SALINITY FACTOR 285 
These values are estimates and, in past years, there have been 
wide fluctuations in the amount of irrigated acreage owing 
primarily to variations in available water supplies. For example, 
in E] Paso County, the irrigation acreage reached a peak of over 
67,000 acres in 1950 and dropped back to slightly less than 57,000 
acres in 1954. 
The first point to consider is the salt burden of the river, which 
is expressed as dissolved solids in tons (column 6). These data 
indicate that the salt burden from Otowi Bridge to San Marcial 
increases significantly, but, from the reservoir area at Elephant 
Butte to Fort Quitman, Texas, it is very uniform, the differences 
probably being within the limits of measurable error. On the other 
hand, the discharge figures (column 5) indicate that there is a 
marked decrease in stream flow until essentially all the water 
has been used below El Paso. This decrease in flow is the result 
of diversions to the irrigated lands along the river above Fort 
Quitman. The effect on quality of water of a nearly constant 
salt burden and a decrease in stream flow is reflected in columns 
3 and 4 which show the total concentration of dissolved solids in 
parts per million and as conductivity expressed in micromhos per 
centimeter. There has been an approximate sixfold decrease in 
discharge from Elephant Butte to Fort Quitman and slightly in 
excess of a sixfold increase in total concentration of salts over the 
same stretch of the river. Thus, flow decreases and the concentra- 
tion of salt increases, while the salt burden is virtually constant. 
This indicates that the tonnage of salt which is carried back to 
the stream in the return-flow drainage is approximately equal to 
the amount of salt diverted from the river in the irrigation 
water. If this were not the case, the tonnage of dissolved solids 
would probably decrease in a downstream order. 
Although the total dissolved solids do not change materially 
from Elephant Butte to Fort Quitman, there is a marked increase 
in the content of sodium and chloride present (Table 3). These 
data illustrate the effect of use and reuse of water on composition. 
The tonnage of sodium has increased threefold and the sodium 
concentration, over 30 times; chloride tonnage has increased 
twelvefold and concentration, 117 times. On the other hand, there 
