Mangroves rebound following hurricanes, helping protect against greenhouse gas, study shows

Karl Schneider
Naples Daily News

Mangrove wetlands have been called nature’s nursery for their ability to shelter a variety of aquatic life.

They also protect shores from storm surge and provide habitat for birds.

And new research details another benefit: keeping carbon out of the atmosphere.

Researchers out of Florida Gulf Coast University’s Everglades Wetland Research Park housed at the Naples Botanical Garden studied red mangrove wetlands at Naples Bay to determine how Hurricane Irma affected the capacity for the plants to store carbon.

Lauren Griffiths, lead author of the study, and Bill Mitsch, director at the research park, found mangroves have the ability to rebound and will continue storing carbon in leaves and branches within a couple years following a hurricane, but carbon stores below ground in and around the roots systems remain low.

Red mangroves at sunrise in the 10,000 Islands. The Everglades area offers a multitude of outdoors opportunities.

“Specifically looking at the Naples sites where I was studying, the really big takeaway was below ground carbon decreased at every site pre- to post-hurricane,” Griffiths said.

She has a couple ideas as to why that could be, one of which being carbon-rich sediment is permanently washed away, but said it’s alarming because the total amount of carbon being stored decreases.

Carbon, specifically carbon dioxide, acts as a greenhouse gas when released into the atmosphere by trapping heat that should radiate off the Earth’s surface, leading to the planet and oceans warming. There is more carbon in the atmosphere today than at any point in the last 800,000 years, according to a 2020 study published by the National Oceanic and Atmospheric Administration.

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Red mangroves are especially good at capturing carbon below ground. Near Naples Bay, the tidal flows back and forth between the freshwater creeks and the salty bay waters bring sediments through the root systems, which catch the carbon-rich silt and hold it underwater.

During Hurricane Irma, water levels in Naples Bay suddenly dropped 3 to 4 feet, and as the storm passed the flow reversed and 4 to 5 feet of water rushed into the area, washing that carbon away.

Griffiths said some of that carbon may not be lost altogether as it could be used by the mangroves to regrow the branches and leaves lost to the winds.

Mangroves are resilient, however, and the study concludes that the foliage lost during the storm rebounds within two years of a major hurricane.

“We did see a loss of carbon in the soil immediately after the hurricane,” Mitsch said. “We then found after about two years, the above ground carbon compensated for that, and the system was back on even keel.”

It makes sense mangroves would rebuild so quickly, he said. Ecosystems are adapted for their environment, and major hurricanes are a regular occurrence in the subtropics here in Florida.

“That’s a very important feature of mangroves,” he said. “They are the perfect ecosystems to have on our coastlines.”

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As intensity and frequency of tropical storms is predicted to increase due to climate change, the study says “mangrove swamps are needed more than ever to provide a carbon sink while being resilient enough to continue to store carbon quickly after they are disturbed.”

Carbon in the atmosphere is rising at a steady rate of 1% each year, the study says, and current mangrove systems must be protected to “continue to store carbon, protect humans from dangerous storms and serve as nurseries for marine life.”

In a Tuesday March 14, 2017 photo, 3-month-old roseate spoonbills perch on a mangrove branch near their nesting area of South Nest Key. Audubon Florida Everglade science researcher, Dr. Jerry Lorenz is studying how wading birds like spoonbills population reflects the health of Florida Bay.  (Carl Juste/Miami Herald via AP)

Griffiths said it’s important to not mess with the water flows serving mangroves.

“What ends up happening in general is we do construction that ultimately affects the freshwater influx to mangroves, and some studies show that can seriously hinder the carbon sequestration of mangroves,” she said. “It’s really important, especially when mangroves are already stressed by something like hurricanes, to kind of limit the stress in other locations like upstream hydrology alterations.”

Karl Schneider is an environment reporter. You can reach him at kschneider@gannett.com. Follow on Twitter @karlstartswithk