differences or changes in water quality. Phytoplankton
samples may be collected in large nonwadeable streams and
rivers to meet specific study-unit objectives.
Algal samples are labeled with a unique 16-character code
that identifies the study unit (stream location), sampling
date, type of sample, subtypes, sample number, and sample
element code. Optional algal samples for the determination
of chlorophyll conce ntrations or ash-free dry mass are
processed in the field, placed on dry ice, and submitted to
the National Water-Quality Laboratory in Arvada, Colorado.
Samples for the identification and enumeration of algal taxa
are preserved with buffered formalin an d shipped to a
contract laboratory for analysis. The Biological
Quality-Assurance Unit has responsibility for laboratory
quality assurance and quality control, entry of contractor
data into the national data base, and storage and
maintenance of taxonomic collections. The Biological
Quality-Assurance Unit also monitors the accuracy of
taxonomic identifications and precision of enumeration by
analyzing split samples from 10 percent of the study-unit
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