Study estimates total input of plastic debris into lakes

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University researchers in New York State have estimated that nearly 10,000 metric tons of plastic debris enters the Great Lakes each year.

The estimate is part of a new study led by Matthew Hoffman, an assistant professor at the Rochester Institute of Technology’s School of Mathematical Sciences, titled Inventory and Transport of Plastic Debris in the Laurentian Great Lakes.

It’s the first attempt to estimate the total input of plastic trash and debris into the Great Lakes, and model where it goes.

“It is a surprisingly large number when you think about it,” Hoffman said.

“Hopefully, that’s somewhat eye-opening, and helps bring attention to the issue, in terms of people realizing all of what goes into the lakes, and hopefully leads more people to address it, through research and clean up.”

The study’s estimates of plastic debris entering the lakes are considered reasonable when compared to previous estimates of plastic waste entering oceans from the coastal U.S.

The new study used census information for communities within 100 km of the lakes and computer modelling with data from the National Oceanic and Atmospheric Administration Great Lakes Coastal Forecast System.

“We predicted the amount of plastic coming in, and then used a numerical model to then see what happens once that plastic enters the water, where it’s transported to,” Hoffman said.

The researchers compared the study’s predictions of the amount of plastic that would be carried near the shore with observational studies of debris found on beaches, including one Hoffman said found Sarnia’s beaches had the most plastic debris of those sampled on Lake Huron.

“Our model results agreed with that,” he added.

Most of the previous research has been with samples collected on beaches or off boats in the water, he said.

“This is the first time putting together models for all the lakes.”

One finding of the study was that plastic debris travels differently in the lakes than it does in oceans, where floating “garbage patches” have been found.

The simulations showed particles that do accumulate on the lakes are periodically pressed towards the shore by sustained wind events.

“As a result, plastic does not accumulate in the middle of any of the lakes for a long period of time,” the study says.

It found most of the plastic coming from Chicago and Milwaukee ends up accumulating on the eastern shore of Lake Michigan, while plastic from Detroit and Cleveland ends up along the southern coast of Lake Erie’s eastern basin. Toronto’s plastic appears to accumulate on the southern coast of Lake Ontario.

The study found Lake Huron receives the second smallest amount of plastic debris annually at more than 600 metric tons.

“There just isn’t as much population right near the shore,” Hoffman said.

Large population centers are the primary sources of plastic pollution in the lakes, and the cities of Chicago, Detroit, Toronto and Cleveland release more plastic particles than accumulate on their own shores.

Lake Superior has the least plastic debris entering, at 32 metric tons a year, and Lake Michigan the highest at more than 5,000 metric tons annually. Lake Erie is next highest at more than 2,500 metric tons, followed by Lake Ontario with more than 1,400 metric tons.

The study estimates the amount of small plastic particles floating in the lakes, but it is significantly lower than the amount projected to be entering the water.

“This is consistent with what’s been seen in the ocean,” Hoffman said.

“Probably, a lot of it’s sinking, but exactly where and how is still unknown.”

The study notes plastic makes up 80 per cent of debris that ends on shore in the Great Lakes.

Research is being done now to understand the impact of plastic ingested by fish and wildlife, and how that is transferred up the food web “as fish are eaten by other fish, or by people,” Hoffman said.

“We hope our study can give some good information on the types of concentrations that are seen, so we can try to estimate what the likely exposure is to fish and other wildlife, to help inform future studies to try to quantify the effects.”

Hoffman, an applied mathematician with a background in oceanographic forecasting research, previously worked on Chesapeake Bay.

“When I moved to Rochester for the job at RIT I decided I should try to get involved in nearby bodies of water,” he said.

In 2013, a study sampled three of the Great Lakes for the first time to classify the plastics and the amounts found. That study discovered a large number of plastic microbeads in the water.

“Since then, there has been more of a focus on the Great Lakes,” Hoffman said.

He said there are several ways he hopes the new study can be used.

“We can actually look now at what the largest concentrations are, where they’re located, and that could certainly help with clean up efforts.”

It could also help to target new regulations, Hoffman said.

 

pmorden@postmedia.com

 

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