Laura Erickson's For the Birds

During my lifetime, the Mississippi Delta area of Louisiana has been shrinking. It’s obvious when you compare maps from the 1940s or 50s with maps from today: the total land area lost is larger than the entire state of Delaware. When I was in the Gulf, I asked physical oceanographer Paul McKay, based in New Orleans, how so much land could possibly have been lost in such a relatively short time.

PAUL MCKAY: Well, there are several processes going on here. Just left on their own, marshes are constantly eroding due to the action of winds and waves and tides, taking sediment away from the ocean side of the marsh, and constantly growing due to the accumulation of sediment coming in from the land margin and from coastal rivers.

What’s been happening in Louisiana is a few different things. First of all, in an effort to control flooding, the Army Corps of Engineers has put levees all up and down the Mississippi River. And that’s done two things: In the upper Mississippi, it’s starved the river of sediment. All the land that would have washed into the river and been transported down to the Gulf of Mexico is being retained in the interior states as farmland. So the amount of sediment in the river is a lot less than it has been historically.

And then also in the lower Mississippi, instead of flooding and draining every spring and depositing the sediment in the marsh, the river is contained between levees. So all the sediment loaded in the Mississippi is being exported offshore and is accumulating in a large bank in the middle of the Gulf of Mexico.

So that by itself starves the marsh and prevents it from growing as much as it normally would. In addition to that, since World War II, the marshes and the offshore areas have been developed for oil and gas production. And in order to have access to the oil and gas wells and to be able to bring oil and gas back on shore, the oil companies have dug channels and canals through the marsh. This allows saltwater to penetrate up into the inland freshwater marshes and it kills the marsh grass, which are not very salt tolerant. And this marsh grass is the only thing holding the land together in this area. So once the marsh grass dies, the land starts to erode and these canals open, which allows more saltwater to come in, which accelerates the process.

So we’ve got two processes working on the land side. We’re not getting as much dirt coming down the Mississippi as much sediment, so we’re starving the marsh. And on the ocean side, saltwater is penetrating further up in, so it tends to kill the grass and allows the marsh to erode out into the ocean.

Much of Louisiana’s coastal wetlands are private property, much owned by oil companies, and people don’t build farms or permanent dwellings on them. So I asked Dr. McKay how significant this land loss really is.

Well, most of this has occurred since shortly before World War II. In the 1920s and 30s, the Army Corps of Engineers got really active in channelizing Mississippi and dredging it and constructing levees. And then since World War II, the oil and gas industries become very active in the marsh. So we’re looking at, on the order of 50 to 70 years, to have seen a massive degradation of the marsh. Areas that used to be near solid land and that used to be freshwater marsh are now open saltwater.

It’s extremely significant for a couple reasons. One, for coastal protection. These marshes are the only thing that really attenuates the storm surge coming up from the Gulf from a hurricane. As the surge comes up, it floods the marsh, it dissipates, friction from the grass tends to reduce the surge and keep it from reaching inland areas such as New Orleans. With the marsh being degraded, with lots of open area and with canals and shipping channels, the storm surge is able to funnel straight up these channels and reach much further inland than it ever used to be.

On top of that, there’s the ecological aspect. The marshes are the incubators where 90% of all commercially fish species in the Gulf of Mexico breed. They either come into the marsh to breed, or in the case of things like shrimp, they breed offshore, and then their larvae are washed up into the marsh in the estuaries where they settle into the sediment and that’s where they grow to maturity. Without healthy marshes, most of the commercial seafood species out there are going to have a much more difficult time reproducing, and stocks are going to be much lower.

When I took a boat out in Barataria Bay, we used the DeLorme map from 2004. Several of the islands we could clearly see on the map no longer exist. It’s hard to even imagine the outcry if Wisconsin or Minnesota, say, lost a land mass the size of Delaware in little more than half a century. But that’s the way it is down in Louisiana, where oil that has reached some of the remaining islands will kill enough marshgrass to shrink them even more.

I’m Laura Erickson, speaking for The Birds.