Amazon Mangroves ‘Twice as Carbon Rich’ as Its Rainforests
By Daisy Dunne
The vast mangroves of the Amazon store twice as much carbon per hectare as the region's tropical forests, new research shows.
The relatively understudied ecosystem also stores 10 times more carbon than Amazon savannahs—a type of grassy plain with sparsely populated trees, according to the study.
However, the wetlands face threats from deforestation and climate change, the researchers say. Introducing more measures to protect mangroves will be key to preserving its large carbon store, they add.
The findings provide "yet more evidence of the extraordinary carbon stocks found in mangroves" worldwide, another scientist told Carbon Brief.
The Amazon is well known for its 167m hectares of rainforest, but is less known for being home to close to 1m hectares of "mangrove" forests.
Mangroves are trees and shrubs that grow in coastal waters across the tropics and subtropics. They are most easily recognized by their tall protruding roots, which they use to anchor themselves against incoming tides.
The new study, published in Biology Letters, is the first to make an on-the-ground estimate of how much carbon is stored in the Amazon's vast wetlands.
It finds that, on average, Amazon mangroves store 511 tonnes of carbon per hectare—roughly double that of the region's rainforests. Writing in their research paper, the authors said:
"The carbon stocks of the Amazon mangroves were over twice those of upland evergreen forests [rainforests] and almost 10-fold those of tropical dry forest [savannahs]."
For the study, the researchers visited nine mangroves—along with three salt marshes (a type of coastal grassland)—within the Brazilian Amazon.
At each site, they took measurements of the amount of carbon stored "aboveground," in the trees and fallen leaf litter, and "belowground," in the roots and soil.
To measure carbon stocks, the researchers measured changes to "biomass"—the weight amassed from the production of new leaves and shoots, or the thickening of a tree trunk, for example.
Plants take in CO2 from the atmosphere during photosynthesis and later use it to build and extend their trunks, stems and roots. Because of this, measuring changes to biomass gives scientists an idea of how much carbon is being stored in a given area over time.
The researchers then compared their estimates to previous data on carbon storage in the Amazon rainforest.
The chart below shows the average amount of carbon stored in tonnes per hectare by Amazon mangroves (far left) and Amazon rainforests (second left). The charts also include results from the salt marshes (second right) and data taken from a previous study by the researchers undertaken in desert-like "Caatinga" and savannah-like "Cerrado" ecosystems.
On the chart, green shows the results for aboveground carbon, brown shows the results for shallow belowground carbon and black shows the result for deep belowground carbon. (Rainforest soil tends to be shallow and nutrient-poor, while deep deposits of soil can build up in mangrove forests.)
Estimated carbon stock in tonnes per hectare in Amazon mangroves and forests, "Caatinga" (desert-like) mangroves and forests, salt marshes and "Cerrado" (savannah) ecosystemsBoone Kaufmann et al. (2018)
The results show that, on average, Amazon mangroves store around twice as much carbon per hectare as Amazon forests.
The majority of the carbon stored by mangroves is held in the soil, the research shows. Wetland soils tend to be carbon-rich because they are waterlogged, which slows the rate at which plant matter decomposes.
When decomposition is slow, carbon-rich materials are able to build up, explained Dr. Mark Spalding, a marine scientist and honorary fellow at the University of Cambridge, who was not involved in the study. He told Carbon Brief:
"The soils are very carbon rich. This is because they are permanently waterlogged and, so, carbon doesn't break down. Freshwater peats have similar soil carbon concentrations."
The tightly-packed nature of mangrove trees also enhances carbon storage in comparison to forests, which tend to be more sparse, he added.
The results suggest that protecting the Amazon wetlands could play a larger role in slowing climate change than previously thought, the authors say.
Amazon wetlands are currently threatened by deforestation—often to make way for fish farming—as well as rising temperatures, which could cause wetlands to dry out by increasing rates of evaporation. In their research paper, the authors said:
"The vast extent of Brazilian mangroves coupled with the large quantities of greenhouse gas emissions that results from deforestation underscores their potential value in climate change mitigation."
The findings provide evidence of the "extraordinary carbon stocks found in mangroves," Spalding said, but a key question remains about how stable this carbon is:
"Whether this carbon is short-lived or whether a significant proportion is being buried for the long-term in offshore sediments is a very important research question."
Tropical Forests Lost 40 Football Fields of Tree Cover Per Minute in 2017 https://t.co/Xp1B25yonb @EARTHWORKS @GreenpeaceAustP— EcoWatch (@EcoWatch)1530135305.0
Reposted with permission from our media associate Carbon Brief.
This week marks the official start of fall, but longer nights and colder days can make it harder to spend time outdoors. Luckily, there are several inspiring environmental films that can be streamed at home.
1. Kiss the Ground<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="ccc5f0c92a5603e68aec39e56b0db02a"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/K3-V1j-zMZw?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p><strong>Streaming On: Netflix</strong></p><p><strong>Premiere Date: Sept. 22</strong></p><p>Between <a href="https://www.ecowatch.com/wildfires-california-washington-oregon-photos-2647585008.html" target="_self">wildfires devastating the U.S. West Coast</a> and <a href="https://www.ecowatch.com/tropical-storm-beta-landfall-2647760268.html" target="_self">storms battering the Gulf</a>, the impacts of the <a href="https://www.ecowatch.com/climate-change/" target="_self">climate crisis</a> can feel overwhelming right now. <em><a href="https://kissthegroundmovie.com/" rel="noopener noreferrer" target="_blank">Kiss the Ground</a> </em>offers an alternative to all of the bad news by focusing on solutions.</p><p>The film, directed by Josh and Rebecca Tickell and narrated by Woody Harrelson, explains how we can heal the Earth through "regenerative agriculture," farming practices that draw carbon dioxide from the atmosphere and into soil as a way to restore soil health, which in turn boosts ecosystems and food supplies.</p><p>"<em>Kiss the Ground </em>shows how feasible it is to make these changes at a grassroots level immediately and make a truly substantive impact with low cost and easy to implement solutions," Executive Producer RJ Jain said in an email. "This is why I got involved."</p>
2. Public Trust: The Fight for America's Public Lands<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="5338f7a2931e356910026e5fd76fac56"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/jsKMTAaj_wQ?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p><strong>Streaming On: YouTube</strong></p><p><strong>Premiere Date: Sept. 25, 2 p.m. EDT </strong></p><p>This <a href="https://www.patagonia.com/films/public-trust/" target="_blank">award-winning documentary</a> tells the stories of Indigenous activists, journalists, whistleblowers and historians working to protect America's <a href="https://www.ecowatch.com/tag/public-lands" target="_self">public lands</a>. The film focuses on three political struggles: the shrinking of <a href="https://www.ecowatch.com/tag/bears-ears" target="_self">Bears Ears</a> National Monument in Utah, the mining of Boundary Waters Wilderness in Minnesota and the opening of the <a href="https://www.ecowatch.com/tag/Arctic-National-Wildlife-Refuge" target="_self">Arctic National Wildlife Refuge</a> to fossil fuel exploration.</p><p><em>Public Trust</em> was directed by David Garrett Byars and produced by Jeremy Rubingh. Patagonia Films, Patagonia founder Yvon Chouinard and actor Robert Redford are executive producers. It will be <a href="https://www.youtube.com/watch?v=OGjnIG7puzY" rel="noopener noreferrer" target="_blank">released</a> on YouTube in time for <a href="https://www.ecowatch.com/national-public-lands-day-2640656776.html" target="_self">National Public Lands Day</a>.</p><p>"Our country is fortunate to have millions of acres of public lands, including National Parks, Monuments, Wildlife Refuges and Wilderness set aside for future generations," Redford said. "Sadly, these lands that belong to you and me are under unprecedented threats from the greed of big corporations, eager to weaken restrictions in the pursuit of profits. Many of our current politicians are also to blame. <em>Public Trust</em> tells the story of citizens who are fighting back. It's a much-needed wake-up call for all of us who want to preserve our unique and wild cultural heritage."</p>
3. David Attenborough: A Life on Our Planet<span style="display:block;position:relative;padding-top:56.25%;" class="rm-shortcode" data-rm-shortcode-id="156438a30836a765d7a92982545fc334"><iframe lazy-loadable="true" src="https://www.youtube.com/embed/B_OFZvAd05Y?rel=0" width="100%" height="auto" frameborder="0" scrolling="no" style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe></span><p><strong>Streaming On: Netflix</strong></p><p><strong>Premiere Date: Oct. 4</strong></p><p>Beloved nature broadcaster <a href="https://www.ecowatch.com/tag/David-Attenborough" target="_self">David Attenborough</a> has spent his career introducing viewers to the wonders of our planet. In recent years, his footage of albatrosses swallowing <a href="https://www.ecowatch.com/tag/plastics" target="_self">plastic</a> in <em>Blue Planet II</em> has been credited with <a href="https://www.ecowatch.com/2018-fighting-plastic-waste-2624606566.html" target="_self">helping to ramp up</a> the global fight against plastic pollution. Now, in this <a href="https://www.wwf.org.uk/" rel="noopener noreferrer" target="_blank">World Wildlife Fund</a> (WWF)-produced <a href="https://www.attenborough.film/" rel="noopener noreferrer" target="_blank">documentary</a>, he reflects on the defining moments of his career and the devastating changes he has witnessed.</p><p><em>David Attenborough: A Life on Our Planet,</em> which was also produced by Silverback Films and directed by Alastair Fothergill, Jonnie Hughes and Keith Scholey, features an intimate conversation between Attenborough and Sir Michael Palin as the broadcaster reflects on his life and a career that took him to every continent on Earth. In addition to streaming on Netflix, the movie will be available in select theaters starting Sept. 28.</p><p>"For decades, David has brought the natural world to the homes of audiences worldwide, but there has never been a more significant moment for him to share his own story and reflections," WWF executive producer Colin Butfield said in a <a href="https://www.wwf.org.uk/updates/david-attenborough-life-our-planet" target="_blank">statement</a>. "This film coincides with a monumental year for environmental action as world leaders make critical decisions on nature and climate. It sends a powerful message from the most inspiring and celebrated naturalist of our time."</p>
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