Blue carbon of Mexico, carbon stocks and fluxes: a systematic review

Abstract

Mexico has more than 750,000 ha of mangroves and more than 400,000 ha of seagrasses. However, approximately 200,000 ha of mangroves and an unknown area of seagrass have been lost due to coastal development associated with urban, industrial and tourist purposes. In 2018, the approved reforms to the General Law on Climate Change (LGCC) aligned the Mexican law with the international objectives established in the 2nd Article of the Paris Agreement. This action proves Mexico’s commitment to contributing to the global target of stabilizing the greenhouse gas emissions concentration in the planet. Thus, restoring and conserving mangrove and seagrass habitats could contribute to fulfilling this commitment. Therefore, as a first step in establishing a mitigation and adaptation plan against climate change with respect to conservation and restoration actions of these ecosystems, we evaluated Mexican blue carbon ecosystems through a systematic review of the carbon stock using the standardized method of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We used the data from 126 eligible studies for both ecosystems (n = 1220). The results indicated that information is missing at the regional level. However, the average above and below ground organic carbon stocks from mangroves in Mexico is 113.6 ± 5.5 (95% CI [99.3–118.4]) Mg Corg ha−1 and 385.1 ± 22 (95% CI [344.5–431.9]) Mg Corg ha−1, respectively. The variability in the Corg stocks for both blue carbon ecosystems in Mexico is related to variations in climate, hydrology and geomorphology observed along the country’s coasts in addition to the size and number of plots evaluated with respect to the spatial cover. The highest values for mangroves were related to humid climate conditions, although in the case of seagrasses, they were related to low levels of hydrodynamic stress. Based on the official extent of mangrove and seagrass area in Mexico, we estimate a total carbon stock of 237.7 Tg Corg from mangroves and 48.1 Tg Corg from seagrasses. However, mangroves and seagrasses are still being lost due to land use change despite Mexican laws meant to incorporate environmental compensation. Such losses are largely due to loopholes in the legal framework that dilute the laws’ effectiveness and thus ability to protect the ecosystem. The estimated emissions from land use change under a conservative approach in mangroves of Mexico were approximately 24 Tg CO2e in the last 20 years. Therefore, the incorporation of blue carbon into the carbon market as a viable source of supplemental finance for mangrove and seagrass protection is an attractive win-win opportunity.

Seagrass blue carbon stocks and sequestration rates in the Colombian Caribbean

“…Seagrasses are sparsely distributed along the Colombian Caribbean, but their C org stocks in 1 m-thick soils (241 Mg C org ha −1 on average) are well above the values from global estimates (140 Mg C org ha −1 ) 5 and other tropical regions such as Mexico, US and Indonesia (ranging 23 , 33 – 35 from 71 to 170 Mg C org ha −1 . Estimates of soil short-term CAR (122 g C org m −2 year −1 ) in Colombian seagrass meadows is higher than in the Dutch Caribbean (84 g C org m −2 year −1 ) 25 and Australian (36 g C org m −2 year −1 ) 21 meadows.…”

“…Such differences in biotic and abiotic habitat characteristics result in up to 18-fold variability in C org storage capacity across seagrass ecosystems 17 . An increasing number of studies are reporting seagrass blue carbon stocks and accumulation rates at local, regional and global scales 5 , 18 – 23 . However, there is a scarcity of seagrass blue carbon estimates in American countries, with the exception of Mexico, Canada, the United States in North America, and a few studies in Central and South America (Brazil, Panama and Dutch Caribbean) 5 , 20 , 23 – 29 .…”

“…An increasing number of studies are reporting seagrass blue carbon stocks and accumulation rates at local, regional and global scales 5 , 18 – 23 . However, there is a scarcity of seagrass blue carbon estimates in American countries, with the exception of Mexico, Canada, the United States in North America, and a few studies in Central and South America (Brazil, Panama and Dutch Caribbean) 5 , 20 , 23 – 29 . The scarcity of seagrass blue carbon studies in these key regions is limiting our capacity to derive robust global estimates while precluding their incorporation into national carbon accounting and the implementation of blue carbon strategies within Nationally Declared Contributions to mitigate climate change.…”

Carbon Fluxes and Stocks by Mexican Tropical Forested Wetland Soils: A Critical Review of Its Role for Climate Change Mitigation

“…Carbon stocks observed in Mexican mangroves soils were higher than the carbon stocks reported on tropical mangroves of Kerela, India (13.9 kg C m −2 ) [ 47 ], Sofala, Mozambique (15.9 kg C m −2 ) [ 48 ] and Honduran mangroves (5.7–10.6 kg C m 2 ) [ 49 ]. Despite its good storage of carbon in the soil of Mexican mangroves, its extent has decreased almost 55% from 1970 to 2018 (1,420,000 ha to 775,555 ha) [ 50 ], mainly by land use change or conflict between cattle ranches and fishermen in mangrove areas [ 51 ]. Owing to this, projects for reforestation and restoration of mangroves are necessary.…”

Evaluation of the mangrove system in the estero "Arroyo los Coamiles" (Punta de Mita, Nayarit, Mexico)

“…With respect to the hydrological dynamics of this estuary, there is no evidence that it connects to the sea, even during live tides, however, during the rainy season it is possible to favor the connection with the sea by overflowing, it was investigated through direct communication that the local inhabitants open a communication channel to the sea so that marine species of fishing use can enter only during the summer, according to the conductivity reading there is no filtration of salt water so most of the year is fresh water. (Herrera, et al, 2016) It should be noted that according to water quality studies, the basin does not present values in the parameters and variables measured that indicate any type of alteration or disturbance, which indicates that the water body that supports this system and the nearby basin that feeds it are in good condition, reinforcing the idea of the functionality of this ecosystem (García Velasco et al, 2019).…”