Provided / Jennifer Kent
INCLINE VILLAGE, Nev. Microplastics, small fragments of fibers from clothing, packaging and other plastic residues, have invaded lakes and watersheds globally and in alarming quantities, according to new research published in the scientific journal Nature with the title “Plastic debris in lakes and tanks”. Lake Tahoe, known for its purity and high level of legal protection, had the third-highest plastic concentration of 38 lakes tested worldwide and higher than surface waters in ocean eddies where floating islands of debris emblematic of the world plastics collect the pollution crisis.
“One of the top priorities in Lake Tahoe is maintaining clear, pristine water quality,” said Sudeep Chandra, professor of limnology and director of the Global Water Center at the University of Nevada, Reno. “Clarity is the signature of Lake Tahoe and the mantra Keep Tahoe Blue it is not taken lightly. With this study, we now know that plastic exists in high concentrations in Lake Tahoe and could impact the ecosystem and animals that live in the lake. This shows us that there are always emerging issues that need to be addressed so that we can try to preserve the lake in the future.”
Still unknown is how plastic is entering these freshwater ecosystems, particularly the Tahoe Basin. Even lakes mostly undisturbed by humans have seen some level of microplastics.
“The results are remarkable because they show the magnitude of plastic concentrations in freshwater systems even in remote and highly protected areas,” Chandra, who is also University of Nevada, Reno at Lake Tahoe affiliated research faculty, he said.
The global research was conducted by Veronica Nava, a visiting postdoctoral fellow at the University of Nevada, Reno, of the University of Milano-Bicocca in Italy. Under the supervision of Professor Barbara Leoni of Milano-Bicocca, Nava worked with colleagues from all over the world, including Chandra.
“The transport mechanism of these plastics is not clear, especially when talking about very small fragments or textile fibers,” said Nava. “We wear a lot of synthetic clothes, most of which are made from polyester, and they end up in aquatic systems. Even from far away, there can be atmospheric circulation and patterns that can carry these plastics for a long time.”
Another culprit is single-use plastics. These objects when used and discarded break and are believed to enter the watershed in various ways.
“It’s not that plastic isn’t useful,” Nava said. “There are many applications where plastics need to be used and other materials can be much more harmful to an ecosystem. However, there are some types of plastic, especially disposable plastic, which can be avoided by eliminating it as a problem”.
Lake Tahoe has a record of science-led conservation policies and programs to address human impacts. Not only has wastewater been transported out of the reservoir for decades, but $660 million has been invested in water quality improvements through the Lake Tahoe Environmental Improvement Program. In June of this year, the region also began managing the impact of outdoor recreation and tourism more holistically. The new Lake Tahoe destination stewardship plan is addressing the environmental issues plaguing the Lake Tahoe Basin, prioritizing waste enforcement and environmental stewardship and sustainability.
Julie Regan, executive director of the bi-state Tahoe Regional Planning Agency, added additional perspective on the results.
“We are absolutely concerned about the implications for human health and the lake’s vulnerability to microplastics. Lake Tahoe has been solving tough problems through science-led policy for years,” Regan said. “If there’s one area that can work to understand microplastics and reduce their impacts, it’s our region. This area of research is relatively young, and emerging questions come from each new study.Broadening our understanding of microplastics in the environment, how they travel, their sources, and their impacts is a critical next step to making sure Tahoe doesn’t fall victim to a global problem”.
From Global to Local: How Lake Tahoe Compares
Lead researcher Nava worked with colleagues from around the world, including Chandra, to collect samples from 38 lakes located in 23 different countries, spread across 6 continents and representing a range of environmental conditions. The team compared them to similarly sampled water in subtropical ocean gyres currently considered some of the largest plastic accumulation zones in the world.
By filtering for plastics larger than 250 microns (about the width of three strands of hair), the researchers confirmed the presence of microplastics in all 38 lakes, highlighting high levels of plastic debris from fabrics and clothing such as polyester, polypropylene and polyethylene. . Three of the lakes Lugano and Maggiore on the Italian-Swiss border and Lake Tahoe showed higher concentrations of microplastics than those observed in oceanic eddies.
“If you look at the variables in our study that seemed to be linked to the presence of plastic, Lake Tahoe was different. We didn’t have any of these consistent variables,” Nava said.
Two types of lakes have been shown to be particularly vulnerable in densely populated areas and large lakes with multiple ways to deposit plastic, such as having a wide watershed, greater water inflows, a large shoreline length, and increased shoreline development. Lakes Lugano and Maggiore, both densely populated and with wastewater intakes, saw the highest concentrations of microplastics. Lake Tahoe, which had the third highest level of plastic, is an anomaly in the study. The area surrounding Lake Tahoe is not densely populated, sewage has been exported for the past 50 years, and policies are in place to limit excessive runoff into the lake.
“We continue to believe that the concentration of plastic is linked to human presence, whether it is littering on the beach or other small ways plastic can end up in the water,” Nava continued.
Large lakes like Lake Tahoe hold water longer than smaller, shallower systems which can impact plastic debris buildup. For Lake Tahoe, that timeline is 650 years. Additionally, the region sees large seasonal influxes of recreationists using the lake.
“What this study emphasizes is that everyone has a role to play,” Regan said. “It is our collective responsibility to take care of Lake Tahoe to pick up our trash, leave no trace, leave only footprints on the Tahoe shoreline, and be aware that our modern, affordable lifestyle comes at a cost.”
The city of South Lake Tahoe recently banned the use of plastic bags and single-use plastic water bottles, which will go into effect in 2024. The non-profit organization League to Save Lake Tahoe has been experimenting with the use of robots scheduled to clean up trash on the lakeshore and coordinate cleanups of large community beaches. The Lake Tahoe Destination Stewardship Plan outlines additional priorities to combat plastic entry into the lake.
Understand the impact
Chandra hopes to help Tahoe managers address the plastic problem by determining where plastic comes from and how to prevent it from accumulating in the lake, while also understanding the impacts of these high levels of microplastics in the lake. These include the potential transfer of plastic debris through the watershed into other systems, changes in water nutrients or oxygen levels, and potable water infiltration.
While not explored in the present study, Chandra plans to pursue these answers in future research.
“At the University of Nevada, Reno at Lake Tahoe, we are ready to meet this challenge,” Chandra said. “My hope is to conduct an experiment with Dr. Nava, as well as our colleagues at the Desert Research Institute, that evaluates the impact of plastic on Lake Tahoe. We are starting to design experiments now and hope to make comparisons with other lakes and Northern California and Oregon, as well as Italy.”
As research progresses, partnerships between scientists and organizations like TRPA, the League to Save Lake Tahoe, the Tahoe Fund, and other groups influential in planning and implementing conservation efforts will continue to prove essential.
“Protecting Lake Tahoe’s incredible water quality is at the heart of everything we do, and our conservation programs to control local pollutant sources have become a model for other areas,” said Regan. “Microplastics and other emerging issues have been on our radar for several years and we are fortunate to have some of the world’s greatest scientists studying our lake and helping us protect it. We hope these findings continue the long tradition of relying on science to guide restoration policies and programs to protect Lake Tahoe for generations to come.”
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