Impact of Community-Based Mangrove Cultivation on Carbon Sequestration Function of Mangrove Ecosystems in Negombo Estuary, Sri Lanka: A Paradigm for Sustainable Livelihood - Ecosystem Interaction

Abstract

Mangrove ecosystems perform a range of ecological functions and provide numerous services to humanity, both locally and regionally. However, the contribution of afforested mangrove areas to ecological services remains understudied. Therefore, the present study focuses on traditional mangrove cultivation and management practices, with a special emphasis on quantifying the carbon sequestration capacity of a community-based managed mangrove area at the Negombo estuary.Kadolkele was selected to represent natural and relatively undisturbed mangrove stands, while Wedikanda represented man-made/cultivated mangrove stands within the Negombo estuary, Sri Lanka. Above- and below-ground biomass of mangrove trees were determined using allometric methods. Average annual biomass increment was calculated using five years of data from the same study plots at the two locations.Mean annual biomass increments and their percentages were recorded as 13.54 ± 0.47 Mg ha⁻¹ yr⁻¹ (9.24%) for Kadolkele and 12.02 ± 0.14 Mg ha⁻¹ yr⁻¹ (8.98%) for Wedikanda. Average annual total organic carbon (TOC) accumulation rates were 7.19 ± 0.25 Mg ha⁻¹ yr⁻¹ for Kadolkele and 6.56 ± 0.07 Mg ha⁻¹ yr⁻¹ for Wedikanda.Generally, the highest biomass and TOC increments were observed near the estuarine shoreline, with a declining trend towards the landward areas. Based on the five-year total woody growth, the annual carbon sequestration capacities were calculated as 7.71 ± 1.29 Mg C ha⁻¹ yr⁻¹ for Kadolkele and 6.90 ± 1.18 Mg C ha⁻¹ yr⁻¹ for Wedikanda. No statistically significant difference was observed (p > 0.05) between the biomass and TOC increments of the two study areas.The results reveal that the carbon sequestration capacity of mangrove areas managed using traditional ecological knowledge is comparable to that of natural mangroves. Cultivated mangrove stands, therefore, demonstrate primary production levels similar to natural stands, highlighting the positive contribution of mangrove cultivation to the overall productivity and carbon assimilation function of the estuary. This also affirms the effectiveness of indigenous methods used for mangrove cultivation and management.