Ways to Mitigate Carbon You Didn't Know: Mangroves

Mexico is home to one of the most valuable ecosystems in the world: mangroves. This group of vegetation is also known as marine forests or coastal wetlands, a differential factor being the ability to withstand high levels of salinity, something that other flood-resistant trees do not tolerate as well. The mangrove ecosystem is home to a great diversity of species including shrubs, palm trees, trees, ferns and epiphytes - plants that grow on trees. Despite the fact that these ecosystems have a great diversity of flora and fauna, they are characterized by dominating the group of species called mangroves, organisms belonging to a botanical family that are distinguished by their stilt-like aerial roots that allow them to breathe in waterlogged soils (CONABIO, 2020).

These ecosystems are highly productive, generating a very particular range of ecosystem services, economic goods and sociocultural meanings. Mangroves occur at river mouths, coastal lagoons, and wetlands. They are born from dividing the sea from the mainland, so they are influenced by fresh water from hydrological basins such as rivers, streams and groundwater and, in the same way, mixed with marine waters rich in salts and minerals. Thanks to these conditions, Mangroves they have physiological adaptations such as the above-mentioned aerial roots that allow them to survive these environments that we would think are inhospitable to a large amount of vegetation (O. Khairnar, 2021; CONABIO, 2020 and 2013).

The mangrove is home to several endangered species.

In general, they inhabit tropical and subtropical coastal areas around the planet, are distributed in 120 countries and cover about 12% of the world's coasts: the most recent global figure for mangrove area, estimated by the Global Mangrove Watch for the year 2016, was 135,881.65 km2. Mexico is one of the countries with the largest area of mangroves in the world, with 9,501 km2. So far, approximately more than 50 species of mangroves are known; in Mexico, we have six species and one variety (CONABIO 2020, 2013; Santamaría 2014; Spalding et al. 2010). At the local level, the characteristics of mangroves change according to environmental gradients related to height, soil type, degree of flooding, salinity levels and natural and human disturbances (CONABIO, 2013). However, wherever they are found, they play an indispensable role in the ecosystem, since they act as a nursery for larval and juvenile stages of a large number of marine organisms and terrestrial fauna that live between the surface and branches of mangroves. The mangrove is home to several species classified as endangered or in some category that makes them vulnerable, such as the jabirú stork, some iguanas, certain crocodiles, raccoons, howler monkeys, spider monkeys and the king of all: the jaguar (O. Khairnar, 2021; CONABIO, 2013).

Beyond the great natural wealth that this type of ecosystem houses, mangroves provide us with different ecosystem services because they act as natural barriers for protection and control of floods, protection against hurricanes, they function as biological filters in the retention and processing of some fertilizers used in agriculture, they supply groundwater and They are large carbon sinks (O. Khairnar, 2021; CONABIO, 2013).

However, even with all these virtues, mangroves in the world have been affected by natural causes, but above all, by the action of human populations. 35% of the world's mangroves have been lost in the last two decades due to different pressures such as natural disasters, pollution, lack of planning for urban, industrial and tourist development, as well as agricultural, livestock and aquaculture development, which have displaced and reduced considerable areas of this vegetation (CONABIO, 2013; Macintosh and Ashton 2003).

Research carried out by the National Commission for the Knowledge and Use of Biodiversity (CONABIO) identified that in Mexico there are 81 mangrove sites with biological relevance and with ecological rehabilitation needs. In addition, these ecosystems are classified as vulnerable ecosystems and species such as red, black, white and botoncillo mangroves are threatened under the criteria of Official Standard 059, where all species in some range of danger of extinction are found in our country (CONABIO, 2013). That is why the protection of the mangrove ecosystem is also broadly considered in the General Wildlife Act (2007), which prohibits any change that affects its integrity, which has been one of the best strategies of the Government of Mexico to stop destruction and promote the recovery of that ecosystem. The need to continue with the establishment of priority sites for conservation and protection is imminent, in the same way, it is essential to become aware of this problem. Mangroves are a type of ecosystem that is fundamental to combat current and future impacts of climate change in our country; in Mexico, the carbon reserve in wetlands has been estimated at 282 megagrams of carbon per hectare (mg/Ha).

Blue carbon refers to carbon captured by living organisms in coastal and marine ecosystems, including marshes, mangroves, and seaweed forests.

Why do we say that the mangrove ecosystem is a climate ally? It is known that as in the case of terrestrial forests, mangroves accumulate carbon fluxes at a considerable rate, with CO2 being one of the most important greenhouse gases (Woodroffe, 2002). In addition to accumulating carbon in biomass, that is, in their stems, leaves, roots and bark, mangroves are being incorporated into another category called Blue carbon. Blue carbon refers to carbon captured by living organisms in coastal and marine ecosystems, including marshes, mangroves, and seaweed forests. Unlike forest carbon, where storage takes place primarily in biomass and in the volume of plant cover (for example, large areas of forest), most of the blue carbon is found in the soil. Some studies estimate that blue carbon has an annual accumulation rate two to four times higher than tropical forests (Alongi, 2016).

Within these ecosystems, CO2 from the atmosphere is absorbed through photosynthesis, where oxygen is returned to the atmosphere and carbon is generally stored in two structures: temporarily in the foliage and stems of plants, while the rest is sequestered for a long period in woody biomass and soils. Blue carbon ecosystems mainly occupy intertidal and shallow-water environments, where their distribution, productivity and vertical accumulation rate are strongly influenced by sea level and the space available to accumulate sediments. These ecosystems represent just over 0.2% of the world's marine surface, yet they are responsible for approximately 50% of the total carbon contained in ocean sediments (McLeod) et al. , 2011).

The ability of mangroves to develop, capture and store carbon depends on the change in sea level within the coastline, on the accumulation of soil in the seabed and on its complex root system. The soils where mangroves live consist of a vertical layer of sediment submerged by the tide, of varying thickness (called variously peat or Mud) that supports anaerobic decay pathways -in the absence of oxygen- and that has a moderate to high carbon concentration. This absence of oxygen allows carbon to decay slowly, so it is capable of accumulating for longer periods of time than an average terrestrial ecosystem (Kirwan and Megonigal, 2013).

To face a global problem, we must think globally.

The rate of carbon accumulation in mangrove soil averages 5.8 mm of soil per year, with the most floodable part of the soil allowing the highest carbon storage due to the higher concentration of particles in it, so mangroves in high intertidal areas have less accumulation in soil than those located closer to the sea. In this regard, some studies have been carried out where it is estimated that 78% of the carbon that the mangrove is capable of capturing is stored in soils, while 20% is stored in biomass and the remaining 2% represents dead or fallen wood (Bautista-Olivares et al. , 2020; Adame et al. , 2020; Ahalaya and Park, 2019).

Globally, mangroves can store up to five times the carbon present in tropical forests per hectare, sequestering more than 2 tons of carbon on average per hectare per year.

Although blue carbon is a cutting-edge form of mitigation, something very similar happens with terrestrial forests: excessive or illegal logging can release large concentrations of carbon into the atmosphere - the same as was previously stored in their bodies - so the protection of this ecosystem is essential to combat climate change.

Better management of mangroves can mitigate CO2 emissions and improve the storage potential of disturbed areas of the ecosystem; however, efforts must also focus on improving predictions of future emissions, not only storage of carbon, but of other greenhouse gases; mangroves are especially functional in limiting the production of methane - gas produced naturally in response to bacterial decomposition of organic matter - as this gas and many microscopic communities produce it incompatible with high levels of salinity (Livesley and Andrusiak, 2012). Management effectiveness is based on understanding how many emissions can be avoided through specific actions, for example, reducing land use change and increasing restoration and protection efforts (Bautista-Olivares et al. , 2018).

With all of the above, we must say that there are still several challenges for the recovery of the mangrove and for effectively mitigating climate change through these coastal ecosystems. On the one hand, we must fight to maintain and protect the surface of mangroves in the country and in the world, because as we saw, that 0.2% of the marine territory is responsible for capturing a lot of atmospheric carbon; on the other hand, we must raise awareness of the value of blue carbon ecosystems in the sequestration and long-term storage of carbon, so intersectoral action, as well as environmental education, are fundamental pillars. It is also important to note that in order to face a global problem we must think globally, so conservation and protection work must focus on understanding and preserving the connectivity between mangroves and their associated habitats such as coral reefs and seagrasses. Finally, one last challenge that we must overcome lies in the financing of this type of project. There is no doubt that marine and coastal ecosystems are important sources of carbon sequestration, so starting to include them within a robust climate strategy is part of the solution; mangroves are more than just coastal patches where a large number of organisms coexist; they are an ecosystem that demonstrates, with its peculiarities, a real strategy to adapt to and mitigate climate change.

About the author:

Xochitl is a contributor to the Toroto blog and a teacher in Sustainability Sciences. He is currently pursuing his doctorate in Sustainability Sciences in the field of Vulnerability and Response to Global Change.

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