Carbon stock and storage pattern in the Sundarbans mangrove forest, NE coast of India

This study covered spatial distribution of mangrove biomass, litter fall and intertidal sediment organic carbon storage pattern in the Indian part of the world’s largest mangrove forest, the Sundarbans. The above and below ground (AGB and BGB) biomass spatially varied with high (57.28 ± 3.17 and 28.24 ± 2.64 Mg ha−1), moderate (44.81 ± 8.13 and 20.88 ± 1.41 Mg ha−1) and low (18.97 ± 3.58 and 9.58 ± 0.87 Mg ha−1) for inner, middle and outer zones of the mangrove biosphere. Trunk, branch and leaves formed 45.8, 34.7 and 19.5% of AGB. The AGB: BGB was 2.07 indicating more carbon stock in trunk than root. Predominant mangroves genus Avicennia contributed 57% of plant biomass. Pore-water salinity negatively regulated the distribution of plant biomass. Mean AGB (40.35 Mg ha−1) and BGB (19.57 Mg ha−1) and mean carbon content (40.5%) yielded 10.35 Tg carbon stock in Indian Sundarbans. Litter fall varied from 8.95 to 12.30 Mg ha−1 yr−1, supplying annually 284.7 Gg organic carbon to sediment. Sediment organic carbon (SOC) content varied from 0.92 to 3.29% (avg. 1.99%) building up an organic carbon stock of 59.14 Tg up to 90 cm depth of the intertidal sediment column. Organic carbon, humic acid (HA) and fulvic acid (FA) in sediment showed a decreasing trend with depth indicating organic matter decomposition and depletion of HA and FA accumulation rate. Based on mean concentration of HA and FA as 300 µg g−1 and 571 µg g−1 and their respective carbon percentage as 54.25 and 46.23, refractory organic carbon stock in the intertidal mangrove sediment was estimated as 1.7 Tg.