Since her arrival at the Wells Reserve at Laudholm in 2008, research scientist Dr. Jennifer Dijkstra has followed two main lines of inquiry. In addition to investigating seaweed, crab, and snail interactions in the salt marsh, she has also looked into how climate change may affect mercury accumulation in coastal food webs.

When Jenn started her post-doctoral fellowship, research director Michele Dionne asked her to work on mercury. "It was a little daunting," Jenn admits. "I had never worked on contaminants, and mercury is not a straightforward contaminant."

Mercury enters an ecosystem both from the atmosphere—coal-fired power plants are a key contributor—and from point sources such as hazardous waste sites and cement factories. Once mercury enters the coastal ecosystem, it is transformed to methylmercury, which is the toxic form that accumulates and dangerously "biomagnifies" up the food chain.

Jenn explains that "the rate of change from mercury to methylmercury depends upon several factors—how much sulfating bacteria there is in the system, the energy in that system, temperature, the length of the growing season.… The whole methylation process is complicated, so we're not trying to explain the nitty gritty. Instead, we are focused on how global warming could affect methylmercury accumulation in coastal food webs. Salt marsh pools are a perfect place to study that, because there is a natural gradient in temperature."

Jenn and Michele worked with colleagues at Dartmouth College and NOAA's National Centers for Coastal Ocean Science to study mercury in killifish (also known as mummichog or salt marsh mud minnow). These common fish are valuable bioindicators because they are low on the food chain; they feed near the level where methylmercury is being formed and are important prey for larger fish and other animals. "If climate warming causes the mercury level to increase in killifish, it will also increase at higher trophic levels," Jenn says. "Eventually that connects to the fish we eat."

The team's experiments, both in the laboratory and in the salt marsh pools of the Little River estuary, showed that as temperature increases, killifish do indeed accumulate more mercury. This suggests that as global temperatures rise, the risk of mercury poisoning will increase for people eating fish.

From Watermark 29(1), Summer 2012