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Researchers Remove Invasive Weeds From Lake Tahoe With UV Light

(Editor's note: This discussion originally aired Aug. 19, 2020)

Lake Tahoe is famous for its pristine water. But experts say the lake is being choked by invasive water plants.

You might recognize Eurasian watermilfoil and curlyleaf pondweed – a lot of people have them in their aquariums.

And you might also recognize them because they get wrapped around your ankles when you swim in a lake that’s full of weeds.

They’re a big problem for Lake Tahoe. And they’re very hard to get rid of. But a group of researchers from the University of Nevada, Reno is working with inventors and conservation groups to take them out – and they say they’ve been killing weeds with UV light.

“We’ve been trying to test different tools and technologies to make a dent or see what the efficacy or the practicality of using these tools to remove plants,” said Sudeep Chandra, Director of the Global Water Center at UNR.

Chandra said the UV light program is being tested to see just how well it works.

Keeping Lake Tahoe clear has long been the goal for conservationists, the invasive plants don't help that effort because they leak phosphorous, the main nutrient for algae, which can hurt clarity levels at the lake.

Chandra said another problem with these plants is they're invading habitats along the shoreline, embayments and marinas. The plants become a home for other invasive species.

“So, not only do these plants impact the clarity of the lake but they can also change the ecology of the lake," he said, "As these plants move around from the edges of the lake and the marinas and embayments, they also create habitat for other species that we don’t want in the lake like warm-water fishes, bluegill, bass, goldfish, then all of the sudden you start creating habitat for other unwanted species and those fish species also poop or excrete nutrients that can cause changes to near-shore water clarity.”

Plus, invasive fish prey on native aquatic life, which native trout use for food.

Chandra said there are several ways invasive species are brought into the lake.

“They can get into the lake from a couple of different ways. Plants, for example, can come in via boat props,” he said.

Boats or boat trailers that go into a lake with the invasive plants can bring them into Lake Tahoe when they're launched there. Lake Tahoe has a robust boat inspection and washing program, which has helped minimize species introduction.

“Another way these plants and sometimes fish, like goldfish, can get introduced is through aquarium dumping,” Chandra said.

People don't realize that dumping their overfilled aquariums into the lake introduces non-native plants into the delicate ecosystem. Chandra said educating the public will help that problem.

To make all those issues worse, climate change is impacting the lake. Chandra said invasive warm-water species of fish now have more time to procreate because the lake stays warmer longer thanks to climate change.

As far as the invasive plant species, Chandra said researchers are still studying the impact the changing climate is having.

John J. Paoluccio is the president of Inventive Resources, Inc., and developer of the UV-C light that is being used in the pilot project.

He said he came up with the idea when he was working at a cave show in college and the cave's owner asked him to remove the algae from the cave's formations without touching them.

Paoluccio thought about what he had learned in college about UV light and water filtration. He decided to give that a try and it worked.

Now, he's using the same idea to kill weeds in Lake Tahoe. Paoluccio and his team are using a specific kind of UV light - known as UV-C to target the plants.

“What we’ve done is we’ve concentrated that light and focused that right on to the plants and that’s what makes it effective at killing the plants,” he said.

In 2017, they started with a small boat that had only a four-foot by eight-foot light array attached to it, but after some success and more funding from Tahoe Regional Planning Agency, the team built a bigger boat and a larger light array. 

At one beach they targeted from the beginning, Paoluccio is noticing a difference.

“Last year, we treated the beach two times, and we’re seeing a lot less plants this year,” he said.

Currently, the plan is to find out exactly how many times the boat needs to pass over an area, the best time of year to treat the plants and at what stage of the plants' growth.

“That’s really what this study is about is learning the right dynamics and how to treat the plants efficiently,” he said.

Paolucci and his team have worked on other projects, including canals in California, but right now, they're focused on Lake Tahoe.

Chandra is optimistic about the efforts so far, but there is still more information to gather.

“Right now, we’re at the stages of testing how well the ultraviolet vessel tool will do at knocking back plants at big scales, acres for example,” he said.

Lake Tahoe's shoreline is filled with nooks and crannies, Chandra said, fighting invasive species can be difficult under those circumstances, which is why conservationists need a variety of tools. 

Chandra believes that the UV light-emitting vessel could eventually become a tool in that fight.

Sudeep Chandra, Director, Global Water Center at UNR;  John J. Paoluccio, President, Inventive Resources, Inc. and developer of the UV-C light 

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Bert is a reporter and producer based in Reno, where he covers the state legislature and stories that resonate across Nevada. He began his career in journalism after studying abroad during the summer of 2011 in Egypt, during the Arab Spring. Before he joined Nevada Public Radio and Capital Public Radio, Bert was a contributor at KQED and the Sacramento News & Review. He was also a photographer, video editor and digital producer at the East Bay Express.