Though the murkiness of the water makes it difficult to see, the top of the photo shows where 8-foot plants are still growing, compared to the bottom of the photo where the treatment has eliminated the plants.
Over the past two weeks, engineers have been testing out a new method of killing off invasive aquatic plants in Lake Tahoe using ultraviolet light — and the results are promising.
A team from Inventive Resources, Inc., a private engineering firm with a focus on environmental services, spent the last two years lab testing the effects of targeted ultraviolet light, specifically ultraviolet-C, on non-native aquatic species like Eurasian watermilfoil.
The research showed UVC light damaged the DNA and cellular structure of the plants, causing them to die.
After approaching the Tahoe Resource Conservation District with the idea, a pilot project was launched in the Lakeside Marina at the end of June. The Lakeside Marina was constructed around 1955 with underwater barriers to limit water movement that could jostle the boats. This altered environment soon became an ideal location for the propagation of invasive plants, which prefer stiller, warmer water. The spread of these plants, which are around 8-feet tall in the marina, pose a major threat to the clarity of Lake Tahoe.
Using a specially-made boat fitted with a drop-down panel of UVC lights, Inventive Resources has spent the last two weeks treating roughly 0.4 acres of the marina.
John Paoluccio, president of Inventive Resources, previously used UV light to eliminate algae in caves. When he heard about the issue of invasive aquatic species in Lake Tahoe, he knew this technology could be applied.
“These plants are so transparent and translucent that the light energy goes right into that plant and basically sunburns and scars the outer tissue. When you do that it releases all the air bubbles out of the plant, and they just drop,” explained Paoluccio. “It causes a cell fusion, and they can no longer reproduce.”
Paoluccio and his team have been testing different exposure times and distances from the bottom of the marina, all while monitoring the water hourly for levels of dissolved oxygen, pH, temperature and turbidity. So far there have been no significant changes.
“The biomass is so minimal with Eurasian watermilfoil and other aquatic plants that as it’s dying back, it just disintegrates. We’ll monitor that, too, as far as water quality pre- and post-treatment,” said Nicole Cartwright, aquatic invasive species program manager for the Tahoe RCD.
Tahoe RCD will also monitor the microorganisms underneath the sediment to see if there are any impacts from the UVC treatment.
“We are already submitting to try to get funding to do environmental documentation to make this a method once we can prove it,” said Cartwright. “Once the pilot’s done we really do want to take this technology and make it bigger.”
Paoluccio is also eager to see the technology grow.
“If you had a 30-foot barge out there, you could do a very large area very quickly,” said Paoluccio. “Acres are not a big deal.”
Tahoe RCD facilitated this pilot project using seed money from Tahoe Fund and a $260,000 grant from the California Tahoe Conservancy.
“We’re excited because it’s a great private-public partnership,” said Amy Berry, CEO of the Tahoe Fund. “We’re going to need to try a lot of new innovative ways to fight this problem. Some may work and some may not. But the idea is that we can’t just sit back and let the weeds destroy Tahoe.”
Tahoe RCD and other members of the multi-agency Lake Tahoe Aquatic Invasive Species Coordinating Committee have had success with other methods of fighting invasive species around Lake Tahoe, too. The invasive plant population was significantly reduced in Emerald Bay using sun-blocking bottom barriers and diver-assisted suction removal.
This January, the Tahoe Keys Property Owners Association announced that it has applied for a permit for small-scale demonstrations of aquatic herbicides in 2018. The Tahoe Keys was created in the late 1950s by dredging an estimated 5 million cubic yards of material from the marsh at the mouth of the Upper Truckee River. Aquatic invasive plants, primarily curly leaf pondweed and Eurasian watermilfoil, have taken over more than 90 percent of the neighborhood’s 172-acre lagoon system.
