STREAM POLLUTION 
391 
free iron in the water did not exceed 20 p. p. m. Iron as it occurs in most natural 
flowin<>: waters, therefore, is not a major limiting factor in the distribution of fishes 
in fresh-water streams. Besides in fresh-water streams and rivers the constant re- 
aeration of water readily offsets any important oxygen loss through iron compounds, 
as has been reported from bog lakes and certain deep lakes where large quantities 
of iron were found. 
In pollution studies of the inland fresh-water streams, therefore, the determina- 
tion of total iron is helpful in locating the source of acid in highly acid waters, as a 
1. MISSOURI 
J. MISSOURI 
K. OHIO 
L TENNESSEE 
BELOW HEADWATERS 
PERCENT 17 STATIONS 
HEADWATERS 
10 STATIONS 
24 STATIONS 
94 STATIONS 
OF CASES 121 DETERMINATIONS 
lie DETERMINATIONS 
252 DETERMINATIONS 
149 DETERMINATIONS 
M GULF COAST STREAMS 
N RIO GRANDE 
0. COLORADO RIVER SVSTEU 
P COLUMBIA RIVER SYSTEM 
13 STATIONS 
0 STATIONS 
10 STATIONS 
37 STATIONS 
118 DETERMINATIONS 
I2G DETERMINATIONS 
38 DETERMINATIONS 
62 DETERMINATIONS 
Figure 19. — Continuation of comparisons of free carbon dioxide values, stippled graph A figure 18, being the standard. 
combination of high iron and high acidity suggest the source of acidity as pyrite or 
coal beds if no specific chemical effluent is responsible for these conditions. 
AMMONIA 
Total ammonia determinations were made by the Nessler method as described 
by American Public Health Association (1933). 
Decomposing organic matter, if nitrogenous, will liberate into stream water, 
ammonium compounds representing a considerable portion of the total nitrogen. As 
ammonium compounds present at once both a hazard due to the high toxicity of 
ammonium carbonate for most aquatic animals, and an important source of nitrogen 
