Underwater research methodologies for limnological investigations at Lake Tahoe, California-Nevada: periphyton, groundwater and zooplankton studies

Abstract

The Tahoe Research Group has developed SCUBA-aided methodologies for determination of biomass and measurement of the primary productivity of the attached algal community in situ, measurement of ground water influx, and manipulation of whole-planktonic communities. Periphyton primary productivity is measured by the introduction of a radioactive tracer, 14 C-carbonate into a hemispherical dome which covers a known area of substrate. Periphyton is then collected from a known area of rock substratum with a two-stage brushing syringe sampler for biomass measurements. This in situ method of measuring primary productivity over laboratory techniques has the advantage of not disturbing the naturally occurring community. Experimental results therefore more closely approximate the true values of periphyton primary productivity. Existing methodologies using seepage meters and sediment interstitial water samplers serviced by SCUBA have also been employed to estimate the nutrient content and rate of seepage of ground water into Lake Tahoe. SCUBA has also been used in zooplankton investigations, during the deployment of large subsurface enclosures.