Indicator
Littoral Periphyton Biomass
2019 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 beneficial use of the shorezone. When periphyton dies off and breaks free each year, beaches can be fouled and water contact recreation affected. Regional programs such as stormwater reduction aim to reduce the amount of algae in the nearshore. Algae in the nearshore is monitored by UC Davis. 

Status
2019 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
  • There has been no significant change in periphyton in Tahoe since monitoring began 30 years ago.
  • A 2020 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).
  • Agencies and the Tahoe Science Advisory Council are reviewing nearshore algal monitoring and assessing opportunities to modify the program to include all nearshore algae.
  • 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. A second type of sampling, referred to as “synoptic” monitoring occurs once a year at 40 additional sites. The timing of synoptic monitoring varies annually and is intended to capture biomass at its peak in the spring. The synoptic monitoring includes the collection of chlorophyll a at a sub-set of the sites, as well as a rapid assessment method that quantifies a periphyton biomass index (PBI).
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 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.
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.
Delivering and Measuring Success

No related projects or programs defined for this indicator.

Rationale Details
Monitoring shows that there has been no significant change in periphyton biomass in Tahoe since the current monitoring began in 2000.
Monitoring shows that there has been no significant change in periphyton biomass in Tahoe since the current monitoring began in 2000.
Confidence Details
A 2020 independent peer review of Tahoe’s periphyton monitoring confirmed that the program was technically sound and consistent with the current standards.
UC Davis has monitored periphyton in Lake Tahoe since 2000.
Moderate. Agencies and the Tahoe Science Advisory Council are reviewing nearshore algal monitoring and evaluating the inclusion of metaphtyon in future monitoring which could provide a more complete picture of all nearshore algae.
Additional Figures and Resources

No photos available.

No documents available.