DEPARTMENT OF BOTANICAL RESEARCH. 



87 



EREMOGRAPHY. 



7'he First Stage in the Recession of Salton Sea, by D. T. MacDougal. 



The studies on the recession phenomena of the Salton Sea have been 

 carried on continuously since 1906. About half of the original depth 

 of 84 feet has been lost by the balance of evaporation and seepage over 

 inflow and underflow. The rate of fall of the level of the water has 

 been reduced from over 50 inches yearly to less than 40. The loss 

 from January to April was less than the amount received from rains 

 and from overflow of irrigation systems during the winter of 1915-16, 

 so that the lake has now altered from a constantly falUng level to an 

 oscillating level. This and the fact that the emerging beaches are 

 now occupied by halophytic or salt plants only are used as criteria to 

 mark the end of the first stage of the recession. 



The reduction of the total body of water from an original total of 

 about 3 or 4 cubic miles to half that amount has been accompanied 

 by a concentration of salts dissolved from about 0.33 per cent to 1.6 per 

 cent. The variations in the principal constituents during the last three 

 years are given below: 



The concentration of calcium was checked during the first few years 

 of the recession of the lake by reason of the fact that it was being 

 deposited as travertine as a result of the activity of a group of organ- 

 isms, and it is now showing a 



higher concentration, the water Revegetation of Cormorant Island. 



having become too salty for 

 the algae and bacteria earlier 

 concerned in this action. 



The larger islands have be- 

 come j oined with the mainland, 

 but Cormorant Island, origi- 

 nally freed from all seed-plants, 

 is still separated by a mile of 

 salt water from the north- 

 eastern shore. Its reoccupa- 

 tion by plants has proceeded 

 as shown in the table here- 

 with (the census for 1916 was 

 taken in May). 



