Stock assessment of the blue carbon pool of selected patches of mangrove sediment in the Vembanad Lake was done using the standard protocols on a per ha basis and multiplied with the estimated area to derive the blue carbon stock of the particular fragmented mangrove stands of the species Avicennia officinalis (Indian Mangrove), twice (in the post and pre-monsoon) during October 2017-March 2018. The treatments included ‘aged’, ‘recent’, ‘healthy’ and ‘degraded’ mangroves of the selected species and ‘control’ without mangroves. The overall mean carbon stock in the A. officinalis sediments in selected locations of the Vembanad Lake area was 136.09 Mg C/ha (Mg=mega gram=1 tonne). This value is far low compared to the mean global soil organic carbon stock in the mangrove ecosystem (386 Mg C/ha). This finding suggests ample opportunity for more carbon sequestration in the selected mangrove ecosystems in Vembanad Lake, toward climate change mitigation measures. The treatments differed significantly in the cumulative stock of blue carbon and layer-wise blue carbon density in sediment (p<0.05), the highest seen in ‘healthy’ mangroves in both seasons. The overall range of layer-wise blue carbon density in sediment was found to be 0.003 to 0.56 Mg/m3 . Spatial maps prepared for layer-wise blue carbon density in the sediment revealed its depth-wise increase. Layer wise blue carbon stock in sediment had a significant correlation with total organic carbon and organic matter (p<0.01) and with the C/N ratio of the sediment (p < 0.05). Based on the results, this study suggests total organic carbon and the C/N ratio of sediment as possible predictive indicators of sediment blue carbon.

Mangrove sediment, blue carbon, dry bulk density, climate change, GIS, Vembanad Lake