Download Module PDF

As we discovered in previous modules, blue carbon refers to the carbon that is stored in marine and coastal ecosystems, particularly in mangroves, seagrasses, and saltmarshes. These ecosystems are highly productive and efficient at capturing carbon dioxide from the atmosphere, through the metabolic process of photosynthesis, and storing it in their biomass and sediments in the form of organic matter. The particulate organic matter that derives from adjacent terrestrial or marine ecosystems and that is carried in the water column, is also captured and stored in their sediments. Blue carbon is an important component of the global carbon cycle, as it helps to mitigate the impacts of climate change by removing carbon dioxide from the atmosphere.¹

To understand the relevance of blue carbon ecosystems to remove carbon dioxide from the atmosphere, it is important to quantify the amount of carbon stored in these ecosystems and the rates at which it is stored. This requires field assessments to measure the carbon that is contained in the biomass and in the sediment of the blue carbon ecosystems.²

Quantifying blue carbon in the field is a specialized task that requires expertise and training in ecological sampling and carbon accounting methods.³ This task is normally carried out by scientists. However, there are citizen science initiatives that aim to engage the public in collecting data on blue carbon ecosystems.^4,5

To go deep…

• The Blue Carbon Initiative
• The International Partnership for Blue Carbon

Carbon is an element that can be found in two forms, as inorganic carbon, and as organic carbon. Inorganic carbon refers to carbon compounds that are found as minerals such as calcium carbonate (CaCO₃), in the atmosphere in the form of carbon dioxide (CO₂) or dissolved in the ocean water in the form of carbon dioxide (CO₂), bicarbonate (HCO₃^–) and carbonate (CO₃^2-). Atmospheric or oceanic CO₂ is converted into organic carbon (phosphoglycerate, C₃H₇O₇P) by photosynthetic organisms. Mangrove and saltmarsh plants use atmospheric CO₂ whereas seagrass use dissolved CO₂. Phosphoglycerate is the precursor of all organic matter, which includes many compounds such as sugars, lipids, nucleic acids and proteins.

When we talk about blue carbon, we refer to the organic carbon amount in the biomass of living mangroves, saltmarsh, or seagrass plants, and in the organic matter that is buried in the sediment (microorganisms and plant and animal remains). In saltmarshes and seagrasses, the main stock of blue carbon lies in the sediment because the plants are small, whereas the blue carbon stock in the living biomass of mangrove trees is much higher.

Note that kelp, the marine forests composed of large brown seaweeds also store important quantities of organic carbon. These seaweeds grow on hard substrate 1 to 25 meters below the ocean’s surface and thus do not store carbon in sediment like other blue forests. Instead, kelp stores carbon in their living biomass temporarily, with shreds of kelp – known as detritus – eventually making their way to the seafloor where this carbon may be stored for hundreds of years. The science surrounding kelps´ capacity for long-term carbon storage is contentious and highly complex due to the variability and difficulty of measuring these blue carbon stocks. For this reason, this module will not include protocols for how to measure blue carbon in kelp.

Test your Knowledge!

1. What are the two forms of carbon mentioned in the text?
2. What is inorganic carbon, and where can it be found?
3. How is atmospheric or oceanic CO₂ converted into organic carbon?
4. Which plants use atmospheric CO₂, and which use dissolved CO₂? 
5. What is the precursor of all organic matter? 
6. Where is the main stock of blue carbon in saltmarshes and seagrasses? 
7. How does the blue carbon stock in the living biomass of mangrove trees compare with that of saltmarshes and seagrasses? 

To quantify blue carbon in the biomass of mangrove, saltmarsh and seagrass ecosystems, you need to estimate the biomass density, or the amount of dry biomass per unit area. This can easily be done in saltmarsh and seagrass ecosystems by collecting plant material from a known area, then weighing the samples after drying to a constant weight. To sample a known area, you can use a square structure, known as a quadrat, or a cylinder, known as a core, to collect its biomass. The estimation of the biomass density of a mangrove forest is only possible using allometric equations, i.e. equations that relate tree diameter, height, and/or volume to biomass. There are different allometric equations available for different mangrove species and regions.

After acquiring samples, the carbon content of the biomass must be measured using a CHN (carbon, hydrogen and nitrogen) analyzer. The equipment burns the sample under high-temperature and the resulting gas mixture is separated into individual components of carbon, hydrogen, and nitrogen, which are then detected and quantified. An alternative way is using a conversion factor that relates biomass to carbon content. The conversion factor may depend on the species in question.

To quantify the blue carbon stored in the sediment, you can directly measure the organic carbon of soil samples with a CHN analyzer or measure the organic matter and use a conversion factor relating organic matter to carbon content. There is an easy method to estimate organic matter content, called loss-on-ignition (LOI). It involves heating sediment samples to a high temperature to burn off the organic matter (which is converted into gaseous carbon, that is, carbon dioxide) and then weighing the remaining ash. The difference in weight between the original sample and the ash represents the amount of organic matter, which can be converted to organic carbon using a conversion factor.

You can access the sedimentary blue carbon protocol in the module resources here. It serves as a valuable guide to delve into the fascinating realm of blue carbon and gain insights into the assessment of coastal sediments.

Test your Knowledge!

1. What do we need to measure to quantify blue carbon in plants? 
2. How can we measure the amount of plant material in saltmarshes and seagrasses?
3. How can we estimate the amount of plant material in mangroves?
4. How can we measure the amount of carbon present in the plant material?
5. How can we measure the blue carbon stored in the sediment?
6. What is the “loss-on-ignition” method, and how does it help us estimate the amount of organic matter in the sediment?

To go deeper…

New manual for measuring, assessing, and analyzing coastal blue carbon.

Citizens can certainly play a role in contributing to blue carbon accounting, conducting field assessments of blue carbon following a scientific standardized protocol and after being trained by professionals. In this module, we present a protocol to measure the sedimentary blue carbon to be conducted by teachers and their students. This initiative started in the ambit of an environmental education network for coastal ecosystem services, established in the Algarve region, southern Portugal, by researchers of the Marine Plant Ecology Research Group of the Centre of Marine Sciences of Algarve, together with local schools, ONGs and Environmental Education Centers.

Click here to learn more and access the article, “Ocean Literacy to Mainstream Ecosystem Services Concept in Formal and Informal Education: The Example of Coastal Ecosystems of Southern Portugal”.

Several examples of citizen-driven blue carbon science projects have been conducted in various locations worldwide. Here are a few noteworthy examples:

1. “Seagrass Watch”: Seagrass Watch is a global citizen science program that trains volunteers to monitor seagrass meadows in their local areas. Seagrass meadows are important blue carbon ecosystems, and monitoring their health and extent can provide valuable data for research and conservation efforts.
2. “Mangrove Watch“: Mangrove Watch is a citizen science program focused on the monitoring and management of mangrove ecosystems in Australia and other countries. Mangroves are important blue carbon ecosystems, and the program provides training and resources for volunteers to collect data on the health and extent of mangrove forests.
3. “Blue Carbon Lab“: Blue Carbon Lab is a citizen science project focused on the collection of data on blue carbon ecosystems in Australia. Volunteers are trained to collect data on seagrass beds, salt marshes, and other coastal ecosystems, which can be used to inform conservation and restoration efforts.

To go deeper…

• See more on using citizen science to estimate surficial soil blue carbon stocks in Great British saltmarshes citizen science.⁶

1. Identify the study area: Determine the location and extent of the area you want to assess for blue carbon. This could include mangroves, seagrasses, and saltmarshes.
2. Select the sampling method: Choose a suitable method for sampling the blue carbon ecosystem. There are several methods available, including core sampling.
3. Collect the data: Once you have selected the sampling method, you can begin collecting the necessary data. This may involve collecting sediment samples, measuring water depth, or taking measurements of vegetation cover. For more information, see the “Blue Carbon Protocol” in the resources.
4. Analyze the data: After collecting the data, you will need to analyze it to determine the amount of carbon stored in the ecosystem. This may involve laboratory analysis of sediment samples.
5. Interpret the results: Once you have analyzed the data, you can interpret the results to understand the carbon storage capacity of the blue carbon ecosystem. You can also use the results to identify areas for conservation or restoration.
6. Communicate the findings: Share the results of your blue carbon assessment with relevant stakeholders, including government officials, local communities, and conservation organizations. This can help to raise awareness of the importance of blue carbon ecosystems and inform policy decisions related to conservation and restoration efforts.
7. Other activities may include:
   • Habitat assessments: Conducting habitat assessments to identify areas with high biodiversity and blue carbon potential. This can involve field surveys, remote sensing, and other methods to determine the distribution and extent of different ecosystems.
   • Biodiversity sampling: Collecting data on species composition, abundance, and distribution within different habitats. This can involve using techniques such as transect surveys, point counts, and camera traps.
   • Carbon sampling: Collecting sediment and plant samples to measure the amount of carbon stored in blue carbon ecosystems.
   • Community engagement: Engaging with local communities to raise awareness of the importance of biodiversity and blue carbon ecosystems, and to involve them in monitoring and conservation efforts.
   • Restoration activities: Implementing restoration activities to enhance biodiversity and blue carbon storage capacity. This can involve restoring degraded habitats, planting seagrass beds, and mangrove reforestation.
   • Data analysis and reporting: Analyzing the data collected from biodiversity and carbon sampling activities, and reporting on the results. This can involve using statistical methods to analyze data and presenting the results in maps, graphs, and other formats.

By combining biodiversity sampling with blue carbon assessments, it is possible to gain a comprehensive understanding of the ecological and carbon storage values of coastal ecosystems. This information can be used to inform conservation and restoration efforts, as well as to raise awareness of the importance of these ecosystems for climate mitigation and adaptation.

When organizing a field trip to a blue carbon ecosystem, it is important to ensure the safety of the participants and the preservation of the environment. Be sure to follow all rules and regulations established for field trips and promote awareness of the importance of preserving the blue carbon ecosystem.

We now aim to improve the sedimentary blue carbon assessment protocol and apply it to other regions and countries to be performed by schoolteachers and their students. The process is educational and scientifically sound, and it may provide sets of data that can be used in blue carbon scientific assessments. A Georeferenced Data Base Portal was developed to upload the data obtained, after scientific validation.

Georeferenced Database

Introduce the following data into the Georeferenced Database:

1. Sampling date
2. Name of site
3. Coordinates (latitude and longitude)
4. Type of habitat (high saltmarsh, low saltmarsh, seagrass, mangrove, non-vegetated, other_specify)
5. Dominant species
6. Volume of sample (Volume = 5cm³ x 5 syringes = 250cm³, or otherwise if other volumetry was used)
7. Weights P1 to P6
8. Carbon content (% ) if available.

Get ready to dive into the blue carbon movement and unleash your impact in safeguarding our precious coastal ecosystems! Together, we can delve deeper into the realm of blue carbon and unlock its power in combating climate change. Let’s embark on an exciting journey of exploration, knowledge acquisition, and proactive measures to nurture a healthier planet. Step up and venture into Module 5.