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Making waves: Researcher studies fluid dynamics

WATER WORLD: Physicist Mathew Wells conducts research using a depth probe to measure variations in temperature, salinity and other properties in Lake Ontario. In his lab, he studies different densities of water dyed with food colouring. (Photos by Ken Jones.)

by Dan Falk

Have you ever poured coffee into a mug, added some milk, given it a good stir, and then watched the two liquids merge as one? Now imagine the coffee cup enlarged by a few thousand times, and you’ll get an idea of what Mathew Wells investigates for a living.

Wells teaches in the department of physical and environmental sciences at U of T Scarborough. He calls himself a “physical oceanographer,” although he admits that it “sounds odd to talk about oceanography” when your subject is a lake – even one as large as Lake Ontario.

But Wells’ passion for water – how it flows and how other things move and disperse within it – goes far beyond our local Great Lake. He’s been near water, and inspired by water, virtually all his life. Born in Tasmania, Wells worked and studied in Australia before taking a university position in the Netherlands and then at Yale. The geophysicist moved to Toronto and his current job at U of T Scarborough in 2006.

“I’ve always loved the outdoors, so when I went on to do graduate studies, I was really keen to not be stuck in a lab,” he says. He now specializes in making mathematical models of how the water in lakes and oceans mixes, and how other liquids disperse within it. He conducts blackboard calculations and computer simulations – along with a healthy dose of field work. He was out on Lake Ontario with graduate students this past fall, measuring the water temperature at different depths from their instrument-laden boat. They found, among other things, that the temperature remains at a fairly steady 17 degrees Celsius down to a depth of 30 metres, and then drops off sharply, down to a frigid 4 degrees.

But getting that data wasn’t as easy as it sounds. “It was really quite choppy,” he says. Wells is used to rough water by now – he once sailed from Australia to Antarctica – but his students had to adapt; most of them had never been on the lake before. Just keeping one’s balance is hard enough, let alone doing a scientific experiment amid the waves. “It’s hard to read a laptop when the deck is moving,” he says.

His recent project involved water not far from campus – Frenchman’s Bay, near Pickering. The city has been looking at strategies to improve the bay’s water quality, and Wells became interested in helping to tackle the challenge, choosing to conduct research there because it is a good site to study general processes with potentially relevant applications for the future. “The bay could be a really beautiful asset to the city,” he says, if the water was cleaner. But at the moment, the bay is thick with algae, fertilizer, and natural sediment, and it’s not unusual to see dead fish floating on the surface.

Naturally, city planners there would like to see clean water and live fish, and have considered various ways to improve the harbour – but, as Wells discovered, none of the proposals are as simple as they seem. One possibility is to widen the channel connecting the bay to Lake Ontario. That would increase the rate of mixing between water in the bay and in the lake, but it would also lower the water temperature in the bay.

“The fish won’t go there if it’s too polluted or if there’s too much sediment,” Wells explains. “But they also won’t go there if the temperature fluctuations are too great.” In other words, widening the channel would improve water quality, but wouldn’t make life any easier for fish living in the bay. “So you’d solve one problem but you’d create another problem – they’re all kind of related,” Wells says. “It’s a real-world problem.”

Another option is to construct a “settling pond” somewhere upstream from the bay, allowing sediment and fertilizer to settle further away from the bay itself. (He notes that this idea was proposed by his colleague, Professor Nick Eyles, of U of T Scarborough.) As with widening the channel, such a project would cost millions.

With Wells’ expertise, the town will have an edge in the tough decisions that lie ahead. “Choosing the best plan is a political decision,” Wells says, “but it should be informed by good science as well.”

Another issue that Wells is currently tackling has worldwide implications: the problem of “invasive species.” The problem is of particular concern in the Great Lakes, where tiny zebra mussels may be the most famous invader. These diminutive mollusks are native to rivers of southern Ukraine, but have been turning up in the Great Lakes since the late 1980s. How did they get here? The most likely explanation is that they were accidentally transported to North America in the ballast water that giant freighters use in their hulls for stability. (The water is pumped in when the ship unloads, and then pumped out when the ship takes on cargo.)

Wells wants to know exactly how these invasive species get distributed – a problem that demands both mathematical modeling and hands-on field work. He’s currently collaborating with a biologist from Fisheries and Oceans Canada in attempt to see just what happens to ballast water when it’s released. This past summer they injected a fluorescent red dye into the ballast water of a ship near Goderich on Lake Huron, and carefully tracked its spread as the water was released from the ship. Next summer they’ll do similar research on the St. Clair River near Windsor.

“How far and how fast do invasive species disperse? That’s a practical question,” he says. “But there’s also some neat mathematics and physics in how you model that… It’s very non-linear. So even though people have been studying it for a really long time, it’s still an urgent problem.”

Professor Don Cormack, chair of the department of physical and environmental sciences, praises Wells’ research and his efforts to include students. “Mathew's work is a great example of how good science can shed light on some of the most important environmental problems facing society today,” says Cormack.

Wells’ research is also making waves. It is supported by various grants, including a five-year discovery operating grant from the Natural Sciences and Engineering Council of Canada, along with an NSERC Research Tools and Infrastructure Grant, equipment awards from the Ontario Innovation Trust and the Canadian Foundation for Innovation, funds from the U of T Connaught Committee for research, and an award from the Canadian Aquatic Invasive Species Network.

As important and practical as this line of research is, Wells admits he’s drawn to it for another reason, too – and one can see a hint of it in his eye-catching photos and demonstrations of different coloured liquids mixing in small-scale laboratory experiments. “It’s also very beautiful,” he says.

© University of Toronto Scarborough