Tuesday February 1, 2011
Lakes and rivers pollute air, too
LAKES and rivers emit far more of a powerful greenhouse gas than previously thought, counteracting the overall role of nature in soaking up climate-warming gases.
A review of 474 freshwater systems indicated they emitted methane equivalent to 25% of all carbon dioxide – the main greenhouse gas blamed for stoking climate change – absorbed by the world’s land areas every year. Trees and other plants absorb carbon dioxide as they grow.
“Methane emissions from freshwater sources were greater than expected,” David Bastviken, lead author of the study at Linkoping University in Sweden, said. “Some of the carbon that is being captured and stored by the Earth will be counteracted by methane from these freshwater sources,” according to the study by experts in Sweden, the United States and Brazil in the journal Science.
Emissions of methane, released by decaying vegetation and other organic matter in rivers, reservoirs, lakes and streams, have not previously been properly built into models used to understand global warming, Bastviken said.
“This means that forests and other local environments, being carbon sinks, are even more important” in helping offset global warming, he said. Land-based stores “may be more rare than expected.”
Bastviken said the freshwater methane emissions were not a new environmental threat since the presence of the gas in the atmosphere was previously known, even if scientists were unsure where it came from.
Methane is about 25 times more powerful than carbon dioxide as a greenhouse gas. Bastviken said the findings were not an argument for draining wetlands or lakes to limit methane emissions – that might well backfire and release carbon stored in sediments. – Reuters