Ecosystem carbon stocks of mangroves across broad environmental gradients in West-Central Africa: Global and regional comparisons

Abstract

Globally, it is recognized that blue carbon ecosystems, especially mangroves, often sequester large quantities of carbon and are of interest for inclusion in climate change mitigation strategies. While 19% of the world’s mangroves are in Africa, they are among the least investigated of all blue carbon ecosystems. We quantified total ecosystem carbon stocks in 33 different mangrove stands along the Atlantic coast of West-Central Africa from Senegal to Southern Gabon spanning large gradients of latitude, soil properties, porewater salinity, and precipitation. Mangrove structure ranged from low and dense stands that were <1m in height and >35,000 trees ha-1 to tall and open stands >40m in height and <100 ha-1. Tremendous variation in ecosystem carbon (C) stocks was measured ranging from 154 to 1,484 Mg C ha-1. The mean total ecosystem carbon stock for all mangroves of West-Central Africa was 799 Mg C ha-1. Soils comprised an average of 86% of the total carbon stock. The greatest carbon stocks were found in the tall mangroves of Liberia and Gabon North with a mean >1,000 Mg C ha-1. The lowest carbon stocks were found in the low mangroves of the semiarid region of Senegal (463 Mg C ha-1) and in mangroves on coarse-textured soils in Gabon South (541 Mg C ha-1). At the scale of the entirety of West-Central Africa, total ecosystem carbon stocks were poorly correlated to aboveground ecosystem carbon pools, precipitation, latitude and soil salinity (r2 = ≤0.07 for all parameters). Based upon a sample of 158 sites from Africa, Asia and Latin America that were sampled in a similar manner to this study, the global mean of carbon stocks for mangroves is 885 Mg C ha-1. The ecosystem carbon stocks of mangroves for West-Central Africa are slightly lower than those of Latin America (940 Mg C ha-1) and Asia (1049 Mg C ha-1) but substantially higher than the default Intergovernmental Panel on Climate Change (IPCC) values for mangroves (511 Mg C ha-1). This study provides an improved estimation of default estimates (Tier 1 values) of mangroves for Asia, Latin America, and West Central Africa.

Total ecosystem carbon stocks of mangroves across broad global environmental and physical gradients

“…In contrast, those from Liberia (3,346 mm precipitation) were 950 Mg C/ha (; see also Schile et al. and Kauffman and Bhomia ). However, there is commonly a wide range in TECS of individual stands within estuaries where climatic conditions would not vary.…”

“…Interstitial salinity and pH were measured from porewater samples collected in the core holes using portable handheld refractometers and pH meters following methods described in Kauffman and Bhomia (). Care was taken to ensure that no surface water mixed with the porewater.…”

“…To date, a globally synthetic understanding of mangrove C stocks has been hampered, in part, by the wide variation in environmental settings and drivers that influence their productivity and C dynamics. For example, hydrologic and salinity environments in mangroves range from hypersaline (>96 PSU) and hyperarid (~22 mm annual precipitation), to essentially freshwater environments in the highest rainfall areas of tropical coastlines (Kauffman and Bhomia , Schile et al. ).…”

And details for land‐use carbon footprints arise from quantitative and replicated studies

“…This is in contrast to the single site (Vietnam) reported by Henriksson et al, where predictions of losses were not measured but based upon best guesses of losses from early "blue carbon" studies (eg Donato et al 2011 andPendleton et al 2012, of which Kauffman was a coauthor). Kauffman and Bhomia (2017) showed that, on a global scale, the ecosystem carbon stocks of mangroves range from >100 to <2000 Mg C ha −1 . This broad range in ecosystem carbon stocks underscores the importance of its measurement in order to reliably determine land-use carbon footprints.…”

Measuring mangrove carbon loss and gain in deltas

“…However, many of these sites are selected based on ease of access, location, or other preferential factors. Although mangrove carbon can be extremely high in certain geographic settings, this is not the case everywhere, as has been shown by case studies in Mozambique and West Africa (Stringer et al 2015, Kauffman andBhomia 2017). Extrapolating high local carbon values can skew regional and global estimates.…”