Scott Hackley preparing to measure Algal Growth Potential. Photo: A. Toy

Algal Growth Potential Bioassays

Beginning in August 2013, TERC began routine monitoring of Algal Growth Potential (AGP) at 10 shallow nearshore sites and 2 mid-lake sites, with funding provided by the Lahontan Regional Water Quality Control Board.  The purpose of the AGP experiments is to compare levels of algal growth in water collected from nearshore and offshore sites. AGP is the peak biomass in samples (measured as chlorophyll a) achieved during a 2-week lab incubation and the results largely reflect the ability of phytoplankton to grow in ambient water from a site.  Availability of the nutrients nitrogen (N) and phosphorus (P) in the water and levels of nutrients previously taken up by algae are important factors which contribute to growth.

Four times a year, samples of lake water containing phytoplankton are collected from just below the surface at sites around the lake.  The nearshore sites include Tahoe City, Kings Beach, Crystal Bay, Glenbrook, Zephyr Cove, Timber Cove, Tahoe Keys, Camp Richardson, Rubicon Bay, Sunnyside and Emerald Bay (added in Dec.).  A north and a south mid-lake site are also sampled.  The water is returned to the lab at TERC, divided to flasks and incubated under controlled light and temperature for approximately two weeks. Algal growth as measured by changes in chlorophyll a is tracked throughout the experiment.  The peak chlorophyll a achieved is the AGP for a site.

The Lahontan Regional Water Quality Control Board standard for AGP specifies mean annual AGP at nearshore sites should not exceed 2X the mean annual AGP at a mid-lake reference station. AGP is a method to identify more productive nearshore waters.

TERC researchers collecting nearshore water near Kings Beach for an AGP experiment. Photo: S. Hackley