NASA Examines Louisiana Delta System, Looks At Global Forecasts

MIKE ISLAND, Louisiana. – Erosion, sinking land and rising water levels due to climate change have killed the woods of Louisiana where a 41-year-old Native American chief played as a child. Nearby, in the Mississippi Delta system, middle school students can stand on islands that emerged in the year they were born.

NASA is using high-tech airborne systems as well as boats and mud-clearing work on the islands for a five-year, $ 15 million study of these adjacent areas of Louisiana. One is harnessed to a river and grows up; the other is disconnected and dying.

Scientists at NASA and a half-dozen universities from Boston to California aim to create computer models that can be used with satellite data to let countries around the world know which parts of their declining deltas may be strengthened and what are the lost hopes.

“If you have to choose between saving one area and losing another instead of losing everything, you want to know where to put your resources to work to save the livelihoods of everyone who lives there,” said lead scientist Marc. NASA Jet Simard. Propulsion laboratory.

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As the oceans rise due to climate change, the of the world River deltas – home to seafood nurseries and over 300 million people — are sink and shrink.

To find out where to shore up dying deltas, NASA studying the water entering and leaving the Atchafalaya and Terrebonne basins in Louisiana, the sediments they carry, and the plants that can slow the flow, trap sediment and remove carbon from the air.

Louisiana holds 40% of the country’s wetlands, but they are disappear quickly – approximately 2,000 square miles (5,180 square kilometers) of the state has been lost since the 1930s. about 80% of the country’s wetland losses, according to the US Geological Survey.

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Using two types of radar and a spectrometer measuring more colors than the human eye can distinguish, high-altitude NASA planes collected information such as the height of the water, the slope, sediment, and plant types and density. Some measurements are as precise as a few centimeters (less than an inch).

On ships and islands, scientists and students from across the country, sample and measure everything from currents to tree diameters. Their findings will be used to calibrate airborne instruments.

“I’ve been working here for 15 years, and one of the hardest parts of working in a delta is you can only touch a small piece of it at a time and understand a small piece at a time,” said Robert Twilley. , professor of oceanography and coastal sciences at Louisiana State University. “We now have the ability to work with NASA to understand the entire delta. ”

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The Mississippi River drains 41% of the continental United States, collecting 150 million tonnes (130 million metric tonnes) of sediment per year. But, largely because of flood prevention dikes, most of the sediment drains into the Gulf of Mexico rather than settling in wetlands.

“The deltas are the babies of the geological timescale. They are very young and fragile, in a delicate balance between sinking and growing, ”says NASA on the Delta-X project website.

In geological time, young means thousands of years. At this scale, Louisiana’s Wax Lake Delta takes its first breaths. It dates back to 1942, when the Army Corps of Engineers dug an outlet from the lake to reduce the threat of flooding in Morgan City, about 20 miles away. Sediments from the Atchafalaya River filled the lake and then began to create islands in the gulf.

The new islands are covered with black willow trees and, in spring, thigh-high butterweed topped with small yellow flowers.

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The older wetlands in the areas studied by Delta-X planes are more diverse, their soil rich in humus from generations of plants. Along near Hog Bayou, blue buntings and scarlet tanagers soar through the magnolia branches and skinks climb the trees. In the swamps, ospreys nest atop bald cypress trees and alligators float in the water below.

In addition to working at LSU, Twilley has spent about nine years as Executive Director of the Louisiana Sea Grant College Program, which uses the Wax Lake Delta as a Classroom for middle and high school students.

“We take the children and make them stand on an earth that was formed in the year they were born. Said Twilley.

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In contrast, the adjacent Terrebonne basin is shrinking so rapidly that the government pay to move the Biloxi-Chitimacha-Choctaw Indian Band of Jean Charles Island from an endangered island to higher ground.

This group is not the only Native American group to lose ground.

“The wooded areas that we used to roam when we were kids – they are dead,” said Chief Shirell Parfait-Dardar of the Grand Caillou / Dulac Band of the Biloxi-Chitimacha Indians, based less than 80 kilometers from Wax. Lake delta.

“Ghost forests” are common in degraded deltas where salt water seeps in as the land sinks and erodes, LSU’s Twilley said.

Louisiana is considering two projects that would divert sediment from the Atchafalaya River to build land in the Terrebonne Basin, but a decision is more than a year away, according to the state’s Coastline Restoration and Preservation Authority.

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The study of Delta-X becomes downright granular. A team from the California Institute of Technology studying how sediments move and settle on Earth and other planets will analyze the amounts of sediment in high tide and low tide water samples, breaking down the particles into a hundred sizes.

One way LSU researchers measure the amount of soil formed by sediment is by sprinkling white feldspar dust on the ground.

They return to see how deep it is buried by new sediment. They do this by injecting liquid nitrogen into hollow tubes to freeze the dirt and mud around them. When the tubes are pulled, the frozen “popsicles” show a white ring. They measure from there to the top.

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In the Terrebonne Basin, such sedimentation cannot keep up with subsidence and sea level rise. “So the wetlands are essentially drowning,” Twilley said.

Planes and boats came out in March and April and will leave in the fall for a second round of measurements. And two international satellites are program for launch next year, each carrying one of two types of radar used over Louisiana.

To assess how plants affect the movement of water, the long wavelengths of L-band radar can measure water level changes in open and vegetated canals, NASA’s Simard said. And the high-frequency Ka-band radar can measure the surface height of open water, showing how it tilts and where it moves.

“All the tools they implement are really impressive,” said Indiana University sedimentary geologist Douglas Edmonds, who is not part of the project but has worked with many researchers.

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“The project itself puts its finger on a really critical question for many deltas around the world – how this deltaic land is formed and what processes prevail,” he said.

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Follow Janet McConnaughey on Twitter: @JanetMcCinNO

Copyright 2021 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.


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