ESTIMATION OF BELOW GROUND CARBON STOCKS IN  SELECTED MANGROVES AND COASTAL ECOSYSTEMS IN SOUTHERN SRI LANKA

An increment in the atmospheric carbon dioxide (CO_2(g)) level directly affects climate change through the global warming scenario. In that case, coastal ecosystems play an important role by storing CO_2(g) within their ecosystem pools. Moreover, mangroves, salt marshes, and seagrass meadows are named “Blue Carbon Ecosystems” and are the most carbon-dense coastal ecosystems in the world. However, most of the carbon-stock assessments have been carried out on blue carbon ecosystems only. Thus, the information  available on the other coastal ecosystems as a holistic entity are scarce. Therefore, the current study focused on assessing the carbon-stocks in mangroves and the other neighboring coastal ecosystems in the Southern coastal zone of Sri Lanka. Galle, Kalametiya, Hambanthota, and Bundala study sites were subjected to investigation and were considered model sites. The main objective of the study was to assess the Soil Organic Carbon (SOC) content in mangroves and other neighboring coastal ecosystems. Further, three specific objectives were set: 1)-to assess the soil factors that could be potentially influenced the soil organic carbon content, 2)-to determine the LULC changes during the past two decades (1996-2020) and study the possible impacts that occurred from LULC changes on soil carbon stocks of the  selected study sites (Kalametiya and Hambantota) 3)-to assess the level of anthropogenic influence on carbon stocks in the selected sites. The total SOC content was measured by the Loss On Ignition (LOI) method, and standard allometric equations. The effects of soil properties (pH, conductivity, and dry-bulk density) on soil organicm carbon were assessed.  Questionnaire surveys were also carried out to collect data. On-screen digitization method was performed to create LULC maps using ArcGIS-10.3 software. Statistical analysis was  performed using parametric (one-way ANOVA, two sample proportion test) and non-parametric (Kruskal Wali's test, Chi-Squared test), Generalized Linear Models (GLM), and  Principal Component Analysis (PCA). According to the results, the average SOC contents in Hambantota, Bundala, Galle, and Kalametiya were 105.17 ± 21.57 Mg C ha^-1, 106.36 ± 24.81 Mg C ha^-1, 258.28 ± 93.58 Mg C ha-¹, and 259.85 ± 140.77 Mg C ha^-1 (p