Effect of vegetation structure on carbon assimilation capacity of mangrove ecosystems in the east coast of Sri Lanka

Abstract

Mangroves are proven as highly potential of providing an efficient carbon sink, both on short and longer time scales. Capacity of carbon sequestration abilities of mangroves is not only a trait that is governed by their genetic make-up, but also by environmental conditions. Total capacity of carbon retention by mangrove ecosystems therefore is partly determined by their vegetation structure. Vegetation sampling was carried out at six (6) randomly selected locations in mangrove areas of Batticaloa and Uppar lagoons on the east coast of Sri Lanka. Vegetation structure was determined by adopting standard methods and allometric relationships were used to determine mangrove plant biomass. Carbon content was determined by K2Cr2O7 oxidation method. Rhizophora apiculata and Excoecaria agallocha were the predominant species in Batticaloa mangroves, with representing high IVI values, 83.03 and 174.58 respectively, while Rhizophora mucronata and Avicennia marina were dominant Uppar lagoon with IVI values were 87.73 and 63.94 respectively, may reason of dissimilarities of soil salinity and nature of inundations. Chemical analysis revealed that nearly half of the biomass of wood and roots mangrove species (5) encountered in study area contained organic carbon. Accordingly higher TOC stock was retained by Batticaloa mangroves (149.71 t/ha) than Uppar lagoon mangroves (135.20 t/ha). Positive correlations (p<0.05) were revealed between TOC in mangrove trees with vegetation structural complexity (CI) and leaf area index (LAI), which easily quantify in the field.