Relevance of Soil Aggregates on Carbon Sequestration in Mangrove and Rice Ecosystems of Sundarbans Delta

Abstract

Mangrove ecosystems are net carbon sinks. These have high carbon sequestration potential in soil, sediments, and water column. The soil organic carbon (SOC) which is protected by the aggregates is called the slow pool. In this pool, the organic matter is partially decomposed. Carbon which is present between aggregates is called inter-particulate organic carbon and the carbon which is present within aggregates is called intra-particulate organic carbon. It is also called particulate organic matter carbon (POM-C). Many reports have suggested that macroaggregates (>250μm) provide less protection to carbon in comparison to micro aggregates (<250μm), to decomposition. The present paper depicts the comparative analysis of particulate organic carbon (POC) sequestration and soil aggregate stability in mangrove and rice ecosystem of the Sundarban delta. In our study seven different sites were selected based on the degradation status of mangroves from 1930 to 2013 by National Remote Sensing Agency (NRSA), Hyderabad in Sagar Island, Sundarban, India. In order to estimate the POC sequestration and soil aggregate stability aggregate fractions of different sizes were extracted from the sample with the help of Yoder apparatus. POC in soil aggregates of each class were estimated with the help of C/N analyser. Samples were collected from all the two depths (0-15 cm and 15-30 cm) of all sites. To estimate the aggregate stability Mean weight diameter (MWD) was calculated. In mangrove, The average mean weight diameters (MWD) of soils were in between 0.088 to 0.145 mm whereas in rice it was in between 0.120 to 0.438 mm among the seven different sites. This shows that more aggregate stable soil is under the rice system than that of mangrove system. The soils of the top layer had more aggregate stability than the sub-soil in both the (mangroves and rice) systems. The MWD of soil aggregate under the rice system was higher than in the mangroves system. Macroaggregate are generally formed through the cementation of microaggregates. Earlier studies have suggested that aggregate transformation is strongly regulated by microbial activity. Fungal hyphae physically bind the microaggregate together to form macroaggregate and it also stabilize the contents present in microaggregate. This paper investigates the significant impact of all three factors (i.e. ecology, site and depth) on the aggregate stability and POC sequestration.