Increase in summer algae may not indicate long-term trend
October 1, 2010
SOUTH LAKE TAHOE, Calif. – Despite the appearance of more algae attached to submerged rocks in the near-shore areas of Lake Tahoe, scientists are reluctant to ascribe the apparent increase to actual population growth.
Scott Hackley, staff research associate at TERC and principal author of the “Lake Tahoe Water Quality Investigations,” said he has heard people who frequent the near-shore area report an increase in periphyton growth this year, but said the algal population fluctuates year to year based on “an interaction of factors.”
“I would caution those that rely on anecdotal or visual evidence,” he said. “We have been compiling data since the 1980s. We are continuing to collect data and we will look to identify trends or dramatic shifts over a sustained period of time.”
Factors that interact to facilitate periphyton growth include lake surface level, presence of nitrogen and phosphorus, the amount of sunlight available to the algae, the length of springtime and water temperature, Hackley said.
For instance, the apparent increase in algae during this year’s swimming season (May, June and July) – when many residents and tourists frequent the shore – was due, in large part, to this year’s unusually late spring run-off, Hackley said.
Algae population typically peaks in March and April, but due to the persistence of colder temperatures during those months this year, spring run-off from streams carrying nutrients necessary to stimulate growth was delayed.
Low lake surface elevation this year also contributed to growth, as algal communities typically located deeper underwater were closer to the surface where sunlight required for photosynthesis is readily available.
The consequences of lowered lake levels on algae were particularly noticeable for Incline West, Sand Point, Deadman Point, Sugar Pine Point and Rubicon Point sites according to the study. During periods of low lake elevation, definite increases in baseline (algae) were observed, the study added.
Hackley said more work needs to be done, more data collected and more trends identified, before scientists are willing to definitively say that periphyton population is increasing in the near-shore of Lake Tahoe.
“We are committed to monitor the health of the near-shore,” Hackley said. “We are striving to get a better understanding of algal growth.”