Limnologist Katie Webb Explains the Threats Facing the Unique Ecology of Lake Tahoe

Lake Tahoe, CA/NV…Lake Tahoe is one of California’s greatest natural treasures. It is a beauty to behold, with forested mountains surrounding the deep blue shimmering surface. It is famous for many recreational activities- snowboarding, skiing, hiking, mountain biking, boating, fishing, and sunbathing. But the clear blue waters of Tahoe are in trouble. Invasive species, climate change, and sedimentation all threaten the unique ecosystems of the lake.

Lake TahoeOn the research vessel Bob Richards, Katie grabs a quick bite to eat in between dive sites on Lake Tahoe.
Image credit: Brant Allen.

Katie Webb, a research associate with the UC Davis Tahoe Environmental Research Center, is one of the lucky few people who gets to spend nearly all of her days on the lake – and is paid for it! She gives us an account of her work as a limnologist (a scientist who studies freshwater ecology) on the lake and why it is so important to preserve the beautiful blue waters of Lake Tahoe.

What is the core mission of the Tahoe Environmental Research Center?

The Tahoe Environmental Research Center (TERC) is dedicated to research, education, and public outreach on lake ecosystems, and their surrounding watersheds and airsheds. Lake ecosystems include the physical, biogeochemical, and human environments, and the interactions among them. We are committed to providing objective scientific information for restoration and sustainable use of the Lake Tahoe Basin.

What are the greatest threats facing Tahoe’s ecology?

The greatest threats facing Lake Tahoe are the introduction of non-native species, nutrient and fine sediment particle inputs to the lake from human activity within the Tahoe Basin, and impacts from climate change.

Lake TahoeA nearshore area of Lake Tahoe has been infested with Asian clams. Their dead shells litter the bottom of the lake causing increased calcium levels. Algal also increases near clam beds due to nutrient excretion from Asian clams.
Image credit: UC Davis TERC.

One threat to Lake Tahoe which has received a lot of attention in the past few years in the appearance of the Asian clam (Corbicula fluminea), a non-native bivalve. Asian clams compete with native species for food and space. They also exude nutrient-rich waste that can increase algal blooms along the shore, and their shells can increase the calcium content of the water. This calcium-rich water may create a more favorable environment for the introduction of the quagga mussel, an invasive who has already caused much ecological and economic damage across the mid-west. Lake Tahoe luckily hasn’t seen any mussels yet and it is important that we keep it this way by having vessels that might be carrying them inspected before being placed in the lake. We are currently researching and implementing different methods in order to control, and maybe eventually eradicate the Asian clam population in Lake Tahoe.

Tell us about projects you’ve worked on in the last year.

It has been a busy year! The main project I’ve been working on is monitoring the 5-acre deployment of rubber bottom barriers that were installed in Emerald Bay in October 2012. These barriers come in 10-by-100 foot sections that weigh 300 pounds, held down by miles of rebar. These mats smother and kill the clams, and after they are removed the native species recover quickly.

Lake TahoeKatie rolls out a rubber bottom barrier over clam beds in Lake Tahoe.
Image credit: Brant Allen.

The clam population, which has been in the southern portion of the lake since 2002, has recently spread to Emerald Bay, a beautiful State Park on the South West side of Lake Tahoe.

In previous studies, we found that the application of thin rubber bottom barriers over Asian clams living in the sediment produces a high mortality rate in the clams, and therefore can serve as an effective management tool. UC Davis scientific divers visit the barriers bi-monthly to collect data on clam mortality rates, dissolved oxygen levels, and water chemistry data from under the barriers. All of this data provides researchers and managers with a “look under the barriers,” so we can assess the barriers’ effectiveness and determine when mortality is high enough that they can be removed.

Lake TahoeAn aerial view of the rubber bottom barriers being installed in Emerald Bay.
Image credit: Katie Webb.

This past fall a collaboration of researchers from TERC, Miami University, and Stony Brook University began to look at the impacts from the Rim Fire in Yosemite on lakes within the burn area, and those affected by the dense smoke from the fire, such as Lake Tahoe. This research will provide a better understanding of the potential impacts of fire on lakes, both in the immediate area as well as those hundreds of miles away. I have also been working on smaller projects looking at surface currents in Lake Tahoe, as well as helped with the installation of instrument chains in multiple locations around the lake that will eventually provide real time data to the TERC website.

Lake TahoeKatie Webb prepares to survey invasive weed densities in Lake Tahoe.
Image credit: Brant Allen.

How are you expecting climate change to affect Tahoe?

Over the past decade, long-term trends suggest we already seeing the effects of climate change on Lake Tahoe. Snow has declined as a fraction of total precipitation, from an average of 51% in 1910 to only 36% in present times. This means we have more rain and less snowpack in the mountains, which equals less water storage. When we are unable to depend on snowpack to store water during the winter, this leads to longer and more intense droughts. Rivers and streams may dry up during the late summer months, and we may see Lake Tahoe water levels reach historic lows.

In addition to less snowfall, we have also seen the average surface water temperature of Lake Tahoe increase from 50.2°F in 1968 to 52.8°F in 2012. An increase of 1.6°F may not seem like a large change but warming water temperatures can lead to big changes in the lake.

Non-native warm water fish species have been introduced into Lake Tahoe over the past 50 years. Historically, only shallow marinas have had water warm enough for these fish species to survive and reproduce in. However, as water temperatures increase around the lake, these fish species are able to leave the shallow marinas and move into other nearshore areas of the lake, which have been too cold for them in the past. As they move into these new areas, they compete with native fish species for habitat, food, and other important resources. Increased water temperature will also affect lake mixing and algae growth in Lake Tahoe. In 2013, TERC produced a State of Climate Change report. This report has tons of good information on the trends we have already observed in the Tahoe Basin, as well as what we can expect to see in the future.

Lake TahoeKatie helps maintain and clean instruments on monitoring buoys located around Lake Tahoe.
Image credit: Brant Allen.

We’ve heard about the disappearing clarity of Lake Tahoe; what causes this?  How does it affect the biology of the lake?

The clarity of Lake Tahoe is impacted by many different factors. Fine sediment particles and increased nutrient inputs into the lake have been the main factors attributed to clarity loss over the past century. Fine sediment particles are very light and don’t settle at the bottom of the lake quickly. When they are suspended in the water column, they can cloud the water and reflect sunlight, leading to a loss in clarity. Certain human activities within the basin, such as using fertilizers on lawns, can cause an increased amount of nutrients to get washed into Lake Tahoe. As on land, fertilizers provide the phytoplankton, or microscopic plants, in the lake with more nutrients to grow. Phytoplankton growth is highest in the summer months, which is why you see Lake Tahoe clarity change from 88.3ft in the winter of 2012, to only 64.5ft during the summer that same year. More phytoplankton in the water column equals less clarity.

Lake TahoeAverage annual secchi disk depth (indicates water clarity) has been steadily decreasing since the 1960s.
Image courtesy of UC Davis TERC.

How has the recent drought in California impacted the lake?

The extremely dry conditions in California and Nevada over the past few years are starting to become apparent in Lake Tahoe as the drought continues. The lake level has dropped several feet over the past 3 years. This is easily seen around the shoreline of Lake Tahoe, as much more beach area has been exposed from the lake. Lake Tahoe is so large that this shoreline effect will probably be the biggest change seen in the lake.

However, after Lake Tahoe reaches its natural rim of 6,223 ft, water will no longer be released from the lake into the Truckee River. The Truckee River provides habitat for fish and other aquatic organisms immediately downstream of Lake Tahoe, as well as water for the cities of Reno and Sparks. The Truckee River is also the main source of water into Pyramid Lake, which is home to several endangered and endemic species, including the Lahontan Cutthroat trout and the cui-ui sucker fish. These species rely on the Truckee River for spawning grounds in the spring, as well as almost all water input into Pyramid Lake. If the drought continues, the biggest impacts will not be seen on Lake Tahoe, but on the downstream areas that rely on water releases from Lake Tahoe.

What do you feel are the hidden gems of Tahoe?  Are there things that the lake provides that people don’t know as much about?

The best-hidden gem in the Tahoe Basin is getting in Lake Tahoe and putting your face in the lake! Put on a pair of goggles and start exploring around the beaches and granite boulders along the east shore or Rubicon Point and you will know what I am talking about. There is so much life, and simple, yet beautiful things to see when you swim in the lake. If more people spent more time swimming and kayaking the near shore areas of the lake instead of going to popular beaches or exploring by motorized boats, they would know why Lake Tahoe is so special and unique. I have never found another lake quite like it and you get an awesome appreciation for it when you jump in!

What is the best part about your job?

There are a lot of cool parts to my job because, in my opinion, I have the best job in the world 99% of the time! I’ve always wanted to work on/in/around water since I was little. It’s safe to say that working on Lake Tahoe is the ultimate dream job for me. Almost everyday out on Lake Tahoe is absolutely beautiful no matter the season. Our boat, the research vessel (R/V) Bob Richards, has the best office view you could ever imagine.

Lake TahoeA view from Katie’s “office”.
Image credit: Katie Webb.

At TERC we collaborate with researchers from all over the United States and the world. It is great to meet and work with people from other countries and research institutions, who are working to save freshwater ecosystems as well. I have adventures on a daily basis – that is one of the things I love the most about my job. Every day is new and different!

What are the hardest parts about your job?

Being miserably cold sometimes during the winter is hands down the hardest part of my job. We are out on the lake year-round. You can imagine that from November until May, it can be extremely cold at times. We still have to dive during the winter, even when the nearby mountains are smothered with snow. We are fortunate enough to have dry suits – the warmer version of a wetsuit – but I still come up shivering! My hands are so frozen sometimes that our deck hand on the boat has to undo all of the clips and zippers on my dive gear for me because my fingers just don’t work anymore.

Lake TahoeUC Davis divers Katie Webb and Brant Allen prepare for an icy cold winter dive in Emerald Bay.
Image credit: Allison Gamble.

Water temperatures in Tahoe can get down into mid – low 30’s in the spring. When the water is this cold, no amount of neoprene on your head can stop you from getting an ice cream headache when you first enter the water. Other times, it will be so cold when we are on the boat that water freezes as soon as it hits the boat deck. Just a few weeks ago, we were night sampling and the deck quite literally turned into an ice rink. It was nerve-racking to walk on the ice, hoping to not slip and fall into the lake!

Why is it so important that we try and preserve Tahoe’s ecosystems?

Lake Tahoe is a beautiful, one-of-a-kind lake, known worldwide for its beauty. We are very lucky to have the opportunity to live and recreate here, so it is our duty to “tread lightly” and protect it. It is much easier to use the ecosystem wisely now than to try to go back and restore the damage after it has been done.

Lake TahoeIt is rough getting up early for work sometimes but it’s hard to beat a perfect sunrise at the “office” on Lake Tahoe.
Image credit: Katie Webb.

Keep Tahoe Blue

Katie’s story is inspiring – she works to save the unique ecology of Lake Tahoe, despite the many less-than-favorable conditions that she must face. Limnologists are working everyday to ensure that this beautiful lake has a future.  Since we don’t all get to bask in the beauty of Lake Tahoe every single day – yes, some of us are a bit jealous – there are other ways to get involved. If you want to find out how you can help Lake Tahoe, visit the League to Save Lake Tahoe and discover ways to “Keep Tahoe Blue”. As a volunteer, you have the opportunity to survey and remove invasive aquatic species, perform beach cleanups, and engage others in education as a steward of the lake. You can also donate to TERC to support research and educational outreach programs for the public. At Pucci Foods we care deeply about the environment and preserving the unique natural wonders of the world. Join us in celebrating those who strive to save special places like Lake Tahoe.