A biological accountant's dream
The Madu Ganga estuary is a 915-hectare complex coastal wetland, recognized as a Ramsar Wetland of International Importance. This ecosystem is a network of the Madu Ganga and the smaller Randombe Lake, connected by channels and dotted with islands. The entire system is fed by 11 freshwater tributaries and connects to the Indian Ocean through a narrow canal, creating a brackish water environment ideal for mangroves. The water body itself covers 770 hectares, with the remaining 145 hectares made up of islands.
This area contains some of Sri Lanka’s last remaining tracts of pristine mangrove forest. Fourteen true mangrove species thrive here, with Rhizophora apiculata being the most common. The dense, interlocking root systems of these trees stabilize the shoreline, filter pollutants, and are a physical barrier against coastal erosion and storm surges. The biodiversity is high, with 303 plant species and 248 vertebrate species recorded. The fauna includes 111 bird species, 70 fish species, and 31 types of reptiles, including estuarine crocodiles.
Valuing the invaluable
The Madu Ganga has become a site for the science of ecosystem service valuation. This discipline attempts to assign monetary values to the benefits nature provides to humans. These benefits are often taken for granted because they do not have a price tag in a traditional market. The services provided by the Madu Ganga mangroves are numerous, including direct uses like providing nursery grounds for commercially important fish and prawns, and resources for the local cinnamon industry.
The indirect services are even more substantial. One 2022 study focused specifically on the climate regulation services of the Madu Ganga mangroves. It calculated the economic value of the carbon stored in the mangrove biomass and soil, as well as the value of ongoing carbon sequestration. Using metrics like the marginal cost of carbon abatement and the social cost of carbon, the study arrived at a total estimated value of $155,494,645 for these climate regulation services alone. An earlier UNEP study calculated the net present value of the 145 hectares of mangrove at US$259,896 per hectare over a 30-year period, purely for its direct and indirect benefits, not including tourism. These studies are powerful economic arguments for the conservation of such ecosystems.