HOUSTON -- (Aug. 16, 2010) -- A new study by geochemists at Rice University finds that damming and other human activity has completely obscured the natural carbon dioxide cycle in Texas' longest river, the Brazos.
"The natural factors that influence carbon dioxide cycling in the Brazos are fairly obvious, and we expected the radiocarbon signature of the river to reflect those influences," said study co-author Caroline Masiello, assistant professor of Earth science at Rice. "But it looks like whatever the natural process was in the Brazos, in terms of sources and sinks of carbon dioxide, it has been completely overprinted by human activities."
The study, which is available online in the journal Biogeochemistry, is the first to document such an overwhelming influence of human activity on carbon dioxide in a major river.
With humans adding some 8.5 gigatons of carbon dixoide to the atmosphere each year through the burning of fossil fuels, scientists are increasingly interested in studying how the atmosphere and biosphere exchange carbon dioxide. Plants take up carbon dioxide from the air via photosynthesis and store it in their leaves and stems. Some of that stored carbon gets buried in the soil and locked away for hundreds or thousands of years. But much is also washed into rivers, where rapid decomposition can quickly return it to the atmosphere. Understanding when and where that plant carbon dioxide is returned to the atmosphere is essential if policymakers are to plan effective carbon-sequestration strategies.
One method scientists use to gauge how effectively ecosystems store carbon is radiocarbon dating. The technique involves precisely measuring the amount of radioactive carbon-14 in samples from an ecosystem. Because about half of the carbon-14 atoms in a material will decay and become nitrogen-14 every 5,730 years, scientists can determine the age of a material based on how much carbon-14 it still contains.
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