Long-Term UV & Light Monitoring in Lake Tahoe
Sunlight drives life in Lake Tahoe — but not all sunlight is the same. Ultraviolet radiation (UV) is the most energetic portion of incoming solar radiation and can have powerful photochemical and biological effects in aquatic ecosystems. Despite its importance, long-term records of underwater UV in lakes are rare.
UC Davis researchers have maintained an 18-year record of underwater UV and photosynthetically available radiation (PAR) in Lake Tahoe, one of the clearest large lakes in the world. This long-term dataset is uniquely valuable for understanding how climate variability affects the underwater light environment.
Why UV Monitoring Matters
Our research has revealed that Lake Tahoe experiences dramatic year-to-year shifts in UV transparency, sometimes changing by orders of magnitude. These changes are closely linked to regional dry and wet climate cycles:
- Wet years increase runoff, delivering more particulate matter and colored dissolved organic matter from surrounding watersheds. These materials absorb UV radiation, reducing its penetration.
- Dry years reduce external inputs, allowing UV radiation to penetrate much deeper into the water column.
While visible light (PAR) varies less dramatically, the ratio of UV to PAR can shift significantly from year to year, altering the spectral quality of the light aquatic organisms experience.
Implications for Climate Change
As climate change intensifies precipitation extremes, clearwater lakes like Tahoe are likely to experience increasingly large fluctuations in underwater UV and overall light conditions. These shifts can influence:
- Phytoplankton productivity
- Nutrient cycling
- Food web dynamics
- Photochemical reactions in the water column
Because light regulates many fundamental biological and chemical processes, changes in UV exposure can reshape ecosystem structure and function.
The Value of Long-Term Data
Short-term studies cannot capture the effects of multi-year climate cycles. By sustaining nearly two decades of underwater irradiance monitoring, UC Davis has created one of the most comprehensive UV datasets available for any large lake.
This long-term perspective allows scientists to connect climate variability, watershed inputs, and underwater light conditions — providing critical insight into how Lake Tahoe and other clear alpine lakes may respond to a warming, more variable future.