Blue Carbon Cycling in the Coastal Areas of Qatar

Earth Sciences Chemistry Environmental Chemistry Geochemistry Marine Science
blue carbon sabkha coastal ecosystem carbon sequestration mangroves hypersaline environment tidal salt marshes

Research Background

Global climate change, particularly global warming, has exerted immense pressure on the global carbon cycle. As a significant carbon sink, the ocean absorbs large amounts of carbon dioxide (CO₂), leading to ocean acidification, which adversely affects marine organisms reliant on carbonate minerals. Coastal wetlands, such as intertidal salt flats (sabkhas), mangroves, and saline lake inlets, are crucial blue carbon storage sites with significant climatological implications. Blue carbon refers to carbon absorbed and stored from the atmosphere and oceans, with its storage capacity and mechanisms influenced by various physical, geochemical, and ecological factors, including the upwelling of dissolved carbon, mineralization of carbonate minerals, and microbial carbon cycling in sediments.

The coastal areas of the Qatar Peninsula possess unique geochemical characteristics, providing an ideal setting for studying blue carbon storage. However, the relationship between carbon storage, organic matter (OM) degradation, and microbial activity in Qatari coastal sediments has not been thoroughly investigated. Therefore, this study aims to explore the carbon storage capacity of three unique coastal sites in Qatar (mangroves and two sabkhas with contrasting geology and tidal influences) using biological and geochemical tools, revealing how biogeochemical indicators affect their blue carbon storage potential.

Research Team and Publication Information

This study was conducted by a research team from the University of Toronto and Qatar University, with key authors including Ivan Strakhov, Hadil Elsayed, Zach A. Diloreto, and others. The paper was published on October 22, 2024, in the journal Geo-Bio Interfaces, titled Blue Carbon Cycling in the Coastal Areas of Qatar.

Research Methods

The research team conducted field sampling at three coastal sites in Qatar in December 2021 and October 2022, including Khor Al Adaid Sabkha (KAAS), Dohat Faishakh Sabkha (DF), and Al Khor Mangroves (AK). Researchers collected sediment cores approximately 40 cm deep, analyzed sediment porewater, and performed depth profiling of pH, oxygen (O₂), redox potential, and hydrogen sulfide (H₂S) at the sediment surface using microsensors. Additionally, high-resolution transmission electron microscopy (TEM-EDXS) and scanning transmission X-ray microscopy (STXM) were used to reveal the templating effects promoting magnesium carbonate nucleation in coastal hypersaline environments. Microbial DNA sequencing was employed to analyze the microbial community composition at various sediment depths.

Key Findings

  1. Geochemical Conditions at the Sediment-Water Interface: Microsensor data showed that the overlying water at all study sites was oxic and alkaline, with significantly higher oxygen concentration and redox potential in the top 0.1 cm of sediment. However, the porewater rapidly became anoxic below the surface, with redox potential dropping, pH approaching neutral, and hydrogen sulfide concentration significantly increasing in deeper sediments.

  2. Depth Profiles of Sediment Characteristics: At KAAS Sabkha, total organic carbon (TOC) content was highest at the surface and gradually decreased with depth, with total inorganic carbon (TIC) showing a similar trend. At DF Sabkha, TOC content significantly increased in deeper sediments, particularly at 11 cm and 35 cm depths. At AK Mangroves, TOC content was highest at the surface, decreased with depth, but increased again in deeper layers.

  3. Microbial Community Composition: The microbial community composition varied significantly across sites. At KAAS Sabkha, Proteobacteria dominated the surface sediments, while Firmicutes dominated the deeper layers. At DF Sabkha, Chloroflexi and Proteobacteria were predominant in the surface sediments, while Firmicutes dominated the deeper layers. At AK Mangroves, Proteobacteria were dominant in the surface sediments, while Firmicutes and Euryarchaeota dominated the deeper layers.

  4. Formation of Carbonate Minerals: Through X-ray diffraction (XRD) and TEM-EDXS analysis, the research team identified abundant dolomite in the sediments of DF Sabkha and AK Mangroves, particularly in the deeper layers. Dolomite formation was closely related to organic matter degradation, especially in the deeper sediments of DF Sabkha, where dolomite nucleation was associated with buried microbial mats.

Research Conclusions

The study revealed that carbon cycling and storage in three unique coastal environments in Qatar are influenced to varying degrees by hydrodynamic deposition, oxic/anoxic conditions, organic matter degradation, inorganic carbon phases, and microbial community composition. At DF Sabkha, organic and inorganic carbon content was strongly correlated with organic matter degradation rates, with dolomite nucleating near buried microbial mats. At KAAS Sabkha, organic carbon, inorganic carbon, and total phosphorus were only linked to sediment depth, with carbon stored beneath a highly alkaline sediment-water interface where oxygenic and anoxygenic phototrophy fixed carbon dioxide in a dense surface microbial mat. At AK Mangroves, inorganic carbon was correlated with the burial of degraded mangrove-derived organic matter, with dolomite abundant in the surface sediments.

Research Highlights

  1. Blue Carbon Storage Mechanisms: The study revealed multiple mechanisms of blue carbon storage in Qatari coastal sediments, including organic matter degradation, carbonate mineral formation, and microbial activity.
  2. Dolomite Formation: The study found that dolomite formation is closely related to organic matter degradation, particularly in the deeper sediments of DF Sabkha, where dolomite nucleation is associated with buried microbial mats.
  3. Role of Microbial Communities: The study emphasized the critical role of microbial communities in carbon cycling and storage, particularly the dominance of Firmicutes and Proteobacteria in deeper sediments.

Research Significance

This study provides important insights into the mechanisms of blue carbon storage in coastal wetlands, particularly the formation of carbonate minerals and the role of organic matter degradation in hypersaline environments. The findings have significant implications for global carbon cycle models and coastal wetland conservation, especially in the context of addressing climate change and ocean acidification.

Additional Valuable Information

The study also highlighted that the blue carbon storage capacity of Qatar’s coastal areas is threatened by rapid climate change and land-use changes. Therefore, protecting the natural carbon storage capacity of these coastal regions is crucial, particularly in the face of industrial development and human activities.