Mississippi River Flooding Impacts Wildlife and Ecology

“It’s going to be a long-term benefit for everything living out there”

05-23-2011 // Craig Guillot

While flooding is a natural process and ultimately beneficial for wildlife, the enclosure of the Mississippi River has led to a unique event. The opening of two spillways in Louisiana to relieve pressure on the levees is funneling high waters into millions of acres of ordinarily-dry wildlife habitat.

As a mass exodus of animals flee low-lying areas and search for higher ground, experts say better management of the river could more evenly distribute waters and make habitat flooding less severe.

America’s Largest Swamp Turned Turbulent Lake

Deer struggle in the flood

In southwestern Louisiana, the opening of the Morganza spillway is expected to flood more than 3 million acres in and around the Atchafalaya Basin. At 3,000 square miles it is the largest swamp in the United States and has vast expanses of bayous and bottomland hardwoods. It is home to deer, bobcat, beaver, coyote, mink, fox, alligator, muskrat, hog, armadillo, opossum, raccoon and the endangered Louisiana black bear.

Forecasts predict that the entire basin will be flooded and some parts could see up to 15 feet of water. Though the area is sparsely populated, the flooding is expected to impact more than 25,000 people, many who have since evacuated small towns such as Krotz Springs and Butte LaRose. As the waters continue to rise they will create a turbulent, rapidly-moving river that will head south to the Gulf of Mexico.

During normal spring floods, small elevated parts of land usually provide refuge for animals but with such high waters expected, animals may have to flee the basin. Kenny Ribbeck, chief of the Wildlife Division of the Louisiana Department of Wildlife and Fisheries, said that animals are accustomed to periodic flooding but not on this scale.

“The flooding is going to displace a lot of animals. Some won’t make it. Most will run or swim for the levees to cross them and look for refuge or habitat,” said Ribbeck.

David Muth, Louisiana state director for NWF, said the unnatural event of sending heavy floodwaters through these basins is a consequence of encasing the river with levees. With the river unable to naturally overflow its banks and evenly send waters down distributaries, officials have to channel those waters into spillways, creating much bigger floods in those habitats than would occur naturally.

“If flooding was more spread out and evenly distributed through the delta, with communities made more resilient, it would be less severe and traumatic for wildlife in the basin,” said Muth.

Muth said the most important thing about better managing the river through more diversions is that it would allow nutrient-rich sediment to flow to Louisiana's rapidly-deteriorating coast.

The high waters will ultimately force wildlife into contact with man. For hundreds of miles along the Mississippi River, "battures" no more than a half-mile wide provide refuge for all sorts of animals, even in cities such as New Orleans and Baton Rouge. Rising river waters have forced many animals up onto the levees and over it into communities.

Encounters between wildlife and people will become more common as the waters rise. Just outside of New Orleans, a 10-foot alligator was shot and killed by authorities after it was spotted on a busy area near the levee. Fear of poisonous snakes being driven into neighborhoods has also put many riverside communities on edge.

Doug Inkley, senior scientist at NWF said that in the short-term a fair number of animals will perish. Some won’t be able to escape the waters; they may get caught in the current and will drown trying to find land. Others may ultimately starve after finding themselves trapped on debris piles, while a few may perish on highways after running out of the basin. Most will sense the impending floods before the waters get too high and seek refuge.

“Animals have incredible abilities to sense what is going on but there is only so much they can do to get out of harm’s way. Somehow they just know,” said Inkley.

The effects on the animals will largely depend on the species and their mobility. Aside from low-lying nests, birds will be least impacted because they can fly and survive in the treetops. Raccoons and opossums will also be able to sustain themselves for some period in the trees. Other small mammals such as rabbit, bobcat and armadillo may be able to swim out of harm’s way or cling to large piles of debris that will likely build up near heavily-forested areas.

“Some of these animals are going to exist on the drift piles, eating any vegetation that they can get a hold of,” Ribbeck said.

Black bear mom and cubs

Biologists are most concerned about the Louisiana black bear. According to the Black Bear Conservation Coalition, there are between 500 and 1,000 in the state. There isn’t a firm estimate of how many may be living in the basin but Ribbeck said there was a study in progress that will now be interrupted. The flood also happens to coincide with birthing season. New cubs have just emerged from their dens and weigh no more than 20 pounds.

“You’re talking about an animal that could easily get caught out in the flood zone and could succumb trying to get to higher ground,” Ribbeck said.

Freshwater Intrusion in Saltwater Habitat

With millions of gallons of fresh river water pouring into the brackish and saltwater Lake Pontchartrain, the flow has the potential to dramatically change the lake. Martin O’Connell, Ph.D., director of the Nekton Research Laboratory of the Pontchartrain Institute for Environmental Sciences at the University of New Orleans, said the impacts will depend on a number of factors including weather patterns and how long the spillway is open.

When it was last opened in 2008 impacts were minimal, but when the spillway was fully opened in 1997 the lake turned to freshwater and took almost a year to recover.

In 1997 it was a situation where there wasn’t a lot of wind, it was hot and there were big algae blooms. There were a lot of fish kills and it was a nasty situation,” said O’Connell.

During past openings, the river water generally flowed out toward the south shore of the lake then made its way toward Lake Borgne and the Gulf of Mexico.

Saltwater lake plants near the spillway will eventually die off but mobile species such as Redfish and Speckled Trout will simply move to avoid the approaching fresh water.

“They know and will start moving. Adult fish, shrimp, crab will be able to assess the situation and avoid what is going on with the water. Unlike [plants] they have that mobility,” he said.

Some have expressed concern about the polluted waters of the Mississippi River entering the lake. O’Connell said that the lake has a remarkable ability to heal and cleanse itself as it did after Hurricane Katrina when “toxic soup” waters were dumped from New Orleans into the lake.

His biggest concern is the threat of non-native freshwater species such as Asian Carp traveling through the lake and entering freshwater rivers on the north shore. In the Great Lakes, Asian Carp have been blamed for tremendous damage to native species.

“If they find their way up to the north shore and start reproducing, it is going to be a bad situation,” O’Connell said.

Deer struggle in the flood

Wildlife will find a way

The good news is that wildlife is remarkably resilient. Ribbeck said that while the flooding is expected to be very high in the Atchafalaya, it is a positive step that the Corps is slowly opening the bays. That slow “trickle” instead of a tsunami-style wall of water will give wildlife more time to escape and seek refuge. Instead of a couple of days as it was in 1973, animals may now have a week or more to escape.

Muth said that while there will be short-term population losses and breeding impacts, the ecosystem will see positive long-term impacts. Replenishing the basin with nutrient-rich waters from the Mississippi can help spark more green growth. And while the opening of the Morganza was a manmade act, tremendous flooding can sometimes be Mother Nature’s way of cleansing the land.

“It’s going to be a long-term benefit for everything living out there,” said Muth.

Wildlife has already proven its ability to quickly rebound in the face of natural disasters. Muth recalled a trip to some cheniers in Cameron Parish after Hurricane Rita in 2005 when, after a 15-foot storm surge swept over the island he saw fresh coyote, deer and raccoon tracks four months later.

“I would not have believed it possible for any of those animals to survive violent flooding like that but some did. A lot of them died but there will always be survivors. Creatures have adapted to live with flooding. They’ll carry on,” Muth said.

Related Resources
  • Report
    Mississippi River Flooding: Natural Solutions for an Unnatural Disaster

    In a new report, the National Wildlife Federation has identified five ways government policies and practices are contributing to the extraordinary flooding and resulting impacts, as well as five specific recommendations to help policymakers avoid and minimize catastrophes like this.

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