STREAM POLLUTION 393 
Table 2. — Dissolved ammonia in various stream waters during the warm season, June to October, 
inclusive, 1934 
[For convenience of comparison, data are expressed as percents of total number of determinations for each stream unit] 
River system 
Number 
of stations 
Number 
of deter- 
minations 
Dissolved ammonia in parts per million 
0.0-0. 9 
1.0 1.9 
2. 0-2. 9 
3. 0-3. 9 
4.0-4. 9 
5. 0-5. 9 
Greater 
than 6.0 
72 
178 
21 
58 
21 
( 2 ) 
Entire Mississippi system. 
182 
478 
24 
49 
22 
3 
2 
( 2 ) 
( 2 ) 
Coastal streams 
58 
91 
7 
55 
33 
1 
1 
1 
1 Derived from ammonia determinations at 72 stations throughout the entire Mississippi system and in coastal streams, at each 
of which stations good mixed fish faunae and associated organisms were thriving. 
1 Less than 0.5 percent. 
It may be seen that excepting the restricted local areas where heavy pollution 
was found (data not presented in tlxis table) the dissolved ammonia in flowing streams 
in general lies below 3 p. p. m. Tliis is due to a variety of physical and chemical 
factors, chief among which is the constant turn-over of the moving stream waters. 
The good fish faunae showed a preference to waters containing less than 2 p. p. m. 
dissolved ammonia, as 79 percent of the cases of this group were found in water 
containing less than 1.9 p. p. m. dissolved ammonia. The remaining 21 percent were 
apparently thriving in waters containing between 2 and 3 p. p. m. dissolved ammonia, 
with one case (the maximal indicated by footnote 2 in the 3-3.9 column) in waters 
carrying 3.5 p. p. m. dissolved ammonia. Tliis maximal dissolved ammonia value 
among the stations where good fish faunae were taken was found at Reeds Landing, 
Minn., where the Mississippi River was flowing rapidly over a sandy bottom at a 
point just below extensive beds of aquatic vegetation in the foot of Lake Pepin. 
It must be noted that without exception those waters carrying 2 to 3 p. p. m. ammonia 
and at the same time supporting the good fish fauna were high in dissolved oxygen ; 
that is, 5.5 to 7 p. p. m., were of low turbidity, and were flowing over good bottoms. 
Toleration of dissolved ammonia above 2 p. p. m. under field conditions was always 
associated with otherwise good to exceptionally favorable conditions. 
The toxic effects of ammonia compounds have been the subject of many investi- 
gations; and aquatic animals have been shown to be particularly sensitive to ammo- 
nium carbonate, the form in which ammonia is most frequently found in inland waters, 
(Shelford, 1917; Belding, 1928; Steinmann, 1928; and McCay and Vars, 1931). 
Thirty p. p. m. of ammonia will Id 11 some tench, trout, and salmon rather rapidly 
(Weigelt, 1885), and 55 to 77 p. p. m. will kill sinners and carp in a few minutes to a 
few hours (Clark and Adams, 1913). A review of the literature on ammonia, how- 
ever, shows that some observers obtained toxic effects with much smaller quantities. 
Ellis and Chipman (1936) have repeated many of the earlier tests and extended 
the observations to daphnia and gammarids, as well as fish, finding that pH is a large 
factor in regulating the toxicity of ammonium compounds for aquatic animals, 
ammonium salts becoming more toxic in more alkaline media. Tliis fact explains 
the relatively high toxicity of ammonium carbonate to aquatic organisms as compared 
with other ammonium salts. From these data (presented in section on ammonia 
pollutants) curves were drawn showing that the toxicity of ammonium compounds 
increases 200 percent or more between pH 7.4 and pH 8.0. The lower limit of toxicity 
