Abstract:
Characterization of the micro-tidal mangrove forests in Negombo estuary, located on the west coast of Sri
Lanka, with respect to its capacity to remove atmospheric carbon and sequestration in above and below
ground plant components is the objective of this study. These mangroves constitute both natural stands
(e.g. Kadolkele) and woodlots planted, protected and managed by fishermen (e.g. Wedikanda) to extract
twigs and branches to construct “brush parks”, a traditional method of fishing in this estuary. Both types
of mangrove stands support high species richness and structural diversity, indicating planted mangrove
areas have reached a semi-natural state. Allometric relationships were used to calculate biomass
increment. Differences in litterfall, above and below ground biomass increment and net primary productivity
(NPP) of the two types of mangrove areas were statistically insignificant, thus indicating that
they are structurally and functionally comparable. Average rate of mangrove litterfall in Negombo estuary
was 802 ± 25 g m 2y 1. The average above ground biomass increment was 1213 ± 95 gm 2y 1 and below
ground increment was 267 ± 18 gm 2y 1, thus the average NPP of these mangroves was
2282 ± 125 g m 2y 1. NPP showed a decreasing trend fromwater towards land, in line with plant density
and leaf area index. A statistically significant relationship was found between vegetation structure
(represented by complexity index), NPP and rate of organic carbon accumulation in mangroves. Potential
carbon accumulation capacity of mangroves of Negombo estuary was estimated to be approximately
12 t ha 1y 1, which is equivalent to the amount of carbon emitted as CO2 through combustion of 19,357 L
of diesel or 22,212 L of gasoline in motor vehicles. Potential atmospheric carbon removal capacity of
Negombo estuarine mangroves (350 ha in extent) therefore was estimated to be 4143 t y 1, which is
equivalent to removal of CO2 emitted through combustion of 6,779,000 L of diesel or 7,779,000 L of
gasoline within a year
