Biology professor Dan Cristol and seven of his students recently published a paper entitled “The Movement of Aquatic Mercury Through Terrestrial Food Webs” in the journal Science.
“For many years, people have studied birds that eat fish, such as eagles, herons, cormorants and kingfishers for contaminants like mercury.” Said Cristol. “We set out to study the fish-eating birds and other birds and we expected the fish-eating birds to have mercury and the other birds not to. The surprise was that they all had mercury in their blood."
The research team was composed of Cristol; four Master's degree students, Ariel E. White ('07), Rebecka L. Brasso ('07), Scott L. Friedman ('07) and Anne M. Condon ('08); and three undergraduate students, Rachel E. Fovargue (’09), Kelly K. Hallinger (’09) and Adrian P. Monroe (’08).
The collection process took place on the Shenandoah River, where the team spent a summer living, collecting, researching and analyzing together.
“It was truly the most genuine field effort I’ve ever been involved in,” Cristol said.
Since the project’s beginning in 2005, many of the students involved have been undergraduates. In its first year, two of the students who accompanied Cristol to the Shenandoah River had just finished their freshman year.
The paper describes the effects of mercury biomagnification, which is the movement of mercury up the food web, such as from a fish or water bug to a hawk or other predator in the surrounding area. It looks specifically at the South River, a tributary of the Shenandoah River, which was contaminated with mercury from 1930 to 1950.
The group studied 18 bird species, 13 bird species that fed exclusively on terrestrial sources and five that consumed aquatic sources of mercury. Sixteen species were found to have significantly elevated mercury concentrations relative to birds from other, uncontaminated sites.
The researchers collected prey delivered to nestlings of songbirds at the study sites. The most prevalent food item was spiders, which comprised 20 to 30 percent of the biomass of each bird’s diet.
The average total mercury concentration in these spiders was extremely high. Spiders observed in non-contaminated sites had negligible levels.
“Spiders are like little, tiny wolves, basically, and they’ll bio-accumulate lots of contaminants in the environment,” said Cristol in a press release. “The spiders have a lot of mercury in them and are delivering the mercury to these songbirds.”
The question that remains, Cristol explained, is “how are the spiders getting their mercury?”
To find the answer, this upcoming summer the research team will study the spiders and try to determine what they eat. They already know the spiders have a diverse diet, but the big question is whether they’re eating aquatic or terrestrial food.
“The simplest explanation would be that there are bugs that grow in the river, like dragonflies, and you know how they got their mercury because they grew up in the river," Cristol said. “If the spiders are eating those, the whole story is complete - the cycle from river to spider to songbird.”
However, Cristol does not expect this to be the case.
“The other scenario,” he continued, “is that years ago in a flood mercury was deposited in the flood plane, far from the river, and that mercury is now circulating wholly in the terrestrial food web.”
Cristol highlights the role of students in his research. Although he is the primary author of the paper, he said that he considers himself “just one person on a team.”
For Cristol, this experience - the research, paper and publication in the journal - highlight the real-world applications undergraduate research can have.
“There are many people that I meet at scientific conferences, who, when they hear I teach at William and Mary, in other words a student-oriented university, conclude that the kind of research we do here with students would never land in an important international scientific journal,” Cristol said.
“I’m as surprised as anyone," he said, "but this demonstrates that nothing about undergraduate research has to be second-rate. "