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Delta blues: Mississippi marshlands

Updated Tuesday 2nd November 2010

The Saving Species team are joined by Quenton Fontenot who is an Associate Professor in Biological Sciences at Nicholls State University, Louisiana. They discuss the value of coastal marshlands and highlight the resiliant nature of the Mississippi Delta

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Copyright The Open University


Presenter:  This is a very evocative scene of Southern Louisiana.  We’re looking at Roy’s Shrimp Co, a couple of shrimp boats and that even the path leading up to it is now inundated, completely covered in water.  Whereabouts are we exactly?

Quenton:  Well we’re actually in Leeville Louisiana, and we’re standing in a marsh parking lot between Bayou Lafourche and Louisiana Highway 1.

Presenter:  And I’m with Quenton Fontenot, who’s an ecologist from Nicholls State University in Louisiana.  Apart from being a professional ecologist, you’ve grown up here, lived here pretty much all your life.

Quenton:  Absolutely.

Presenter:  How has this landscape changed over time?

Quenton:  There’s a lot more water and a lot less land driving down on, from Baton Rouge to Grand Isle Louisiana, through this route, through our marshes.  As a boy, I remember everything being just grass.  It looks like, would look like a large meadow on the area.

Presenter:  Right.

Quenton:  And most of that meadow has gone now and has been replaced with water.

Presenter:  Now, we can see stretches of water, lots of nice birds around though, egrets we saw and an ibis earlier and a great blue heron took off and squawked at us rather noisily.  Oh and what’s that just landed by us here?

Quenton:  Oh that is another heron.

Presenter:  Yes, looks like a fledgling heron, just coming to have a little peek at us.

Quenton:  Yeah.

Presenter:  Why has this habitat changed? It looks as though this is an ecosystem that isn’t particularly resilient to change?

Quenton:  Well, quite the contrary, it’s actually a very resilient ecosystem.  Well it has what it needs to sustain itself.  What this area is suffering from is subsidence, and essentially what happens is, when the Mississippi River built this area, each year it would flood, it would bring in a lot of nutrients and a lot of sediment, and the sediment would settle over the marsh, and over time that sediment gets compacted.  Imagine if you dig a hole in your yard and you put, and you have the pile of dirt next to it, and a week later that pile is going to be smaller because the dirt compacts.  Well the same thing when the Delta was built by the Mississippi, the Delta itself compacts over time, and under a natural hydrology the river would bring sediments back out to those areas and deposit sediments on top of areas that are subsiding, and so we actually build land with an active delta.

Presenter:  I see.  So if things are working properly the land is actually building up?

Quenton:  Correct.  And what we’ve done is we’ve levied the Mississippi River for flood control and we’ve cut off the Mississippi River from this area.  And it’s not just that, it’s also that there’s a lot less sediment in the river itself flowing in the water column because of all the dams and different structures up river that prevent the sediment from coming further down here.

Presenter:  But why is it sinking then? What does cutting off that water supply, why does this subsidence happen?

Quenton:  Well it’s a natural process for a river delta for the land to subside because this is new soil that’s laid down by the river.  And so it naturally compacts.  But what we’re seeing is the compaction but we’re not seeing the accretion that a river flow would bring each year.  And so as a river would bring its new sediments to this area, it would build land up faster than land subsides.

Presenter:  Now this is only one of the many habitats that form the ecology of the Mississippi Delta from the North, way down here to the Southern tip.  What are the pressures on the rest of it, and are they separate or connected?

Quenton:  Well.  Right, so if we were to get into a boat here in Bayou Lafourche and we started going inland away from the Gulf of Mexico, the salinity would get less and less; we move into more fresh water.  We would go from a salt marsh habitat to a brackish marsh habitat, to a fresh marsh habitat, to cypress swamps. You know, it will come more and more fresh, and those different types of habitats are all connected.  You know, a lot of people imagine a salt marsh being as a salt marsh isolated from the cypress swamps.  But in these big river estuaries the cypress swamps are connected to these salt marsh estuaries.  I want you to think about them as one ecosystem instead of separate individual components.

Presenter:  So what’s happening at the moment in terms of thinking of them as one ecosystem? Especially when there are so many different pressures on the ecosystem itself?

Quenton:  Well I think that we’re starting to realise how important these different components that the ecosystem are, in that they have to be able to interact with each other.  There are organisms like the blue crab that spawn offshore, their larvae offshore, then they come in shore as juveniles and we’ll find them up into the cypress swamps as maceration grounds, and then once they mature they move back down, and so this whole interconnectivity of the estuary is important for organisms like the blue crab, and we see other things, other important fish species like the bay anchovy, which also moves throughout the entire estuary.  And so I think if we wanted to manage this estuary to the best of our ability we need to understand that the connectivity needs to remain for those types of organisms to try to keep this whole system healthy.

Presenter:  Now, as we look at this particular habitat, salt water, brackish water, coming in to cover the grasslands, but it’s not all bad news is it, because the interface between the grasslands and the water itself is extremely important.

Quenton:  Right.  What we see is that if you look out in to the marsh and you can see what we call the marsh edge, and that’s where the grass meets the water.  So it’s a very distinct edge, and that is probably the most critical habitat in this whole coastal estuary because that is where the baby shrimp, the baby crabs, the baby fish, that’s where they like to be.  They’re protected from predators, but they also have an abundant food source right there in that area.  And so one of the issues that we’re facing is that, you know, we’re losing a lot of our marsh land and the immediate thought would be well you must be losing your fisheries.  But if you think about it, the way that coastal erosion down here is happening, we see pockets of marsh opening up, that the marsh is becoming fragmented, which means that, as the marsh becomes fragmented, there’s more and more marsh edge, that really critical habitat, and so.

Presenter:  Because you’re creating islands of grasslands.

Quenton:  That’s right.

Presenter:  You’re actually increasing the edge.

Quenton:  So even though we’re losing a large volume of our marsh, we’re increasing the amount of edge material, and so the thought is, is that we’re going to continue to diminish the amount of marsh, diminish it, diminish it, diminish it, keep a certain amount of edge, but to the point to where once those little islands are completely gone then all of the edge is gone all at once, and it’s almost like a very fast slippery slope that we’re worried that we may be on.  So we don’t know where we are in relation to how much more edge do we have left to get versus how much marsh is left.

Presenter:  So there could be a point at which the populations naturally increase as these edges increase and then there could be a crash in populations?

Quenton:  Yes.  And the crash, theoretically, would be very, very fast, because all of a sudden we’re going to have one storm like Katrina come through.  A very strong violent storm that could wipe out most of those small pieces of marsh that provide a lot of edge habitat, and then once they’re gone they’re gone.

Presenter:  What’s your best guess as to what will happen to these marshlands? You know, satellite imagery shows that they have shrunk considerably, as you say, over just a number of years.  Can it be reversed?

Quenton:  Yes.  And I think the best thing that we can do, and there’s plans and works to do this, is to actually dredge sediment from the bottom of the Mississippi River and pump that to areas that are now open water, and it’s called a sediment slurry process, and that is where, again, you know, there’s not enough sediment in the column, water column of the Mississippi, but in the bottom of the Mississippi, there’s a lot of sediment that we can grab with a dredge and easily pump it to areas that we need to move to, to rebuild marshlands.

Presenter:  There is an argument, though, that it’s probably a bad idea to tamper with marshlands at all.  You know, trying to rebuild them might even cause greater problems.

Quenton:  Well, I can’t imagine a greater problem than losing our marshland.  It all becomes just wide open and so it may not be an ideal marshland but it’s better than no marshland to me, so.

Presenter:  What is your work focused on in terms of trying to help this ecology?

Quenton:  A lot of the work that we deal with are fishery species and a lot of our work, well, most of our work is conducted in the upper parts of the estuary, in the cypress swamps, to where we’re monitoring the fish populations up there, and what we're finding is that there’s a large number of what we would expect to be marine species using those cypress swamps.  We’re finding brown shrimp, we’re finding croakers, we’re finding red drum; all these types of species that you’d expect to catch right here in Leeville, we’re catching up near Thibodaux, in those areas.  And what we’re trying to do is show the importance of those species.  We’re also finding small fish like bay anchovies that are coming up from coastal areas, and those are very important food fish for fish that live in the cypress swamps.  And so that’s an energy transfer from the coast going upstream to the cypress swamps, where if you think about river systems, usually you’d think about energy and nutrients going downstream.

Presenter:  Right.

Quenton:  But these migratory organisms, so it’s very important that those migratory pathways for those organisms remain unobstructed, so that the natural movement of the organisms within the ecosystem goes up and down.

Presenter:  Because it’s a two-way street it seems.

Quenton:  It’s a two-way street, absolutely.

Presenter:  Very interesting.

Quenton:  Yeah.

Presenter:  Well Quenton, thank you very much for talking to us today.  One, my only wish apart from having these swamplands back is that they make the road a bit quieter.

Quenton:  Oh yes.  It’s a very busy road.

Presenter:  There’s no chance of that is there?

Quenton:  No, no.

Presenter:  It, with all the oil production going on down there.

Quenton:  Probably 90% of this traffic is oil traffic.

Presenter:  Listen to it and look at it.  Good and it’s a beautiful scene.  If we look that way, away from the road, it’s quite a beautiful scene. And we’re looking at gulls picking at things in the water, and who’s this coming in, this is an egret landing amongst the gulls.

Quenton:  I’d say a great blue.

Presenter:  Oh, it’s a great blue, look at that, standing into the wind looking extremely proud of himself.  Not a bad spot.

Quenton:  No, no.  Very nice spot – I hope it’s here for the years to come.

Aerial view of the old, mighty Mississippi River running through Louisiana farmland on a cold wet winters day Copyrighted image Icon Copyright: David Mcshane |

Mississippi river in Louisiana





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