Covering only 6% of our land surface, wetlands store 10-20% of Earth’s terrestrial carbon; they include marshes, peat bogs, swamps, river deltas, mangroves, tundra, lagoons and river floodplains. Wetlands slow the decay of organic material by trapping and locking it away under low oxygen conditions over long periods of time. These waterlogged areas have sequestered about 771 gigatonnes (771 billion tonnes) of greenhouse gases—CO2 and methane—an amount equivalent to the carbon content of today’s atmosphere.
If the decline of wetlands continues through human and climate change-related causes, the release of greenhouse gases from these sinks will significantly compound the global warming problem. For instance, drained tropical swamp forests release about 40 tonnes of carbon per hectare per year. Drained peat bogs release 2.5 to 10 tonnes of carbon per hectare per year.
Warming world temperatures are already speeding both rates of decomposition of trapped organic material and evaporation. Sea level rises will further impact functional coastal wetlands.
Sixty percent of wetlands worldwide (up to 90% in Europe) have already been destroyed in the past 100 years; mostly through drainage for agriculture but also through pollution, dams, canals, groundwater pumping, urban development and peat extraction.
“Wetlands act as sponges and their role as sources, reservoirs and regulators of water is largely underappreciated by many farmers and others who rely on steady water supplies. [Wetlands] also cleanse water of organic pollutants, prevent downstream flood inundations, protect riverbanks and seashores from erosion, recycle nutrients and capture sediment.”–Prof. Wolfgang Junk of the Max-Planck Institute for Evolutionary Biology
Wetlands provide rich habitats for small organisms which feed fish and other water life; they in turn nourish mammals and birds. The biodiversity of some wetlands is comparable to that of rainforests or coral reefs.
“Lessening the stress on wetlands caused by pollution and other human assaults will improve their resiliency and represents an important climate change adaptation strategy,” says Junk. “Wetland rehabilitation represents a viable alternative to artificial flood control and dredging efforts that may be needed to cope with the larger, more frequent floods predicted in a hotter world.”
Prof. Junk, of the Max-Planck-Institute for Evolutionary Biology, notes that maintenance of wetlands is much cheaper than rehabilitation and that poorer countries will have fewer means to rehabilitate their wetlands to cope with climate change.
Wetland-friendly development alternatives must be actively sought and promoted.
Things to Consider:
- The peat bogs of Siberia, North America and Scandinavia contain a third of all carbon in the world’s soils. Those in Scotland contain more than 90 percent of the carbon in British soils and forests.
- The world’s most threatened wetlands include those around the Mediterranean, where for two millennia the population has been draining wetlands and floodplains for agriculture — and more recently for urban areas, tourist developments, and to eradicate malarial mosquitoes.
- Wetlands along the flood-prone Mississippi once stored 60 days of the river’s floodwater; today they can store only 12 days’ worth.
- Around Africa’s Lake Victoria, wetlands are so degraded they can no longer filter nitrate and phosphate runoff from surrounding land. The result: eutrophication and an explosive growth of lake-clogging water hyacinth.
- In Malaysia, 90 percent of freshwater swamps have been drained for rice cultivation.
- Both Spain and Greece drained 60 percent of their wetlands in the last century. Pumping of groundwater for agricultural irrigation is drying Spanish wetlands such as the Doñana reserve, one of Europe’s top sanctuaries for wintering birds, where the water table is falling one meter every two years.
- Wetlands constitute an estimated 20% of South America but they are poorly mapped or classified by characteristics.
- The vast, remote and relatively pristine Pantanal, spanning 160,000 square km, is confronted by increasing development pressure. Its catchment area straddles Brazil, Bolivia and Paraguay, while Uruguay and Argentina are downstream.
Nina Munteanu is an ecologist, limnologist and internationally published author of award-nominated speculative novels, short stories and non-fiction. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. Visit www.ninamunteanu.ca for the latest on her books.