Effect of Summer Use of a Mountain Watershed on Bacterial Water Quality

Abstract The water quality of a mountain watershed during the summers of 1970, 1971, and 1972 is presented. Samples were collected at six sample sites in the watershed. The standard plate count at 20C and the aerobic bacteria enumerated on trypticase soy agar at 20C numbered about 5 × 10 3 cells/ml in July, and remained at this concentration for the rest of the summer. The standard plate count at 35C was generally constant at near 50 cells/ml each summer at all sample sites. The total coliforms in 9 out of 17 cases exhibited a tenfold increase in numbers in late July or August over the values of 10 or less per 100 ml found in June. Fecal coliforms in 11 out of 17 cases increased 10 to 100‐fold in concentration in July or August over values obtained in June or September. Maximum numbers of fecal streptococci were usually seen at all sample sites in July or August except for 1972, when sheep ( Ouis aries ) were being grazed in September. A stream in a natural area of the watershed appeared to be less polluted than other streams in the watershed which were influenced by human use. The use of the fecal coliform to fecal streptococci ratio to determine the source of pollution appeared to be of questionable value in this study.