Abstract:
Unique location in the land-sea interface makes mangrove ecosystems most vulnerable to the impacts of predicted
sea level rise due to increasing anthropogenic CO2 emissions. Among others, carbon sink function of these
tropical ecosystems that contribute to reduce rising atmospheric CO2 and temperature, could potentially be
affected most. Present study was undertaken to explore the extent of impact of the predicted sea level rise for the
region on total organic carbon (TOC) pools of the mangrove ecosystems in Negombo estuary located on the west
coast of Sri Lanka. Extents of the coastal inundations under minimum (0.09 m) and maximum (0.88 m) sea level
rise scenarios of IPCC for 2100 and an intermediate level of 0.48 m were determined with GIS tools. Estimated
total capacity of organic carbon retention by these mangrove areas was 499.45 Mg C ha−1 of which 84%
(418.98 Mg C ha−1) sequestered in the mangrove soil and 16% (80.56 Mg C ha−1) in the vegetation. Total
extent of land area potentially affected by inundation under lowest sea level rise scenario was 218.9 ha, while it
was 476.2 ha under intermediate rise and 696.0 ha with the predicted maximum sea level rise. Estimated rate of
loss of carbon sink function due to inundation by the sea level rise of 0.09 m is 6.30 Mg C ha−1 y−1 while the
intermediate sea level rise indicated a loss of 9.92 Mg C ha−1 y−1 and under maximum sea level rise scenario,
this loss further increases up to 11.32 Mg C ha−1 y−1. Adaptation of mangrove plants to withstand inundation
and landward migration along with escalated photosynthetic rates, augmented by changing rainfall patterns and
availability of nutrients may contribute to reduce the rate of loss of carbon sink function of these mangrove
ecosystems. Predictions over change in carbon sequestration function of mangroves in Negombo estuary reveals
that it is not only affected by oceanographic and hydrological alterations associated with sea level rise but also
by anthropogenic processes, therefore the impacts are site specific in terms of distribution and magnitude.
