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?