New Waves September 2010

Breaking news about water resources research and education in Texas

A river flipped: TWRI grant recipient studies Brazos's carbon cycle

A River flipped - TWRI Grant Recipient Fan-Wei Zeng A new study by geochemists at Rice University has found that damming and other human activities have 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 in the Department 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, 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, according to the authors.

Fanwei Zeng, first author of the study and a doctoral student in biogeochemistry at Rice, was a recipient of a 2007-08 Texas Water Resources Institute (TWRI) research grant. With the $5,000 research grant, Zeng began her study of the Brazos and found that carbonate input to rivers can be detected using carbon isotopes.

"We wanted to know if Texas is more like New York or more like Brazil," Zeng said. "Because it is hot and humid in Texas, we expected the geochemistry of Texas' rivers to more closely resemble the geochemistry of tropical rivers."

To test the idea, Zeng began collecting and analyzing water samples at seven sites along the Brazos in 2007. Zeng, Masiello and co-author Bill Hockaday, now an assistant professor of geology at Baylor University, used radiocarbon dating to determine the age of the carbon dioxide in the samples.

In a 2009 study, Zeng and Masiello found that human activity—namely the use of seashells as road base material in the late 19th and early 20th centuries—skewed the radiocarbon results in Buffalo Bayou, a heavily urbanized watershed that runs through downtown Houston. The team believes the "old" carbon from the southern Brazos is also from dissolved seashells in old roads.

"The Brazos may be a special case," Zeng said. "The upstream damming is not usual in the developed world, but the dissolved carbonate from seashells may be somewhat unusual."

The research was funded by the Texas Water Resources Institute, the U.S. Geological Survey, the National Institutes for Water Research, and Hans O. and Suse Jahns.

Read the full Rice News release here.

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