Indicator
Littoral Periphyton Biomass
2023 Evaluation
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This indicator measures the amount of attached algae in the nearshore of Lake Tahoe. Attached algae or periphyton refers to a suite of organisms that grow attached to submerged surfaces (e.g. rocks, boats, buoys, piers). In Lake Tahoe, these include stalked diatoms, filamentous green algae, and cyanophytes. Excessive periphyton growth impacts the aesthetic qualities and impairs the beneficial use of the shorezone. Regional programs such as stormwater management aim to reduce the amount of algae in the nearshore, through nutrient load reduction. Algae in the nearshore is monitored by UC Davis.

Status

Annual average values per routine monitoring site.

Data is provided by UC Davis. Access detailed datasets on Tahoe Open Data, including: Monitoring Locations and  Periphyton Data.

2023 Evaluation
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Status
Insufficient Data to Determine Status or No Target Established
Trend
Little or No Change
Confidence
Moderate
Applicable Standard
WQ6: Attain 1967-71 mean values for periphyton biomass in the littoral zone.
Key Points
  • Multiple analyses of the long-term periphyton dataset have suggested there has been no significant change in periphyton in Tahoe since monitoring began 30 years ago (Atkins et al., 2021; Hackley et al., 2016).
  • In 2020 Tahoe Science Advisory Council organized an independent peer review of Tahoe’s periphyton monitoring confirmed that the program was technically sound. The reviewers hypothesized that stakeholder perceived increase in nearshore algal could be driven by metaphtyon (detached algae which are not captured in the existing monitoring program). The recommendation was consistent with the Lake Tahoe Nearshore Evaluation and Monitoring Framework (Heyvaert et al., 2013).
  • The updated nearshore algae monitoring program (inclusive of periphyton and metaphyton) began in 2023. The design includes In-situ sampling at eight sites, UAV aerial surveys around those sites, and helicopter flights along the entire shoreline within a week of in-situ sampling events.
  • Work in the nearshore areas of Tahoe found that primary production increased by 40% in 2021 when the lake was blanketed in smoke from the Caldor, Tamarack, and Dixie fires (Smits et al., 2024).
  • Work from other alpine lakes in Sierra, suggests that biomass is increasing as a result of climate change-driven warming (Sadro et al., 2018).
Evaluation Map
Description

Periphyton Monitoring Locations

About the Threshold
Attached algae or periphyton refers to a suite of organisms that grow attached to submerged surfaces (e.g. rocks, boats, buoys, piers). In Lake Tahoe, these include stalked diatoms, filamentous green algae, and cyanophytes. The communities occupy different portions of the nearshore and exhibit different growth patterns. Stalked diatoms species and filamentous green algae dominate the shallow area between the low and high lake level (eulittoral zone) and grow rapidly in the spring in die off in the summer. Cyanophytes are more stable communities that dominate the deeper portions of the nearshore. Excessive periphyton growth impacts the aesthetic qualities and impairs the beneficial use of the shorezone. When periphyton dies off and breaks free each year, beaches can be fouled and water contact recreation affected. Periphyton growth can also be a safety concern for people attempting to navigate slippery algae-covered surfaces. The monitoring program has historically been focused on attached algae (periphyton), but in recent years there has been concern that that floating algae (metaphyton) has increased along Lake Tahoe’s shoreline. The monitoring program has been modified to include both attached and free-floating algae to provide a more comprehensive assessment of nearshore algal conditions.
Nitrogen and phosphorus together support the growth of algae in Lake Tahoe. Phosphorus is a nutrient important to the growth and reproduction of plants and is considered a pollutant of concern in the Lake Tahoe Region. It has also been hypothesized the excrement from crayfish in the lake augments periphyton growth. Stalked diatoms and green filamentous algae may be the most responsive to fluctuations in nutrient input. The stalked diatoms and filamentous green algae that inhabit the shallow waters grow rapidly in the spring with the influx of nutrients and die back rapidly during summer when nutrients are less abundant as water warms. Biomass is generally higher on the north and west beaches and lower at the lower in the east and south, a pattern that has remained relatively stable over time. Lake level influences periphyton community composition, at lake elevations below 6225 feet blue-green algae contribute substantially to the periphyton levels, while at higher lake levels stalked diatoms and filamentous green algae dominate. Recent observations during wildfires of 2021 suggest that smoke cover and ash deposition impact primary production in the nearshore (Smits et al., 2024). Filamentous algal blooms (FABs) in the nearshore of clear lakes with high water quality have been observed around the world. Their increasing frequency is unexplained, but likely the result of complex changes and the interactions between climate change, nutrient transport, lake hydrodynamics, and ecological change (Vadeboncoeur et al., 2021).
Delivering and Measuring Success

EIP Action Priorities

EIP Indicators

Example EIP Projects

Lake Clarity Indicators

Monitoring Programs

Rationale Details
Insufficient Data to Determine Status or No Target Established. UC Davis has monitored periphyton in Lake Tahoe since 2000. Monitoring also occurred between 1982 and 1985 and 1989 to 1993. The primary periphyton monitoring work is regular sampling work referred to as “routine” sampling at nine sites annually (the number of locations has varied historically from six to ten). At each location algal biomass (as chlorophyll a) is sampled five times annually from natural rock surfaces at a depth of 0.5 meters below the water level at the time of sampling.
Little or No Change. Multiple analyses of the long-term periphyton dataset have found that there has been no significant change in periphyton in Tahoe since monitoring began 30 years ago (Atkins et al., 2021; Hackley et al., 2016).
Confidence Details
Moderate. The monitoring program provides a long-term consistent record of periphyton biomass in Tahoe’s nearshore. The peer review highlighted a number of improvements to the sampling design that would improve the overall ability to draw inferences from the data (Brothers et al., 2020). Those changes have largely been adopted.
High. The analysis of periphyton biomass change has been replicated and is a peer-reviewed finding. While the threshold does not include metaphyton, recent concern that the stakeholder reported change maybe related to changes in the metaphyton algae community.
Moderate. If one confidence rating is high and the other is moderate, the overall confidence rating is the lower confidence rating.
Additional Figures and Resources

No photos available.

No documents available.

References

Atkins, K.S., Hackley, S.H., Allen, B.C., Watanabe, S., Reuter, J.E., Schladow, S.G., 2021. Variability in periphyton community and biomass over 37 years in Lake Tahoe (CA-NV). Hydrobiologia 848, 1755–1772. https://doi.org/10.1007/s10750-021-04533-w

Brothers, S., Ted Ozersky, Steven Francoeur, 2020. Lake Tahoe Periphyton Monitoring Program Engaged Review. Tahoe Science Advisory Council.

Hackley, S.H., Watanabe, S., Hymanson, Z., Schladow, S.G., 2016. Evaluation of Trends in Nearshore Attached Algae: 2015 TRPA Threshold Evaluation Report. Tahoe Environmental Research Center University of California, Davis, Incline Village, NV.

Heyvaert, A., Reuter, J., Chandra, S., Susfalk, R., Schladow, S.G., Hackley, S., Ngai, C., Fitzgerald, B., Morton, C., Caires, A., Taylor, K., Hunter, D., Allen, B., Arneson, P., 2013. Lake Tahoe Nearshore Evaluation and Monitoring Framework (v10.e) (Final Report prepared for the USDA Forest Service Pacific Southwest Research Station.). Desert Research Institute, Reno, NV.

Sadro, S., Sickman, J.O., Melack, J.M., Skeen, K., 2018. Effects of Climate Variability on Snowmelt and Implications for Organic Matter in a High-Elevation Lake. Water Resources Research 54, 4563–4578. https://doi.org/10.1029/2017WR022163

Smits, A.P., Scordo, F., Tang, M., Cortés, A., Farruggia, M.J., Culpepper, J., Chandra, S., Jin, Y., Valbuena, S.A., Watanabe, S., Schladow, G., Sadro, S., 2024. Wildfire smoke reduces lake ecosystem metabolic rates unequally across a trophic gradient. Commun Earth Environ 5, 265. https://doi.org/10.1038/s43247-024-01404-9

Vadeboncoeur, Y., Moore, M.V., Stewart, S.D., Chandra, S., Atkins, K.S., Baron, J.S., Bouma-Gregson, K., Brothers, S., Francoeur, S.N., Genzoli, L., Higgins, S.N., Hilt, S., Katona, L.R., Kelly, D., Oleksy, I.A., Ozersky, T., Power, M.E., Roberts, D., Smits, A.P., Timoshkin, O., Tromboni, F., Zanden, M.J.V., Volkova, E.A., Waters, S., Wood, S.A., Yamamuro, M., 2021. Blue Waters, Green Bottoms: Benthic Filamentous Algal Blooms Are an Emerging Threat to Clear Lakes Worldwide. BioScience 71, 1011–1027. https://doi.org/10.1093/biosci/biab049