蓝碳简介

Introduction to blue carbon

气候变化是当今人类社会面临的共同挑战，对全球自然生态系统产生显著影响，温度升高、海平面上升、极端气候事件频发给人类生存和发展带来严峻挑战。为此，以中国为代表，许多国家将目标对准导致气候变化的“元凶”—二氧化碳，提出要实现碳达峰、碳中和。当前我国实现这一目标所面临的形势还十分严峻。为实现上述减排目标，增强生态系统的固碳能力，是减缓气候变化的主要有效措施。海洋作为地球生态系统中最大的碳库，是维持全球碳收支平衡和应对气候变化的关键，相较于陆地生态系统参与碳循环形成的“绿碳”，海洋碳库中由生物驱动且易于管理的那部分碳通量和储量被形象地称为“蓝碳”（Blue Carbon)。虽然已经在实施陆地绿色碳汇，但海洋碳库包含全球93%的CO₂，分别是大气和陆地碳存量的50和20倍，具有巨大的发展潜力，每年至少有25%的人类行为产生的CO₂被海洋生态系统捕获为蓝碳。

Climate change is a common challenge faced by human society today, and it has a significant impact on the global natural ecosystem, with rising temperature, rising sea level, and frequent extreme weather events posing serious challenges to human survival and development. For this reason, many countries, represented by China, have set their targets on the “culprit” of climate change which is carbon dioxide and proposed to achieve carbon peak and carbon neutrality. At present, it is still very serious for China to achieve this goal. In order to achieve the above emission reduction targets, enhancing the carbon sequestration capacity of ecosystems is the main effective measure. As the largest carbon reservoir in the earth’s ecosystem, the ocean is the key to maintaining the global carbon balance and coping with climate change. Compared with the “green carbon” formed by terrestrial ecosystems that participate in the carbon cycle, the biologically driven and easily managed portion of the ocean carbon pool is known as “blue carbon”. Although land-based green carbon sinks are already being implemented, the ocean carbon pool contains 93% of the world’s CO2, 50 and 20 times more than atmospheric and terrestrial carbon stocks, respectively, and has enormous potential for development, with at least 25% of the CO2 generated by human actions being captured as blue carbon by marine ecosystems each year.

 2009年联合国环境规划署（UNEP）、联合国粮食及农业组织（FAO）和联合国教育、科学及文化组织（UNESCO）政府间海洋学委员会（IOC）联合发布蓝碳报告，全球55%以上的初级生产是蓝碳，而且沿海蓝碳生物群落（红树林、海草、盐沼生态系统等）的生产效率远高于亚马逊雨林。然而，这些蓝碳生物群落正在以比雨林快5-10倍的速度退化和消失，因此迫切需要保护和恢复。

In 2009, UNEP, FAO, UNESCO and IOC jointly released the Blue Carbon Report, and more than 55% of global primary production is blue carbon, and coastal blue carbon biomes (mangroves, seagrasses, salt marsh ecosystems, etc.) are far more productive than Amazon rainforest. However, these blue carbon biomes are degrading and disappearing at a rate 5-10 times faster than the rainforest and therefore need urgent protection and restoration.

 除了可见的滨海蓝碳外，还有大量的不可见蓝碳生物群落，由体积微小但极其丰富的微生物组成，包括浮游植物、细菌、古细菌和病毒，它们占蓝碳总量的95%。这些微生物可以与可见的蓝碳生物群落相互作用，将它们的有机碳转化为难溶形式，延长有机碳在海洋中的停留时间。我们今天在沿海面临的环境问题（如富营养化、缺氧、酸化等）也与看不见的蓝碳过程相互作用，但机制尚不清楚。因此，海洋生态系统研究应同时考虑可见和不可见的蓝碳生物群落，了解它们的相互作用及其与环境问题的关系对于海洋生态系统管理和可持续发展至关重要。

In addition to the visible coastal blue carbon, there is a large invisible blue carbon biome consisting of tiny but extremely abundant microorganisms, including phytoplankton, bacteria, archaea and viruses, which account for 95% of the total blue carbon. These microorganisms can interact with the visible blue carbon biomes to convert their organic carbon into insoluble forms and prolong the residence time of organic carbon in the ocean. The environmental problems we face today in the coast (e.g. eutrophication, hypoxia, acidification, etc.) also interact with invisible blue carbon processes, but the mechanisms are not yet clear. Therefore, marine ecosystem studies should consider both visible and invisible blue carbon communities, and understanding their interactions and their relationship to environmental problems is essential for marine ecosystem management and sustainable development.

图1 红树林-我国重要的蓝碳生态系统

蓝碳挑战

The blue carbon challenges

虽然2009年提出的蓝碳最初概念是指覆盖沿海和开放水域的海洋生态系统捕获的碳，但蓝碳的实际研究和开发主要涉及大型动物群，如在沿海地区红树林、海草和盐沼。经过多年的沿海蓝碳推广，IUCN于2014年发布了《海洋碳行动呼吁》，强调了海洋碳汇在减缓气候变化中的重要性，并确定了公海蓝碳的关键成分，将蓝碳从沿海地区扩展到海洋环境。事实上，看不见的微生物是海洋中蓝碳的重要组成部分，但迄今为止很大程度上被忽视了，这些微生物，包括浮游植物（微藻）、蓝藻、细菌、古生菌和病毒，含量极其丰富，占海洋生物量的90%和海洋产量的95%。每年超过3600亿吨的CO₂被海洋浮游植物固定，其中1.39%被生物泵（BP）输送到海底进行长期储存，其余的固定有机碳主要通过呼吸成CO ₂，但一小部分有机碳通过微生物碳泵（MCP）分流到生物学上无法进入的阶段，要么是难溶的，要么是浓度极低的。MCP是大量的海洋溶解有机碳（DOC）/惰性溶解有机碳（RDOC）的主要贡献者，其数量相当于大气中CO₂的总存量。古气候的研究表明，RDOC池和气候变化之间存在不可分割的联系。MCP效应存在于所有水环境甚至土壤环境中，与可见的蓝碳生态系统相连，因为所有蓝碳宏观生物群落（红树林、海草、盐沼等）都将DOC释放到水中，MCP可以将其进一步转化为RDOC^[1]。

Although the original concept of blue carbon, introduced in 2009, referred to carbon captured by marine ecosystems covering coastal and open waters, actual research and development of blue carbon has mainly involved macrofauna, such as mangroves, seagrasses and salt marshes in coastal areas. After years of coastal blue carbon promotion, the IUCN released the Calls for Action on Ocean Carbon in 2014, highlighting the importance of ocean carbon sinks in climate change mitigation and identifying the key components of blue carbon in the open ocean, extending blue carbon from coastal areas to the marine environment. Indeed, invisible microorganisms are an important but hitherto largely neglected component of blue carbon in the oceans, and these microorganisms, including phytoplankton (microalgae), cyanobacteria, bacteria, archaea and viruses, are extremely abundant, accounting for 90% of ocean biomass and 95% of ocean production. Over 360 billion tons of CO2 are fixed annually by marine phytoplankton, of which 1.39% is transported to the seafloor by the biological pump (BP) for long-term storage. The rest of the fixed organic carbon is mainly CO2 through respiration, but a small fraction is shunted through the microbial carbon pump (MCP) to biologically inaccessible stages that are either insoluble or at very low concentrations. The MCP is the contributor of DOC/RDOC in amounts equivalent to the total atmospheric CO2 inventory. Paleoclimate studies show an inextricable link between RDOC pools and climate change. MCP effects are present in all aquatic and even soil environments, linked to visible blue carbon ecosystems, as all blue carbon macrobial communities (mangroves, seagrasses, salt marshes, etc.) release DOC into the water, which can be further converted to RDOC by MCP.

图2所示，使沿海水域成汇而不是大气二氧化碳的来源的生态工程图。

    除了保护和恢复沿海蓝碳（红树林、盐沼、海草等）外，减少陆地养分输入可以避免对有机碳呼吸的启动效应，从而通过生物泵（BP）和微生物碳泵（MCP）增加海洋中的碳固存。

In addition to protecting and restoring coastal blue carbon (mangroves, salt marshes, seagrasses, etc.), reducing terrestrial nutrient inputs can avoid the initiating effect on organic carbon respiration and thus increase carbon sequestration in the ocean through the biological pump (BP) and microbial carbon pump (MCP).

中国的蓝碳战略

China’s blue carbon strategy

中国海域包括渤海、黄海、东海和南海，海岸线长1.8万公里，从北温带延伸至热带。入海的河流有1500多条，其中世界第三大河由长江流入东海，黄河携带大量泥沙流入渤海，珠江流入南海。如此丰富的栖息地蕴藏着巨大的生物多样性和碳储存能力。另一方面，中国沿海地区人口稠密，大部分地区受到港口建设、潮带围垦、海水养殖等严重的人类行为影响。河流中营养物质和有机物的排放以及海洋养殖活动对生态系统的健康和可持续性具有根本性的影响，许多河口水域目前正遭受由富营养化和微生物过程引起的藻华、缺氧和酸化。

China’s seas include the Bohai Sea, Huanghai Sea, East and South China Seas, with a coastline of 18,000 km, extending from the northern temperate zone to the tropics. There are more than 1,500 rivers entering the sea, among which Yangtze River, the third largest river in the world flows into the East China Sea, the Yellow River carries a large amount of sediment into the Bohai Sea, and the Pearl River flows into the South China Sea. Such rich habitats harbor enormous biodiversity and carbon storage capacity. On the other hand, China’s coastal areas are densely populated and most of them are heavily influenced by human actions such as port construction, tidal zone reclamation, and mariculture. The discharge of nutrients and organic matter from rivers and mariculture activities have a fundamental impact on ecosystem health and sustainability, and many estuarine waters are currently suffering from algal blooms, hypoxia and acidification caused by eutrophication and microbial processes.

 中国蓝碳工程的一个有效策略是在部署恢复可见的沿海蓝碳（有根植物）的同时，努力在水域特别是河口和陆架区域进行不可见的微生物固碳，只有这样，蓝碳项目才能对减缓气候变化产生实质意义。在实践中，应采取以下措施：建立覆盖河流集水区、河口和陆架水域代表性地点的长期监测和观测网络；为各种生态系统中不同形式的蓝碳的核心测量建立标准；建立蓝碳生态价值评估机制；建立流域-沿海-近海环境碳核算体系；建立陆海一体化补偿政策，促进与农业的蓝碳交易；建立低碳经济蓝碳自愿减排交易框架。

An effective strategy for the blue carbon project in China is to deploy the restoration of visible coastal blue carbon (rooted plants) along with efforts to sequester invisible microbial carbon in waters, especially in estuaries and shelf areas, only then can the project have a substantial impact on climate change mitigation. In practice, the following measures should be taken: establish a long-term monitoring and observation network covering representative sites in river catchments, estuaries and shelf waters; establish standards for core measurements of different forms of blue carbon in various ecosystems; establish a blue carbon ecological value assessment mechanism; establish a watershed-coastal-offshore environmental carbon accounting system; establish an integrated land-sea compensation policy to promote blue carbon trading with agriculture; establish a low-carbon economy and blue carbon voluntary emission reduction trading framework.

参考文献

[1] Jiao N, Hong W, Xu G, et al. Blue carbon on the rise: challenges and opportunities[J]. National science  Review, 2018, 5(4):5.

投稿者：艾伽伊 博士研究生
审核导师：袁益辉 研究员