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2019 | Buch

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Blue Carbon in Shallow Coastal Ecosystems

Carbon Dynamics, Policy, and Implementation

herausgegeben von: Dr. Tomohiro Kuwae, Dr. Masakazu Hori

Verlag: Springer Singapore

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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Über dieses Buch

This book presents a comprehensive and innovative understanding of the role of shallow coastal ecosystems in carbon cycling, particularly marine carbon sequestration. Incorporating a series of forward-looking chapters, the book combines thorough reviews of the global literature and regional assessments—mainly around the Indo-Pacific region and Japan—with global perspectives to provide a thorough assessment of carbon cycling in shallow coastal systems. It advocates the expansion of blue-carbon ecosystems (mangroves, seagrass meadows, and salt marshes) into macroalgal beds, tidal flats, coral reefs, and urbanized shallow waters, demonstrating the potential of these ecosystems as new carbon sinks. Moreover, it discusses not only topics that are currently the focus of blue-carbon studies, i.e., sedimentary carbon stock and accumulation rate, but also CO2 gas exchange between the atmosphere and shallow coastal ecosystems, carbon storage in the water column as refractory organic carbon, and off-site carbon storage. Including highly original contributions, this comprehensive work inspires research beyond the specific regions covered by the chapters. The suite of new concepts and approaches is refreshing and demonstrates that blue-carbon research is indeed a vibrant new field of research, providing deep insights into neglected aspects of carbon cycling in the marine environment. At the same time the book provides guidance for policy makers to deliver benefits to society, for example the inclusion of blue carbon as a carbon offset scheme or the Nationally Determined Contribution (NDC) in the Paris Agreement, and also for building resilience in coastal socio-ecosystems through better management. This book is intended for all those interested in the science and management of coastal ecosystems.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Blue Carbon: Characteristics of the Ocean’s Sequestration and Storage Ability of Carbon Dioxide

Abstract

The first life on Earth evolved in the ocean about 3.5 billion years ago. Photosynthetic organisms, which first appeared in the ocean, eventually changed the oxygen and carbon dioxide concentrations in the atmosphere to the current concentrations. This gaseous exchange was the first and can be considered as the most important ecosystem service provided by marine ecosystems. That service has been on-going from the first primitive photosynthetic organism to the present and reflects the ability of the oceans to absorb carbon dioxide. Nevertheless, recent discussions of sequestration of CO₂ have mainly promoted the concept of land-based green carbon sequestered by terrestrial ecosystems.

The Blue Carbon Report, which was released in 2009, has shown that more than 50% of the carbon dioxide absorbed by the plants on Earth is actually cycled into the ocean; the remainder of the carbon dioxide absorbed by plants is stored in terrestrial ecosystems. More than half of the carbon stored in the ocean has been sequestered by shallow coastal ecosystems, which account for only 0.5% or less of the total ocean area. In addition, there is good evidence that shallow coastal ecosystems have been greatly affected by human activities and continue to be seriously denuded. However, the importance of shallow coastal ecosystems has not yet emerged as common knowledge within society in general, and full comprehension of the role of shallow coastal ecosystems has not yet been applied to climate change mitigation and adaptation strategies. For example, shallow coastal ecosystems are not considered in the inventory of absorbed carbon dioxide. One reason is that the sequestration and storage processes of blue carbon are complex, and it is still difficult to determine what criteria are essential for calculating the relative efficacy of carbon sequestration in shallow coastal ecosystems versus terrestrial ecosystems. In this chapter, which introduces this book, we give an overview of the key points of the Blue Carbon Report. We then try to provide a better understanding of the blue carbon concept by explaining the important characteristics of blue carbon ecosystems. We use the carbon absorption process in seagrass meadows as an example to illustrate important concepts.

Masakazu Hori, Christopher J. Bayne, Tomohiro Kuwae

Chapter 2. Carbon Sequestration in Sediment as an Ecosystem Function of Seagrass Meadows

Abstract

Seagrass meadows have the potential to sequester large amounts of organic carbon (OC) in underlying sediments as detrital OC. This ecosystem function of seagrass meadows depends not only on the high primary productivity of seagrasses and associated algae, but also on the physical and hydrological properties of seagrass meadows that accumulate fine-grained mineral sediment and allochthonous organic matter and stabilize the sediment. The burial efficiency of OC in marine sediment is constrained principally by (i) structural recalcitrance of accumulated organic matter, (ii) enhancement of OC preservation through organic–mineral interactions, and (iii) the length of the oxygen exposure time in the reactive layer of sediment. We discuss how these mechanisms contribute to and constrain OC sequestration in seagrass sediments. From the sediment source–sink perspective, long-term carbon sequestration capacity can be viewed as an emergent property of coastal vegetated ecosystems such as seagrass meadows. Sequestration of OC also depends on the nature of the OC supplied, which is largely determined by the origin of the OC. The major sources of OC to seagrass meadow sediments are reviewed and classified in terms of their mode of transport and degradability in the early diagenetic process. The available methods of evaluating various OC sources, including recently developed environmental DNA techniques, are also critically reviewed. Finally, available data are compiled on the concentration and burial rate of OC in seagrass meadow sediments and a tentative global estimate of the long-term (~1000 years) OC sequestration rate in seagrass meadows as 1.6–9.4 Tg C year⁻¹ is provided. This is lower than previous estimates of the global OC burial rate in seagrass meadows.

Toshihiro Miyajima, Masami Hamaguchi

Chapter 3. Carbon Sequestration in Mangroves

Abstract

Mangrove ecosystems are widely regarded as highly productive, and the high ability of mangroves to store carbon is currently receiving much attention in the context of climate change. Globally, mangroves are estimated to occupy an area of 152,361 km². A model relating mangrove biomass to temperature and precipitation has been used, together with global mangrove distribution maps, to estimate the total aboveground biomass worldwide as 2.83 Pg dry weight (95% confidence interval 2.18–3.40 Pg), and the base area average as 184.8 t dry weight ha⁻¹ (95% CI 142.1–222.0 t ha⁻¹). Almost half of the total global mangrove biomass is in Southeast Asia. The global mangrove belowground biomass has been estimated to be 1.11 Pg dry weight (95% CI 0.74–1.64 Pg). Thus, the total estimated biomass (aboveground + belowground) is 3.94 Pg dry weight. Estimates of carbon storage as necromass (dead organic matter) in mangrove soils differ. By one estimate, 5.00 Pg C is stored globally as necromass. By another estimate, ~2.6 Pg C is stored globally, and the whole mangrove ecosystem stores ~4.4 Pg C.

Tomomi Inoue

Chapter 4. Carbon Sequestration by Seagrass and Macroalgae in Japan: Estimates and Future Needs

Abstract

In this chapter, we estimated carbon sequestration by seagrass and macroalgal beds, defined as the integration of annual plant tissue (organic carbon) production, in Japan. Each of the main four beds, eelgrass beds (Amamo-ba), Sargassum beds (Garamo-ba), warm-temperate kelp beds (Arame-ba), and cold-temperate kelp beds (Kombu-ba), exhibited a distinctive geographic distributional pattern along Japan’s coasts that depended on regional climate and topographic characteristics. The total area of the four beds was approximately 230,000 ha nationwide, based on an analysis of the latest satellite images and information on past distributions of the beds. Carbon sequestration of each seagrass or macroalgal bed was evaluated as integrated annual plant tissue production converted to organic carbon, which was defined by subtracting dissolved organic matter production from net primary production. Plant tissue production of the main constituent macrophyte of the seagrass and macroalgal beds was directly measured in each coastal region, and production values from past reports were also collected and utilized. Annual carbon sequestration by seagrass and macroalgal beds in Japan, expressed in a CO₂-converted base, was about 4.7 million tons per year, which is comparable to the CO₂ emissions of the industrial sectors of agriculture and fisheries.

Goro Yoshida, Masakazu Hori, Hiromori Shimabukuro, Hideki Hamaoka, Toshihiro Onitsuka, Natsuki Hasegawa, Daisuke Muraoka, Kousuke Yatsuya, Kentaro Watanabe, Masahiro Nakaoka

Chapter 5. Carbon Storage in Tidal Flats

Abstract

Tidal flat ecosystems are important habitats in shallow coastal waters. In this chapter, carbon storage in a bivalve (Corbicula japonica), phytoplankton, and sediment is estimated at two tidal flats in a eutrophic coastal area of Osaka Bay in Japan. First, we estimate the carbon storage of the bivalve from the rate of organic carbon production and shell production measured by monthly field investigations. We then estimate the carbon storage of phytoplankton based on phytoplankton biomass measurements and a model of gross primary production and respiration based on incubation experiments. To assess carbon storage in sediment, biodegradation tests of sedimentary organic carbon taken from the intertidal zone and the subtidal zone were carried out for 100 days; the residual sedimentary organic carbon is considered to represent long-term storage of carbon in sediment. Finally, the carbon storage functions of bivalves, phytoplankton, and sedimentary organic matter in tidal flat ecosystems are summarized.

Toru Endo, Sosuke Otani

Chapter 6. Air–Water CO2 Flux in Shallow Coastal Waters: Theory, Methods, and Empirical Studies

Abstract

The fact that the ocean is one of the largest sinks of atmospheric CO₂ on Earth is an important consideration in the prediction of future climate changes and identification of possible mitigation strategies for global climate change. Recently, carbon storage in vegetated coastal habitats (blue carbon ecosystems) has been explored as a new option to mitigate climate change. However, the complexity of the mechanisms that control air–water CO₂ fluxes in shallow coastal ecosystems has precluded their adequate quantification. Spatiotemporal extension of accurate values of these fluxes will be an important milestone for assessing the contribution of blue carbon ecosystems to mitigation of climate change. In this chapter, we explain the theoretical understanding of air–water CO₂ fluxes and methods for their measurement. We then discuss results of empirical measurements of air–water CO₂ fluxes in shallow coastal waters. We conclude that statistical analyses of augmented air–coastal-water CO₂ flux data based on long-term measurements and multiple methods should lead to a quantitative understanding of the current status and future air–water CO₂ fluxes in shallow coastal waters at national and global scales.

Tatsuki Tokoro, Kenta Watanabe, Kazufumi Tada, Tomohiro Kuwae

Chapter 7. CO2 Fluxes in Mangrove Ecosystems

Abstract

Mangroves have long been recognized as a potential sink of carbon owing to their high productivity and carbon sequestration potential. The short term CO₂ dynamics of mangroves are often put under lenses to examine their potential to combat the human induced CO₂ emission. Mainly three types of CO₂ fluxes take place within a mangrove ecosystem namely (i) atmosphere-biosphere CO₂ exchange, (ii) soil CO₂ efflux and (iii) air-water CO₂ flux. In this chapter, we have compiled all types of the CO₂ flux data from mangrove ecosystems with special emphasis on the Sundarban, the world’s largest mangrove forest and analyzed the regulating factors of these fluxes. Summarizing all the studies, it can be inferred that the terrestrial compartments of mangroves acts as net sink for CO₂, though the soil continually emit CO₂ (apart from few exceptions). Almost all the mangrove surrounding waters act as source of CO₂, however, the magnitude of air-water CO₂ fluxes are much less than the inward fluxes of CO₂towards the canopy, hence the ecosystem as a whole acts as a net sink for CO₂. Light conditions, air temperature, salinity, tidal cycle and so forth are mainly found to regulate the atmosphere-biosphere CO₂ flux, whereas, soil temperature, moisture and waterlogging are the principal factors regulating the soil CO₂fluxes. In case of air-water fluxes, the main governing factors are the variation in salinity, pore-water flushing during ebb tide and wind speed.

Anirban Akhand, Abhra Chanda, Sourav Das, Sugata Hazra, Tomohiro Kuwae

Chapter 8. CO2 Flux in Tidal Flats and Salt Marshes

Abstract

Tidal flats and salt marshes are sites where CO₂ is released to the environment by decomposing organic matter and CO₂ is absorbed by vegetation through photosynthesis. It is thought that on balance, carbon is stored in tidal flats and salt marshes. To explore this topic, we reviewed published estimates of air–water, air–sediment, water–sediment, and air–marsh fluxes of CO₂ in tidal flats and salt marshes. We also carried out multiyear measurements of CO₂ flux and related parameters at two field sites in Osaka Bay, Japan, having flat intertidal and salt marsh areas. The CO₂ fluxes were measured using the eddy correlation and chamber methods. The air–sediment CO₂ flux data from tidal flats indicated net absorption of atmospheric CO₂ into the sediment during daytime hours. The air–water CO₂ flux data indicated that CO₂ was emitted from the water surface in small amounts, with temporal fluctuations and seasonal changes that were strongly related to salinity, as has been documented in the literature. We found that CO₂ was absorbed into salt marsh and intertidal sediment and that CO₂ was emitted from subtidal sediment as well as from the water surface of the tidal flat ecosystem during periods of submersion. The air–sediment CO₂ flux and its temporal fluctuation at the field sites appear to be regulated by vegetation such as the reed Phragmites australis and microphytobenthos.

Sosuke Otani, Toru Endo

Chapter 9. Quantifying the Fate of Captured Carbon: From Seagrass Meadows to the Deep Sea

Abstract

To help evaluate the sequestration and carbon dioxide storage function of seagrass meadows, we describe the processes by which carbon is sequestered in eelgrass beds and transported from shallow coastal waters to the deep sea. A part of the carbon taken up by eelgrass is decomposed and returned to biological production or the water column’s dissolved inorganic carbon pool, some is accumulated and stored in the shallow sea bottom, and the rest flows out into the deep sea. Here, we describe the growth of eelgrasses and the processes of decomposition, sedimentation, and transportation of eelgrass-derived organic carbon using the Seto Inland Sea as a model site. We estimated the amount of carbon sequestered and stored in eelgrass beds, the fate of eelgrass-derived organic carbon, and the amounts accumulated in the shallow coastal water and transported to the deep sea. According to our estimates based on calculations from tracking carbon over a 1-year period, of the 73,000 tons of carbon sequestered by eelgrass annually in the Seto Inland Sea, 40.9% is accumulated in the Seto Inland Sea and 8.3% flows out to the deep sea. In other words, the eelgrass beds in the Seto Inland Sea have an annual potential capacity of 36,000 tons of carbon storage. In addition, most of the organic carbon was accumulated in the shallow coastal waters rather than in the deep sea.

Katsuyuki Abo, Koichi Sugimatsu, Masakazu Hori, Goro Yoshida, Hiromori Shimabukuro, Hiroshi Yagi, Akiyoshi Nakayama, Kenji Tarutani

Chapter 10. Carbon Dynamics in Coral Reefs

Abstract

Coral reefs show high organic and inorganic carbon production and create unique landforms on tropical coastlines. The balance between organic and inorganic carbon production is determined by benthic organisms such as corals, macroalgae, and seagrasses, and also by reef hydrodynamics, which in turn determine CO₂ sinks and sources within the ecosystem. Many studies have shown that net organic carbon production in coral reef ecosystems is almost zero (balanced), with net positive calcification resulting in reefs acting as CO₂ sources. However, the relationships among productivity, benthic organisms, and hydrodynamics have not been well documented; more detailed information is required from both field observations and coupled physical–biological models. Reef sediments have low organic carbon content (median, 0.35% dry weight), approximately 50% those of tropical and subtropical seagrass beds (median, 0.67%) and 5% those of mangrove forests (median, 6.3%). Sedimentation rates do not vary significantly between these three ecosystems, so organic carbon input and decomposition in the surface sediments are key factors controlling organic carbon burial rates. Coral reefs provide calm conditions that enhance sedimentation of fine sediments, which facilitates the development of seagrass beds and mangrove forests. Seagrass meadows and mangrove forests in turn trap fine sediments from terrestrial sources and prevent high-turbidity water from reaching coral reefs. Coral reefs, seagrass meadows, and mangrove forests are thus interdependent ecosystems; to effectively store and export blue carbon in tropical coastal areas, it is necessary to maintain the health of these ecosystems.

Atsushi Watanabe, Takashi Nakamura

Chapter 11. CO2 Uptake in the Shallow Coastal Ecosystems Affected by Anthropogenic Impacts

Abstract

Shallow coastal ecosystems (SCEs) are generally recognized as not only significant organic carbon reservoirs but also as sources for CO₂ emission to the atmosphere, thus posing a dilemma regarding their role in climate change mitigation measures. However, we argue that SCEs can act as sinks for atmospheric CO₂ under a given set of biogeochemical and socioeconomic conditions. The key properties of SCEs that show net uptake of atmospheric CO₂ are often characteristic of human-dominated systems, that is, high nutrient inputs from terrestrial systems, input of treated wastewater in which labile carbon has been mostly removed, and the presence of hypoxic waters. We propose a new perspective on the potential of human-dominated SCEs to contribute to climate change mitigation, both serving as carbon reservoirs and providing direct net uptake of atmospheric CO₂, in light of human systems–ecosystem interactions. Namely, if we view the land and a SCE as an integrated system, with appropriate management of both wastewater treatment and SCE, we will be able to not only suppress CO₂ release but also capture and store carbon.

Tomohiro Kuwae, Jota Kanda, Atsushi Kubo, Fumiyuki Nakajima, Hiroshi Ogawa, Akio Sohma, Masahiro Suzumura

Chapter 12. Carbon Offset Utilizing Coastal Waters: Yokohama Blue Carbon Project

Abstract

Although the coastal port city of Yokohama has carried out a campaign to improve conditions for marine ecosystems, the nation of Japan has not yet utilized coastal waters as an option for global warming countermeasures. Based on the concept of blue carbon ecosystems advocated by the United Nations Environment Programme, since 2011 Yokohama City has been conducting a social experiment called the Yokohama Blue Carbon Project, which serves to counter climate change and includes a novel carbon offset campaign. Yokohama City, which was chosen by the Japanese government as an environmental Future City in countering global warming, is aiming to transition from being a port city to a marine environmental city. In this chapter, we describe the successes and challenges of the Yokohama Blue Carbon Project and we report on the project’s involvement in the World Triathlon Series held in Yokohama as an example of a carbon offset credit framework utilizing coastal waters.

Masato Nobutoki, Satoru Yoshihara, Tomohiro Kuwae

Chapter 13. The Future of Blue Carbon: Addressing Global Environmental Issues

Abstract

In this chapter, we first summarize the quantitative data for carbon flows and stocks in various shallow coastal ecosystems, which were reviewed in the previous chapters. The capability of net uptake of atmospheric CO₂ and soil organic carbon accumulation in global shallow coastal ecosystems are estimated to be about 1070 Tg C year⁻¹ and about 140 Tg C year⁻¹, respectively, with considerably large variabilities and uncertainties. Next, we discuss future needs for scientific and technological progress to constrain these large variabilities and uncertainties. We then review how blue carbon is being discussed at international conferences and within frameworks on climate change. Finally, we discuss how conserving, restoring, and utilizing blue carbon ecosystems can meet social needs in the future. In particular, the management of blue carbon ecosystems can serve not only as a mitigation measure against climate change but also as an adaptation measure.

Tomohiro Kuwae, Masakazu Hori

Correction to: The Future of Blue Carbon: Addressing Global Environmental Issues

Tomohiro Kuwae, Masakazu Hori

Titel: Blue Carbon in Shallow Coastal Ecosystems
herausgegeben von: Dr. Tomohiro Kuwae
Dr. Masakazu Hori
Verlag: Springer Singapore
Electronic ISBN: 978-981-13-1295-3
Print ISBN: 978-981-13-1294-6
DOI: https://doi.org/10.1007/978-981-13-1295-3