By mapping their spatial distribution and identifying environmental controls, researchers show that plant growth, soil chemistry, and tidal processes jointly regulate these highly stable carbon pools.
BC, produced by incomplete combustion of biomass and fossil fuels, consists of highly condensed carbon structures that can persist for centuries to millennia. Part of it dissolves into water as dissolved black carbon (DBC), a mobile form that transports carbon from land to aquatic systems and influences global carbon cycling. Mangrove ecosystems, known as “blue carbon” habitats, store large amounts of carbon in waterlogged soils that slow decomposition. Despite their major role in coastal carbon storage, the distribution and dynamics of BC in mangrove soils remain poorly understood, limiting accurate assessments of coastal carbon sequestration and transport processes.
A study (DOI: 10.48130/ebp-0026-0001) published in Environmental and Biogeochemical Processes on 28 January 2026 by Junjian Wang’s team, Southern University of Science and Technology, reveals how black carbon dynamics enhance long-term carbon storage and connect terrestrial and marine carbon cycles in mangrove ecosystems.
Using a land–sea transect and a soil-depth profile in Zhangjiang Estuary mangroves, the researchers quantified total organic carbon (TOC), BC, dissolved organic carbon (DOC), and DBC, calculated key stoichiometric ratios, and then combined correlation tests with machine-learning (random forest) and structural equation modeling (SEM) to identify the environmental drivers and pathways behind observed spatial patterns; they also applied BPCA molecular markers to compare the condensation/stability of BC versus DBC. These measurements showed that variability differed strongly among pools: TOC and DOC were highly heterogeneous (CV 42.8% and 53.6%), BC was comparatively uniform (CV 13.0%), and DBC was most variable (CV 63.1%). Mean BC was 1.27 ± 0.16 g/kg (0.95–1.67 g/kg), generally lower than more urban-influenced mangrove/coastal sites but slightly above some regional shelf sediments, while BC/TOC averaged 8.26% ± 3.34% (3.50%–17.41%), a relatively low proportion that is consistent with limited human disturbance and stronger atmospheric/long-range inputs. Along both gradients, BC and DBC concentrations declined seaward and with depth, yet BC/TOC increased, indicating preferential preservation of recalcitrant BC as other organic matter is lost or diluted by fresh surface litter inputs; BC also tracked TOC closely (r = 0.65), consistent with TOC protection/adsorption and shared depositional controls. DBC was more than twice as high in surface soils as in deeper layers, and DBC/DOC remained low (0.36%–3.07%, mean 1.21% ± 0.56%) but rose with DOC (r=0.48), suggesting shared transport plus DOC-facilitated dissolution and microbial processing that releases both DOC and DBC. BPCA results indicated highly condensed aromatic BC (B6CA+B5CA = 78.3% of BC markers) and a higher condensation index in BC than DBC (B6CA/B5CA: 1.44 vs 0.40), supporting selective dissolution of less-condensed BC into DBC. Driver analyses identified plant biomass as the strongest positive control on BC, TN as a key regulator of TOC and DBC (but negatively associated with BC/TOC), and pH and minerals (especially Ca) as major controls on ratios and BC/DBC stability; SEM further showed that landward distance and depth act largely indirectly by reshaping biomass, TN, pH, clay, bulk density, and water content, collectively reinforcing long-term BC persistence in subsoils while constraining DBC production and mobility with depth.
This study highlights black carbon as a stable and essential contributor to mangrove blue carbon storage, linking long-term carbon sequestration with carbon transport to coastal waters. By clarifying the mechanisms controlling BC and DBC dynamics, the findings improve coastal carbon accounting and climate predictions, while emphasizing that conserving vegetation, soil integrity, and hydrological stability can strengthen mangrove-based climate mitigation.
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References
DOI
10.48130/ebp-0026-0001
Original Source URL
https://doi.org/10.48130/ebp-0026-0001
Funding Information
This work was supported by the Natural Science Foundation of China (Grant Nos 42321004, 42192513, and 42477227), the Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM909), the Guangdong Basic and Applied Basic Research Foundation (Grant No. 2023A1515110245), and the High-Level University Special Fund (Grant No. G03050K001).
About Environmental and Biogeochemical Processes
Environmental and Biogeochemical Processes is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.