Global climate change has helped warm the waters of the Mississippi River and, as a result, extend the growing season along the delta by more than two weeks longer than in 1983, according to a newly published study from Louisiana researchers.
The results have implications for the state’s planned coastal restoration work and on the talks being held about how to turn any additional marsh growth into carbon credits to provide money for more coastal work.
“If you’ve got a longer growing season, you’re likely to have more growth,” said David White, Loyola University New Orleans professor of biological sciences. The co-author of the study was Jenneke Visser, associate director of the Institute for Coastal and Water Research at the University of Louisiana at Lafayette.
Published in the journal Aquatic Botany, the study is the result of 30 years of monitoring two sections of the Mississippi River delta in the Delta National Wildlife Refuge. The purpose of the work was to see how the plants on river-formed mudflats evolve over time.
The latest study is an outgrowth of that research and focuses on two areas off of Brant Pass.
As the Mississippi River brings in water, nutrients, sediment and even pollution through this offshoot of the main river, mudflats form in the shallow water. Initial plants will start growing on this new land, but different plants will take over as the mudflats continue to grow and change.
Researchers found that between 1983 and 2012, increased river water temperatures increased the growing season by seven-tenths of a day per year and produced more plant mass.
The growth was hampered by the amount of water and sediment coming through the pass, but researchers say that doesn’t mean diversions aren’t necessary.
White explained the natural diversion of river water into the area is what provided the initial land that allowed the plants to grow at all. As theses marshes developed, perennial plants took over, only to be covered when new sediment was deposited.
Without the sediment to provide a foundation, the land wouldn’t be there.
“That’s what we need in the way of diversions,” White said. “The plants are still going to grow, they’re just going to start growing above ground a little later.”
Another use for the research would be in the efforts of private companies to turn the carbon stored by new wetland plants into money from global and state carbon markets.
Carbon markets buy and sell greenhouse gas reductions as a way to combat climate change and could be a way for the state to raise money through marsh creation to pay for future restoration projects.
Additional marsh creation means the state or other entities could accumulate carbon credits through creating wetlands to be sold to companies or other entities looking to offset the greenhouse gases they release.
New Orleans company Tierra Resources has been working for years on setting up carbon credit with Louisiana wetlands. With support from a number of sources including Entergy, Tierra Resources got a carbon credit methodology certified in 2012.
“The increase in plant growth observed in our delta means that more carbon dioxide is removed by photosynthesis, which means less in the atmosphere, which means less global warming,” White said.
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