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Blue carbon on the rise: challenges and opportunities

Blue carbon on the rise: challenges and opportunities Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 464 Natl Sci Rev, 2018, Vol. 5, No. 4 PERSPECTIVES ENVIRONMENT/ECOLOGY Special Topic: Marine Carbon Sequestration and Climate Change 1,∗ 2 3 4 Nianzhi Jiao , Hong Wang , Guanhua Xu and Salvatore Arico` extremely abundant microbes, includ- BLUE CARBON ON THE RISE Climate Change and Convention on Bio- ing phytoplankton, bacteria, archaea and logical Diversity, and the development of Climate change is a global concern that viruses, which contribute up to 95% of a program of financial support and other requires urgent solutions. As a signatory the world’s blue carbon [4–6]. These mi- policies. Since then, ‘Blue Carbon Ac- to the Paris Agreement, China has com- crobes can interact with the visible blue tion’ has been in action in the protec- mitted to have its greenhouse gas emis- carbon biomes, transforming their or- tion and restoration of mangroves, wet- sion reach a peak by the year 2030, which ganic carbon into refractory forms, pro- lands, etc. in many regions and countries means that severe countermeasures for longing the residence time of the organic such as Australia, Dhabi, Indonesia, In- reducing emissions have to be put into carbon in the ocean. The environmental dia, Kenya, Madagascar, Vietnam and the practice. This is a hard mission given issues we are facing in the coastal water USA. that development is still the top prior- today (such as eutrophication, hypoxia, Significant progress has been made ity in the years to come for China. Un- acidification, etc.) also interact with the in coastal blue carbon research in re- der such circumstances, enhancing car- invisible blue carbon processes, but the cent years, such as the description of blue bon sequestration becomes an effective mechanisms are not yet clear. There- carbon status and carbon sequestration approach to achieving the goal. While ter- fore, both visible and invisible blue car- potentials at the global scale [7,8] and restrial green carbon sink is already in bon biomes should be taken into con- regional scale [8]; the assessment of im- practice, the ocean carbon reservoir, con- sideration for marine ecosystem services, pacts of wetland destruction and the pro- taining 93% of global CO ,as50and and understanding their interactions and posal of corresponding policy [7]; the 20 times the carbon inventories of atmo- their relationship with environmental is- evaluation of the eco-value of blue car- sphere and land, respectively, has great sues is critical for marine ecosystem man- bon in sea grasses, salt marshes and man- potential to expand. Each year, at least agement and sustainable development. groves (e.g. in Philip Bay and Western 25% of the anthropogenic CO has been Harbor, Australia, with an estimate of the captured by marine ecosystems as blue rooted plants to be 1.03 million tons of carbon [1]. BLUE CARBON INITIATIVE AND carbon and a price of $15.38 million) [9]; In 2009, the United Nations Environ- PROGRESS proposal of countermeasures for conser- ment Programme (UNEP), the Food and vation and restoration of blue carbon The IOC, Conservation International Agricultural Organization of the United (e.g. in Scotland, Columbia, Korea and (CI) and the International Union for Nations (FAO) and the Intergovernmen- other countries) [10,11]; as well as sce- Conservation of Nature (IUCN) jointly tal Oceanographic Commission (IOC) nario simulation of blue carbon bene- launched the Blue Carbon Initiative in of the United Nations Educational, Sci- fit function and market price [ 12]. In 2011, aimed at promoting the manage- entific and Cultural Organization (UN- 2017, the Intergovernmental Panel on ment of marine and coastal ecosystems ESCO) jointly published the Blue Carbon Climate Change (IPCC) launched the through international cooperation, and report, pointing out that more than 55% writing process of the Sixth Assessment maintaining carbon sink function in of global primary production is blue car- Report on Climate Change, with a Spe- the mitigation of climate change. ‘Blue bon [2]. Moreover, the production effi- cial Report on the Ocean and Cryosphere Carbon Action’ set up two working ciency of the coastal blue carbon biomes in which blue carbon is included. groups. One is the scientific group (mangroves, sea grass, salt marsh ecosys- toward the establishment of blue carbon tems, etc.) is much higher than that of the measurement and monitoring protocols, Amazon rain forest. However, these blue data acquisition and quality control, carbon biomes are being degraded and CHALLENGES AND disappearing at rates 5–10 times faster field survey handbooks as well as blue OPPORTUNITIES carbon conservation planning and than rainforests [3], thus protection and Although the original concept of blue management guidelines. The other is the restoration are in urgent need. carbon proposed in 2009 refers to the policy working group toward integration Besides the visible coastal blue car- carbon that is captured by marine ecosys- of the blue carbon project into the bon, there are enormous invisible blue tems covering both coastal and open United Nations Framework Convention on carbon biomes composed of tiny but Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 PERSPECTIVES Jiao et al. 465 which found that, in all cases, if there waters [3], practical research and devel- LAND–SEA INTEGRATED are too many inorganic nutrients, there opment of blue carbon have predom- COUNTERMEASURES FOR inantly involved macrofauna, such as will be less organic carbon preserved in CARBON SEQUESTRATION AND mangrove, seagrass and salt marsh in the the environment. Therefore, land–ocean SUSTAINABLE DEVELOPMENT coastal zone. After years of promotion integrated management and engineering OF THE COASTAL ECOSYSTEM of the coastal blue carbon, the IUCN become necessary, such as reducing the Chemical fertilizers have been exces- published the Call for Action on Ocean application of chemical fertilizers in farm- sively applied in farming for decades, es- Carbon in 2014, which highlights the im- ing and eliminating sewage discharge into pecially in developing countries. Exces- portance of ocean carbon sinks in the rivers so as to reduce the N, P inputs sive nitrogen (N) and phosphorus (P) mitigation of climate change, and identi- into the sea. Such eco-engineering is not are then washed out into rivers and ulti- fies the key components of blue carbon aimed at changing the natural ecosys- mately discharged into the coastal waters, in open oceans, expanding the blue car- tems, but rather protecting them by causing eutrophication and algal blooms. bon from coastal zones to oceanic envi- reducing eutrophication and red-tides Although algal blooms seemingly pro- ronments [13]. In fact, the invisible mi- occurrence while increasing carbon se- duce more organic carbon, this carbon crobes are an essential part of blue carbon questration through the MCP. This idea is basically labile and can be respired in the ocean, but have been largely over- also brings new policy as bonus-based rapidly. In addition, the labile DOC pro- looked so far. These microbes, including carbon trade rather than penalty-based duced by primary producers has priming pollution policy, as is being used in phytoplankton (microalgae), cyanobac- effects on the river discharged terrestrial many countries nowadays. The bonus- teria, bacteria, archaea and viruses, are RDOC, namely remobilizing RDOC for based policy would be such that any tiny but extremely abundant, contribut- microbial uptake and respiration, which economy loss claimed due to the reduc- ing up to 90% of the marine biomass and can create high CO concentrations in tion of farming fertilization (should not 95% of the marine production [4–6]. An- 2 the water, making the carbonate equilib- be the case if fertilization is scientifi- nually, over 360 billion tons of CO is rium system move toward proton gen- cally applied, though) and sewage work fixed by marine phytoplankton, 1.39% of eration causing acidification in ambient which is transported down to the seafloor in the watersheds can be compensated by water, and excess CO escape from wa- by the biological pump (BP) for long- the eco-value or carbon price of the in- ter to atmosphere as outgassing. That is term storage [14]. The rest of the fixed crement of carbon sequestration in the why productive estuarine and coastal wa- organic carbon is mainly respired into sea. Once a carbon-accounting system ters are often sources rather than sinks of CO , but a small portion of the organic for the watershed-coastal-offshore envi- atmospheric CO . Meanwhile, this pro- carbon is shunted through the micro- ronments is established, a blue carbon cess consumes a large quantity of oxy- bial carbon pump (MCP) to biologically sequestration-based voluntary emission gen, resulting in hypoxia. Anoxic con- inaccessible phases, being either refrac- reduction trading mechanism could be ditions could cause massive death of tory or at extremely low concentrations easily developed. macro- and microbiomes, resulting in [15]. The MCP is a major contributor to the breeding of anaerobic bacteria that the tremendous marine refractory DOC transform organics into CH ,H S, N O (RDOC) reservoir, which is equivalent in 4 2 2 BLUE CARBON STRATEGY IN and other toxic substances, which in turn amount to the total inventory of CO in CHINA are destructive for the ecosystem. On the atmosphere [16]. Paleoclimate stud- The China Seas include the Bohai Sea, top of that, excess discharge of nutrients ies show that there was an inextricable the Yellow Sea, the East China Sea and (N, P) shapes the C/N and C/P ele- link between the RDOC pool and climate the South China Sea, with coastlines of mental ratios in favor of remobilization change [17,18]. The MCP effects exist 18 000 km, stretching from the north- of RDOC for respiration, lowering the in all water environments and even soil ern temperate zone to tropic zones. There MCP efficiency and carbon sequestra- environments [19], connecting with the are more than 1500 rivers to the China tion. Therefore, reducing terrestrial input visible blue carbon ecosystem, as all the Seas, including the world third largest of inorganic nutrients becomes a feasible blue carbon macro-biomes (mangrove, river, the Yangtze River to the East China countermeasure for the enhancement of sea grass, salt marsh, etc.) release DOC Sea, the Yellow River carrying a huge carbon sequestration in coastal waters into the water, which can be further trans- amount of sediment to the Bohai Sea and (Fig. 1). This idea is supported by a sta- formed by the MCP into RDOC. Such the Pearl River to the South China Sea tistical data analysis of organic carbon processes are influenced by environmen- connecting the Tibetan plateau with the versus nitrate in various natural environ- tal conditions and thus allow manipula- ‘warm pool’ in the West Pacific. Such rich ments [20] as well as by experimental tions to pursue maximum outputs of the habitats harbor great biodiversity and results in estuarine and offshore waters, sum of the BP and MCP (Fig. 1). Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 466 Natl Sci Rev, 2018, Vol. 5, No. 4 PERSPECTIVES Figure 1. A demo of eco-engineering to make coastal waters into sinks rather than sources of atmospheric CO . In addition to the conservation and restoration of coastal blue carbon (mangroves, salt marshes, sea grasses, etc.), reducing terrestrial nutrient inputs could avoid the priming effects on organic carbon respiration and thus increase carbon sequestration in the ocean through both the BP and the MCP. Despite coastal rooted plants like carbon-storage capacity. On the other activities have fundamental impacts on mangroves, saltmarshes and sea grasses hand, China’s coastal zones are also the ecosystem’s health and sustainabil- ity. Many of the estuarine waters are having high carbon production, their highly inhabited, with most of them currently suffering from algal bloom, coverage in China’s coastal areas is receiving severe anthropogenic impacts hypoxia and acidification caused by eu- small and the annual buried amounts of such as harbor construction, tidal zone reclamation, as well as mariculture. Dis- trophication and the following microbial organic matter from them are limited charges of nutrients and organic mat- processes as pointed out in the ‘Chal- (Table 1). Meanwhile, their production ter from rivers as well as sea-farming lenges and Opportunities’ section above. of DOC has never been counted due Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 PERSPECTIVES Jiao et al. 467 Table 1. Carbon sequestration fluxes of various ecosystems in China’s seas. The references were from [22]. Ecosystems Burial flux DOC export flux References −1 −1 (Tg C yr ) (Tg C yr ) Macrofauna Mangrove 0.04 – Liu et al., 2014; Wang et al., 2016 Salt marsh 0.26 – Wang et al., 2016; Mei and Zhang, 2008; Suo et al., 2010; Cao et al., 2013; Zhou et al., 2016 Seagrass 0.01 0.30 Zhou et al., 2016; Jiang et al., 2017; Zheng et al., 2008; Krause-Jensen and Duarte, 2016; Gan et al., 2016; Cao, 2017 Mariculture 0.14 0.50 Zhang et al., 2017; Krause-Jensen and Duarte, 2016; Gan et al., 2016; Cao, 2017; Bureau, MoAFA, 2017 Open waters (mainly microbes) Bohai Sea 2.0 1.51 Hu and Zhao, 2017; Hu et al., 2016; Wei et al., 2002; Liu et al., 2015; Shang, 2011 Yellow Sea 3.6 13.20 Hu and Zhao, 2017; Hu et al., 2016; Song et al., 2017 East China Sea shelf 7.4 15∼35 Deng et al., 2006; Yuan et al., 2017; Hu and Zhao, 2017 South China Sea shelf 4.8 31.82 Hu and Zhao, 2017; Chen et al., 2006; Hung et al., 2007; Wu et al., 2015, 2017 be relatively refractory. If it keeps the re- sequestration in the waters, especially es- to lack of study. Take the case of DOC calcitrance under controlled nutrient in- tuarine and shelf regions. Only in that release from cultured seaweeds, for ex- puts (as discussed in the above section) case will the blue carbon project become ample (although cultivated seaweeds are instead of being remobilized under eu- essentially meaningful for the mitigation not counted as blue carbon officially, trophic conditions and respired in the of climate change. In practice, the follow- its buried debris and derived RDOC marine environments, it would be a sub- ing measures should be implemented: to do contribute to marine carbon sink). stantial contribution to marine carbon se- establish long-term monitoring and ob- The total production of China’s seaweeds −1 culture is about 3.52 Tg C yr .If questration [24]. Together with the BP servation networks covering representa- 23–26% of this carbon is released as flux on the continental shelf (7.4 Tg C tive sites in the river catchments, estuaries −1 DOC [21], and assuming that only half yr )[22], the East China Sea is actu- as well as shelf waters; to establish stan- of the DOC becomes refractory (in ally a significant carbon sink. In fact, the dard protocols for core measurements of the water column, 77–94% of the bulk total carbon export flux of China’s con- different forms of blue carbon in various −1 ecosystems; to establish the mechanisms DOC is refractory [22]), a conserva- tinental shelves is up to 90 Tg C yr of blue carbon eco-value assessment; to tive estimate of the RDOC derived from (Table 1); this recognition changes the overall image of China’s seas as ‘sources’ establish a carbon-accounting system for seaweed culture would be 0.5 Tg C −1 as perceived from the exchange of CO the watershed-coastal-offshore environ- yr [22], which is even higher than between the atmosphere and sea surface. ments; to establish a land–ocean inte- the total burial flux of organic carbon Such ‘sources’ are actually due to the res- grated compensation policy to promote from the coastal blue carbon in China. piration of terrestrial DOC and the out- blue carbon trading with the farming in- When looking at blue carbon on larger gassing of imported high-dissolved inor- dustry; to establish a framework for vol- scales, terrestrial inputs of DOC to the ganic carbon (DIC) deep water from the untary emission reduction trading with coastal waters and marginal sea export of Western Pacific [ 22]. It is therefore worth blue carbon for low carbon economy. DOC to oceanic waters become essen- pointing out that, even if a marine region tial for the mitigation of climate change. is the source of atmospheric CO ,car- Each year, a great deal of DOC is dis- bon sequestration could take place at the charged into China’s seas by rivers. For ACKNOWLEDGEMENTS same time, just like the case of oceanic up- example, the annual DOC flux of the We thank the participants of the 1st Yanqi Lake welling areas. Yangtze River to the East China Sea is conference and the PICES-ICES WG on Biological −1 Based on the above understanding, 1.62 Tg C yr [22], and the annual ex- Driven Carbon Pumps for their discussions and an effective strategy for China’s blue car- port flux of DOC from the East China comments; Glynn Gorick and Tingwei Luo for Sea to the Western Pacific is 15–35 Tg C bon project would be that, while deploy- their help with the figure. This work was supported −1 yr [23]. Such DOC has been exposed ing restoration of the visible coastal blue by the National Key Research Program of China to a variety of environmental conditions carbon (rooted plants), efforts should (2016YFA0601400), the State Oceanic Adminis- before it is exported and is supposed to be made in invisible microbial carbon tration project (GASI-03-01-02-05), the National Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 468 Natl Sci Rev, 2018, Vol. 5, No. 4 PERSPECTIVES Natural Science Foundation of China (91751207), 4. Sogin ML, Morrison HG and Huber JA 15. Jiao N, Herndl GJ and Hansell DA et al. Nat Rev the Chinese Academy of Sciences consulting et al. Proc Natl Acad Sci USA 2006; 103: Micro 2010; 8: 593–9. program (2016ZWH008A-008), the NSFC–CAS 12115–20. 16. Hansell DA, Carlson CA and Repeta DJ et al. discipline strategy program (L1624030) and the 5. Suttle CA. Nat Rev Micro 2007; 5: 801–12. Oceanog 2009; 22: 202–11. Fundamental Research Funds for the Central 6. Pomeroy LR, Williams PJI and Azam F et al. 17. Rothman DH, Hayes JM and Summons RE. Proc Universities (20720170107). Oceanog 2007; 20: 28–33. Natl Acad Sci USA 2003; 100: 8124–9. 1, ∗ 2 3 Nianzhi Jiao , Hong Wang , Guanhua Xu and 7. Sifleet S, Pendleton L and Murray BC. Nicholas 18. Ridgwell A. Proc Natl Acad Sci USA 2011; 108: Salvatore Arico` Institute Report 2011; 11: 06. 16485–6. State Key Laboratory of Marine Environmental 8. Pendleton L, Donato DC and Murray BCetal.PLoS 19. Liang C, Schimel JP and Jastrow JD. Nat Micro- Science, Xiamen University, China One 2012; 7: e43542. biol 2017; 2: 17105. State Ocean Administration, China 9. Carnell P, Ewers C and Rochelmeyer E et al. 20. Taylor PG and Townsend AR. Nature 2010; 464: Ministry of Science and Technology, China The Distribution and Abundance of ‘Blue Carbon’ 1178–81. Intergovernmental Oceanographic Commission of within Port Phillip and Westernport. Melbourne: 21. Krause-Jensen D and Duarte CM. Nature Geosci United Nations Educational, Scientific and Cultural Deakin University, 2015. 2016; 9: 737–42. Organization (UNESCO), France 10. Burrows MT, Kamenos NA and Hughes DJ et al. 22. Jiao N, Liang Y and Zhang Y et al. Comprehensive Corresponding author. Assessment of Carbon Budgets and Potential analysis of carbon pool and fluxes in China Sea E-mail: jiao@xmu.edu.cn Blue Carbon Stores in Scotland’s Coastal and Ma- and its adjacent oceans. Sci China Earth Sci 2018; rine Environment. Edinburgh: Scottish National doi:10.1007/s11430-018-9190-x. REFERENCES Heritage, 2014. 23. Yuan D, He J and Li J et al. Sci China Earth Sci 11. Sondak CFA and Chung IK. Ocean Sci J 2015; 50: 2018; 61: 659–67. 1. Le Quere C, Moriarty R and Andrew RM et al. 1–8. 24. Jiao N, Robinson C and Azam F et al. Biogeo- Earth Syst Sci Data 2015; 7: 47–85. 12. Zarate-Barrera TG and Maldonado JH. PLoS One sciences 2014; 11: 5285–306. 2. Bowler C, Karl DM and Colwell RR. Nature 2009; 2015; 10: e0126627. 459: 180–4. 13. Howard J, Sutton-Grier A and Herr D et al. Front 3. Nellemann C, Corcoran E and Duarte CM et al. Ecol Environ 2017; 15: 42–50. Blue Carbon: The Role of Healthy Oceans in National Science Review 14. Katherina S, Christian H and Matthias Binding Carbon: A Rapid Response Assessment. 5: 464–468, 2018 Z. Global Biogeochem Cycles 2005; 19: GRID-Arendal: United Nations Environment Pro- doi: 10.1093/nsr/nwy030 155–72. gramme, 2009. Advance access publication 15 February 2018 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png National Science Review Oxford University Press

Blue carbon on the rise: challenges and opportunities

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Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 464 Natl Sci Rev, 2018, Vol. 5, No. 4 PERSPECTIVES ENVIRONMENT/ECOLOGY Special Topic: Marine Carbon Sequestration and Climate Change 1,∗ 2 3 4 Nianzhi Jiao , Hong Wang , Guanhua Xu and Salvatore Arico` extremely abundant microbes, includ- BLUE CARBON ON THE RISE Climate Change and Convention on Bio- ing phytoplankton, bacteria, archaea and logical Diversity, and the development of Climate change is a global concern that viruses, which contribute up to 95% of a program of financial support and other requires urgent solutions. As a signatory the world’s blue carbon [4–6]. These mi- policies. Since then, ‘Blue Carbon Ac- to the Paris Agreement, China has com- crobes can interact with the visible blue tion’ has been in action in the protec- mitted to have its greenhouse gas emis- carbon biomes, transforming their or- tion and restoration of mangroves, wet- sion reach a peak by the year 2030, which ganic carbon into refractory forms, pro- lands, etc. in many regions and countries means that severe countermeasures for longing the residence time of the organic such as Australia, Dhabi, Indonesia, In- reducing emissions have to be put into carbon in the ocean. The environmental dia, Kenya, Madagascar, Vietnam and the practice. This is a hard mission given issues we are facing in the coastal water USA. that development is still the top prior- today (such as eutrophication, hypoxia, Significant progress has been made ity in the years to come for China. Un- acidification, etc.) also interact with the in coastal blue carbon research in re- der such circumstances, enhancing car- invisible blue carbon processes, but the cent years, such as the description of blue bon sequestration becomes an effective mechanisms are not yet clear. There- carbon status and carbon sequestration approach to achieving the goal. While ter- fore, both visible and invisible blue car- potentials at the global scale [7,8] and restrial green carbon sink is already in bon biomes should be taken into con- regional scale [8]; the assessment of im- practice, the ocean carbon reservoir, con- sideration for marine ecosystem services, pacts of wetland destruction and the pro- taining 93% of global CO ,as50and and understanding their interactions and posal of corresponding policy [7]; the 20 times the carbon inventories of atmo- their relationship with environmental is- evaluation of the eco-value of blue car- sphere and land, respectively, has great sues is critical for marine ecosystem man- bon in sea grasses, salt marshes and man- potential to expand. Each year, at least agement and sustainable development. groves (e.g. in Philip Bay and Western 25% of the anthropogenic CO has been Harbor, Australia, with an estimate of the captured by marine ecosystems as blue rooted plants to be 1.03 million tons of carbon [1]. BLUE CARBON INITIATIVE AND carbon and a price of $15.38 million) [9]; In 2009, the United Nations Environ- PROGRESS proposal of countermeasures for conser- ment Programme (UNEP), the Food and vation and restoration of blue carbon The IOC, Conservation International Agricultural Organization of the United (e.g. in Scotland, Columbia, Korea and (CI) and the International Union for Nations (FAO) and the Intergovernmen- other countries) [10,11]; as well as sce- Conservation of Nature (IUCN) jointly tal Oceanographic Commission (IOC) nario simulation of blue carbon bene- launched the Blue Carbon Initiative in of the United Nations Educational, Sci- fit function and market price [ 12]. In 2011, aimed at promoting the manage- entific and Cultural Organization (UN- 2017, the Intergovernmental Panel on ment of marine and coastal ecosystems ESCO) jointly published the Blue Carbon Climate Change (IPCC) launched the through international cooperation, and report, pointing out that more than 55% writing process of the Sixth Assessment maintaining carbon sink function in of global primary production is blue car- Report on Climate Change, with a Spe- the mitigation of climate change. ‘Blue bon [2]. Moreover, the production effi- cial Report on the Ocean and Cryosphere Carbon Action’ set up two working ciency of the coastal blue carbon biomes in which blue carbon is included. groups. One is the scientific group (mangroves, sea grass, salt marsh ecosys- toward the establishment of blue carbon tems, etc.) is much higher than that of the measurement and monitoring protocols, Amazon rain forest. However, these blue data acquisition and quality control, carbon biomes are being degraded and CHALLENGES AND disappearing at rates 5–10 times faster field survey handbooks as well as blue OPPORTUNITIES carbon conservation planning and than rainforests [3], thus protection and Although the original concept of blue management guidelines. The other is the restoration are in urgent need. carbon proposed in 2009 refers to the policy working group toward integration Besides the visible coastal blue car- carbon that is captured by marine ecosys- of the blue carbon project into the bon, there are enormous invisible blue tems covering both coastal and open United Nations Framework Convention on carbon biomes composed of tiny but Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 PERSPECTIVES Jiao et al. 465 which found that, in all cases, if there waters [3], practical research and devel- LAND–SEA INTEGRATED are too many inorganic nutrients, there opment of blue carbon have predom- COUNTERMEASURES FOR inantly involved macrofauna, such as will be less organic carbon preserved in CARBON SEQUESTRATION AND mangrove, seagrass and salt marsh in the the environment. Therefore, land–ocean SUSTAINABLE DEVELOPMENT coastal zone. After years of promotion integrated management and engineering OF THE COASTAL ECOSYSTEM of the coastal blue carbon, the IUCN become necessary, such as reducing the Chemical fertilizers have been exces- published the Call for Action on Ocean application of chemical fertilizers in farm- sively applied in farming for decades, es- Carbon in 2014, which highlights the im- ing and eliminating sewage discharge into pecially in developing countries. Exces- portance of ocean carbon sinks in the rivers so as to reduce the N, P inputs sive nitrogen (N) and phosphorus (P) mitigation of climate change, and identi- into the sea. Such eco-engineering is not are then washed out into rivers and ulti- fies the key components of blue carbon aimed at changing the natural ecosys- mately discharged into the coastal waters, in open oceans, expanding the blue car- tems, but rather protecting them by causing eutrophication and algal blooms. bon from coastal zones to oceanic envi- reducing eutrophication and red-tides Although algal blooms seemingly pro- ronments [13]. In fact, the invisible mi- occurrence while increasing carbon se- duce more organic carbon, this carbon crobes are an essential part of blue carbon questration through the MCP. This idea is basically labile and can be respired in the ocean, but have been largely over- also brings new policy as bonus-based rapidly. In addition, the labile DOC pro- looked so far. These microbes, including carbon trade rather than penalty-based duced by primary producers has priming pollution policy, as is being used in phytoplankton (microalgae), cyanobac- effects on the river discharged terrestrial many countries nowadays. The bonus- teria, bacteria, archaea and viruses, are RDOC, namely remobilizing RDOC for based policy would be such that any tiny but extremely abundant, contribut- microbial uptake and respiration, which economy loss claimed due to the reduc- ing up to 90% of the marine biomass and can create high CO concentrations in tion of farming fertilization (should not 95% of the marine production [4–6]. An- 2 the water, making the carbonate equilib- be the case if fertilization is scientifi- nually, over 360 billion tons of CO is rium system move toward proton gen- cally applied, though) and sewage work fixed by marine phytoplankton, 1.39% of eration causing acidification in ambient which is transported down to the seafloor in the watersheds can be compensated by water, and excess CO escape from wa- by the biological pump (BP) for long- the eco-value or carbon price of the in- ter to atmosphere as outgassing. That is term storage [14]. The rest of the fixed crement of carbon sequestration in the why productive estuarine and coastal wa- organic carbon is mainly respired into sea. Once a carbon-accounting system ters are often sources rather than sinks of CO , but a small portion of the organic for the watershed-coastal-offshore envi- atmospheric CO . Meanwhile, this pro- carbon is shunted through the micro- ronments is established, a blue carbon cess consumes a large quantity of oxy- bial carbon pump (MCP) to biologically sequestration-based voluntary emission gen, resulting in hypoxia. Anoxic con- inaccessible phases, being either refrac- reduction trading mechanism could be ditions could cause massive death of tory or at extremely low concentrations easily developed. macro- and microbiomes, resulting in [15]. The MCP is a major contributor to the breeding of anaerobic bacteria that the tremendous marine refractory DOC transform organics into CH ,H S, N O (RDOC) reservoir, which is equivalent in 4 2 2 BLUE CARBON STRATEGY IN and other toxic substances, which in turn amount to the total inventory of CO in CHINA are destructive for the ecosystem. On the atmosphere [16]. Paleoclimate stud- The China Seas include the Bohai Sea, top of that, excess discharge of nutrients ies show that there was an inextricable the Yellow Sea, the East China Sea and (N, P) shapes the C/N and C/P ele- link between the RDOC pool and climate the South China Sea, with coastlines of mental ratios in favor of remobilization change [17,18]. The MCP effects exist 18 000 km, stretching from the north- of RDOC for respiration, lowering the in all water environments and even soil ern temperate zone to tropic zones. There MCP efficiency and carbon sequestra- environments [19], connecting with the are more than 1500 rivers to the China tion. Therefore, reducing terrestrial input visible blue carbon ecosystem, as all the Seas, including the world third largest of inorganic nutrients becomes a feasible blue carbon macro-biomes (mangrove, river, the Yangtze River to the East China countermeasure for the enhancement of sea grass, salt marsh, etc.) release DOC Sea, the Yellow River carrying a huge carbon sequestration in coastal waters into the water, which can be further trans- amount of sediment to the Bohai Sea and (Fig. 1). This idea is supported by a sta- formed by the MCP into RDOC. Such the Pearl River to the South China Sea tistical data analysis of organic carbon processes are influenced by environmen- connecting the Tibetan plateau with the versus nitrate in various natural environ- tal conditions and thus allow manipula- ‘warm pool’ in the West Pacific. Such rich ments [20] as well as by experimental tions to pursue maximum outputs of the habitats harbor great biodiversity and results in estuarine and offshore waters, sum of the BP and MCP (Fig. 1). Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 466 Natl Sci Rev, 2018, Vol. 5, No. 4 PERSPECTIVES Figure 1. A demo of eco-engineering to make coastal waters into sinks rather than sources of atmospheric CO . In addition to the conservation and restoration of coastal blue carbon (mangroves, salt marshes, sea grasses, etc.), reducing terrestrial nutrient inputs could avoid the priming effects on organic carbon respiration and thus increase carbon sequestration in the ocean through both the BP and the MCP. Despite coastal rooted plants like carbon-storage capacity. On the other activities have fundamental impacts on mangroves, saltmarshes and sea grasses hand, China’s coastal zones are also the ecosystem’s health and sustainabil- ity. Many of the estuarine waters are having high carbon production, their highly inhabited, with most of them currently suffering from algal bloom, coverage in China’s coastal areas is receiving severe anthropogenic impacts hypoxia and acidification caused by eu- small and the annual buried amounts of such as harbor construction, tidal zone reclamation, as well as mariculture. Dis- trophication and the following microbial organic matter from them are limited charges of nutrients and organic mat- processes as pointed out in the ‘Chal- (Table 1). Meanwhile, their production ter from rivers as well as sea-farming lenges and Opportunities’ section above. of DOC has never been counted due Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 PERSPECTIVES Jiao et al. 467 Table 1. Carbon sequestration fluxes of various ecosystems in China’s seas. The references were from [22]. Ecosystems Burial flux DOC export flux References −1 −1 (Tg C yr ) (Tg C yr ) Macrofauna Mangrove 0.04 – Liu et al., 2014; Wang et al., 2016 Salt marsh 0.26 – Wang et al., 2016; Mei and Zhang, 2008; Suo et al., 2010; Cao et al., 2013; Zhou et al., 2016 Seagrass 0.01 0.30 Zhou et al., 2016; Jiang et al., 2017; Zheng et al., 2008; Krause-Jensen and Duarte, 2016; Gan et al., 2016; Cao, 2017 Mariculture 0.14 0.50 Zhang et al., 2017; Krause-Jensen and Duarte, 2016; Gan et al., 2016; Cao, 2017; Bureau, MoAFA, 2017 Open waters (mainly microbes) Bohai Sea 2.0 1.51 Hu and Zhao, 2017; Hu et al., 2016; Wei et al., 2002; Liu et al., 2015; Shang, 2011 Yellow Sea 3.6 13.20 Hu and Zhao, 2017; Hu et al., 2016; Song et al., 2017 East China Sea shelf 7.4 15∼35 Deng et al., 2006; Yuan et al., 2017; Hu and Zhao, 2017 South China Sea shelf 4.8 31.82 Hu and Zhao, 2017; Chen et al., 2006; Hung et al., 2007; Wu et al., 2015, 2017 be relatively refractory. If it keeps the re- sequestration in the waters, especially es- to lack of study. Take the case of DOC calcitrance under controlled nutrient in- tuarine and shelf regions. Only in that release from cultured seaweeds, for ex- puts (as discussed in the above section) case will the blue carbon project become ample (although cultivated seaweeds are instead of being remobilized under eu- essentially meaningful for the mitigation not counted as blue carbon officially, trophic conditions and respired in the of climate change. In practice, the follow- its buried debris and derived RDOC marine environments, it would be a sub- ing measures should be implemented: to do contribute to marine carbon sink). stantial contribution to marine carbon se- establish long-term monitoring and ob- The total production of China’s seaweeds −1 culture is about 3.52 Tg C yr .If questration [24]. Together with the BP servation networks covering representa- 23–26% of this carbon is released as flux on the continental shelf (7.4 Tg C tive sites in the river catchments, estuaries −1 DOC [21], and assuming that only half yr )[22], the East China Sea is actu- as well as shelf waters; to establish stan- of the DOC becomes refractory (in ally a significant carbon sink. In fact, the dard protocols for core measurements of the water column, 77–94% of the bulk total carbon export flux of China’s con- different forms of blue carbon in various −1 ecosystems; to establish the mechanisms DOC is refractory [22]), a conserva- tinental shelves is up to 90 Tg C yr of blue carbon eco-value assessment; to tive estimate of the RDOC derived from (Table 1); this recognition changes the overall image of China’s seas as ‘sources’ establish a carbon-accounting system for seaweed culture would be 0.5 Tg C −1 as perceived from the exchange of CO the watershed-coastal-offshore environ- yr [22], which is even higher than between the atmosphere and sea surface. ments; to establish a land–ocean inte- the total burial flux of organic carbon Such ‘sources’ are actually due to the res- grated compensation policy to promote from the coastal blue carbon in China. piration of terrestrial DOC and the out- blue carbon trading with the farming in- When looking at blue carbon on larger gassing of imported high-dissolved inor- dustry; to establish a framework for vol- scales, terrestrial inputs of DOC to the ganic carbon (DIC) deep water from the untary emission reduction trading with coastal waters and marginal sea export of Western Pacific [ 22]. It is therefore worth blue carbon for low carbon economy. DOC to oceanic waters become essen- pointing out that, even if a marine region tial for the mitigation of climate change. is the source of atmospheric CO ,car- Each year, a great deal of DOC is dis- bon sequestration could take place at the charged into China’s seas by rivers. For ACKNOWLEDGEMENTS same time, just like the case of oceanic up- example, the annual DOC flux of the We thank the participants of the 1st Yanqi Lake welling areas. Yangtze River to the East China Sea is conference and the PICES-ICES WG on Biological −1 Based on the above understanding, 1.62 Tg C yr [22], and the annual ex- Driven Carbon Pumps for their discussions and an effective strategy for China’s blue car- port flux of DOC from the East China comments; Glynn Gorick and Tingwei Luo for Sea to the Western Pacific is 15–35 Tg C bon project would be that, while deploy- their help with the figure. This work was supported −1 yr [23]. Such DOC has been exposed ing restoration of the visible coastal blue by the National Key Research Program of China to a variety of environmental conditions carbon (rooted plants), efforts should (2016YFA0601400), the State Oceanic Adminis- before it is exported and is supposed to be made in invisible microbial carbon tration project (GASI-03-01-02-05), the National Downloaded from https://academic.oup.com/nsr/article/5/4/464/4862478 by DeepDyve user on 13 July 2022 468 Natl Sci Rev, 2018, Vol. 5, No. 4 PERSPECTIVES Natural Science Foundation of China (91751207), 4. Sogin ML, Morrison HG and Huber JA 15. Jiao N, Herndl GJ and Hansell DA et al. Nat Rev the Chinese Academy of Sciences consulting et al. Proc Natl Acad Sci USA 2006; 103: Micro 2010; 8: 593–9. program (2016ZWH008A-008), the NSFC–CAS 12115–20. 16. Hansell DA, Carlson CA and Repeta DJ et al. discipline strategy program (L1624030) and the 5. Suttle CA. Nat Rev Micro 2007; 5: 801–12. Oceanog 2009; 22: 202–11. 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Journal

National Science Review – Oxford University Press

Published: Jul 1, 2018

References

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