A DAY IN THE LIFE OF A BLUE CARBON SCIENTIST Studying seagrasses to analyse their climate change mitigation potential Pemika Apichanangkool is a docto...
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A DAY IN THE LIFE OF A BLUE CARBON SCIENTIST Studying seagrasses to analyse their climate change mitigation potential Pemika Apichanangkool is a doctoral student at the University of Technology in Sydney (UTS), Australia and is studying the role of seagrasses for climate change mitigation. The objective of her research is to compare the carbon stocks between pristine and degraded seagrass beds. Many habitats contain large stores of carbon laid down by vegetation and other natural processes over centuries. If these ecosystems are degraded or damaged by human activities, their capacity to function as a carbon sink is lost and significant emissions of carbon dioxide (CO2) can contribute to climate change. Conserving and restoring terrestrial forests, and more recently peatlands, has been recognized as an important component of nature-based solutions to climate change mitigation. These approaches have now been further broadened to manage other natural systems that contain rich carbon reservoirs and to reduce the potentially significant emissions from their conversion and degradation. In particular, the coastal ecosystems of salt marshes, mangroves and seagrasses sequester and store large quantities of coastal “blue carbon” in both the plants and in the sediment below them. These ecosystems are being degraded and destroyed at a rapid pace along the world’s coastlines, resulting in globally significant emissions of carbon dioxide into the atmosphere and ocean, and contributing to climate change.

Pemika’s research results show clear evidence of the important role of seagrass as a “blue carbon” reservoir and the negative effect of seagrass loss on atmospheric carbon. This brief gives you an insight into Pemika’s research activities.

Unless otherwise indicated, all photos © Pemika Apichanangkool

This study examines the mono-specific meadow of E. acoroides and T. hemprichii, the two common seagrass species. These two seagrass species show differences in their growth form and canopy size. T. hemprichii has leaves growing between 10-40 cm long, while E. acoroides has leaves that can become up to 150 cm tall. Sampling was also conducted at a site with degraded seagrass beds, located at Kao Bae Na, Haad Chao Mai National Park, Trang Province, the Andaman Sea, Thailand. In order to learn

Enhalus Acoroides © Ekkarak Rattanachot, Pemika Apichanangkool

Thalassia Hemprichii © Ekkarak Rattanachot, Pemika Apichanangkool

Field study The majority of the work in the field consisted of the collection of sediment samples (cores) and measurement of the productivity of the benthic community by determining changes in dissolved oxygen (DO) in an incubation chamber. Field trips were conducted in the tropical seagrass meadows of Thailand and Australia. The sediment and seagrass samples were collected from the study sites using coring techniques and are then shipped to the University laboratory at UTS, Sydney, Australia. Samples were collected from pristine seagrass beds in Laem Yong Lam, Haad Chao Mai National Park (Thailand). This is the single largest seagrass meadow in Thailand and covers 18 km2 with nine seagrass species distributed from intertidal to subtidal zones.


The pristine seagrass bed, Laem Yong Lam, Haad Chao Mai National park, Trang province, Thailand

more about the history of the degraded site, Pemika used information from the literature, did interviews with local residents, and carried out a site survey. This way, she gathered knowledge about when the seagrass loss occurred, the causes of the seagrass loss, and the species composition before loss. Kao Bae Na is situated near the Kuan Tung Ku estuary and a mangrove forest area. In 1999, four dominant species were reported at the site: E. acoroides, Cymodocea rotundata Asch. & Schweinf., H. ovalis and T. hemprichii. Due

Degraded site at Ellie point Cairns Harbour in the Great Barrier Reef World Heritage Area (GBRWHA), Queensland, Australia. Z. muelleri subsp. capricorni declined in area from 307 ha in 2001 to 92.1 ha in 2010. The monitoring of this seagrass area between 2009-2010 showed that the Z. mueller subsp. capricorni beds have declined rapidly.

Large patch of seagrasses occurred along the Kao Bae Na shoreline in 1999 with four dominant species, namely H. ovalis, C. rotundata, T. hemprichii and E. acoroides. © Mukai et. al, 1999

Loss of seagrass at Kao Bae Na. No seagrass were found in this area in 2012. © Ekkarak Rattanachot, Pemika Apichanangkool

to elevated sediment loads resulting from land development, specifically from the development of a port, and local, urban population growth within the catchment area, the meadow was completely lost after about 10 years. In addition, Kao Bae Na is located near an area with high boat traffic. The boat propellers further scarred the degrading seagrass meadow. Further sampling is conducted at a second degraded site, located at Cairns Harbour in the Great Barrier Reef World Heritage Area (GBRWHA), Queensland, Australia. Seagrass meadows at Cairns harbour are categorized as a ‘high risk area’ in the GBRWHA due to the threats from coastal development, port activities, and urban and industrial run off. The research examines degraded areas of a seagrass species called Zostera muelleri subsp. capricorni. The Z. muelleri subsp. capricorni meadows have been declining in biomass and area since 2004.


To determine where to collect the cores for each treatment, quadrats are positioned to estimate seagrass percent cover. The shoot density (i.e. number of shoots per m2) in each plot is estimated by counting the number of shoots (leaves) per quadrat.

Sample Collection The objective of the research is to compare the carbon stock of pristine seagrass beds with that of degraded sites through sediment coring. Pemika also wants to know how the seagrass abundance (for example the percentage of seagrass cover, biomass, and shoot density) influences the ability of the meadow to sequester carbon. For both seagrass species - T. hemprichii and E. acoroides - she chooses sampling areas with a high seagrass coverage on the one hand (75% seagrass leaves covering a 50x50 cm quadrat), and sampling areas with low seagrass coverage on the other hand (12% seagrass leaves covering a 50x50 cm quadrat). To determine where to collect the samples, quadrats are placed in seagrass areas which have both high and low seagrass coverage. These quadrats now represent her research plots.


Once the plots are all in position – both at the pristine and the degraded sites – a series of sediment cores are collected from each plot, using PVC cores which are 30 cm deep and have a 10 cm inner diameter. Other cores are taken from the pristine site only to collect plant samples. The sediment cores are sliced into different sections before being transported from Thailand to Australia. The sediment is preserved in ice during transportation and dried at the laboratory for 48 hours at 50°C. The plant samples are cleaned of sediment and sorted into live and dead material. The live plant samples are separated into above-ground (leaves, sheath, vertical stem) and belowground (roots and rhizomes) parts before being dried at 50°C for 24 hours and weighed.





Images of the sediment coring process. A) Sediment collection using the PVC cores. B) Cores are transported to the beach immediately after coring. C) Sediment cores are sectioned to determine their depths using a steel ruler. D) The separated core sections are transferred to plastic bags.


Measurement of benthic net community production Benthic net community metabolism (production) is estimated by measuring changes in dissolved oxygen (DO) in an incubation chamber. The chambers are incubated under dark (i.e. a black spray-painted chamber) and light (i.e. a clear chamber) conditions for 2 hours. The water samples are immediately analyzed for oxygen concentration using a Dissolved Oxygen Probe in a dark bottle. Community respiration (R) is estimated using the change detected in DO concentration in the dark incubation chamber, while the net community production (NCP) is estimated using the change detected in the DO concentration in the clear incubation chamber. The result of the photosynthesis and respiration ratio defines the community type (autotrophic or heterotrophic community) which, in turn, determines the role of a community as carbon sink or source. Measurements of salinity and oxygen concentration in sea water using a conductivity probe (left) and a Dissolve Oxygen Probe (below).


Light and dark incubation chambers are set up at the pristine seagrass beds.

Sampling Design The diagram below shows the sample preparation process which prepares the sediment so it can be analyzed for its carbon content. At a pristine site, sediment cores are collected and sliced into 3 sections before being transported to the laboratory. The sediment is dried at 50°C for 48 hours. For Corg analysis, dried samples are sieved before being ground into a fine powder using a ball grinder. The dry weight of the sediment is obtained to calculate the bulk density. This is important because the bulk density data is used to estimate the sediment organic carbon stock.


Laboratory studies Back at the laboratory in Sydney, different processes take place. Sample preparation The now dried sediment samples are sieved to separate large particles of shell, wood, and rock, and then ground into a fine powder with the ball grinder. The above-ground and below-ground plant samples are also ground to a powder using the ball grinder. Now all samples are ready for further analysis of their total carbon and nitrogen content and their isotopic composition (the number and abundance of atoms of the same element).

The ball grinder.


Grain size analysis The grain size distribution of the sediment is analyzed using a particle size analyzer. The relative distribution of the particle volume is measured to determine sediment particle size classes.

The particle size analyzer to analyze grain size distribution

Carbon and nitrogen analysis Total carbon and nitrogen content is analyzed using a TCN analyser. To determine how much organic carbon is held in the sediment, calcium carbonate (inorganic carbon) is removed from the samples through acidification. The acidified dried sediment samples are put into the TCN analyzer which records the percentage organic carbon (OC) in sediment (%OC).

Analysis of total carbon and nitrogen content: TCN analyser (LecoTruSpec) © P. Chotikarn

Isotopic analysis For isotopic analysis, acidification is also used to remove calcium carbonate from sediment samples. The stable isotopic composition of samples is analyzed using mass spectrometry. The different isotopes of an element are separated on the basis of their mass-to-charge ratio. This way one can, for example, determine the source of organic matter in the sediment. Pemika compares the stable isotopic composition of the sediment with that of the seagrass of suspended particulate matter and epiphytes (non-parasitical plants growing upon another plant).

Analysis of total carbon and nitrogen content: PC program for the TCN analyser © P. Chotikarn


What’s next? Publishing the data and results Pemika is now processing all these data and conducting a full analysis. The results of this analysis will be submitted as articles to peer reviewed journals. In the academic field, it is important to submit to and have your results published in a scholarly journal so the quality of your work is assessed, and accepted, as part of the scientific literature. For example, the peer reviewers check the submitted article for its accuracy and assess the validity of the research methodology and procedures. It sometimes happens that some revisions have to take place in order for the article to get published. Asking the experts for advice During this process Pemika is meeting with other scientists and experts at different conferences or seminars to discuss her methods and preliminary results. For example, Pemika attended the 10th International Seagrass Biology Workshop

© Ekkalak Rattanachot


Conference (ISBW10) in Rio de Janiero, Brazil (November 2012). Pemika presented a poster of her research into sedimentary carbon pools and many of her colleagues provided useful comments, shared experiences and discussed ideas about the direction of future blue carbon research. Pemika also described her methods and the preliminary results of her study at the 5th workshop of the International Blue Carbon Scientific Working Group (May 2013, Sydney, Australia). This expert group provides the scientific foundation for the Blue Carbon Initiative by synthesizing current and emerging science on blue carbon and by providing a robust scientific basis for coastal carbon conservation, management and assessment. Processing the data to fill blue carbon knowledge gaps for tropical seagrass meadows Current carbon stock data that exists for seagrass meadows is based on data from temperate

© Ekkalak Rattanachot

seagrass areas. Pemika’s work provides some insights into the carbon storage of tropical seagrass meadows. A combination of sediment analyses and benthic net production measurements suggests that seagrass degradation results in a loss in gross primary production and reduces the capacity of sediment to store organic carbon. The preliminary results of her study confirm that lost or degraded seagrass meadows store less carbon in the biomass and sediment. Moreover, they produce carbon emissions during the degradation process. Estimations of carbon stocks show that, where seagrass is completely lost, organic carbon in the degraded sediment is several times lower

than in the sediment of the pristine seagrass beds. Her study will also look at any potential difference in carbon storage for below-ground biomass (rhizome and root) versus the living biomass above ground (leaves, stem, and sheath). Pemika will also further look into the influence of seagrass canopy structures and cover on the sink capacity of tropical seagrass meadows. In pristine seagrass beds, there are a number of seagrass species that are distributed along the shoreline. Seagrasses are variable in their morphology and size, and show differences in density and percentage cover. Stay tuned for the final results of Pemika’s research to be published shortly!

Degraded Site

Pristine Seagrass Beds

Seagrass loss

Suspended sediment


Sediment erosion

Seagrass beds



Sulphate reduction bacteria

Alterd hydrology



Release organic matter

© UTS/Pemika Apichanangkool

The IAN diagram explains the negative impact of seagrass loss on the Blue Carbon sink capacity of seagrass. Seagrass loss can affect water velocity, and consequently support the sedimentation of large grain size deposits into the beds. Larger sediment grain sizes support oxygen availability for the microbial community, which increases the metabolic activity, thus causing the decomposition of organic matter. This way, CO2 is released through re-mineralization processes. This degraded site therefore acts as a source of carbon emissions. Without living seagrass biomass, there is no organic matter burial into the sediment. Sediment re-suspension and erosion occurs without seagrass structure. Pristine seagrass beds support organic carbon accumulation by burial, trapping and filtering of organic matter from the water column. They prevent sediment re-suspension, allow small sediment grain sizes to settle into the beds and act as a Blue Carbon sink (Pollard & Moriarty 1991; Zonneveld et al. 2010; Fonseca & Koel 2006; Keulen & Borowitzka 2002).


This research project was executed by the University of Technology Sydney (UTS), and supported by the International Union for Conservation of Nature (IUCN) and the Total Foundation. The work feeds into the work of the Blue Carbon Initiative. www.thebluecarboninitiative.org

About IUCN IUCN, International Union for Conservation of Nature, helps the world find pragmatic solutions to our most pressing environment and development challenges. IUCN’s work focuses on valuing and conserving nature, ensuring effective and equitable governance of its use, and deploying naturebased solutions to global challenges in climate, food and development. IUCN supports scientific research, manages field projects all over the world, and brings governments, NGOs, the UN and companies together to develop policy, laws and best practice. IUCN is the world’s oldest and largest global environmental organization, with more than 1,200 government and NGO members and almost 11,000 volunteer experts in some 160 countries. IUCN’s work is supported by over 1,000 staff in 45 offices and hundreds of partners in public, NGO and private sectors around the world.


About UTS UTS, University of Technology Sydney, is a dynamic and innovative university in central Sydney. One of Australia’s leading universities of technology, UTS has a distinct model of learning, strong research performance and a leading reputation for engagement with industry and the professions. The Plant Functional Biology and Climate Change Cluster (C3) was formed in 2008 with funding from the UTS Research Investment Strategy. The C3 uses the UTS Science state-of-theart research facilities and this fosters a crossdisciplinary approach that attracts researchers with backgrounds in physics, atmospheric modelling and oceanography. Membership has grown to over 70 researchers, associates, adjuncts and PhD and Honours candidates. All are involved in a diverse range of research areas reflecting core member expertise in both marine and terrestrial ecosystems. Cluster members work collaboratively with Australian institutes and overseas organisations in Europe and North America. An important additional aspect of C3's charter is to support the undergraduate teaching of the next generation of biologists and ecologists to give them the skills and tools to improve our understanding of climate change issues.

Dorothée Herr UTS, Peter Ralph, Pemika Apichanangkool [email protected] [email protected]

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