Continued research and syntheses by UGA Odum School of Ecology faculty and alumni To better understand how global changes are altering the loss of carbon from tropical landscapes through rivers, University of Georgia Odum School of Ecology Ph.D. alumnus Chip Small ’10 and professor Catherine Pringle are coordinating an effort to synthesize our understanding of these processes.

Their efforts build on Pringle’s long-term National Science Foundation-funded research program in lowland Costa Rica that has resulted in a more than twenty-year record of stream chemistry that is the only one of its kind for all of lowland Central America. Distinctive patterns in stream solute chemistry have emerged in this dataset that are related to carbon cycling and seasonal and episodic climatic phenomena. This has led Pringle and her students to become involved in synthesis efforts with other tropical ecologists, working in rivers in other tropical regions of the world, to better understand their research findings in Costa Rica in a more a global context.

In February 2011, Small and Pringle organized a special session at the American Society of Limnology and Oceanography meeting in San Juan, Puerto Rico, where they presented results of synthesis work that began in a workshop they hosted in April 2010 at La Selva Biological Station, Costa Rica. The workshop, “Carbon Cycling in Tropical Streams,” was funded by the NSF and brought together twenty-two researchers who study carbon in tropical aquatic ecosystems around the world. The ASLO session featured invited talks on carbon dynamics in the Amazon River by Jeff Richey (University of Washington) and on the Amazon floodplain by John Melack (University of California Santa Barbara). Other speakers in the session presented new findings on carbon dynamics from the Congo, Mekong, and Ganges Rivers. An invited overview of the synthesis project will be submitted to the journal Nature Geoscience in the coming months.

Small and Pringle were motivated to organize the workshop because the role of rivers and streams in carbon cycling has been little studied. “Increased levels of carbon dioxide in Earth’s atmosphere from burning fossil fuels is a major driver of global warming and has led scientists to intensively study the natural carbon cycle to understand how the biosphere will respond,” said Small. “Much of this focus has been on measuring gas exchange in forests and other terrestrial ecosystems, but rivers and streams transport large amounts of carbon away from local watersheds and have been largely overlooked in many regional and global carbon budgets.”

Pringle said that tropical streams and rivers in particular appear to be especially important, due to warmer temperatures which result in higher rates of carbon processing by microbes, but relatively few studies have focused on carbon in tropical streams. “It’s significant that many nations in the tropics have rapidly developing economies,” she said, “and carbon dynamics in tropical streams and rivers are expected to be disproportionately affected by pressure from urbanization and land-use change, compounded by the effects of climate change.”

Pringle’s long-term research project in lowland Costa Rica has been funded continuously by the NSF for twenty years and is currently funded through NSF’s Long-term Research in Environmental Biology (LTREB) Program. Over fifty peer-reviewed journal articles and nine book chapters resulting directly from this project are in print or in press. Through the Odum School of Ecology, the project has provided tropical research experience for more than seventeen UGA undergraduate students, many through NSF’s Research Experiences for Undergraduates Program. It has resulted in five dissertations and eight masters theses, with two more dissertations in progress. Three Costa Rican nationals have obtained graduate-level degrees—two Ph.D. and one MS—at the University of Georgia and three Odum School of Ecology Ph.D. alumni—Alonso Ramirez, MS CESD ’97/Ph.D. ’01, director of research at El Verde Field Station and associate professor at the University of Puerto Rico; Marcelo Ardon, Ph.D. ’06, assistant professor at Eastern Carolina University; and Chip Small, Ph.D. ’10, postdoctoral associate at the University of Minnesota—continue to be involved in the long-term research program.