An early frost turned some of the water plants brown, but their presence shows that the delta continues to grow.
Robert Twilley of the Louisiana Sea Grant College at LSU drives a tour boat down the Wax Lake Outlet. The trees in the background help protect the Morgan City area from hurricane winds and storm surge.
Order out of chaos: Nature has a plan for Wax Lake Delta
CENTERVILLE – The stretch of Louisiana coast between the Wax Lake Outlet and Atchafalaya River deltas is a tangle of contradictions.
Much of Louisiana’s coastal wetlands are being eroded away. But not here. These deltas are growing.
The plants that play a starring role in that growth can’t stand saltwater. Yet tides exert a powerful influence on how and where they take root.
Coastal erosion often is blamed on the work of humans: flood control levees that divert the sediment that should enrich coastal wetlands, canal-cutting that allows saltwater into freshwater marsh, even the introduction of the nutria, whose gluttony robs the wetlands of the grasses that keep land in place.
But not here. People and nature are working together on building this new land. And there is order in the way they go about it.
That order creates a buffer against storm surge and hurricane winds, protecting St. Mary Parish people from hurricanes. And it can even filter the nitrate runoff coming down the river to create the dead zone in the Gulf.
Robert Twilley is the director of the Louisiana Sea Grant College Program at LSU, and a published specialist in the way deltas form in St. Mary Parish, Latin America and the Pacific.
Twilley, a geomorphologist, said there’s a joke about how in the Wax Lake Delta, geologists and biologists are finally operating on the same time scale.
Geologists often measure time and natural processes in millions of years. But here, standing on a stretch of land called Camp Island in the Atchafalaya Wildlife Management Area, the land is less than half a century old.
Twilley was one of the academics, officials and wildlife specialists who took reporters on a tour of the Wax Lake Delta on Friday to promote the work of restoring Louisiana’s coastal wetlands.
On one side of the narrow stretch of land is the water that pours down the Atchafalaya system, diverted from the Red and Mississippi rivers by the Old River control structure north of Baton Rouge. It carries the sediment that began the process of building this land
On the other side is a swampy stretch of land punctuated by stubby, isolated trees and small pools of open water. Birds are flying in, darting around and taking off again. They don’t pay much attention to a duck hunter’s shotgun blasts coming from across the open water on the other side.
The water that flows by here contains the sediment of the kind that makes life hard for the Port of Morgan City board, which struggles to find funding to dredge commercial waterways open a few miles away. But here the sediment creates land.
Camp Island, which is big enough to be home to camps and even something like public restrooms, began to emerge from the water during the flood of 1973. But the process was under way before then, at least as far back as the 1940s. That’s when the Wax Lake Outlet was cut through the wetlands to provide additional flood protection for the Morgan City area by diverting some of the water coming down the Atchafalaya.
Twilley and Alisha Renfro, a wildlife scientist with the National Wildlife Federation, dug into the water to pull out a core sample. Here, the bottom 80% of the sample was a mineral-rich mixture deposited by the river. The top and most recent portion of the core was material left behind by the living and dying of plants.
At some point, aquatic vegetation begins to colonize the sediment.
“When it does, it starts putting down roots and putting down organic material that the plant is producing,” Twilley said.
And as that process is repeated over and over again, the organic material begins to rise.
“So much of the ecology out here, what we see relative to the ecology, is because of elevation,” Twilley said. “That’s the key. For every increment of change in elevation, I can tell you which plants are going to colonize in that region.”
Near the end of the tour, closer to the mouth of the delta, Twilley eases the tour boat he’s steering out of the channel and into a stand of spiky grass sticking out of the water. There are no trees here, and no stretches of land.
He uses a hook to dip into the 18 inches of water beneath the boat for a strand of what looks like overcooked spinach.
The grass and subsurface plants are still living, dying and building new delta.
Not much organic material has accumulated yet.
Trying to pull out of the grass again, the boat gets grounded, if that’s the word in a place where there is no ground. Using an oar to push the boat clear doesn’t work. The material beneath the boat is loose and can’t be used to get purchase for a good push.
One of the other boats gives us a tow back into the channel, and we head back up the channel.
Remember that spinach-like plant?
“This is the delta,” Twilley said. “The emergent delta.”
He waves his hand toward the open water to the southwest.
“There’s a lot of delta forming out there,” Twilley said. “You just can’t see it. It’s all underwater.”
Heading northeast again, small trees begin to reappear along with plants like cattails that hug the slivers of land that poke out of the water.
Some of the smaller plants have withered and turned brown. That happened when the area got an unexpected November frost, Twilley said.
But the same thing happened in July because of a different kind of weather. Hurricane Barry pushed saltwater into the delta, killing some of the plants.
Even this close to the Gulf, the emerging delta is a freshwater ecology. But the tides do play their role as they influence the water level.
Science has divided the delta into zones. Subtidal areas might be anywhere from just under the water to about 19 inches below. That’s home to underwater plants. “Supratidal” areas are at least 13 inches above the water and can support the high end of the succession, including trees.
In between are “intertidal” areas where the emerging land is from just under the water to maybe 13 inches above it.
Each zone has its own family of vegetation.
The tour began with a quick run down the outlet from its junction with the Intracoastal Waterway. Here the succession is advanced enough to support tall stands of willows along both banks.
Along the way, Twilley talked about how the local delta can absorb maybe a third of the nitrates that come down the river in the form of runoff from fertilized fields up north. If they reach the Gulf, they can feed algae that robs the water of oxygen, creating the notorious dead zone.
But in the delta, the same nitrates can fertilize the plants that help turn water into land.
And he talked about the value of trees and the importance of the freshwater system.
“The only tree that can stand saltwater is the mangrove, and they can’t stand frost,” Twilley said. “We do have some mangroves along the coast.”
Better are the willows and other trees that line the banks here.
“It’s the nourishment of the river that allows this blanket of trees,” Twilley said. “And it is storm surge protection, premium storm surge protection.
“It knocks down the wind. And if you want roughness to knock down the storm surge, trees are the best. Not wetlands, grasses.
“Trees are the best.”