The History of Louisiana Coastal Wetlands

This is the first post in a series on the Louisiana coastal wetlands. In this post, I’ll introduce you to the wetlands and talk about how they formed. In future posts, I’ll discuss how they work, why they are important to not only the state but also the nation, and the modern issues that are threatening their future.

Many definitions exist for wetlands, but the most important feature is that the area is wet for an extended period. According to the U.S. Fish and Wildlife Service, “all areas considered to be wetlands must have enough water at some time during the year to stress plants and animals that are not adapted to life in water or saturated soils.”¹ Regulatory definitions require that the land be inundated with water often enough and long enough to support plants that are adapted for life in saturated soils.

Although wetland areas make up a very small percentage of the total land in the United States, they serve very important functions, and Louisiana contains a disproportionately large percentage of this country’s wetlands due to its position at the mouth of the mighty Mississippi River.

The Mississippi River drains 41% of the continental United States, as depicted in the figure below. It empties into the Gulf of Mexico through its massive delta, which comprises most of Louisiana’s coastal wetlands. The Mississippi River Delta is the seventh largest deltaic region in the world; it comprises 4 million acres (6,000 square miles) of wetlands, an area twice the size of the Everglades in Florida. This area represents 25% of the nation’s coastal wetlands and 40% of its saltwater marshes. It’s easy to see how this vast coastal ecosystem is known to many as “America’s wetland.”

For the last 6,000 years, Louisiana’s coastal wetlands have grown through a natural flood and sedimentation process. Our nation’s largest river transports water, sediment, and organic matter from 31 states from New York to Montana, and as far north as Canada. Historically, spring rains swell the Mississippi and bring huge quantities of nutrient-rich sediment downriver, where the river overflows its banks to fertilize and build land along the way.

As the river nears its Gulf coast outlet, the land becomes increasingly flat and the tidal influences start pushing back on the river. This is the deltaic region, where the river slows down, spreads out, and drops much of its sediment and nutrient load to create and replenish the delta’s wetlands. Over the centuries, the sediment builds up and subsides under its own weight and through decomposition. However, the Mississippi’s sediment load is so great that as long as the natural sedimentation process continues, the delta continues to grow. Unfortunately, for roughly the last century human actions and policies have been in direct opposition to these natural renewal processes, to the detriment of Louisiana’s coastal wetlands.

Louisiana’s coast is a permanent or temporary home to an enormous array of plants and animals. A marsh, especially a salt marsh, is a difficult place to live. Species have to deal with the tidal influence, which changes not only the wet and dry conditions twice a day, but in some areas the salinity as well. Soil conditions are mostly anaerobic (lacking free oxygen) and require highly specialized plants to be able to deal with these conditions. Because wetland ecosystems are characterized by a range of highly specialized flora and fauna, they are among the most sensitive of ecosystems, with relatively narrow margins for biological failure.

We’ll talk more about the ecology of Louisiana’s coastal wetlands in the next post.

– Jonathan Putman