STREAM POLLUTION 
379 
HYDROGEN-ION (pH) LIMITS 
Hydrogen-ion concentration measurements in the laboratory and aboard Quarter- 
boat 348 were made electrometrically with calomel and quinhydrone electrodes 
(Leeds, Northrup Co., Philadelphia, type 7701-Al). In the field the Youden appa- 
ratus (W. M. Welch Co., Chicago, type 5270) bridging the quinhydrone electrode 
against standardized phthalate solution was used because of greater portability. 
When field conditions were such that neither of these two pieces of apparatus were 
available, the determinations of hydrogen-ion concentrations were made colorimet- 
rically by the method of Gillespie (1920). Sterile tubes, solutions, and stoppers 
were used in preparing the tube series for the Gillespie sets, which were calibrated 
against the calomel electrode and kept in a dark box except when measurements 
were being made. Although fractional values were recorded (i. e., hundredths), in 
presenting the data the value is given to the nearest tenth pH. 
The hydrogen-ion concentration of the inland streams of the United States, 
southern Canada, and northern Mexico, excepting badly polluted portions of these 
waters, as seen in a review of some 10,000 readings made during the past 5 years, 
lies in general between values of pH 6.7 and pH 8.6, with the extreme range (in our 
data) of pH 6.3 and pH 9.0 in streams for which no specific pollution factor affecting 
the hydrogen-ion concentration was readily observable. Swamp waters, bog streams, 
and particularly swam]) lakes not infrequently show an acidity between pH 4.5 and 
pH 6.0, vet at the same time may support mixed fish faunae. In some small western 
streams and pools containing fishes examined by the writer in North Dakota, Mon- 
tana, and New Mexico an alkalinity of pH 9.5 was occasionally found in alkali dis- 
tricts or near mineral springs. In such waters small poeciliids and cyprinids were 
uniformily the dominant fishes. 
In figures 11, 12, 13, and 14, 7,228 pH readings from inland stream waters repre- 
senting 1,125 localities are presented. These data were collected during the warm 
season, June to September, 1930-35, and are comparable with the dissolved oxygen 
data in the preceding section. The composite, figure 11 A, was constructed from 
2,280 readings representing 409 localities where good fish faunae, as previously defined, 
were found. This composite covers a range between pH 6.3 and pH 9.0, with 97 
percent of the cases between pH 6.7 and pH 8.6. Superimposing the graph of the 
composite on the graphs presenting the data from the various river systems, however, 
shows that, except in cases of extreme pollution, the pH values as such of stream 
waters, both polluted and unpolluted, do not differ materially from those of the 
composite. 
The data from the various river systems (other than the composite) are pre- 
sented without regard to pollution, except that no pH readings of water in the im- 
mediate vicinity of flumes and conduits from which effluents were escaping have 
been included. The extreme pH range of the flowing waters of inland streams of the 
United States, both polluted and unpolluted, as found in these field studies was 
pH 3.9 to pH 9.5, although various effluents poured into these same waters were 
found to range from pH 1.0 to pH 11.0 at the point of entrance into the stream. 
These observations show that dilution and the buffer action of various substances 
99773° — 37 3 
