Variability in soil organic carbon stock and isotopic signature in tropical island mangrove forests of India

This study estimated the soil organic carbon (SOC) stocks in contrasting hydro-geomorphic settings, particularly estuarine (4 sites) and marine (3 sites) environmental settings, across South Andaman Island, Andaman and Nicobar Islands, India, and discussed the factors responsible for variation between the sites and across macro and mesoscale hydro-geomorphic settings. The results showed similar mean SOC stock in estuarine (345.31 +/- 97.22 Mg C ha(-1)) and marine mangroves (307.02 +/- 103.93 Mg C ha(-1)). However, SOC stocks increased from seaward fringe to interior and decreased towards landward fringe and landward mudflats. Furthermore, the soil characteristics such as bulk density and SOC content varied significantly across the sites and between the estuarine and marine hydro-geomorphic settings (p < 0.001). The mean carbon isotopic composition (delta C-13) of mangrove soils (- 28.0 +/- 0.8 parts per thousand) of the South Andaman Island was about 2 parts per thousand higher than that of the mangrove leaves (- 30.3 +/- 1.9 parts per thousand), which indicated that the mangrove soils predominantly contained a mixture of detritus from mangrove litters and terrestrial C-3 plants. Furthermore, the delta C-13 values differed significantly across sites and mesoscale hydro-geomorphic settings (p < 0.001). Comparing the present results with earlier reports of similar environmental settings (estuarine and marine), it is evident that local factors played a key role in controlling the OC distribution in mangrove soils of the South Andaman Island. Therefore, it is emphasized that the knowledge of variability in SOC stock of mangroves of different environmental settings is imperative for the precise estimation of their carbon storage and climate change mitigation potential.