Millions of seagulls feast at landfills across North America, but the problem isn’t that they are eating trash. It’s what comes out the other end.
That’s according to a recent study by two researchers at Duke University, one of whom was inspired by a birdwatching trip to the South Wake Landfill. Scott Winton, who was a graduate student at Duke’s Nicholas School of the Environment at the time, was hoping to spot a rare bird or two. What he saw instead was a huge flock of ring-billed gulls, which he later realized would fly to nearby Jordan Lake after feasting on trash all day.
“We design landfills to have barriers underneath them so that the ‘trash juice’ doesn’t leach out into groundwater and cause problems,” said Winton, now a postdoctoral scholar at the Swiss Federal Institute of Technology Zurich. “But these gulls are effectively short-circuiting that system by flying back out and landing in the water supply.”
These observations led Winton and a colleague, Mark River, to wonder whether the nitrogen and phosphorus from gull droppings was comparable to other sources, such as stormwater and agricultural runoff. Their study, published in the journal Water Research, is the first to examine the transport of nutrients from landfill to surface waters via seagulls, and it focused on Jordan Lake, a source of both recreation and drinking water for the Triangle.
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After analyzing the gull droppings, they calculated how much nitrogen and phosphorus the flock was moving from the landfill using a “nutrient export model,” which factors in average bird weight, how long food is retained in the gut and their feeding schedule. Winton said based on their estimations, approximately 50,000 ring-billed gulls added nearly 1.2 tons of phosphorus to Jordan Lake last year through their droppings.
“This is kind of a phenomenon that has been ignored, so nobody’s really done the math to figure out how much of an impact the gulls could have,” Winton said. “I think we’ve made a good case that it can be significant.”
High amounts of nitrogen and phosphorus in a lake promote rapid growth of algae and fuel a process known as eutrophication. As the algae dies, it accumulates at the bottom of the lake, where it is broken down by oxygen-consuming microorganisms that deplete oxygen levels in the water. Ultimately, sustained eutrophication can kill fish and other organisms and make the water cloudy and more difficult to treat for drinking.
Jordan Lake has a history of algal growth and has failed to meet federal Clean Water Act standards. Last year, the state Department of Environmental Quality suspended the “SolarBees” project that attempted to break up algal blooms after two years of use showed no improvement in water quality, and earlier this year a new aeration system was approved that will cost $4.1 million.
Eliminating seagull poop would not completely solve Jordan Lake’s eutrophication problem, the Duke study acknowledges. But Winton believes it may be one way to reduce costs of other strategies.
For now, though, seagull poop is not something that state regulators are factoring in to their strategy to protect water quality, said Patrick Beggs, watershed restoration specialist at the state Department of Environmental Quality. Beggs said he and his colleagues were not aware of any previous studies looking at nutrient loading of lakes from seagull droppings.
“I’m not questioning that they add a lot of nutrients,” he said. “If anybody’s pooping in the lake, they’re adding nutrients.”
One possible way to lessen the volume of gull poop would be to prevent them from feeding in great numbers at the nearby landfill. Airports work to keep flocks of birds away with pyrotechnics, noise cannons, traps and even the introduction of other animals, such as a border collie named Sky at Southwest Florida International Airport near Fort Myers. A landfill in New Jersey uses a team of falconers to drive a colony of 5,000 seagulls away each day.
South Wake Landfill manager Casey Fulghum said the county has studied the resident seagulls and found that most are migratory birds present between November and March. The landfill staff has also determined that most of the gulls go to Harris Lake and other smaller surrounding lakes, while a large number of eagles and other predatory birds at the landfill seem to originate from Jordan Lake.
The landfill tries to discourage birds from hanging around, in part by reducing the availability of food.
“We work very hard to keep the open area of our landfill to a minimum, and all waste is covered on a daily basis per state requirements,” Fulghum said. He said the landfill operator has tried to use propane cannons to disperse the birds with limited success. “The noise was generally considered more problematic than the bird population,” he said.
Beggs at DEQ said that even if it were possible to reduce the size of the landfill gull population, he worries the birds would simply find other places to feed.
“In other places they’ve tried to do things, like removing geese from a golf course, but at some point they’re feeding somewhere,” said Beggs. “In the end, we still have to expect that human habits will have to change with pre-existing development and new development in order to start removing nitrogen and phosphorus from the watershed.”
Jeremy Frieling: 919-829-4610