Unlocking the Next Chapter of Lake Clarity Science
For decades, Lake Tahoe research and management have focused on reducing the amount of fine sediment entering the lake — a key driver of declining clarity. While these efforts have been successful, lake clarity has recently plateaued, suggesting that additional processes are now influencing how light moves through the water.
New research at UC Davis TERC is focused on one of the most important remaining questions:
What role do tiny living particles — picoplankton — and their interactions with inorganic particles play in controlling Lake Tahoe’s clarity?
A New Perspective on Lake Clarity
Particles in the 1–6 micron size range are the primary drivers of water clarity loss in Lake Tahoe. Historically, these particles were assumed to be mostly inorganic — fine sediments entering the lake from the watershed.
However, the lack of continued clarity improvement despite reductions in sediment inputs suggests a more complex story. Increasing evidence points to a growing role for organic particles, including microscopic algae known as picoplankton, which may now contribute significantly to light scattering in the lake.
Understanding whether clarity is being driven by inorganic particles, organic particles, or their interaction is critical — and may represent a turning point in how we manage and protect Lake Tahoe.
What Are Picoplankton?
Picoplankton are extremely small phytoplankton (typically <2 microns) that are too small to be captured by traditional monitoring methods. Despite their size, they can:
- Contribute significantly to total algal biomass and productivity
- Influence nutrient cycling and food web dynamics
- Affects how light is scattered and absorbed in the water column
Previous research suggests that picoplankton may account for up to half of Lake Tahoe’s phytoplankton biomass — yet they are not currently included in routine monitoring programs.
The Missing Link: Aggregates
Another key piece of the puzzle is how particles — both living and non-living — stick together to form aggregates, sometimes called “lake snow.”
These aggregates are formed in part by sticky substances released by phytoplankton, including picoplankton. These substances bind particles together, changing how they:
- Scatter light
- Sink through the water column
- Remain suspended in surface waters
This means that even if the total amount of particles remains the same, changes in how particles clump together can significantly impact water clarity.
Our Research Plan
TERC is developing a long-term monitoring program to study picoplankton and aggregate dynamics together for the first time in Lake Tahoe.
This integrated approach includes:
Picoplankton Monitoring
Using advanced flow cytometry, we will:
- Count and classify picoplankton (including bacteria and algae)
- Distinguish living vs. non-living particles
- Track changes across depth, season, and environmental conditions
Aggregate Imaging
Using in situ holographic imaging, we will:
- Capture high-resolution 3D images of fragile particle aggregates
- Measure their size, shape, and abundance
- Understand how aggregates influence light scattering and settling
Linking Biology and Physics
We will also measure phytoplankton exudates — the natural compounds that make particles “sticky” — to determine:
- When and why aggregation increases
- How biological processes influence clarity
- How environmental conditions (temperature, nutrients, wildfire smoke) affect these dynamics
Key Questions We Are Addressing
This research is designed to answer four critical questions:
- What fraction of clarity-reducing particles are living organisms vs. inorganic sediments?
- Is warming temperature increasing the role of biological particles in clarity loss?
- How do aggregation processes influence light penetration in the lake?
- How are phytoplankton and picoplankton driving particle behavior and clarity outcomes?
Why This Work Matters
This research addresses one of the most important remaining uncertainties in Lake Tahoe science. If clarity is increasingly influenced by biological processes rather than watershed inputs alone, then:
- Management strategies may need to evolve
- Climate change may play a larger role than previously understood
- New approaches to protecting clarity will be required
By integrating cutting-edge technology with long-term monitoring, this program will provide the data needed to refine models, improve predictions, and guide future restoration efforts.
A New Era of Lake Clarity Science
Lake Tahoe has long been a model system for environmental management. This next phase of research represents a shift toward understanding the interplay between biology and physics in shaping water clarity.
By studying picoplankton and particle aggregation together, TERC is working to solve one of the lake’s most persistent mysteries — and ensure that efforts to protect Tahoe remain effective in a changing climate.
For more information email Stephanie Hampton @ UC Davis.