January 17, 2011
According to a new paper published in Science, current carbon accounting methods significantly overstate the amount of carbon that can be absorbed by forests, plains, and other terrestrial ecosystems. That is because most current carbon accounting methods do not consider the methane and carbon dioxide released naturally by rivers, streams, and lakes. This new paper suggests that rivers, streams, and lakes emit the equivalent of 2.05 billion metric tons of carbon every year. (By comparison, all the terrestrial ecosystems on the world’s continents are thought to absorb around 2.6 billion metric tons of carbon each year). This is, as the lead author of the paper said, is a “major accounting error”.
This paper makes it clear that freshwater ecosystems play a valuable role in the world’s carbon cycles—especially given how little of the earth’s surface they cover. In addition, this paper also highlights just how little we know about natural carbon cycles. Previous papers have suggested that freshwater ecosystems may also be storing large quantities of carbon dioxide—perhaps as much as 600 million metric tons. There is an urgent need for further study, as precise measurements of natural carbon sources and sinks are vital for shaping policies on conservation, deforestation, and other issues.
Citation: Bastviken D, Tranvik LJ, Downing JA, Crill PM, Enrich-Prast A. Freshwater methane emissions offset the continental carbon sink. Science. 2011 Jan 7;331(6013):50.