According to a new study published in Science Advances on May 22, 2020, Louisiana’s coastal marshlands are in danger of disappearing within the next 50 years because of sea-level rise due to global warming.
Coastal wetlands represent a family of ecosystems that are prone to potentially irreversible collapse because of external stresses. The wetlands at the base of the Mississippi River have crossed a “tipping point,” according to the study, which is based on hundreds of measurements of the Mississippi Delta.
The team of researchers found that marshes can withstand a certain amount of relative sea-level rise — amounting to about a tenth of an inch per year. However, sea levels are currently rising at a rate of one to two inches a year due to climate change and land subsidence.
“Previous investigations have suggested that marshes can keep up with rates of sea-level rise as high as half an inch per year, but those studies were based on observations over very short time windows, typically a few decades or less,” said Torbjörn Törnqvist, Lead researcher and Tulane University earth and environmental science professor.
This means that sea-level rise at the current rate could reach up to 6 to 9 millimeters per year in 50 years, completely submerging any coastal marshes. “We are, if you believe this study, past the tipping point,” Törnqvist said. “There is no way back anymore.”
Louisiana’s mitigation strategy
In May 2019, Louisiana released a sweeping plan called LA SAFE, detailing climate adaptation strategies and underscoring the problem of coastal land loss. The plan is a detailed blueprint for coping with global warming, according to Digital Journal.
Louisiana’s coastal land loss continues at the alarming rate of nearly a football field every hour. This loss of coastal wetlands continues, even though the state is separately working on a $50 billion, 50-year Coastal Master Plan, focusing on coastal restoration and flood risk reduction projects.
Louisiana has lost 2,000 square miles of coastal wetlands over the past century due to erosion and land subsidence. However, it has been challenging for researchers to predict the fate of the remaining 6,000 square miles. The thing is this – Even though the LA SAFE master plan has been fully implemented, it is likely Louisiana will continue to experience net land loss,” the LA SAFE executive summary says.
The actual study
To get a complete picture covering the vulnerability of the marshlands, 355 boreholes were made across the Mississippi Delta (MD) that were used for a paleo-marsh analysis that covers the past 8,500 years.
The information gleaned from the study shows that because of extensive damming in the drainage basin, the present-day sediment supply from the Mississippi River is likely lower than it was during the early Holocene. Bottom line? “On balance, however, early Holocene conditions—a period with no detrimental human impacts—likely favored marsh resilience compared to the present day,” reads the study’s conclusion.
The loss of the coast is inevitable, Törnqvist said, but drastically curbing greenhouse gas emissions to prevent sea-level rise would slow land loss so that the coast doesn’t wash away in a matter of decades.
