ACKNOWLEDGMENT 3 



in planning and management on a national or regional scale. The 

 primary objectives of NASQAN are (1) to account for the quantity and 

 quality of surface water moving within and from the United States, (2) 

 to depict areal variability, (3) to detect changes in stream quality, and 

 (4) to provide the groundwork for future assessments of changes in 

 stream quality (Ficke and Hawkinson, 1975). 



As part of NASQAN, phytoplankton samples are obtained seven 

 times a year from about 540 stations. The samples are processed for 

 generic identification and enumeration by the U.S. Geological Survey's 

 Central Water-Quality Laboratory in Atlanta, Ga., in accord with the 

 methods of Greeson and others (1977) and Greeson (1979). All data are 

 stored in the computerized data files (WATSTORE and BIOTAB) of 

 the U.S. Geological Survey. 



In early 1979, a retrieval was made for all phytoplankton data con- 

 tained in BIOTAB. The data included those collected as part of 

 NASQAN, as well as those data collected as part of other activities of 

 the U.S. Geological Survey. About 80 percent of the file represented 

 NASQAN data. During the 5-year period between October 1973 and 

 October 1978, a total of 17,959 phytoplankton samples were processed. 

 Using the almost 18,000 samples as a basis, this publication lists, 

 describes, and provides a detailed taxonomic key for the identification 

 of commonly occurring and dominant genera of algae observed in the 

 phytoplankton of the United States. A summary of environmental con- 

 ditions under which each algal genus was observed is included. Also in- 

 cluded is a glossary and an extensive list of selected references. 



Of the approximately 500 genera of freshwater algae reported in the 

 United States (Greeson, 1970), the U.S. Geological Survey has ob- 

 served 321 genera in the phytoplankton (table 1). Fifty-two genera 

 reported in 5 percent or more of the samples were considered to be 

 commonly occurring (table 2). Forty-two genera were dominant in 1 

 percent or more of the samples (table 3). A dominant genus was con- 

 sidered to be one that comprises 15 percent or more of the total cell 

 count of a sample. Table 4 lists in alphabetical order by taxonomic 

 groupings the 58 genera of algae that were either commonly occurring 

 or dominant in the samples. 



ACKNOWLEDGMENT 



The author acknowledges with sincerest appreciation the many per- 

 sons of the U.S. Geological Survey who made this publication possible. 

 A special thanks is extended to James M. Bergmann, developer of 

 BIOTAB, for his assistance with data retrievals; to the field personnel 

 who performed their duties under extremely demanding conditions; 

 and to the supervisors and analysts in the U.S. Geological Survey's 

 laboratory in Atlanta for their perseverance in spite of an overwhelm- 

 ing number of samples. 



