Alabama’s Mobile-Tensaw Delta is a more-than 400-square-mile (1,036-square-kilometer) expanse of cypress swamps, oxbow lakes, marshland, hardwood stands and rivers unusually rich in plant and animal diversity.
It's also a critical conduit between the rest of Alabama and the Gulf of Mexico, draining two-thirds of the state and cleaning water and warehousing silt that could damage Mobile Bay and its renowned fisheries.
But the delta — which many in the U.S. have never heard of and many in Alabama have never experienced — faces pressure from development and climate change.
So residents, scientists and environmentalists are working to protect the entire watershed, from northern Alabama to the Gulf, and to raise awareness.
Here's what to know:
Ecological diversity
The Mobile-Tensaw Delta is an important spawning ground and habitat for hundreds of fish species. There are hundreds of bird species, rare flowers and carnivorous plants.
Yet its ecological riches are only a fraction of what exists in the rest of Alabama, including the 44,000-square-mile (113,959-square-kilometer) Mobile River watershed that feeds the delta.
American elms, decimated by disease in other parts of the country, thrive in the delta and its watershed, reflecting “this ancient, ancient heritage” of genetically hardy trees, says Bill Finch, a forest researcher. Alabama is central to the nation’s oak diversity, with about 40 species, compared to about a dozen in the Great Smoky Mountains National Park.
The state's fish diversity is unmatched on the continent, with about 350 species, including more than 230 in the Mobile River basin. There are over 100 crawfish species, almost three dozen turtle species. More mussel species than all of South America.
“I know I live in the most beautiful place in the world,” says 77-year-old Lucy Hollings, who has lived in the delta all her life. “It’s a piece of heaven to me.”
Potential threats
Yet the delta and its watershed are by no means pristine or untouched.
Forests of giant cypress and water tupelo were clear cut as recently as the 1980s by loggers who used helicopters to airlift logs from swamps. Chemical plants, paper mills and a factory that made the now-banned insecticide DDT have contaminated land and water. Upstream dams altered waterflow into the delta, blocked fish passage and led to extinction of dozens of freshwater species, some found only in the watershed.
Over 21 million tons of coal ash stored in an unlined pit near the Mobile River also present a potential threat to the delta, though the coal-fired power plant that generated the waste agreed in January to remove it. The state did not require its removal, although a breach could be potentially catastrophic for the delta. The EPA recently denied the state’s request to handle coal ash permits, saying its policies weren’t protective enough.
But other threats are unresolved. A canal built to connect the Tennessee and Tombigbee rivers in northern Alabama could allow invasive Asian carp to reach the Mobile River system and the delta, potentially devastating native fish. The Fish & Wildlife Service says a few carp have been found and removed downstream of the canal, with biologists relying on early detection while other control measures are considered.
Stronger hurricanes and saltwater surges also have caused serious erosion and killed trees, biologists say.
Increased rainfall and sea level rise with climate change also will push saltwater farther into the delta — potentially causing forested areas to convert to marshland and shrinking the important area where saltwater and freshwater mix. That adds urgency to efforts to acquire more land outside the delta for species to move in the future, says Judy Haner, the Alabama Nature Conservancy’s coastal programs director.
Plans in progress
This spring, The Nature Conservancy of Alabama bought 8,000 acres (3,237 hectares) of forested wetland between the Tombigbee and Alabama rivers at the top of the delta. The land, which regularly floods and is an important bird habitat and fish-spawning and feeding area, was in danger of being logged to produce wood pellets for European power plants.
“It would’ve been a horrible loss to the system,” says Conservancy Director Mitchell Reid, who calls the land “a critical piece of the puzzle” as the group works to protect the upper delta by keeping large tracts intact.
The Nature Conservancy also is working with the U.S. Army Corps of Engineers to design fish bypasses around two aging dams on the Alabama River to allow species to swim up from the Gulf and delta to historical spawning grounds.
While similar projects out West often focus on one species, Reid says, the Alabama plan could benefit about 20. Biologists hope it will lead to rediscovery of the critically endangered Alabama sturgeon, which hasn’t been seen for more than 15 years, and recovery of the threatened Gulf sturgeon in the Mobile River watershed.
The conservancy also is working to restore ecosystems in urban areas as far north as Birmingham, about 200 miles (322 kilometers) from Mobile, to prevent floodwater from sending sediment down rivers that could harm the delta.
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