Study uses remote sensing to monitor plastic debris in rivers and lakes

The research, published in Nature, a peer-reviewed scientific journal, helps to increase the understanding of plastic debris behavior in freshwater environments.

Plastic pollution in oceans continues to be a growing environmental issue, with the United Nations Environment Programme naming it one of the leading pollution challenges. But, plastic pollution in lakes and rivers, or freshwater environments, has garnered less attention.

That is something the researchers wanted to change, because much of the plastic debris in oceans makes its way there through rivers. Previous studies in removing plastic waste use labor-intensive sampling, which can be time-consuming and expensive.

To help with those challenges, this study used remote sensing technology that can provide cost-effective solutions and reach a wider area. The technology uses spectral reflectance properties, or wavelengths in the electromagnetic spectrum, to pinpoint specific types of plastic. It's important to find the specific wavelength of the plastic materials, so that the sensing technology can filter out materials found naturally in freshwater environments, such as seaweed, sediments, driftwood, and water foams.

"We could use this technology to identify different types of plastics in the water simultaneously. This is key information that we need when employing other technology, like drones, to capture and remove plastic debris in natural environments," said Mohammadali Olyaei, a Ph.D. student in the Department of Civil, Environmental, and Geo- Engineering and lead author on the paper.

Conducting their research at the St. Anthony Falls Laboratory allowed the researchers to use actual conditions of the Mississippi River to test their theory since the river runs through the laboratory space. The researchers used a combination of a remote sending platform (spectroradiometer) and a digital single-lens reflex (DSLR) camera to monitor and classify various types of debris, based on their spectral signatures, which can aid in effectively removing plastic debris.

"If we can develop technology at the Mississippi headwaters, in a place like Minnesota, to catch plastic debris, we can protect the downstream states and the entire ocean from plastic pollution. As soon as these plastics begin to spread more and more, their control becomes more and more challenging," said Ardeshir Ebtehaj, Associate Professor in the Department of Civil, Environmental, and Geo- Engineering and corresponding author of the study.

The researchers hope to continue this on a larger scale to increase their understanding of where this plastic debris comes from, how it moves across river systems, and how they can remove it.

In addition to Olyaei and Ebtehaj, the team included Christopher R. Ellis, a senior research associate at the St. Anthony Falls Laboratory.

This work was funded by the Minnesota Environment and Natural Resources Trust Fund (ENTRF) as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR). The ENRTF is a permanent fund in Minnesota that provides funding for the protection and conservation of Minnesota's natural resources.