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Marine Ecologists Pinpoint Pollutants in Caribbean Coral

Kirby Webster, CAS/MS '08, collects samples. (Photo courtesy of Kiho Kim)

In order to understand where we are, we have to know where we’ve been.

“How do you fix a problem if you don’t know where the problem is coming from?” said marine ecologist Kiho Kim, chair of the environmental science program in the College of Arts and Sciences.

That thinking underpins Kim’s latest research study, published in the October issue of Global Change Biology. To trace the impact of nitrogen pollution on the ecosystem, we must learn what the environment was like before people — whose activities created the problem — intervened.

Nitrogen pollution, the result of widespread use of synthetic agricultural fertilizers and of human sewage, is particularly pronounced along the coast—in the Gulf of Mexico and the Caribbean. Its pernicious consequences include decreased water transparency, the loss of desirable fish species, and the emergence of toxic phytoplankton species.

“We can’t simply say our coastal ecosystem is being polluted by nitrogen,” said Kim. The consequences may be the same, but differentiating the source of the pollutants is critical to crafting sustainable solutions.

Kim and his team of graduate students, David Baker, CAS/MS ’04, and Kirby Webster, CAS/MS ’08, began their search for answers at the Smithsonian Institution’s National Museum of Natural History.

Through a chemical analysis of 300 coral samples from the museum’s Invertebrate Zoology Collection, the researchers reconstructed a record of nitrogen in the Caribbean over the last 150 years. Agricultural and sewage pollution create different signatures in organisms like coral. By deciphering these signatures, the team concluded that fertilizer, used on farms, front yards, and golf courses, has been the dominant source of nitrogen pollution for the last 50 years.

However, with the introduction of more advanced, environmentally responsible agricultural practices over the last decade, fertilizer nitrogen pollution is declining. Sewage-derived nitrogen however, is on the rise.

“We determined that poor storm water treatment and sewage were really to blame over the last decade,” said Kim. “Our next step is to document this process in action.”

His research area is Guam, a small island facing big changes in the next few years, which presents a perfect laboratory for study.

Over the next four years, the United States military plans to relocate Marines from Okinawa, Japan, to Guam, swelling the Pacific island’s population by 20 percent. Guam already has poor waste water infrastructure, and the influx of military personnel will further strain the island’s resources. For Kim, the transition presents a unique opportunity to observe and document, in real time, the impact of increased sewage-derived nitrogen on the health of the coral reefs.

“This is a much tighter story; it’s an opportunity to focus in on the impact of sewage pollution as it’s occurring,” he said.

“The goal is always to develop a research question that’s both interesting and impactful. When you have both things going for you, it’s a lot of fun.”

Kim has already begun collecting baseline data in Guam, thanks to a small grant from the National Science Foundation. As with his previous work, he’s brought AU students on board to assist with the research.

“Students keep me energized,” he said. “When you work by yourself, you’re not challenged to think in new ways. Having three heads working in different ways on the same problem leads to elegant solutions.”