2 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



when he stated that "* * * it is quite possible to arrange plants and 

 animals of a stream in the order of their preference for, or tolerance of, 

 organic impurities, in such a way that a graded list of them may serve 

 as an index to grades of contamination." 



W. C. Purdy (1922), a plankton specialist with the U.S. Public Health 

 Service, clearly recognized the value of biological indicators when he 

 concluded, "If it be true that the biological life of a stream is distinctly 

 and profoundly affected by the numerous factors which form the en- 

 vironment, it follows that the organisms in a stream constitute in a 

 general way a reflection of the prevailing environmental conditions of 

 the stream." 



Thienemann (1939) was the first to demonstrate that groups of 

 species were characteristic of a given type of environment. Community 

 structure as an indicator of environmental conditions thereby became a 

 firmly established concept. Fjerdingstad (1950) was the first to con- 

 sider algal community-dominant species, associate species, and ac- 

 cidental species. Perhaps the most well known paper considering com- 

 munity structure as an indicator was by Patrick (1949). In it, she coined 

 the terms "healthy," "semihealthy," "polluted," and "very polluted" to 

 describe the variability one might expect in the organisms and yet in- 

 dicate the degree of degradation that had taken place in a stream. 



Subsequent to Patrick's paper, the emphasis changed from studies 

 that were purely qualitative in nature to quantitative expressions of 

 community structures, associations, and diversities. 



With the realization of the importance of biota as indicators and of 

 the need to characterize the quality of water, including the biological 

 quality, in major waterways of the United States, the U.S. Public 

 Health Service initiated the National Water Quality Network in 1957. 

 Samples for determining the physical, chemical, and biological quality 

 at 128 stations were collected through 1962 (Williams, 1962, 1964, 

 1966). The network continued until the late 1960's as the Water Pollu- 

 tion Surveillance System under the purview of the Federal Water 

 Pollution Control Administration (now the U.S. Environmental Protec- 

 tion Agency) (Weber, 1966). 



The changing emphasis toward the preservation of environmental 

 quality during the 1960's awakened the need for a long-term data base 

 with which changes in water quality could be determined. As a result, 

 the U.S. Geological Survey initiated the National Stream-Quality Ac- 

 counting Network (NASQAN) in 1973. NASQAN is a series of stations 

 at which systematic and continuing measurements are made to deter- 

 mine the quality of the Nation's streams. Design of the network 

 specifies measurement of a broad range of water-quality 

 characteristics, including biological characteristics, which were 

 selected to meet many of the information requests of groups involved 



