Humans have upset the delicate balance of land gain and loss in the Mississippi River Delta. Dams, levees and channels along the Mississippi have prevented land-forming sediments from reaching the delta, and most of those that do are discharged deep into the Gulf of Mexico. Meanwhile, old land continues to compact and erode, a process aggravated by human activity. As a result, over the past 75 years, almost 5,200 square kilometers (2,000 square miles) of wetlands, which once sheltered coastal cities from storms, have been lost to the ocean.
Clearing a Path
By the 1980s, over 32,000 kilometers (20,000 miles) of navigational channels and canals, used primarily for oil and gas development, crisscrossed the delta, disrupting the natural flow of water and sediments.
The Dead Zone
The Mississippi River stretches over 3,000 kilometers (over 2,000 miles) and carries land-building sediments to the delta. But it also carries pollutants, like nitrates washed into the river from farmland, that end up in the Gulf of Mexico. Nitrates promote the growth of algae, which then die and decay. Bacteria feed on the decomposing algae and consume so much oxygen that they have created an enormous "dead zone" the size of New Jersey where few forms of life can survive (brown water).
By the Numbers
Over the past 50 years, the Mississippi River Delta has lost on average a tennis court of land every 13 seconds.
"It took the Mississippi River 6,000 years to build the Louisiana coast. It took man 75 years to wash away a third of it." -Bob Marshall, The Times-Picayune, 2007