SOURCES OF CONTAMINATION 



227 



able size again, it held about 2200 parts per million of 

 salts (15). 



Evaporation from free water surfaces is the direct cause 

 of the high alkali content of certain irrigation waters. 

 Lake Tulare, California, which has no outlet, was once 



Fig. 32. The More Tender Trees are being Killed with 

 Rising Alkali, while Alfalfa is Still Unaffected. 



considered a source of irrigation water. Due to evapora- 

 tion its waters increased in concentration from 1400 parts 

 per million in 1880 to 3500 parts per million in 1888, and 

 to 5200 parts per million in 1889 (20). Irrigation water 

 for the Carlsbad district, New Mexico, is stored in a large 

 reservoir or lake fed by the Pecos River. It was found 

 that for several weeks in May and June, 1899, the evapora- 

 tion of this water which already contained between 2000 

 and 3000 parts per million of total salts, was equal to over 



