Science guides attack plan on invasives

By Jim Sloan/Tahoe In Depth

While Tahoe’s boat inspection program has become a model for resource managers across the country, the inspections are just a part of the overall work to prevent and control aquatic invasive species at Lake Tahoe.

In places where invasives have achieved a foothold, the Tahoe Regional Planning Agency, the Tahoe Resource Conservation District (Tahoe RCD), and other resource agencies, nonprofits, and researchers in California and Nevada have assaulted infected areas with a battery of high-tech attacks and old-fashioned hand-to-hand combat.

Crews remove bottom barriers used to kill aquatic invasive species on the South Shore of Lake Tahoe. Photo: Tahoe Resource Conservation District

Tahoe RCD has had great success removing Eurasian watermilfoil from parts of the lake, including Emerald Bay, Crystal Shores, and Tahoe Vista, while continuing work at Lakeside Marina, Fleur du Lac, and the Truckee River.

At Lakeside Marina, for instance, 1.5 acres are in the process of being treated. The plant infestations were surveyed and divers from Marine Taxonomic Services placed the barriers and suctioned up the plants.

Tahoe RCD has conducted a pilot project in which ultraviolet light is used to damage the plant cells of aquatic invasive plants. This project was funded by the Tahoe Fund and the California Tahoe Conservancy, and the technology was provided by John Paoluccio, the president of Inventive Resources, Inc. Paoluccio originally developed the UV light application 10 years ago as a means of removing algae from the walls of caves that couldn’t be treated with chemicals or touched. When he heard about the weed problem at Tahoe, where he has a summer home, he offered to test his system on Eurasian watermilfoil and curlyleaf pondweed infestations.

It looks promising.

In the lab, “time-lapse video shows the plants dying back and disintegrating,” said Nicole Cartwright, Tahoe RCD executive director.

Monitoring of that project is still ongoing as researchers also examine if the UV light had any effect on water quality, temperature, and native macroinvertebrates.
Despite these encouraging results, Cartwright notes that the crews must continue to monitor treated areas to ensure the invaders don’t return. And some of the techniques that have worked on Eurasian watermilfoil haven’t worked as well on curlyleaf pondweed, which produces hard-shelled seeds call turions that often survive the best efforts to eliminate them.

“We’ve learned how to control satellite populations, but the Tahoe Keys will continue to be our source until we control the problem there,” Cartwright said. “And we haven’t conquered anything that large yet.”

Dennis Zabaglo, the aquatic resources program manager at TRPA, said the Tahoe Keys Property Owners Association has worked for years to control the spread of aquatic invasive weeds in the development’s various lagoons. The Keys area was originally a marsh before it was developed with homes and manmade waterways, and Zabaglo noted that the former marsh area naturally has a lot of nutrients and protection from open water that makes it a productive breeding ground for invasive weeds and animals.

“The Keys area is ground zero for the spread of these invasives to the lake,” Zabaglo said.

In addition to manually removing the weeds, which can make navigation difficult, the property owners have installed a back-up station where boats heading out to open water can pause and briefly go into reverse as a way of releasing any weed fragments before they reach the lake. TKPOA has also deployed a “bubble curtain” that boats will be able to drive through on their way out to the lake to dislodge weed debris.

The problem of aquatic plants in the Keys has remained so persistent that the property owners have applied for permission to test herbicides on the weedy areas. That proposal will become part of a larger environmental impact study considering a wide array of treatment options before it can move ahead.

“The potential use of an herbicide in the Tahoe Keys is of great interest to the public and a great concern to some,” Zabaglo noted. “An environmental analysis will help us understand the risks and whether it’s appropriate from an environmental standpoint. We need to investigate all the different methods, so it’s important to make this part of a comprehensive analysis.”

Holding back the spread of aquatic invasive species is just part of the test as resource managers work to maintain Tahoe’s clarity and fragile ecosystem, Zabaglo said. New threats are always popping up, and climate change that is slowly warming Tahoe’s water is inviting to new invaders.

“There will inevitably be something new— a new weed or a new animal—that is harder to eliminate or harder to detect,” he said.

Gaining a comprehensive view of the problem and the threats is important, so Zabaglo is looking forward to a study this summer that will survey the entire lake and its tributaries to assess and document satellite populations of aquatic invasive species. That kind of overview hasn’t been done to this scale but is critical to helping resource managers identify areas that need attention.

“We need to stay ahead of the problem as best we can,” Zabaglo said. “Once we know the scope of the problem, we’ll be in a better position to eradicate isolated populations and focus on larger infestations.”