Brazilian researchers have developed an index that can measure the health of mangrove soils at different stages. When applied to degraded, restored, and preserved areas, the index revealed that healthy mangroves, including recovered ones, provide ecosystem services at nearly maximum capacity. In contrast, deforested mangroves have only a small fraction of this potential.
The Soil Health Index (SHI) ranges from 0 (worst) to 1 (best) and is described in an article published in the journal Scientific Reports. By translating complex processes into a simple metric, the tool can help managers set conservation and restoration priorities.
The SHI was constructed from a set of variables that together represent the main physical, chemical, and biological processes responsible for soil functioning.
It incorporates attributes related to carbon dynamics, such as soil texture, organic carbon content, and pseudototal iron; the fixation of contaminants, especially different forms of iron minerals; and nutrient cycling, including biological indicators based on the enzymatic activities of soil microorganisms. Together, these variables reflect the soil's functional state and its capacity to provide ecosystem services.
In the search for nature-based solutions to address the climate crisis, mangroves offer an opportunity to generate environmental and social benefits. In addition to being important carbon sinks, they support fishing and help contain coastal erosion, among other services.
Nevertheless, it is estimated that 30% to 50% of the world's mangroves have been lost in the last 50 years. This process may be accelerated by climate change, including rising sea levels and more frequent extreme weather events, as well as deforestation and urban expansion.
Brazil has the second largest mangrove area in the world – about 1.4 million hectares along the coastline, second only to Indonesia – and the most extensive continuous stretch, which is located between the states of Amapá and Maranhão. These areas are important for fishing due to their wide biodiversity, with more than 770 species of fauna and flora.
Results
When applied to the Cocó River estuary in the Brazilian state of Ceará, the SHI revealed contrasting conditions in the area, including recovery in restored areas and the associated implications for ecosystem services. Mature mangroves had the highest SHI values (0.99 ± 0.03), and degraded sites had the lowest (0.25 ± 0.01).
Regions replanted nine and 13 years ago had intermediate values (0.37 ± 0.01 and 0.52 ± 0.02, respectively). The oldest regions performed better, indicating gradual recovery.
"The research sought to quantify important aspects related to the health of mangrove soils and their ecosystem services, such as carbon sequestration, contaminant immobilization, and nutrient cycling. We set up a scale from 0 to 1 to monitor ecosystem restoration in relation to the recovery process," explained environmental manager Laís Coutinho Zayas Jimenez to Agência FAPESP. "My dream now is to use the Soil Health Index in a practical application. To show my peers, the managers, that it's possible to analyze whether a mangrove that has undergone recovery is fully producing ecosystem services and how long it takes for this to happen."
The article is based on her doctoral thesis from the Graduate Program in Soils and Plant Nutrition at the Luiz de Queiroz School of Agriculture at the University of São Paulo (ESALQ-USP). It was developed under the guidance of Tiago Osório Ferreira and with the support of FAPESP .
Jimenez is currently the head of the mangrove sector at the Forestry Foundation's Biodiversity Directorate. She leads a groundbreaking project that aims to measure the carbon stock of São Paulo's mangroves and detect the presence of toxic elements, such as heavy metals, in their soils.
The work is being carried out in partnership with the Center for Carbon Research in Tropical Agriculture ( CCARBON ), a FAPESP Research, Innovation, and Dissemination Center ( RIDC ) based at ESALQ-USP.
The Forestry Foundation is an agency of the São Paulo Department for the Environment, Infrastructure, and Logistics (SEMIL) that is responsible for the state's Conservation Units. At least 16 of the more than 100 units have mangroves.
"Even if the restoration of mangrove functions is rapid, that can't be used as an argument for not protecting them from degradation. While some ecosystem services, such as carbon sequestration and nutrient cycling, have been observed to resume, others, such as controlling coastal erosion, take longer," Jimenez points out.
"Blue carbon"
Mangroves are called "blue carbon forests" because they absorb large amounts of CO₂ from the atmosphere and store organic carbon in the soil for decades more efficiently than tropical forests do. However, changes in land use and pollution increasingly threaten mangrove soils, compromising their functionality.
The global initiative Mangrove Breakthrough aims to restore and conserve 15 million hectares of mangroves globally by 2030. According to the initiative, these ecosystems store the equivalent of more than 22 gigatons of CO₂. Losing just 1% of the remaining mangroves could lead to emissions equivalent to those produced by 50 million cars each year.
"As the study was conducted in a recovery area, the results debunk the idea that the ecosystem is resilient to anthropogenic interventions. We show that it can be degraded at a very rapid rate. But the good news is that the system also recovers quickly, provided that restoration is carried out in an assisted and elaborate manner, respecting the local conditions of the environment in which it's located. This makes it possible to restore the ecosystem's functions and its ability to provide services," says Professor Hermano Melo Queiroz , from the Department of Geography at the Faculty of Philosophy, Languages, and Human Sciences (FFLCH) at USP.
Queiroz is one of the corresponding authors of the article, along with Ferreira, the director of dissemination and a researcher at CCARBON. Other members of the group include Professor Maurício Roberto Cherubin , director of research at the center and a soil health specialist, and Francisco Ruiz .
"In this research, one of the objectives was to translate information on very specific biogeochemical processes for use by environmental managers. By showing that carbon stocks return to restored mangrove areas, the index sends a very important message in the fight against climate change," says Ferreira, who has been researching mangrove areas for over 25 years and contributed to the creation of a database containing information on the entire Brazilian coast.
Ferreira coordinates the project "BlueShore – Blue Carbon Forests for Offshore Climate Change Mitigation," which was developed within the Research Center for Greenhouse Gas Innovation ( RCGI ), an Applied Research Center ( ARC ) set jointly by FAPESP and Shell, featuring the participation from other companies and hosted by the Engineering School (POLI) of USP.
Open and changeable
The researchers point out that one unique feature of the SHI is the ability to include specific information about each ecosystem and its environment for different regions of the country. For example, it is possible to enter data on ecosystem services, such as carbon sequestration and contaminant immobilization, as well as geochemical data, such as the amount of phosphorus.
"The greater the amount of phosphorus, the more beneficial it is for the ecosystem. However, in the case of mangroves, depending on the context, excess phosphorus can cause contamination or eutrophication," says Queiroz.
Eutrophication causes the excessive proliferation of algae and cyanobacteria in mangrove areas. These organisms block sunlight and consume oxygen, resulting in foul odors, fish deaths, loss of aquatic biodiversity, and deterioration of water quality.
Now, the scientists say the next step is to understand what type of carbon is "returning" to these soils and how stable it is.
The study also inspired a new project, "Unraveling the Health of Brazilian Mangrove Soils" , which is funded by FAPESP and will apply a similar methodology in different regions of the country.
The proposal combines soil analysis, remote sensing, and spatial modeling to map the health of mangrove soils and their carbon sequestration potential. The initiative aims to generate the first large-scale map of mangrove soil health in Brazil.
About São Paulo Research Foundation (FAPESP)
The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at www.fapesp.br/en and visit FAPESP news agency at www.agencia.fapesp.br/en to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at http://agencia.fapesp.br/subscribe .
