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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. 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.
Accomplishments
Summary statistics (# observations, mean, median, std. dev.) for periphyton biomass (Chlorophyll a mg / m2) and p-value for trend analysis for change in biomass. Trend analysis combine all routine sites to assess Lake-wide periphyton trends. Where analysis of trend indicated a significant trend, the direction of the trend is indicated. Observations where Lake Elevation >= 6225 ft or where the sampling depth has been submerged for less than 1000 days (< 1000 day) are thought to reflect trend in stalked diatoms and/or filamentous green algae. Observations where lake Lake Elevation <6225 ft or where the depth has been submerged for more than 1000 days (< 1000 day) are thought to be influenced by blue-green algae. Table adapted from (Hackley et al., 2016a).
2019 Evaluation
See how thresholds are evaluated
- 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 algae could be driven by metaphtyon (detached algae which is not captured in the existing monitoring program).
- No attainment call has ever been made for nearshore attached algae because the baseline against which the standard is to be assessed (1967-71 mean values for periphyton biomass) is not known.
- 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.
Evaluation Map
Description
Map of Nearshore Attached Algae 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 algal 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 and 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
- The nearshore attached algae standard does not have a defined numeric target, so it is not possible to assess attainment. The current standard references periphyton biomass as measured between 1967 and 1971 as the goal for biomass in the nearshore. This was the California state standard at the time the thresholds were established in 1982, but at the time of establishment, it was noted that “there were no measurements of periphyton biomass between 1967-1971.”
- 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.