America's Marsh

A third of Louisiana's coastal marsh is gone, and 50 more acres are lost each day

by Tom Moorman Ph.D.

A third of Louisiana's coastal marsh is gone, and 50 more acres are lost each day. Can this crucial wintering ground be saved?

If North America is the land of plenty blessed with abundant natural resources, then Louisiana's coastal marsh is a strong candidate for capital. Shrimp and crabs grow there in greater abundance than anywhere else in North America.Fishermen from all over the continent travel to the Louisiana coast to pursue redfish, speckled trout, and flounder. And the marsh is a nursery for unfathomable numbers of less notable but equally important Gulf menhaden. These fish, along with shrimp and crabs, convert the rich supply of marsh plankton and detritus into animal tissue that becomes food for larger fish, birds, alligators, and humans. Indeed, Louisiana's coastal marsh is the source of 30 to 40 percent of the commercial seafood harvest in the United States. 

But the marshes also provide habitat for tremendous populations of birds, including herons, egrets, ibises and the spectacular roseate spoonbill, whose bright pink plumage contrasts starkly with the subtle greens and browns of the marsh. As for waterfowl, it is hard to overstate the importance of Louisiana's coastal marsh to North America's ducks and geese.

The marsh provides crucial winter and migration habitat at the southern confluence of the Mississippi and Central flyways. Picture a continental funnel where the left half is the Central Flyway and the right half, the Mississippi Flyway. Waterfowl from Ontario to Alberta, from Michigan to Montana, migrate down the funnel and pour into Louisiana's coastal marshes, where they find a smorgasbord of submerged aquatic vegetation, seeds, tubers, and invertebrates on which to feed during winter.

The North American Waterfowl Management Plan's Gulf Coast Joint Venture recognizes the Louisiana coastal marsh as a top priority for conservation of waterfowl. Likewise, Ducks Unlimited's International Conservation Plan identifies the Gulf Coast of Louisiana and Texas as one of five highest-priority regions. The goal of the Gulf Coast Joint Venture is to provide migration and winter habitat to support 13.7 million ducks. Some 9.2 million of those birds use Louisiana coastal habitats, including substantial proportions of the continental populations of gadwalls, blue-winged teal, green-winged teal, northern pintails, lesser scaup, and mottled ducks.

The omission of mallards from this list of most common species may prompt some "mallard purists" to dismiss the coastal marshes, but that would be a mistake. The Louisiana coast provides wintering habitat for more than three-quarters of a million mallards, although mallards are outnumbered there by several other duck species. The Lower Mississippi Alluvial Valley, arguably the most important wintering area for mallards in North America, has wintered between 1 million and 2 million mallards in recent years.

The Louisiana coast will not winter 9 million ducks every year. Some years there are more, and some years less. Breeding success, weather, and habitat conditions throughout the flyways may reduce or increase the number of waterfowl wintering on the coast in any given year.

The number in some years may increase substantially. Picture a scenario where breeding habitat conditions and waterfowl production have both been excellent, consequently pouring millions upon millions of ducks into the funnel. Now picture harsh winter weather settling over much of the Midwest, driving the ducks south. If habitat conditions in key areas like the Mississippi Alluvial Valley happen to be below average, then we have the makings for a "perfect storm" of ducks pouring into Louisiana's coastal marshes. Once there, they depend on its rich habitat for winter survival so they can return north to produce a new generation of waterfowl to travel the flyways.

As early settlers moved west, they found abundant resources in the hardwood forests and prairies of the midcontinent. That abundance was linked to the fertile soils that today are the foundation of North America's agricultural breadbasket. Runoff from storms and winter snowmelt constantly erodes these soils and washes the rich sediment into creeks and rivers. These transport fresh water, sediment, and nutrients into the Mississippi River, which carries them downstream to the Gulf of Mexico.And this in turn fuels the productivity of Louisiana's coastal marsh.

The Mississippi River originated at the end of the last ice age when melting glaciers gave rise to a river system that drains more than a third of the continent. A map of North America reveals that the Mississippi's watershed is funnel-shaped, the very funnel that directs midcontinent waterfowl south in fall and guides them north in spring. The origins of the Louisiana coastal marshes, therefore, are in faraway places like western Pennsylvania, where the Allegheny and Monongahela rivers meet to become the Ohio.Far to the northwest, the Milk River brings sediment from southeastern Alberta and northern Montana's prairie country to the Missouri, where it makes its way ever so gradually to the Mississippi and eventually to the Louisiana coast.

When the Mississippi reaches the Gulf of Mexico, fresh water meets salt water in massive quantities. Tidal counterforce applied by the Gulf of Mexico slows the velocity of the river. When the velocity drops, sediment settles and forms land—not just any land, but rich, fertile deltaic marshland made from some of the most productive, nutrient-laden soils on earth. Delta formation occurs on almost all the world's major rivers, but not all rivers receive sediment as rich as that carried by the Mississippi.

Historically, the Mississippi River delta was dynamic. Each pulse of floodwater reshaped the delta. Over the last 7,500 years or so, the mouth and lower main channel of the Mississippi River have shifted, sometimes to the east, sometimes west, and sometimes by as much as 150 miles. Picture the river as an out-of-control fire hose, its end swinging wildly from the pressure of the water it discharges. These channel shifts occurred because deltaic processes built land that eventually impeded the river's flow. Not to be denied access to the Gulf of Mexico, the river sought alternate routes. If there was no other channel to follow, the river would overrun low-lying marshland, and the force of the water would make a new channel. These channel shifts might have been gradual, or they may have occurred dramatically during major flood events.

In any case, the deltaic processes and associated river channel shifts were critical to the formation and maintenance of the Louisiana coastal marsh. Each time the river channel shifted, its sediment-laden water built new marsh. Meanwhile, marsh created around the abandoned channel began to subside (sink) and erode. Marsh creation was more or less equal to marsh loss during the past 7,500 years or so. The river would build delta, and the raised deltaic marshland would force the river to shift channels. The new channel would build new marsh. The marsh built by the old channel but now cut off from its source of sediments subsided as organic materials decayed and soils compacted. Wind and wave action further eroded these areas.

Sadly, rates of marshland creation and loss are no longer in equilibrium along the Louisiana coast. Marsh loss rates now greatly exceed marsh creation rates. Louisiana loses about 25 square miles of its fertile marsh annually. Fifty acres a day are lost to the Gulf of Mexico.That equates to the loss of an area about the size of one football field every 30 minutes. Roughly 1 million of the 3.1 million acres that existed just a century ago are gone. We are rapidly losing one of the most productive wetland systems on earth and one of the most important waterfowl wintering areas in North America.Very rapidly. In geologic time, this million-acre loss has occurred in what amounts to a split second. In human time, it has spanned less than two generations—about 60 to 80 years. What has changed?

The answer is simple: As with many of the world's major wetland systems, humans have dramatically altered processes that created the Louisiana marsh. Sediment-laden flood pulses still travel the Mississippi to the Gulf of Mexico, but we have successfully tamed the mighty river. No longer does the channel shift. Humans have gained control of the wildly swinging fire hose due to extensive levee systems that contain the river from St. Louis nearly to the Gulf. In Louisiana, levees from Baton Rouge through New Orleans to the small community of Venice contain the river and prevent the wild shifts that created new marshland.

South of Venice, the river's forces are unleashed to build marsh. Unfortunately, also just south of Venice, out in the Gulf of Mexico, the continental shelf ends and deep water begins. Marsh-building processes cannot occur there. The levees effectively force the river's sediment load to be deposited and lost in several hundred feet of water. The Louisiana coastal marsh has been cut off from the sediment-laden river water that was its lifeblood. Strike one.

In the early 1900s, geologists discovered huge deposits of oil and natural gas below Louisiana's coastal marsh. Appetite for fossil fuels increased dramatically in the mid-1900s, and an oil boom ensued in coastal Louisiana.Because the marsh has few roads but plenty of water, oil companies built thousands of miles of canals to extract the oil and gas. Many connected to the Gulf of Mexico by large ship channels that service the principal port cities of Louisiana.Construction of this network of canals and ship channels had serious unintended consequences for the marsh. In fairness to the oil companies, most of the canals were built well before we had an understanding of coastal marsh ecology. Nonetheless, the extensive canal network allowed salt water from the Gulf of Mexico to flow into the interior marsh, where plants were simply intolerant of high salinity or rapid salinity changes. The result was, and continues to be, death of the salt-intolerant vegetation comprising the marsh. When the vegetation dies, tidal energy and wind-generated wave action erode the marsh and convert it to open water of little value to waterfowl, other wildlife, or fisheries. Strike two.

Finally, remember the areas of marsh deprived of sediment after being left behind by natural channel shifts? Subsidence and erosion allowed the Gulf to reclaim them while new marsh was formed where the new river channel deposited sediment. That was simply part of the dynamics of the system. Today, since the Mississippi River channel is restricted and cannot shift, its floodwaters can no longer deliver sediment and nutrients to the marsh, and rates of subsidence and erosion now greatly exceed marsh creation. The result is a dramatic loss of coastal marshlands. Strike three?

Maybe not strike three, but certainly we are in the late innings of a game we cannot afford to lose. The scale and complexity of the problems in coastal Louisiana are daunting. But there is reason for cautious optimism that all may not be lost. In 1998 a plan entitled Coast 2050: Toward a Sustainable Coastal Louisiana was approved or endorsed by a host of state and federal agencies and local governments that have a stake in restoration of the marsh. However, even if the plan is successfully implemented, models used in the planning process project that by 2050 some 450,000 additional acres of marsh would be lost. If that happens, only about 1.5 million acres, or half the marsh present just a century ago, will remain—and that would be a victory, albeit not a wholly satisfying one.

According to the Louisiana Coastal Area Final Study Report , the price to save a sustainable Louisiana coastal marsh is at least $14 billion, but the cost of losing the marsh to the Gulf of Mexico is far greater. Coast 2050 projects a loss of $37 billion in "public use value" by 2050. The estimate takes into account loss of "ecological goods and services" provided by the marsh. Simply stated, it is an estimated value of what we all stand to lose in recreational hunting and fishing opportunities, commercial fisheries harvests, water-quality functions, hurricane protection, navigation and port facilities, oil production infrastructure, and many other functions and values the Louisiana coastal marsh provides to us all.

Regardless of where in North America you call home, if you have a passion for waterfowl, waterfowl hunting, and wild places, take time to learn more about the plight of the Louisiana marsh country and the plans to restore and sustain a meaningful portion of the marsh's astounding productivity. Learn more about what you can do to help. And then act, because while you were reading this, another piece of coastal marsh the size of a football field was lost. By this time tomorrow, 50 more acres will be gone.

Dr. Tom Moorman is director of conservation planning at Ducks Unlimited's Southern Regional Office in Jackson, Miss.