Every year, millions of tons of human-made garbage ends up in the world’s oceans and major lakes.
Some of it sinks to the bottom, while other trash floats out to open waters. Yet more pollution, called “marine debris” once it’s in the water, lingers near shorelines.
Nimish Pujara, an assistant professor of civil and environmental engineering at the University of Wisconsin-Madison, is studying how waves and wave-driven currents transport marine debris along the coasts, from out at sea to shore, or from the shore out to sea. In tackling this less-understood aspect of marine pollution, he also hopes to gain insight into how to protect our shores from debris accumulation and how trash gets out into the ocean.
The National Science Foundation is supporting Pujara’s research with a five-year, $563,000 CAREER award that’s co-funded by its fluid dynamics and environmental engineering programs.
Marine pollution is a staggering global problem. In recent years, the “Great Pacific Garbage Patch” is often used as an example of the scale of the pollution in the world’s oceans. While it paints a vivid picture, the trash that accumulates on or near the shore is just as important for researchers and communities around the world to understand.
“There’s a lot of attention on the plastic pollution in the ocean,” Pujara says. “A lot of that work, and it is important, is done out in the middle of oceans or lakes. But typically, we have been finding that marine debris is more concentrated near coastlines. Coastal areas can also be more sensitive to pollution for a variety of factors, whether that’s ecological, with the habitats found there, or whether that’s related to tourism and recreation, or an economic activity like shipping.”
All of the human-made pollution in the ocean started on land and wound up in the ocean whether by wind or rainwater runoff or accidental/intentional dumping. Before marine debris can coalesce into an oceanic garbage patch or overrun a shore like Hawaii’s Kamilo Beach, it often has to interact with the complex waves and currents that affect water flow around coastal regions.
“Our goal here is to improve how we understand the mechanisms that move debris to the shore, and where it might accumulate,” Pujara says. “But the other side of that is that the shore is often a source of debris. So another question is: How does it wash out to sea?”
Pujara’s research focuses on wave and fluid mechanics. He’s working on other projects that look at nearshore waves and currents, including one in which he is studying how longshore drift pushes sand along shorelines. That gives his team a firm foundation on which to tackle part of a question that’s puzzled researchers studying oceanic pollution for some time now: Where does plastic pollution go once it enters the oceans?
Running models that simulate an entire ocean basin might give some clues to how pollution proliferates. But if, for example, an entire coast is represented by one unit of that model, it’s going to lose the fine detail necessary to understand how things like breaking waves and nearshore currents interact with marine debris as it moves from land to sea. That, in turn, may blunt our understanding of how—and how much—pollution stays near the shore or winds back up on land, compared to drifting further into the ocean.
“All of those complex processes might be totally absent because the model just doesn’t have a fine enough scale to account for them,” Pujara says. “So, from my perspective, looking at this as a physics and engineering problem, our lab has the tools and the knowledge to investigate exactly how that motion works.”
CAREER awards include requirements for education and public outreach. Pujara works with students at Madison East High School and will expand that partnership through his CAREER award. Every year during the project, he plans to do activities with the school’s engineering and math modeling club to demonstrate how marine debris washes ashore.
Pujara also hopes to establish a network of experts, across the United States and internationally, who can lend their experience to help train future generations of researchers in the environmental fluid mechanics field and enhance collaborative research efforts. “Some of that may be techniques, and some of it may be related to specific knowledge that a certain researcher may have,” he says. “There’s a lot of knowledge spread throughout the field that may not exist at every university. But if we can get this going and tap into that, we can enable work that might not otherwise be possible.”