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Greenhouse Gas Exchange in Wetland Ecosystems in the Southeast Asia Region

Lai Yuk Fo, Derrick

Wetlands are generally net sinks of atmospheric carbon dioxide (CO2) owing to a combination of high primary productivity and low decomposition rate. At the same time, they potentially emit a large amount of greenhouse gases, including methane (CH4) and nitrous oxide (N2O), into the atmosphere because of the predominance of an anaerobic environment. Both CH4 and N2O are very potent greenhouse gases, being 25 and 298 times more effective than CO2 in trapping heat on a per unit mass basis over a 100-year time scale. As such, it is essential to quantify the relative magnitudes of the net uptake of CO2 and emissions of CH4 and N2O from wetland ecosystems for assessing their net radiative forcing impacts and overall greenhouse effects.

Recent attention has been given to the dynamics of "blue carbon", a term used for carbon sequestered in the vegetated coastal wetland systems, including mangroves, salt marshes, and seagrass meadows. Although the tropical and subtropical mangrove ecosystems only cover 0.1% of the world's land surface, they are important long-term global C sinks owing to their high rate of C burial per unit area. However, little is known about the dynamics of greenhouse gas fluxes from mangroves. Given that mangroves in Southeast Asia comprise 35% of the global mangrove area and contain 75% of the world's mangrove species, further work should be done in this region to better understand the carbon exchange processes in mangrove ecosystems.

Wetlands in the tropical and subtropical regions are under immense development pressure. Human activities like shrimp culture and harvesting of forest products have resulted in the disappearance of more than 35% of mangrove forests globally over the last few decades. In recognition of the ecological and biogeochemical functions of wetlands, increasing emphasis has been placed on restoring the degraded wetland ecosystems. It has been suggested that wetland restoration can potentially offset 2.4% of the annual CO2 emissions arising from fossil fuels in North America. Nevertheless, there is still a lack of a thorough understanding of the impacts of different restoration practices on carbon sequestration and greenhouse gas emissions in different wetland types.

The objectives of this research are: (a) to quantify the magnitude of the exchange of greenhouse gases from wetland ecosystems in the Southeast Asian region; (b) to examine the influence of environmental and biotic parameters on the spatial and temporal variability of greenhouse gas exchange from wetlands; and (c) to investigate the effects of wetland restoration and creation on greenhouse gas exchange and climate change mitigation. Results obtained from this research will improve the currently limited understanding of greenhouse gas dynamics in mangrove ecosystems in the underrepresented Southeast Asian region. Moreover, findings of the impacts of wetland restoration and creation on greenhouse gas emissions will provide a scientifically sound basis to manage the wetlands in a way that minimizes any possible adverse greenhouse effects.

Fig. 1 Mangrove ecosystem in the Mai Po Marshes Nature Reserve in Hong Kong

Fig. 2 The Hong Kong Wetland Park - a wetland constructed to mitigate the loss of wetland habitats owing to new town development