Major Lakes Phytoplankton Study: Comparison of Composite Sampling Techniques
The Major Lakes Phytoplankton Study was initiated in March 2003 and involved the collection of integrated composite samples of surface water for phytoplankton species identification, enumeration, and estimation of species-specific phytoplankton biovolume. In addition to the phytoplankton work, a change in the surface water compositing scheme for chlorophyll a and phytoplankton taxonomic work was proposed. The previous technique mixed equal parts of samples collected from 1 m below the water surface and at the measured Secchi depth a “discrete composite”. The technique proposed for phytoplankton sampling and for future routine composite sampling for chlorophyll a involved the use of a 10-m long 1.6-cm diameter tube suspended from the surface an “integrated composite” sample. The submerged tube collects a vertically integrated sample of the surface 10 m of the lake. Paired sampling at the Lake Washington Station 0852 off Madison Park was proposed to evaluate potential differences between the two compositing techniques.
As a result of this study and evaluation of discrete chlorophyll a profiles at 0852 and available high frequency fluorescence profiling data, additional changes in the methods and frequency of sampling for phytoplankton biomass are proposed for incorporation into the routine monitoring program. Proposed changes include sampling more frequently at a reduced number of stations and working more cooperatively with University of Washington scientists that are involved in research on Lake Washington and Lake Sammamish. It is believed that a more cooperative working relationship will maximize the use of available resources and provide the best hope of continuing to improve our understanding of how these lakes will respond to environmental change (e.g, population growth and climate change).
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