by Tom Moorman, Ph.D.
The explosion and subsequent sinking of the Deepwater Horizon drilling rig triggered the largest environmental catastrophe in the history of the United States. The blown-out well, located about 40 miles southeast of the mouth of the Mississippi River in more than 5,000 feet of water, spewed tens of millions of gallons of crude oil into the Gulf of Mexico. Species and habitats at risk—some superabundant, others regrettably rare—range from poorly studied deepwater coral reefs to sea turtles, marine mammals, and highly productive wetlands vital to waterfowl and other wetland-dependent migratory birds.
As of press time in early August, BP had successfully staunched the flow of oil with an experimental cap and a "static kill," as efforts to drill relief wells neared completion. But even after the well is permanently sealed, the vast quantities of oil and chemical dispersants applied to break down and sink the oil may present unprecedented future environmental challenges.
Over eons, the muddy, sediment-laden waters of the Mississippi River built a vast area of coastal deltaic marshes interspersed with hundreds of thousands of ponds that provide rich habitat for multitudes of wetland-dependent birds and other wildlife. These wetlands are the heart and soul of this region's commercial and recreational fisheries and the foundation of its culture and the livelihoods of local residents. For waterfowl and millions of other migratory birds, the Gulf Coast marshes are at the end of a vast funnel. Ducks, geese, and many other bird species raised in the Arctic, boreal forest, and prairies fill the funnel each fall as they migrate down the Mississippi and Central flyways. Louisiana's expansive coastal marshes host the majority of these birds—up to 9.2 million ducks and geese in some years. Sadly, since the 1930s over 1.2 million acres of Louisiana's coastal marshes have been lost to saltwater intrusion, erosion, and subsidence. Moreover, vast expanses of marsh have been degraded by the same forces, further diminishing the region's ability to support waterfowl and other wildlife.
The primary cause of Louisiana's enormous wetland losses has been the construction of levees along the lower Mississippi River to control flooding and improve waterborne navigation and commerce. Today, these levees reach almost to the Gulf, robbing the marshes of the sediment-laden waters that created and once sustained them. Unfortunately, the oil spill may increase the risk to wetlands along the Gulf Coast, especially in Louisiana.
While the stakes are exceedingly high, great uncertainty exists about the oil's immediate and long-term effects on wetlands and waterfowl. Essentially, the oil spill is an unplanned large-scale experiment in one of North America's richest and most diverse wetland areas, adding a new dimension of risk to an ecosystem already losing approximately 20,000 acres of wetlands annually. But one thing is certain. This region's coastal wetlands and the fish, wildlife, and people who depend on them cannot sustain such losses much longer.
What Will Happen to the Oil?
As of press time in early August, an estimated 200 million gallons of crude oil had escaped into the Gulf of Mexico. What will become of all this oil? Seeps of oil occur naturally in the Gulf, and the relatively small amounts of oil these seeps release are generally not a serious threat to the marine environment. Certain species of bacteria consume the hydrocarbons in oil and eventually break them down into byproducts such as water and carbon dioxide. The downside is that these bacteria consume oxygen in the process.
Marine scientists fear the sheer volume of oil in the Gulf may cause an explosion of bacteria that will consume lots of oil, but in doing so also consume lots of dissolved oxygen, creating "dead zones" devoid of life. Oxygen depletion could also occur in coastal wetlands and shallow inshore waters, killing fish, shrimp, crabs, clams, and oyster beds. Monitoring is ongoing, and only time will tell to what extent this may happen and what effect it may have on the Gulf's marine life and productive fisheries.
Photo: Dale Humburg, DU