A biologist at Acadia University has discovered sea birds are depositing contaminants on land that they've picked from food sources in the ocean.
"I think we need to be concerned about [the process] because continuing emissions, continuing depositions of these unwanted chemicals, may rise in these food chains," says Mark Mallory, Canada Research Chair in coastal wetland ecosystems and associate professor at Acadia.
"Even at sub-lethal levels we know it's putting stress on various organisms."
Mallory says through birds' faeces and corpses, as well as pieces of food dropped on land, seabirds naturally transfer nutrients, such as potassium and calcium, to areas where they nest. He says research has long shown this bio-transfer allows for enriched soil that helps plants grow.
But through work in the Arctic and more recently along the Nova Scotia coast, he's also discovered they're depositing contaminants — heavy metals — that have made their way into the ocean ecosystem and into the birds.
'High level' of contamination
"All of those dead organisms or dead bits of biological material are going to obviously contain nutrients, but depending on what organism you're talking about, they may have a relatively high level of contamination. And that's certainly true for sea birds because they feed at the top of marine food webs, which can be quite contaminated. "
During the summer of 2013, Mallory and his team tested the soil on the Eastern Shore Islands and looked at the impact of the eider, Leach's storm petrel, black guillemot, double-crested cormorant, great black-backed gull and herring gull. The eiders feed on sea urchins and mussels; other birds eat squid or follow ships and eat waste from the vessels.
The research found traces of elements that are not essential parts of the food chain, such as copper, mercury, zinc, lead and selenium.
The study didn't analyze whether the level of heavy metals are a concern, but Mallory says the process of transferring pollutants should be alarming.
"Altering the soil chemistry with some of these trace elements or heavy metals, at some point you'd probably influence the chemistry that's suitable to grow," Mallory said, adding the contaminants could affect vegetation and wildlife.
"Based on examples we've seen in the Arctic with polar bears and with different types of gulls, where we know there are multiple stressors, we know no single stressor is a smoking gun, but multiple stressors we can link those to physiological effects. "
Mallory says the same process of biotransport would likely occur whenever a group of organisms share a small space, for example herons gathering in wetlands or bat caves. He hopes to extend his research to look at how seagulls might bring in contaminants to their habitats across Nova Scotia.
"They can be quite contaminated. They defecate all over the place which concentrates all those contaminants in an area. What does that mean then for the other organisms in an area?"