It is a lot of fertiliser. That means that we're going to get large phytoplankton blooms, larger than we would normally see because there's extra for them to eat. Large phytoplankton blooms and then these die and sink to the bottom. As they decompose they take up the oxygen in the water. This leads to hypoxia or anoxia, that's either low oxygen or no oxygen in the water: naturally bad for any of the animals that live there.
Helen - Is that already happening on a really large scale? Are we seeing these die-offs taking place?
Robinson - We are, exactly. The dead zone in the Gulf of Mexico, it changes in size from year-to-year, but its biggest has been the size of the State of New Jersey [22,608km2]. It's all usually linked to the amount of water and hence the amount of nitrogen coming from the Mississippi river.
Chris - Does this mean then that if you un-dam and allow the Mississippi river to have its natural course and go back through this natural percolator that you would kill lots of bids with one stone? You'd get your wetlands regenerating themselves, you'd be removing this pollution and you would be benefiting the ocean.
Robinson - Definitely, I think that's the really important thing if you could do that. I think you might need some help from upstream and that is that I think we need to work on best management practices and how much nitrogen fertiliser we put down. Then we can do both, we can lower the actual amount of nitrogen in the Mississippi river then optimise the access into the wetlands.