Scientists discover that groundwater brings nutrients--and possibly contaminants--to coral reef ecosystems

By John B. Stafford

Coffee drinkers may unknowingly be sharing their double lattes with coral reefs, according to Stanford University researchers who have studied the effect of groundwater discharge on coastal oceans.

Their study, published in the January 2006 issue of Limnology and Oceanography, establishes groundwater as an important source of nutrients to coral reefs around the world. Groundwater, the scientists caution, also may increasingly contribute to reef pollution as growing coastal populations introduce foreign chemicals into the marine environment.

"We've seen estrogen, caffeine and fertilizer—all sorts of things you don't naturally find in the ocean," said Adina Paytan, an assistant professor in Stanford's Department of Geological and Environmental Sciences and lead author of the study. "The same is true of ibuprofen, pharmaceuticals and bacteria that has to do with human, bird or dog feces."

Paytan's team, which included five Stanford students, made the discovery by collecting numerous large-volume water samples from reefs in Hawaii, Mexico, the Red Sea, Mauritius and Florida. The researchers looked at radium concentration, which is much greater in coastal groundwater than it is in seawater, to determine how much groundwater was mixing with the seawater near the reefs. More radium in the seawater at the reef means more groundwater.

"We used radium because there's very little radium in the ocean, and the concentration is constant and well known, while in submarine groundwater there's lots of radium," Paytan said. "If we measure in both coastal groundwater and open seawater offshore, we can use the measurement to see how much groundwater is mixing with the ocean water at the coast. In all coastal areas we were looking at, there is much higher radium than in the open ocean, which indicates that it comes from groundwater."

While water temperature, disease and exploding algae growth have contributed to the global decline of coral reefs, Paytan said that more research is needed to determine the impact of contaminated groundwater on reef systems.

"I can't say the reefs are deteriorating because of nutrient loading and pollution from groundwater, and I wouldn't say that because you have to do a much more extensive study to determine this direct link," she explained. "The next step is to look at how land use, land cover and hydrogeology impact the quality of the water discharging at the coast. And then we will look at the receiving end: Do the corals need this nutrient source? Is it good for them or is it something bad?"

According to Paytan, maintaining healthy coral reefs is essential, particularly for coastal communities that rely on them for fishery production and tourism. "We depend on these coastal ecosystems," she said. "They provide multiple services. If our coastal systems are destroyed, it's going to have a huge impact on the population that depends on them."

The Stanford paper demonstrates that groundwater discharge is a global phenomenon, she added. "It shows we can quantify [groundwater discharge] and start thinking about it," she said. "This has not been widely done before, because submarine groundwater is not easy to observe—and if you don't see it, you ignore it. However, it is widespread, and we have to start taking it into account when we're talking about coastal restoration, when we're talking about sustainability and restoration, and when we're talking about the impact of land development on the coast."

The study was co-authored by Stanford students Gregory Shellenbarger and Kristen Davis in the Department of Civil and Environmental Engineering; Joseph Street, Meagan Gonneea and Megan Young in the Department of Geological and Environmental Sciences; and geochemistry Professor Willard Moore of the University of South Carolina. Research was supported by grants from the National Oceanic and Atmospheric Administration, the Bio-X Initiative at Stanford and the Stanford UPS Urbanization Research Fund.

John B. Stafford is a science-writing intern at the Stanford News Service.

Editor Note:

The study, "Submarine Groundwater Discharge: An Important Source of New Inorganic Nitrogen to Coral Reef Ecosystems," appears in the January online edition of Limnology and Oceanography at http://aslo.org/lo/toc/vol_51/issue_1/index.html. Photos can be downloaded at http://newsphotos.stanford.edu (slug: "coral").

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