New study helps restorations pin down how much nitrogen their local mangroves can bury
by Kiran Das-Goel
Mangroves tell stories. Some tell of defending shorelines from rising waters and extreme weather, or sheltering young marine life at its most vulnerable stages. Others whisper of vast amounts of carbon stored in their soils, known as blue carbon.
But one story has flown under the radar. While mangroves are famous carbon-storing powerhouses, their ability to store nitrogen—an element with more local impacts—has rarely received the limelight.
A recent study shows mangroves play an important role in burying nitrogen.
“There’s this big blue carbon movement, while nitrogen has kind of been the underrated little brother,” said biogeochemist Havalend Steinmuller, co-author and assistant professor at Louisiana Universities Marine Consortium.
“Having mangroves bury excess nitrogen is a great ecosystem service,” said Andre Rovai, co-author and principal investigator at the Smithsonian Environmental Research Center. Scientists estimate mangroves save billions globally through nitrogen removal.
Having more nitrogen doesn’t seem like a bad thing on paper. It’s one of the building blocks for life on Earth.
“It’s one of those things that when you add more of it, it can increase productivity,” said Josh Breithaupt, co-author and assistant research faculty at the Coastal and Marine Laboratory at Florida State University. “In some coastal wetlands, more nitrogen’s going to allow them to do more photosynthesis.”
But too much nitrogen has a cost. In the water, nitrogen runoff can lead to massive explosions of algae and harmful algal blooms. When blooms die and decompose, they can pull large amounts of oxygen from the water. Marine life suffocates, and it can be many years before anything can survive in these so-called “dead zones.”
Coastal wetlands intercept nitrogen’s journey from the land to the sea. Before it can seep deeper into an estuary and cause dead zones, mangroves can trap and remove some nitrogen by accumulating it in their root tissues. The dense soils of mangroves can store nitrogen for centuries if undisturbed.
Math to the Rescue
“What motivates conservation?” Breithaupt asked. “Is it habitat preservation, or is it carbon, or in this case, is it nitrogen sequestration?” Most likely, it depends on a location-by-location basis.
Before beginning a restoration project, it’s a good idea to get your numbers straight, according to Rovai. But finding the numbers conservationists need isn’t easy. One of the main challenges with studying nitrogen is a lack of data. Luckily, the new study developed equations for how much nitrogen is in soils, by using already known carbon data.
“Now people can just estimate nitrogen content from carbon content, which might be easier to obtain,” said Rovai. One possible benefit of using the authors’ equations is a more nuanced understanding of coastal ecosystems. As Steinmuller noted, a mangrove in a delta can’t be expected to bury nitrogen in the same way as a mangrove somewhere else.
“Part of what we’re trying to pioneer is a unified framework that will maximize how we manage opportunities for protection and restoration of coastal systems,” said Steinmuller.
Nitrogen, the ‘Underrated Little Brother’
For some, nitrogen might be a more inspiring motivator than carbon for restoration efforts.
Carbon’s story is complicated. It begins in the atmosphere, and understanding its role in a warming world requires learning about processes invisible to the naked eye. It’s an important story, but it’s not always the most accessible.
Nitrogen-fueled dead zones, however, are a different story.
“When water quality goes down, it’s not something you can argue about,” said Breithaupt. “It’s potentially easier to convince people nitrogen is something we need to clean up.”
Ecosystem services have a price. But it’s not one we have to pay when nature is doing the work for us. Mangroves perform nitrogen burial naturally, keeping waterways clean and fisheries healthy. Their work is visible to anyone. It can also be felt in the estimated $8.7 billion mangroves save globally through nitrogen removal.
“It’s important for people to understand the contribution of these systems to society and the services we would have to pay for if nature wasn’t doing it for us,” Rovai said.
Dig Deeper:
Andre Rovai and Why the Military Cares About Mangroves
Digging for Blue Carbon in the Mangroves of Belize
