Seagrass meadows have an important climate protection function due to their long-term carbon storage potential. An international research team led by the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) has now been able to show that seagrass beds have a stronger influence on the carbon and sulfur cycling in
A major global study using teabags as a measuring device shows warming temperatures may reduce the amount of carbon stored in wetlands. The international team of scientists buried 19,000 bags of green tea and rooibos in 180 wetlands across 28 countries to measure the ability for wetlands to hold carbon
Discussions of valuable but threatened ocean ecosystems often focus on coral reefs or coastal mangrove forests. Seagrass meadows get a lot less attention, even though they provide wide-ranging services to society and store lots of climate-warming carbon. But the findings of a new University of Michigan-led study show that seagrass
By Jenny Black The Carbon Cycle It is likely that we have all heard of carbon but what might not be known is the fundamental role it plays in our ecosystems. Carbon will naturally move between the atmosphere and the earth’s surface through interactions between organisms and ecosystems in a
Seagrass meadows have an important climate protection function due to their long-term carbon storage potential. An international research team led by the Leibniz Institute for Baltic Sea Research Warnemünde (IOW) has now been able to show that seagrass beds have a stronger influence on the carbon and sulfur cycling in subtropical coastal areas than previously thought. Of particular interest is the important role of sulfur, which stabilizes organic carbon, regardless of whether it is sequestered in the calcareous sediments of subtropical seagrass meadows or remains in dissolved form. The results of the study were recently published in Communications Earth & Environment. Seagrass ecosystems are particularly worthy of protection as they provide shelter and food for a wide diversity of marine species and act as natural wave breakers that reduce coastal erosion. They also store so-called “blue carbon”—carbon that stays trapped in the ocean and in coastal ecosystems for a long time and therefore cannot have a climate-damaging effect as carbon dioxide (CO2). Seagrass not only stores carbon via photosynthesis in its plant components, but also buries the organic material of other organisms that accumulates in the dense plant cover in its root sediments. How do subtropical seagrass meadows ‘tick?’ “It has been known for some time that not all seagrass meadows ‘tick’ in the same way when it comes to carbon storage. Tropical and subtropical seagrass meadows in particular can sometimes release more carbon than they store,” says Mary Zeller. The marine chemist is an expert in biogeochemical seabed processes and lead author of the new study on the seagrass carbon cycle. “However, as seagrass meadows are particularly widespread in warm ocean regions, we wanted to take a close look at the processes that ultimately determine their carbon balance. This is the only way to correctly estimate their climate protection potential,” says the scientist, who now works at MARUM—Center for Marine Environmental Sciences at the University of Bremen, but was a researcher in IOW’s Geochemistry & Isotope Biogeochemistry working group during the seagrass study. Zeller and her German-American research team focused on subtropical seagrass beds located in Florida Bay in the south of the United States. In order to understand whether and how organic matter—and therefore carbon—is released from the sediments into the water column, they combined state-of-the-art geochemical and molecular methods to analyze sediments, pore water and the surrounding water. The focus of the involved IOW researchers Zeller and Michael Böttcher was to analyze various stable isotopes as biogeochemical markers to understand the complex matter transformation processes, as well as to employ a special method of high-resolution mass spectrometry, which allows the determination of the molecular formula of individual molecule types in complex mixtures of organic molecules. Porewater and sediment inorganic and stable isotope geochemical data. Credit: Communications Earth & Environment (2024). DOI: 10.1038/s43247-024-01832-7 Surprisingly close coupling of the sulfur and carbon cycles The researchers found that almost 10% of all organic matter of the investigated seagrass meadows is bound to their calcareous sediments. This type of sediment is a characteristic of tropical and subtropical seagrass ecosystems, because in the warm environment the metabolic processes of the seagrass plants cause carbonate, which is dissolved in the seawater, to be converted into lime that accumulates in the root area. If these sediments disintegrate, the bound organic substances can dissolve and enter the water column, making them potentially available again to the marine carbon cycle. “We were able to provide direct proof for the first time that seagrass sediments actually release organic carbon. In particular, our molecular analyses have shown that the dissolved organic molecules in the surrounding water correspond to 97% in structure and composition with the lime-associated organic material in the sediments,” Zeller explains. A crucial role in the mobilization of organic substances from the sediments is played by the sulfur chemistry in the seabed, which the seagrass meadows stimulate like a kind of biocatalyst: Their roots actively transport oxygen into the sediment, which facilitates the oxidation of sulfur compounds by microorganisms. This produces acid, which causes the calcareous sediments at the seagrass roots to partially disintegrate, releasing previously bound organic matter. Additionally, these microbial processes produce highly stable organic sulfur compounds that are largely resistant to biological decomposition and degradation by the UV radiation of sunlight. Improved modeling of the climate protection potential of seagrass “The fact that the sedimentary and dissolved carbon pools in seagrass meadows are so closely coupled was previously unknown and was therefore not adequately taken into account in climate modeling,” comments Zeller on the results of the study. “In this context, it is also important that although the organic sulfur generated in seagrass beds mostly exists in dissolved rather than particulate form, it is apparently still a very long-lived carbon reservoir that cannot be easily metabolized into climate-active CO2,” Zeller continues. According to the marine chemist, the study could help to improve modeling of the “blue carbon” storage potential of the widespread tropical and subtropical seagrass meadows. “However, further research is needed to clarify whether the mechanisms found here are universal—i.e., whether they also apply to other ecosystems with similar rhizosphere processes, such as mangroves. It also needs to be clarified whether and what kind of impact environmental changes such as climate change have on these processes,” concludes Zeller. More information: Mary A. Zeller et al, The unique biogeochemical role of carbonate-associated organic matter in a subtropical seagrass meadow, Communications Earth & Environment (2024). DOI: 10.1038/s43247-024-01832-7 This article is republished from PHYS.ORG and provided by Leibniz-Institut für Ostseeforschung Warnemünde.
A major global study using teabags as a measuring device shows warming temperatures may reduce the amount of carbon stored in wetlands. The international team of scientists buried 19,000 bags of green tea and rooibos in 180 wetlands across 28 countries to measure the ability for wetlands to hold carbon in their soil, known as wetland carbon sequestration. While tea bags may seem an unusual instrument to measure this phenomenon, it is a proven proxy method to measure carbon release from soil into the atmosphere. However, this is the first time teabags have been used for a large-scale, long-term study and the tea leaves have revealed which types of wetlands are leaking the most carbon. RMIT University’s Dr. Stacey Trevathan-Tackett led the study as part of an Australian Research Council DECRA Fellowship while at Deakin University. “Climate effects on belowground tea litter decomposition depend on ecosystem and organic matter types in global wetlands” is published in Environmental Science and Technology. The global study involved 110 co-authors on the paper, along with many others who helped, such as undergraduate students and citizen scientists. Core team members included Dr. Martino Malerba and Professor Peter Macreadie from Deakin University and RMIT, Dr. Sebastian Kepfer-Rojas from the University of Copenhagen in Denmark and Dr. Ika Djukic from The Swiss Federal Institute for Forest, Snow and Landscape Research WSL. “This is the first long-term study of its kind, using this teabags method, which will help guide how we can maximize carbon storage in wetlands and help lower emissions globally,” said Trevathan-Tackett, who is now in RMIT’s School of Science. “Changes in carbon sinks can significantly influence global warming—the less carbon decomposed means more carbon stored and less carbon in the atmosphere.” Map of TeaComposition H2O sites across eight macroclimatic zones. Credit: Environmental Science & Technology (2024). DOI: 10.1021/acs.est.4c02116 Reading the tea leaves Tea bags provide a simple and standardized way to identify how climate, habitat type and soil type influence carbon breakdown rates in wetlands. At each site, scientists buried between 40 and 80 tea bags about 15 cm underground and collected these at various time intervals over three years, tagging their GPS location. They then measured their remaining organic mass to assess how much carbon had been preserved in the wetlands. The project used the two types of tea bags (green and rooibos) as measures for different kinds of organic matter found in soils. Green tea consists of organic matter that decomposes easily, whereas rooibos decomposes more slowly. Using both types of tea bags in this project enabled the researchers to gain a more comprehensive picture of the wetlands’ capacity for carbon storage. “This data shows us how we can maximize carbon storage in wetlands globally,” Trevathan-Tackett said. The Findings The team studied the effect of temperature in two ways: using local weather station data for each site and comparing differences in climate regions. “Generally, warmer temperatures led to increased decay of organic matter, which translates to reduced carbon preservation in soil,” Trevathan-Tackett said. The two tea types acted differently with increasing temperature. “For the harder to degrade rooibos tea, it didn’t matter where it was—higher temperature always led to more decay, which indicates that types of carbon we’d typically expect to see last longer in the soil were vulnerable to higher temperatures,” Trevathan-Tackett said. “With increasing temperatures, the green tea bags decayed at different rates depending on the type of wetland—it was faster in freshwater wetlands but slower in mangrove and seagrass wetlands. “Increasing temperatures may also help boost carbon production and storage in plants, which could help offset carbon losses in wetlands due to warmer weather, but this warrants further investigation with future studies.” Freshwater wetlands and tidal marshes had the highest tea mass remaining, indicating a greater potential for carbon storage in these ecosystems. The study’s findings are helping piece together the puzzle of wetland carbon sequestration on a global scale. Within the terrestrial TeaComposition initiative led by Djukic, information on litter decomposition has been collected at about 500 sites worldwide resulting in several peer-review publications. “Applying the common metric across aquatic, wetland, marine and terrestrial ecosystems allows for a conceptual comparison and understanding of key drivers involved in the control of global litter carbon turnover,” Djukic said. “Now that we are starting to get a better understanding of which environments are storing more carbon than others, we can use this information to ensure we protect these areas from environmental or land-use change.” The researchers will combine the data from this project with data from similar studies of land-based carbon sinks, including forests, to inform designs of predictive global models. More information: Stacey M. Trevathan-Tackett et al, Climate Effects on Belowground Tea Litter Decomposition Depend on Ecosystem and Organic Matter Types in Global Wetlands, Environmental Science & Technology (2024). DOI: 10.1021/acs.est.4c02116 This article is republished from PHYS.ORG and provided by RMIT. Explore our blog for insights on the latest research from across the globe. Click here
Discussions of valuable but threatened ocean ecosystems often focus on coral reefs or coastal mangrove forests. Seagrass meadows get a lot less attention, even though they provide wide-ranging services to society and store lots of climate-warming carbon. But the findings of a new University of Michigan-led study show that seagrass ecosystems deserve to be at the forefront of the global conservation agenda, according to the authors. It’s the first study to put a dollar value on the many services—from storm protection to fish habitat to carbon storage—provided by seagrasses across the Caribbean, and the numbers are impressive. Using newly available satellite data, the researchers estimate that the Caribbean holds up to half the world’s seagrass meadows by surface area, and it contains about one-third of the carbon stored in seagrasses worldwide. They calculated that Caribbean seagrasses provide about $255 billion in services to society annually, including $88.3 billion in carbon storage. In the Bahamas alone, the ecosystem services provided by seagrasses are valued at more than 15 times the country’s 2020 gross domestic product, according to the study published online June 21 in the journal Biology Letters. “Our study is the first to show that seagrass beds in the Caribbean are of global importance in their areal extent, in the amount of carbon they store, and in the value of the economic services they provide to society,” said study lead author Bridget Shayka, a doctoral student in the U-M Department of Ecology and Evolutionary Biology. “The findings underscore the importance of conserving and protecting these highly threatened and globally important ecosystems, which are critical allies in the fight against climate change.” One way to prioritize seagrass conservation would be to include those verdant undersea meadows in global carbon markets through projects that minimize loss, increase areal extent or restore degraded beds. The idea of selling “blue carbon” offset credits, which monetize carbon stored in coastal and marine ecosystems, is gaining traction for several reasons. For one, many island nations that have already been impacted by climate change—through increasingly intense hurricanes or rising sea levels, for example—have large areas of valuable coastal ecosystems that store carbon and that provide other services to society. Blue carbon (the name refers specifically to carbon stored in coastal and open-ocean ecosystems while “green carbon” refers more broadly to carbon stored in all natural ecosystems) offset credits could be a way for wealthier countries to compensate for their contribution to human-caused climate change while at the same time benefiting the economies of impacted countries and helping to conserve coastal ecosystems, which are among the most impaired in the world. Threats to seagrass meadows include coastal development, chemical pollution, recreation, shipping and climate change. “Because seagrass ecosystems are both highly important for carbon storage and sequestration, and are highly degraded globally, they represent an important burgeoning market for blue carbon,” said marine ecologist and study senior author Jacob Allgeier, an associate professor in the U-M Department of Ecology and Evolutionary Biology. “Yet, to date, a fundamental impediment to both evaluating seagrass and promoting it in the blue carbon market has been the lack of thorough seagrass distribution data.” For their study, the U-M-led team used newly available seagrass distribution data collected by the PlanetScope constellation of small DOVE satellites. They classified Caribbean seagrass ecosystems as either sparse or dense and estimated the amount of carbon in plants and sediments using data from Thalassia testudinum, the dominant seagrass species in the region. The researchers then calculated a conservative economic value for the total ecosystem services provided by seagrasses in the Caribbean and for the stored carbon, using previously published estimates for the value of services including food production, nursery habitat for fishes and invertebrates, recreation and carbon storage. Grouper, queen conch and lobster are among the commercially harvested animals that rely on Caribbean seagrass. Green sea turtles, tiger sharks and manatees also depend on it. To estimate the dollar value of the carbon stored in Caribbean seagrass beds, the researchers used $18 per metric ton of carbon dioxide equivalents, borrowed from California’s cap and trade program. In addition to Caribbean-wide estimates, the researchers calculated values for individual countries in the region: The Bahamas has the largest share of Caribbean seagrass (61%), providing total ecosystem services valued at $156 billion annually, including $54 billion in carbon storage. Cuba ranks second in areal seagrass coverage (33% of the Caribbean total), with a value of $84.6 billion per year for all ecosystem services, including $29.3 billion for carbon storage. The dollar value of the carbon in seagrasses around Cuba is equivalent to 27% of the country’s 2020 GDP. “Importantly, the degradation of seagrass beds often leads to erosion and sediment resuspension, which can create a positive feedback of increased seagrass loss and the release of C stored in sediments,” the authors wrote. “Blue carbon finance thus represents a potential mechanism by which the global community can invest in conserving and protecting these vital ecosystems.” More than 60 species of seagrasses grow in shallow coastal waters around the world. They evolved from land plants that recolonized the oceans 70 to 100 million years ago. In a separate paper accepted for publication in the journal Proceedings of the Royal Society, Allgeier and colleagues show that the construction of artificial reefs in the Caribbean can help protect seagrass ecosystems from human impacts, including nutrient pollution and overfishing. Seagrasses use photosynthesis to pull carbon dioxide from the atmosphere, then store the carbon in plant tissues. The seagrasses are quickly inundated by sediments, slowing decomposition. As a result, more than 90% of the carbon stored in seagrass beds is in the top meter of sediment. Caribbean seagrasses and associated sediments store an estimated 1.3 billion metric tons of carbon, according to the new study. That’s a big number, but it’s just 1.09% of the carbon contained in above- and below-ground woody biomass in the Amazon, and just 1.12% of the carbon in the biomass and soils of the world’s temperate forests, according to the new
By Jenny Black The Carbon Cycle It is likely that we have all heard of carbon but what might not be known is the fundamental role it plays in our ecosystems. Carbon will naturally move between the atmosphere and the earth’s surface through interactions between organisms and ecosystems in a process known as the ‘carbon cycle’. In the carbon cycle, carbon can be a gas in the form of carbon dioxide (CO₂), or solid within organisms and rocks. On land, in what is known as terrestrial ecosystems, CO₂ can be captured, or sequestered, from the atmosphere and stored within plants in the process called photosynthesis. Here, plants use CO₂ and sunlight to create food for the growth of new plant tissue. This is a very basic description of the carbon cycle but what is not mentioned is the role of the ocean and marine ecosystems. Carbon exists in the sea in multiple forms (as seen in Figure 1). It can be dissolved in the water itself, stored by organisms in their bodies, buried in soil, or stored in rocks (Barnes, 2020). Carbon will move throughout these different stages and will be stored for different lengths of time depending on the stage. For example, carbon stored in plants and animals will be stored for the duration of that organism’s life. After it dies, some of the carbon will be released back into the atmosphere as CO₂ as bacteria breaks it down, and some will be buried within the sediment. Carbon that is buried within the sediment can be trapped and stored for much longer periods of time. In some cases, carbon stored in the plant tissue of rainforests can be retained for decades or centuries, but carbon stored within sediment can last for millennia (Nellemann et al., 2009). Figure 1: the oceans role in the carbon cycle. What is Blue Carbon? Whilst all marine life has a part to play in the carbon cycle, there are certain ecosystems within our oceans that act as major carbon stores, or carbon sinks, capable of capturing carbon in numerous types of forms. Think of it as the oceans equivalent to terrestrial rainforests that capture carbon and store it within their plant tissue and soils (Nellemann et al., 2009). The main blue carbon ecosystems include seagrass meadows, kelp forests and mangrove forests (Macreadie et al., 2019). Carbon that is captured and stored is called blue carbon (Nellemann et al., 2009). Figure 2 shows the three main blue carbon environments mentioned above. Figure 2: three key blue carbon ecosystems; Mangroves, Seagrass Meadows, and Kelp Forests (Nellemann et al., 2009). How is Blue Carbon captured and stored? There are two forms of carbon, organic and inorganic carbon. Inorganic carbon can be found in the environment as CO₂. The storage of atmospheric CO₂ in the oceans is complicated due to the barrier of water between the atmosphere and the blue carbon stores below. Because of this, CO₂ must dissolve into seawater to reach the blue carbon ecosystems below. After dissolving, CO₂ can be used by plants for photosynthesis, or it is mineralised into a hard carbonate by the likes of coral reefs and shell building organisms. Organic carbon on the other hand is found within the tissue of living organisms. Like terrestrial plants, some blue carbon ecosystems such as seagrass meadows can photosynthesise and store carbon within their plant tissue. What is unique about blue carbon ecosystems is that they can store both organic and inorganic carbon that they have sequestered and collected themselves, as well as storing carbon that has been sequestered by other terrestrial and marine ecosystems. Tidal and fluvial systems bring carbon particles from other marine and terrestrial suspended within its waters. Blue carbon ecosystems provide resistance to the flowing particles in the water column. They slow the speed of the water and capture the particles, encouraging them to be deposited into the sediment below. Dense root systems in the sediment provide protection preventing particles from being re-suspended. Over time, the carbon particles build up with old particles being buried below influxes of fresh material burying and protecting the carbon. This unique characteristic is the reason why blue carbon ecosystems can store ten times more carbon by burial than terrestrial ecosystems (McLeod et al., 2011). Figure 3 uses the example of a seagrass meadow of how different sources of carbon particles can be caught and stored within its sediment. Figure 3: seagrass and its role in the blue carbon cycle. Vital Ecosystems Blue carbon ecosystems offer many benefits to our oceans and coastlines including environmental protection, promotion of high biodiversity as well as carbon sequestration and storage. With governments and multi-national corporations acknowledging blue carbon ecosystems as the climate-combating solutions that they are, it is exciting to see blue carbon being given the recognition that it deserves. What is important for the future is continued protection and restoration of these environments. If we help to protect them, they will help us in our fight against climate change. Jenny is a masters student studying Aquaculture, Environment and Society in association with the University of the Highlands and Islands, University of Crete, Université de Nantes, and Radboud University. Her interest in blue carbon began with her Geology BSc dissertation where she investigated carbon storage within the soil of Scottish seagrass meadows. Since then, she has been focusing on the potential of blue carbon ecosystems and how they can be involved in carbon storage, environmental restoration, and food supply. References Barnes, D., (2020). What Is Blue Carbon and Why Is It Important?. Front. Young Minds. 8:154. doi: 10.3389/frym.2019.00154 Kennedy, H., J. Beggins, C. M. Duarte, J. W. Fourqurean, M. Holmer, N. Marb a, J. J. Middelburg. (2010). Seagrass sediments as a global carbon sink: Isotopic constraints. Global Biogeochem. Cy. 24: GB4026. doi:10.1029/2010GB003848 Macreadie, P.I., Anton, A., Raven, J.A. et al. (2019). The future of Blue Carbon science. Nat Commun 10, 3998 https://doi.org/10.1038/s41467-019-11693-w McLeod, E. et al., (2011). A blueprint for blue carbon: toward an improved understanding
