Abstract:
High primary productivity of mangroves facilitates carbon sequestration function of
mangrove ecosystems. Present study is the first one in Sri Lanka that aims at determining the
amount of carbon sequestered by mangrove plants. Allometric relationships and harvest
method were used to determine mangrove plant biomass. Carbon content was determined by
K2Cr2O7 oxidation. Except for the leaves, approximately 50% of biomass is composed of
organic carbon. Lumnitzera racemosa was found to occur in five mangrove areas that
represented three climatic zones. Avicennia marina (36.62 t/ha), Rhizophora mucronata
(27.09 t/ha) and L. racemosa (9.43 t/ha) are the species that contribute most to retain carbon
in Negombo estuary. L. racemosa (30.1 t/ha at Rekawa and 42.24 t/ha at Pambala/Chilaw
lagoon), Ceriops tagal (16.91 t/ha at Rekawa) and Avicennia officinalis were found to be the
most significant species in terms of carbon retention. The greatest carbon retaining species at
Kala Oya mangrove ecosystems were L. racemosa (59.55 t/ha), Excoecaria agallocha (42.73
t/ha) and R. mucronata (45.75 t/ha). Malwathu Oya estuarine mangroves were dominated by
Sonneratia alba (92.81 t/ha) and A. marina (41.53 t/ha) while R. apiculata (79.66 t/ha) and E.
agallocha (25.98 t/ha) at Batticaloa lagoon retained the most carbon. Among the eleven
species considered in the present study, L. racemosa and R. mucronata were proven to be
superior in their capacity of carbon retention in all three climatic zones while Bruguiera
cylindrica and B. gymnorrhiza contributed the least. In terms of carbon sequestration by the
ecosystems, Kala Oya mangroves with 204 t/ha of carbon, ranks the highest, followed by
Malwathu Oya (165 t/ha) and Batticaloa lagoon (150 t/ha) mangroves. Remote location in
sparsely populated areas with poor accessibility, partly due to war situation prevailed in these
three areas for the past three decades would have saved these mangroves from human
interference unlike mangrove areas in Negombo estuary, situated in a very populous area on
the western coast and mangrove wood is predominantly used for “Brush Park” construction, a
traditional fishing device used in this estuary, records the least amount (80 t/ha) of retained
carbon in mangrove plant biomass.
